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5 Med Genet 1995;32:458-464 The dental phenotype in familial adenomatous polyposis: diagnostic application of a weighted scoring system for changes on dental panoramic radiographs Nalin Thakker, Rhodri Davies, Keith Homer, John Armstrong, Tara Clancy, Simon Guy, Rodney Harris, Philip Sloan, Gareth Evans Department of Medical Genetics, St Mary's Hospital, Hathersage Road, Manchester M13 OJH, UK N Thakker R Davies J Armstrong T Clancy S Guy R Harris G Evans Department of Dental Medicine and Surgery, University of Manchester, Manchester M15 6FH, UK N Thakker K Homer P Sloan Correspondence to: Dr Thakker. Received 25 October 1994 Revised version accepted for publication 3 February 1995 Abstract A weighted scoring system (Dental Pan- oramic Radiograph Score) taking into con- sideration the nature, extent, and site of osseous and dental changes on dental pan- oramic radiographs in familial adeno- matous polyposis is described. The weighting takes into consideration the in- cidence of the anomaly in the general population. The reliability of the system was tested by application to 85 people known to be affected by clinical or muta- tion analysis, 30 people lacking mutation in the adenomatous polyposis gene, and 19 people shown to be at low risk (<1%) by linkage analysis. Using the highest thresh- olds, a specificity of 100% and sensitivity of - 68% was obtained. If all positive findings were considered as significant, sensitivity was increased to - 82% but the specificity was reduced to -88%. Significant DPRS findings were observed at a significantly higher frequency in patients aged over 20 compared to the patients aged 20 and un- der. Overall, 68% of the affected subjects had significant changes, and -18% had normal appearance on DPR, with the re- mainder having changes classified as min- imal or equivocal. (J Med Genet 1995;32:458-464) Familial adenomatous polyposis (FAP) is an autosomal dominant condition characterised by the development of multiple adenomatous polyps in the colon and rectum with high risk of subsequent malignant transformation. In ad- dition, extracolonic changes occur in many affected subjects. These include epidermoid cysts, desmoid tumours, congenital hyper- trophy of retinal pigment epithelium (CHRPE), osseous changes in the jaws and skeleton, and dental anomalies. FAP results from germline mutations in the adenomatous polyposis coli (APC) gene on chromosome 5q21. l 2 The adenomatous polyps usually develop in the colon or rectum or both in adolescence or early adulthood and malignant transformation usually occurs between the ages of 30 and 40.' Early identification of affected subjects and prophylactic surgical intervention is essential in preventing the development of colorectal carcinomas. Furthermore, presymptomatic diagnosis is vital since two-thirds of those pre- senting with symptoms will have already de- veloped carcinoma and consequently will have a poorer prognosis.45 In families with a history of FAP, subjects at risk may be diagnosed by using genetic markers closely linked to the APC locus6 or by iden- tification of mutations in the APC gene.'27 However, linked markers may not always be informative or the pedigree structure may be unsuitable for linkage analysis. Furthermore, most mutations are unique within given families.'27 Current mutation screening methods are only able to identify the patho- logical mutation in 60 to 70% of the families. Alternative mutation analysis strategies in- volving in vitro transcriptional/translational as- says may prove to be more efficient.89 In the absence of suitable rapid genetic tests for some families, there is a dependence on clinical screening of subjects at risk for the iden- tification of those affected. This involves reg- ular colonoscopy. In addition, other extracolonic features, such as CHRPE and changes in the jaws, which may antedate the appearance of colonic polyps may prove useful phenotypic markers. CHRPE is reported to be present in between 58 and 100% of cases'0-3 and the presence or absence of CHRPE has been used in optimal risk estimation in FAP. 10 12 Numerous studies have also identified jaw changes including osseous lesions, odontomes, supernumerary teeth, and an increased in- cidence of impacted teeth. 114-24 The use of these changes in a diagnostic test for FAP has been limited because of the presence of similar changes in unaffected people, lack of data on the reliability of such a test, and lack of familiarity of geneticists with features identified on dental panoramic radiographs. In this paper we describe in detail the radiographic changes in FAP patients. In addition, we describe a weighted scoring system for these changes and report its application and reliability in the diag- nosis of FAP. Subjects and methods FAP FAMILIES The families were identified from the North West Regional Polyposis Register, St Mary's Hospital, Manchester and included patients referred from the regional gastroenterology and surgical units, and the University Dental Hos- 458 on April 11, 2022 by guest. Protected by copyright. http://jmg.bmj.com/ J Med Genet: first published as 10.1136/jmg.32.6.458 on 1 June 1995. Downloaded from

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The dental phenotype in familial adenomatous polyposis: diagnostic application of a weighted scoring system for changes on dental panoramic radiographs
Nalin Thakker, Rhodri Davies, Keith Homer, John Armstrong, Tara Clancy, Simon Guy, Rodney Harris, Philip Sloan, Gareth Evans
Department of Medical Genetics, St Mary's Hospital, Hathersage Road, Manchester M13 OJH, UK N Thakker R Davies J Armstrong T Clancy S Guy R Harris G Evans
Department of Dental Medicine and Surgery, University of Manchester, Manchester M15 6FH, UK N Thakker K Homer P Sloan
Correspondence to: Dr Thakker.
Received 25 October 1994 Revised version accepted for publication 3 February 1995
Abstract A weighted scoring system (Dental Pan- oramic Radiograph Score) taking into con- sideration the nature, extent, and site of osseous and dental changes on dental pan- oramic radiographs in familial adeno- matous polyposis is described. The weighting takes into consideration the in- cidence of the anomaly in the general population. The reliability of the system was tested by application to 85 people known to be affected by clinical or muta- tion analysis, 30 people lacking mutation in the adenomatous polyposis gene, and 19 people shown to be at low risk (<1%) by linkage analysis. Using the highest thresh- olds, a specificity of100% and sensitivity of - 68% was obtained. If all positive findings were considered as significant, sensitivity was increased to - 82% but the specificity was reduced to -88%. Significant DPRS findings were observed at a significantly higher frequency in patients aged over 20 compared to the patients aged 20 and un- der. Overall, 68% ofthe affected subjects had significant changes, and -18% had normal appearance on DPR, with the re- mainder having changes classified as min- imal or equivocal.
(J Med Genet 1995;32:458-464)
Familial adenomatous polyposis (FAP) is an autosomal dominant condition characterised by the development of multiple adenomatous polyps in the colon and rectum with high risk ofsubsequent malignant transformation. In ad- dition, extracolonic changes occur in many affected subjects. These include epidermoid cysts, desmoid tumours, congenital hyper- trophy ofretinal pigment epithelium (CHRPE), osseous changes in the jaws and skeleton, and dental anomalies. FAP results from germline mutations in the adenomatous polyposis coli (APC) gene on chromosome 5q21. l 2 The adenomatous polyps usually develop in
the colon or rectum or both in adolescence or early adulthood and malignant transformation usually occurs between the ages of 30 and 40.' Early identification of affected subjects and prophylactic surgical intervention is essential in preventing the development of colorectal carcinomas. Furthermore, presymptomatic
diagnosis is vital since two-thirds of those pre- senting with symptoms will have already de- veloped carcinoma and consequently will have a poorer prognosis.45
In families with a history of FAP, subjects at risk may be diagnosed by using genetic markers closely linked to the APC locus6 or by iden- tification of mutations in the APC gene.'27 However, linked markers may not always be informative or the pedigree structure may be unsuitable for linkage analysis. Furthermore, most mutations are unique within given families.'27 Current mutation screening methods are only able to identify the patho- logical mutation in 60 to 70% of the families. Alternative mutation analysis strategies in- volving in vitro transcriptional/translational as- says may prove to be more efficient.89 In the absence of suitable rapid genetic tests for some families, there is a dependence on clinical screening of subjects at risk for the iden- tification of those affected. This involves reg- ular colonoscopy. In addition, other extracolonic features, such as CHRPE and changes in the jaws, which may antedate the appearance of colonic polyps may prove useful phenotypic markers. CHRPE is reported to be present in between 58 and 100% of cases'0-3 and the presence or absence of CHRPE has been used in optimal risk estimation in FAP. 10 12
Numerous studies have also identified jaw changes including osseous lesions, odontomes, supernumerary teeth, and an increased in- cidence of impacted teeth. 114-24 The use of these changes in a diagnostic test for FAP has been limited because of the presence of similar changes in unaffected people, lack of data on the reliability of such a test, and lack of familiarity of geneticists with features identified on dental panoramic radiographs. In this paper we describe in detail the radiographic changes in FAP patients. In addition, we describe a weighted scoring system for these changes and report its application and reliability in the diag- nosis of FAP.
Subjects and methods FAP FAMILIES The families were identified from the North West Regional Polyposis Register, St Mary's Hospital, Manchester and included patients referred from the regional gastroenterology and surgical units, and the University Dental Hos-
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Table 1 The number, age range, and sex ratio of subjects grouped according to FAP status
Group No Age range M:F
FAP affected A 85 10-77 44:41 FAP unaffected (by mutation analysis) B 30 11-64 11:19 FAP unaffected (by linkage analysis) C 19 12-63 11:8 Clinically low risk D 19 25-62 8:11
Table 2 Dental panoramic radiograph scoring system. Weighted scores for number and size (where appropriate) for each anomaly are shown. Derivation of the scoring system and its application are detailed in "Subjects and methods"
Scoring cniteria
DPR anomaly No Score Size (cm) Score
Osteoma 0 0 <0 5 0 1 4 >0 5<2-0 3 2 7 >20<40 6 3-5 9 >40<60 8 6-8 11 >60 10 (+1-3) (+2)
Dense bone island (DBI) 0 0 <0-5 0 1 2 >0 5<2-0 2 2 4 >20 4 3-5 6 6-8 8 (+ 1-3) (+2)
Hazy sclerosis associated with root(s) of single teeth 1 area 2 - _
>2 areas 4 Hazy sclerosis associated with root(s) of multiple teeth > 1 4 - - Hazy sclerosis not associated with root(s) of teeth 1 2 <1-0 0
>2 4 >1-0 2 Hazy sclerosis diffuse - 12 - -
Odontomes 0 0 1 7 2 9 (+ 1) (+2)
Supernumerary teeth 0 0 (unerupted or erupted) Mesiodens 3
1 6 2 9 (+ 1) (+2)
Unerupted teeth 0 0 1 3 2 5 3 7 (+ 1) (+2)
pital, Manchester. A total of 154 patients from 37 unrelated families were studied. The age range, sex ratio, and clinical status of patients with respect to FAP are detailed in table 1.
Figure 1 Part of a dental panoramic radiograph showing left mandible and maxilla. Well defined radiodense lesions typical of endosteal osteomas are present (arrows), together with an unerupted maxillary canine.
Briefly, the sample included 85 known affected FAP patients (group A: patients who were either known to be affected at the time of examination or were subsequently identified as affected clinically or by mutation analysis) and 30 definitely unaffected people (group B: lack- ing the mutation present in the APC gene of affected members of their family). Two other groups of "unaffected" people from FAP famil- ies were also included: 19 subjects determined by linkage analysis with both intragenic and closely linked flanking markers to be at less than 1% risk ofFAP (group C) and 19 subjects determined by clinical examination to be at low risk (group D). The latter is defined by the absence of polyps and CHRPE at the age of 25.
DENTAL PANORAMIC RADIOGRAPH SCORE (DPRS) All patients were subjected to clinical, oral, and radiographic examination with informed consent and ethical approval. The radiographic examination consisted of dental panoramic radiography (DPR). Additional appropriate in- traoral radiographs were done where indicated to confirm DPR findings but were not used in data analysis. The radiographs were examined blind and independently by three experienced observers including one consultant dental ra- diologist. The grading of radiographs, detailed below, was done retrospectively. The DPR scoring criteria are detailed in table
2. Various anomalies have been identified by us in a pilot study (unpublished data) and by others in previous studies." 1424 These were used to derive definitions of criteria for scoring. Well defined, round endosteal (fig 1) or ex- osteal (fig 2) radiodensities with regular mar- gins were scored as osteomas; well defined radiodensities but with irregularly shaped mar- gins were scored as dense bone islands (DBIs, fig 3), and an ill defined increase in bone density
Figure 2 Area of a dental panoramic radiograph showing exosteal osteomas (large arrows). Endosteal osteomas are also present in the mandible (small arrows).
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Figure 3 Part of a dental panoramic radiograph showing irregular radiodense lesion typical of a dense bone island (arrow).
was scored as hazy sclerosis (fig 4). The size or the extent of the osseous lesions was also noted. In addition, for hazy sclerosis, as-
sociation with teeth was recorded. Other fea- tures used as diagnostic criteria were presence
or absence of odontomes (figs 4 and 5), super-
numerary teeth, and unerupted teeth (fig 5). Unerupted third molars were excluded from analysis. Four possible outcomes were considered;
these included (1) lack of any anomalies, (2) minimal change(s), (3) equivocal change(s), and (4) significant change(s). Each DPR an-
omaly was assigned a score. An overall Dental Panoramic Radiograph Score (DPRS) was de- termined by summation of the score for in-
Figure 4 Part of a dental panoramic radiograph showing hazy sclerosis affecting the body of the mandible. An odontome is present (arrow).
Figure 5 Area of a dental panoramic radiograph from a
patient wearing complete dentures. An unerupted maxillary canine tooth is present (large arrow) in close association with an odontome (small arrow).
dividual anomalies. The significance of the findings was determined by assigning a specific range of values of DPRS to each of the four outcomes (table 3). Where two features of any anomaly were
considered in the scores, for example, size and numbers for osteomas and DBIs, all lesions were individually assigned a size score together with a single numbers score. This is illustrated by considering three osteomas of sizes 0-5 cm, 1 cm, and 4-0 cm. The score for the number of osteomas is 9 and the scores for the sizes are 0, 3, and 6, giving a final anomaly score of 18. The score assigned to each anomaly reflected
its level of clinical significance if the anomaly occurred in isolation. If an anomaly in isolation is considered clinically significant then a score
at or above the summated significance level (.7) is assigned to it, for example, presence of two osteomas of whatever size. In contrast, for an anomaly not considered to be significant if present in isolation because, for example, it is seen in the general population relatively frequently, a relatively low score was given. Thus, in the absence of other features, the DPRS in this case would not exceed that re-
quired to achieve significance. This is il- lustrated by the scores assigned to the presence of single unerupted teeth or a few DBIs of less than 05 cm. The weighting applied to each score is further considered below in the Dis- cussion.
Table 3 Significance of the dental panoramic radiograph scores (DPRS). Calculation ofDPRS is detailed in "Subjects and methods"
Dental panoramic radiograph score Outcome
0-2 Normal 3-4 Minimal change(s) 5-6 Equivocal change(s) .7 Significant change(s)
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Table 4 Frequency of anomalies in each group. The number ofpatients with the anomalies in each group is indicated and percentages are given in parentheses
GroupA Group B Group C Group D Anomaly (n = 85) (n = 30) (n = 19) (n = 19)
Osteomas 46 (54-1%) 0 (0%) 0 (0%) 3 (15-8%) Dense bone islands 36 (42 4%) 2 (6-7%) 1 (5 3%) 3 (15-8%) Hazy sclerosis 28 (32-9%) 1 (3-3%) 2 (10-5%) 2 (10-5%) Odontomes 8 (9-4%) 0 (0%) 0 (0%) 0 (0%) Supernumerary teeth 23 (27-1%) 0 (0%) 1 (5-3%) 0 (0%) Unerupted teeth 12 (14-1%) 0 (0%) 0 (0%) 0 (0%)
Table 5 Frequency of the possible DPR outcomes in each group. The number ofpatients with the different DPR findings in each group is indicated and percentages are given in parentheses
Group A Group B Group C Group D DPR outcome (n = 85) (n = 30) (n = 19) (n = 19)
Normal 15 (17-7%) 27 (90 0%) 17 (89-4%) 13 (68-5%) Minimal change(s) 9 (10-6%) 3 (10-0%) 1 (5-3%) 2 (10-5%) Equivocal change(s) 3 (3 5%) 0 (0%) 1 (5-3%) 2 (10-5%) Significant change(s) 58 (68 2%) 0 (0%) 0 (0%) 2 (10-5%)
In addition to providing a value of diagnostic significance, the DPRS also provides a measure
of severity of the phenotype by including num- ber, size, or extent of changes in the individual scores beyond that necessary to establish out- come in a diagnostic test. This is illustrated by the increasingly higher scores given to in- creasing number of osteomas seen on DPRs even though two or more osteomas or a single osteoma greater than 0 5 cm would be sufficient for diagnosis of FAP.
STATISTICAL ANALYSIS
Unless stated otherwise, the x2 test with Yates's correction was used where appropriate to test for statistical significance with the accepted significance level of p<0 05. Where expected values in the x2 test fell below 5, Fisher's exact probability test was used with the accepted significance level of p<0 05. Bayesian cal- culations were used to derive probability of carrier status using DPRS outcomes as con-
ditional probability.
RELIABILITY OF TEST The reliability of the test was determined by application of the DPRS to the known affected (group A) and unaffected groups (groups B and C). The clinically low risk group was excluded from analysis in view of the recently reported non-penetrance and delayed onset of polyposis (see Discussion). Various parameters (speci- ficity, sensitivity, false positive rate, false neg- ative rate, positive predictive accuracy, negative predictive accuracy, false alarm rate, and ef- ficiency) were determined.
Results The percentage of patients in each of the four groups (A-D) showing changes on DPRs is shown in table 4. There were no statistically significant differences (Fisher's exact prob- ability test) between the frequencies of an-
omalies observed in the two unaffected groups
(B and C); for the purpose of further statistical analysis the groups were combined. The
differences between the frequency of DPR an- omalies in the FAP affected group (group A) and the unaffected groups (groups B and C) were statistically significant. The commonest anomaly seen in the FAP affected group was bony changes: 81% of patients showed osseous changes including osteomas, DBI, or hazy sclerosis (although not all the changes were individually significant by our criteria). Osseous anomalies were also the commonest change seen in the unaffected groups (B and C) al- though they were present in only 8% of the members of these groups combined. Of the patients in group A, 12 showed a single sig- nificant change; eight patients had osteomas, three patients had DBIs, and one patient had hazy sclerosis. Dental abnormalities (odon- tomes, supernumerary teeth, and impacted/ unerupted teeth) were seen in 37% of the FAP patients. In contrast only one person in group B had a dental anomaly (maxillary super-
numerary tooth). Six of the 19 patients (32%) in group D (clinically low risk) had osseous
anomalies but none had dental anomalies. The number of people classified as having
significant changes, equivocal changes, min- imal changes, and normal radiographic ap-
pearance in each group are shown in table 5. The salient features are that in group A, 58 of the 85 subjects showed significant changes compared to 0 out of 30 in group B and 0 out of 19 in group C. Three of 85 patients in group A and one in 49 patients in groups B and C had equivocal changes. When the significant findings were counted as positive and all other categories were classified as negative, there was a statistically significant difference in the fre- quency of positive and negative test outcomes between the affected group (A) and the un-
affected groups (B and C). Using these counts in Bayesian calculation
with a prior probability of 50% ofbeing carrier, the probability of carrier status was ap-
proximately 17% with a negative DPRS find- ing, 54% with minimal or equivocal changes, and 100% (diagnostic) with significant changes.
In the clinically low risk group of 19 people, two showed significant changes, two had equi- vocal changes, two had minimal changes, and 13 had no changes. The reliability of the test when applied to the known affected group (A) and the known unaffected groups (B and C) is shown in table 6. When the significant findings were counted as positive and all other categories were classified as negative, the test had speci-
Table 6 Reliability of DPRS as a diagnostic test using different DPRS outcomes. Two known unaffected groups (B and C) were considered together with the affected group (A)
DPRS (%)
Test parameter . 7 . 5 . 3
Specificity 100 95-9 87-8 Sensitivity 68-2 71-8 82-4 False positive rate 0 4 0 12-0 False negative rate 31-8 28-2 17-7 Positive predictive accuracy 100 96-8 92-1 Negative predictive accuracy 64-5 66-2 74-1 False alarm rate 0 3-2 7 9 Efficiency 79-1 80-6 84-3
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Thakker, Davies, Homer, Armstrong, Clancy, Guy, Haris, Sloan, Evans
Table 7 Age distribution of the affected FAP patients (group A) with significant changes on DPR (DPRS2 7)
Age range No ofpatients with DPRS . 7 (%) Total No
10-20 8 (42-1) 19 21-30 10 (71-4) 14 31-40 22 (76-9) 26 41-50 8 (66-7) 12 51-80 10 (71-4) 14
ficity and positive predictive accuracy of 100% coupled with a false positive rate and false alarm rate of 0%. The sensitivity of the test was 68-2% with a negative predictive accuracy
of 64-5% and a false negative rate of 31-8%. The efficiency of the test was approximately 79%. The sensitivity of the test was only slightly
improved (from 68-2% to 71-8%) by con-
sidering the equivocal findings as positive (table 6). However, if minimal changes were also considered as positive then sensitivity increased to 82-4%. The specificity and the positive pre- dictive accuracy were reduced to 87-8% and 92-1% respectively. The efficiency of the test increased to 84-3% (table 6).
In group A, an increasing incidence of sig- nificant DPR anomalies (DPRS 7) with age
was observed up to the age of 30 (table 7). Forty two percent of patients aged 20 and under had a DPRS .7 compared to 75% of the patients over 20. This difference was
statistically significant. However, the number of patients at extremes of age was small.
Discussion The desirability of early identification ofpeople with FAP in the at risk group is apparent because screening for colonic polyps by colon- oscopy could be limited to these subjects thus saving those unaffected from unnecessary, un-
pleasant, and costly investigations. Although dental changes have been described previously in FAP, their use in the diagnosis of FAP has been limited. This is chiefly because of the non-specific nature of some of the changes and the consequent difficulty in attaching any significance to them in individual patients. In order to overcome this problem we have de- signed a weighted Dental Panoramic Ra- diograph Score (DPRS) which takes into consideration the nature, extent, and site of the changes seen on a dental panoramic ra-
diograph. In applying the weighting to each score, we
have taken into consideration our clinical ex-
perience and previous studies of radiographic anomalies in the general population and in FAP patients. Small radiodensities, with or without regular margins and particularly in the man-
dibular molar and premolar regions, have been described in between 0% and 10%25-31 of the general population. These changes are often seen in relation to the roots of teeth when present and presumably occur in response to pulpal or periodontal pathoses. We have ob- served three types of osseous lesions in FAP patients: osteomas, dense bone islands, and hazy sclerosis. Previous studies ofFAP patients
have grouped these as "osteomatous" lesions or radio-opacities. We have chosen to consider these lesions separately because in our ex- perience, small and often multiple radio-opa- cities with irregular margins (DBIs by our definition) are often seen in unaffected patients. In contrast, solitary osteomas (circular radio- opaque lesions with regular margins) greater than 0 5 cm and multiple osteomas are not seen in such patients. This is confirmed by the absence of osteomas in all the members and the presence of DBIs in three of the 49 (- 6%) members of the unaffected groups (groups B and C) in the present study. These differences are reflected in the weighting given to these entities in the DPRS. Hazy sclerosis in FAP patients has not been previously described. As this appearance may be seen as an inflammatory bone response to periodontal disease in un- affected subjects, an appropriate weighting was given in DPRS to the site and extent of such changes. Overall, hazy sclerosis unrelated to teeth was given a higher score than that as- sociated with teeth. Supernumerary teeth, in particular those in
the maxillary midline (mesiodens), occur in the general population with a frequency of up to 1 %.32 In the absence of other changes, we have given a relatively low score value to the presence of mesiodens and equivocal score value to the presence of any other single supernumerary tooth. Unerupted teeth are relatively common in the general population occurring with an overall frequency of 17%.33 Unerupted third molars are even more common (frequency of - 22%),33 so we have disregarded these in the DPRS. However, other unerupted teeth are included although a low score is given to the presence of a single unerupted tooth.
In the present study, all radiographic an- omalies were significantly more frequent in the affected group than in the unaffected group. The most frequent observation in the FAP patients was the presence of osseous lesions although we did not consider all of these changes to be individually significant in the DPRS. Our data are consistent with previous studies which reported osseous changes in be- tween 76 and 93% and dental changes in 30% of FAP patients." 14-14 The DPRS is a highly reliable diagnostic
index. With a DPRS .7, the specificity and positive predictive rate was 100%, and a false positive rate of0% was obtained. However, the sensitivity is relatively low at 69% and this is not improved significantly by consideration of the equivocal DPRS values as significant. This level of sensitivity may appear surprising given the high prevalence of osseous changes in the affected subjects; however, not all of these were deemed to be significant in the scoring of DPRS. Thirteen of the 85 (- 15%) FAP patients had what we classified as insignificant osseous changes compared to five of the 49 (- 10%) members of the unaffected groups (B and C). The sensitivity is considerably im- proved if all positive findings, that is, the min- imal and equivocal changes, are considered as significant; however, the specificity and the positive predictive accuracy are slightly re-
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duced. Overall, the efficiency of the test is slightly improved (from -79% to -84%). These data are remarkably similar to the pre- viously reported sensitivity and specificity of 82% and 90% respectively for findings char- acteristic of FAP on DPRs.20 Giardiello et allo also reported a similar level of sensitivity (84%) but a much lower specificity (50%). However, they considered the presence of one or more jaw lesions (any well circumscribed area of radio-opacity or an odontome) as significant. This is clearly different from the thresholds used in the present study. The presence of six osteomas has been reported to be diagnostic for FAP'7 but patients with such changes only represent a small percentage ofthe total sample.
In comparison, the other most commonly used extracolonic phenotype marker, CHRPE, is reported to have sensitivity of between 58 and 100% using various diagnostic threshold criteria. lo-" In unaffected populations, CHRPE is reported in up to 43% of people." A high level of specificity (between 94 and 100%) is also reported applying diagnostic thresholds based on type, size, or number of CHRPE lesions or presence of bilateral lesions."1-13 De- pending on the thresholds applied in the DPRS (as discussed above), comparable levels of specificity and sensitivity are obtained in the present study.
Application of DPRS to the clinically low risk group (group D) showed two subjects with a significant score. They were aged 58 and 52, were free of colonic polyps, and did not have CHRPE. One had a single osteoma - 1 cm and the other had an osteoma (- 7 mm) and a small dense bone island (- 5 mm) respectively. Previously reported incidence data indicate that at risk people with no retinal features and negative colonoscopy at the age of 34 years should be considered to be free of FAP. This suggests that the two patients with the sig- nificant DPRS scores in the clinically low risk group represent false positives in our test. How- ever, we have recently described four families with non-penetrance and late onset of polyp- osis.34 Our studies indicate that at least 5% of affected subjects will be free of polyps on sigmoidoscopy at 30 years of age and some still have no polyps in their fifties. Thus the two subjects may represent atypical FAP cases par- ticularly in view of the high specificity of the test determined in this study. Mutation analysis is continuing and should establish which of these possibilities is correct. The higher frequency of significant DPRS
findings in the patients aged over 20 compared to the patients aged 20 and under suggests that there may be an age dependent appearance of the jaw changes. This indicates that the test is more likely to be informative in the older group of patients. The usefulness of DPR in the diagnosis of
FAP is apparent from the data presented here. DPRS provides a highly specific method of determining significance of findings on DPR. In addition, the incidence data should permit use of DPR findings together with oph- thalmoscopy findings and linkage analysis in Bayesian calculations for optimal assessments
of risk where mutation analysis is not feasible. The DPRS is a highly reliable and reproducible index in our hands; however, we have examined a large series of patients to date and have considerable experience in assessment of the radiographs. Further independent assessment of DPRS by other groups is necessary in de- termining the usefulness or otherwise of the test.
Part of this work was funded by a North West Regional Health Authority Medical Innovations Grant to GE, NT, PS, and RH.
1 Groden J, Thliveris A, Samovitz W, et al. Identification and characterization of the familial adenomatous polyposis coli gene. Cell 1991;66:589-600.
2 Nishisho I, Nakamura Y, Miyoshi Y, et al. Mutations of chromosome 5q21 genes in FAP and colorectal patients. Science 1991;253:665-9.
3 Murday V, Slack J. Inherited disorders associated with colo- rectal cancers. Cancer Surv 1989;8:139-57.
4 Alm T, Licznerski G. The intestinal polyposis. Clin Gastro- enterol 1973;2:577-602.
5 Bussey JHR. Fanmilial polyposis coli. Family studies, histo- pathology, dzfferential diagnosis, and results of treatmzent. Bal- timore: John Hopkins University Press, 1975.
6 Spirio L, Nelson L, Ward K, Burt R, White R. A CA- repeat close to the adenomatous polyposis coli gene offers improved diagnostic testing for familial APC. An, _7 Hunm Genet 1993;52:286-96.
7 Nagase H, Nakamura Y. Mutations of the APC (ad- enomatous polyposis coli) gene. Hum Mutat 1994;2:425- 34.
8 Powell SM, Petersen GM, Krush AJ, et al. Molecular diag- nosis of familial adenomatous polyposis. N Engl _7 Med 1993;329: 1982-7.
9 Varesco L, Groden J, Spirio L, et al. A rapid screening method to detect nonsense and frameshift mutations: identification of disease-causing APC alleles. Cancer Res 1994;53:5581-4.
10 Giardiello FM, Offerhaus GJA, Traboulsi EI, et al. Value of combined phenotype markers in identifying inheritance of familial adenomatous polyposis. Gut 1991 ;32: 1170-4.
11 Chapman PD, Church W, Burn J, Gunn A. Congenital hypertrophy of retinal pigment epithelium: a sign of fa- milial adenomatous polyposis. BMJ 1989;298:353-4.
12 Bum J, Chapman P, Delhanty J, et al. The UK Northern Region genetic register for familial adenomatous polyposis coli: use of age of onset, congenital hypertrophy of the retinal pigment epithelium, and DNA markers in risk calculations. .7 Med Genet 199 1;28:289-96.
13 Morton DG, Gibson J, Macdonald F, et al. Role ofcongenital hypertrophy of retinal pigment epithelium in the predictive diagnosis of familial adenomatous polyposis. Br _7 Surg 1992;79:689-93.
14 Gardner EJ, Richard RC. Multiple cutaneous and sub- cutaneous lesions occurring simultaneously with her- editary polyposis coli and osteomatosis. Am _7 Hum Genet 1953;5:139-47.
15 Ziter FMH. Roentogenographic findings in Gardner's syn- drome. _AMA 1965;192:1000-2.
16 Utsunomiya J, Nakamura T. The occult osteomatous changes in the mandible in patients with familial polyposis coli. Br j3 Surg 1975;62:45-51.
17 Ida M, Nakamura T, Utsunomiya J. Osteomatous changes and tooth abnormalities found in jaws of patients with adenomatosis coli. Oral Surg 1981; 15:2- 11.
18 Jarvinen HJ, Peltokallio P, Landtman M, Wolf J. Gardner's stigmas in patients with familial adenomatosis coli. Br 7 Surg 1982;69:718-21.
19 Bulow S, Sondergard JO, Witt R, Larsen E, Tetens G. Mandibular osteomas in familial polyposis coli. Dis Colon Rectum 1984;27:105-8.
20 WolfJ, Jarvinen HJ, Hietanen J. Gardner's stigmas in patients with familial adenomatous coli. Br3t Oral Maxillo-fac Surg 1986;24:410-6.
21 Bulow S. Incidence of associated diseases in familial polyp- osis coli. Semin Surg Oncol 1987;3:84-7.
22 Carl W, Herrera L. Dental and bone abnormalities in patients with familial polyposis coli. Semin Surg Oncol 1987;3:77-83.
23 Offerhaus GJA, Levin LS, Giardiello FM, et al. Occult radiopaque jaw lesions in familial adenomatous polyposis coli and hereditary nonpolyposis colorectal cancer. Gastro- enterology 1987;93:490-7.
24 Takeda Y. Multiple cemental lesions in the jaw bones of a patient with Gardner's syndrome. lirchow Arch A 1987; 411:253-6.
25 Boyne PJ. Incidence of osteosclerotic areas in the mandible and maxilla. J Oral Surg Anesth Hosp Dent Serv 1960;18: 486-9 1.
26 Meister F Jr, Simpson J, Davies EE. Oral health of airmen: analysis of panoramic radiographic and polaroid photo- graphic survey. _7 Am Dent Assoc 1977;94:335-9.
27 Ritchie GM, Fletcher AM. A radiographic investigation of edentulous jaws. Oral Surg Oral Med Oral Pathol 1979; 47:563-7.
463
rotected by copyright. http://jm
nloaded from
Thakker, Davies, Homer, Armstrong, Clancy, Guy, Haris, Sloan, Evans
28 Allatar MM, Baughman RA, Collett WK. A survey of panoramic radiographs for evaluation of normal and pathologic findings. Oral Surg Oral Med Oral Pathol 1980; 50:472-8.
29 Spyropoulos ND, Patsakas AJ, Angelopoulos AP. Findings from radiographs of the jaws of edentulous patients. Oral Surg Oral Med Oral Pathol 1981;52:455-9.
30 Austin BW, Monie AJ. A comparative study of prevalence of mandibular osteosclerosis in patients of Asiatic and Caucasian origin. Austr Dent 1984;29:36-43.
31 Barrett AP, Waters BE, Griffiths CJ. A critical evaluation of
panoramic radiography as a screening procedure in dental practice. Oral Surg Oral Med Oral Pathol 1984;57:673-7.
32 Shafer WG, Hine MK, Levy BM. Developmental ab- normalities of oral and paraoral structures. In: A textbook oforalpathology. 3rd ed. Philadelphia: WB Saunders, 1974.
33 Dachi SF, Howell FV. A survey of 3874 routine full-mouth radiographs. II. A study of impacted teeth. Oral Surg Oral Med Oral Pathol 1961;14:1165-9.
34 Evans DGR, Guy SP, Thakker N, et al. Non-penetrance and late appearance of polyps in families with familial adenomatous polyposis. Gut 1993;34: 1389-93.
464
rotected by copyright. http://jm
nloaded from