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Primary failure of eruption and PTH1R: Theimportance of a genetic diagnosis for orthodontictreatment planning

Sylvia A. Frazier-Bowers,a Darrin Simmons,b J. Timothy Wright,c William R. Proffit,d and James L. Ackermane

Chapel Hill and Pittsboro, NC

Introduction: Primary failure of eruption (PFE) is characterized by nonsyndromic eruption failure of permanentteeth in the absence of mechanical obstruction. Recent studies support that this dental phenotype is inheritedand that mutations in PTH1R genes explain several familial cases of PFE. The objective of our study was toinvestigate how genetic analysis can be used with clinical diagnostic information for improved orthodonticmanagement of PFE. Methods: We evaluated a family (n 5 12) that segregated an autosomal dominantform of PFE with 5 affected and 7 unaffected persons. Nine available family members (5 male, 4 female)were enrolled and subsequently characterized clinically and genetically. Results: In this family, PFE segre-gated with a novel mutation in the PTH1R gene. A heterozygous c.1353-1 G.A sequence alteration causeda putative splice-site mutation and skipping of exon 15 that segregated with the PFE phenotype in all affectedfamily members. Conclusions: A PTH1R mutation is strongly associated with failure of orthodontically assis-ted eruption or tooth movement and should therefore alert clinicians to treat PFE and ankylosed teeth with sim-ilar caution—ie, avoid orthodontic treatment with a continuous archwire. (Am J Orthod Dentofacial Orthop2010;137:160.e1-160.e7)

Primary failure of eruption (PFE), originally de-scribed by Proffit and Vig,1 is characterized bynonsyndromic eruption failure of permanent

teeth in the absence of mechanical obstruction. Thehallmark features of this condition are (1) infraocclu-sion of affected teeth, (2) increasing significant poste-rior open-bite malocclusion accompanying normalvertical facial growth, and (3) inability to move affectedteeth orthodontically.

Many studies have noted the heritable basis of thisdental phenotype,2-8 and recently mutations in parathy-roid hormone receptor 1 (PTH1R) have been identified

aAssistant professor, Department of Orthodontics, School of Dentistry, Univer-

sity of North Carolina, Chapel Hill.bResearch analyst, Department of Pediatric Dentistry, School of Dentistry,

University of North Carolina, Chapel Hill.cProfessor, Department of Pediatric Dentistry, School of Dentistry, University of

North Carolina, Chapel Hill.dProfessor, Department of Orthodontics, School of Dentistry, University of

North Carolina, Chapel Hill.ePrivate practice, Pittsboro, NC

Supported by the University of North Carolina at Chapel Hill Faculty Develop-

ment Funds, grants 1K23RR17442 and M01RR-00046.

The authors report no commercial, proprietary, or financial interest in the

products or companies described in this article.

Reprint requests to: Sylvia A. Frazier-Bowers, Department of Orthodontics,

University of North Carolina, Chapel Hill, NC 27599; e-mail, sylvia_frazier@

dentistry.unc.edu.

Submitted, August 2009; revised and accepted, October 2009.

0889-5406/$36.00

Copyright � 2010 by the American Association of Orthodontists.

doi:10.1016/j.ajodo.2009.10.019

in several familial cases of PFE.9 A detailed clinicalanalysis showed several types of nonsyndromic PFE,including type I and type II, with both types primarilyaffecting the posterior segments, either unilaterally orbilaterally.7 Type II is further characterized by greatereruption potential of the most distal tooth affectedwith PFE. It is not clear whether specific phenotypes(clinical variations described as type I vs type II) are as-sociated with distinct genetic mutations or whether theclinical variation represents the broad spectrum associ-ated with, for instance, PTH1R. It is known that, despiteclinical severity or type, PFE does not respond to ortho-dontic force. Previous studies in our laboratory ruled outAMELX, RUNX2, POSTN, and AMBN as candidategenes for PFE in families and individuals.8 However,recent advances in gene discovery, particularly withPFE, will most likely provide a novel diagnostic toolto aid in the clinical management of orthodontic patientswhen failure of eruption is suspected.

Eruption failure can be a part of a syndrome or occuras an isolated condition, such as PFE. In either case, it iscritically important to distinguish between eruption fail-ure due to local or mechanical causes (cysts, interfer-ence of adjacent tooth, lateral pressure from thetongue, or secondary to a syndrome such as cleidocra-nial dysplasia) and failure of the eruption mechanismcompletely. The orthodontic management of mechani-cal failure of eruption (MFE) is quite different fromthat of PFE.7 In the case of syndrome involvement,

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Fig 1. Pedigree showing segregation of PFE in the fam-ily. An autosomal dominant inheritance pattern was ob-served, with male and female members affected equallyand no skipping of a generation. Five of 12 persons areaffected in this family; subject II:3 was unavailable forthe study. Squares indicate male; circles indicate fe-male. Affection status is as follows: dark circles orsquares denote an affected person; clear denotes unaf-fected. The arrow indicates the index patient who firstcame to the clinic (proband).

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the orthodontic diagnosis triage should include whetherthe syndrome results in MFE, including but not limitedto osteopetrotic bone, fibrous gingival tissue, orimpacted teeth, or whether it is due to delayed eruption.The genetic alteration of at least 1 gene, PTH1R, isevidence that there is also a biologic distinction betweenPFE and other eruption disorders such as MFE.9 Hence,once MFE is ruled out, genetic analysis of PTH1Rshould be a critical part of the orthodontic diagnosticregimen.

PTH1R resides on the small arm of chromosome 3(3p22-21.1) and encodes a G-coupled protein receptorfor both parathyroid hormone (PTH) and parathyroidhormone-related protein (PTHrP). A key function ofPTH is regulation of calcium metabolism, whereasPTHrP plays a major role in skeletal development dur-ing early bone growth by regulating chondrocyte prolif-eration and differentiation. Recessive mutations inPTH1R have been identified in people with Blomstrandchondrodysplasia (BOCD; OMIM: 215045), a geneticdisorder characterized by advanced endochondralbone maturation, increased bone density, and short stat-ure.10 Those affected with BOCD also had abnormali-ties in breast development and several impacted teeth.In BOCD, autosomal recessive mutations have led tomutational inactivation of PTH receptors.10 Other con-ditions associated with mutations in PTH1R includeJansen metaphyseal chondrodysplasia (OMIM:156400), enchondromatosis, and Eiken syndrome(OMIM:600002), all of which include cartilage or skel-etal dysplasia.11-13 Despite the many disorders associ-ated with mutations in PTH1R, the recent report ofPTH1R mutations associated with PFE makes thisa high-priority candidate gene for confirming diagnosisof a nonsyndromic PFE phenotype.9 The objective ofour study was therefore to investigate how genetic anal-ysis can be used with clinical diagnostic information forimproved orthodontic management of PFE.

MATERIAL AND METHODS

Enrollment for this study was based on PFE in atleast 2 family members. All subjects (adults and minors)consented to participate (including a release for dentalrecords). Approval for this study was granted by theBiomedical Institutional Review Board at the Univer-sity of North Carolina at Chapel Hill. Through detailedinterviews, a pedigree (Fig 1) was extended in 1 family.This family consisted of 12 people from 11 to 72 yearsof age. Five male and 4 female members were availablefor clinical and molecular testing. A comprehensiveclinical evaluation was performed to determine (1)a positive diagnosis of PFE with no mechanical or sec-

ondary barrier and also based on at least 1 uneruptedtooth after unsuccessful orthodontic treatment for theproband; (2) the skeletal relationship including vertical(overbite or open bite) and sagittal (Angle Class I, ClassII, or Class III molar relationship) based on clinicalexaminations and cephalometric radiographs; and(3) anomalies in growth or stature either absent or pres-ent. The clinical evaluation included clinical photo-graphs; panoramic and cephalometric radiographswere obtained for participating family members.

Mutational analysis was performed after extractionand purification of DNA from buccal cells (PureGenekit, Gentra Systems, Minneapolis, Minn) or saliva (Or-agene, DNA Genotek, Toronto, Ontario, Canada). Weamplified and sequenced all coding exons of PTH1R(exons 3-16) for the 9 subjects using primer sets as de-scribed previously.9 To include splice junctions in ouranalysis, primer sets were designed to delineate regionsthat included a minimum of 25 bases of intron sequencein addition to the exon sequence. Amplification was per-formed by using Accuprime polymerase chain reactionbuffer and enzyme mix (Life Technologies/Invitrogen,Bethesda, Md) under the following conditions: 10 min-utes at 95�C activation/premelt, followed by 35 cyclesof 30 seconds at 94�C melt, 30 seconds at 60�C anneal,and 3 minutes of 72�C extension. The polymerasechain reaction products were purified by usingExoSaplt (USB, Cleveland, Ohio) and sequenced atthe University of North Carolina at Chapel Hill’sGenome Analysis Core facility.

Fig 2. A-C, Type II PFE was observed in pretreatment photos of subject III:4, with a Class I molar andcanine relationship. D-F, This mild presentation of a unilateral open bite (indicated by the arrow) wasinitially mistaken for isolated ankylosis, which significantly worsened with continuous archwire treat-ment. The resultant posterior lateral open bite could be corrected only with single-tooth osteotomiesto reposition the teeth occlusally.

Fig 3. A-C, Pretreatment records of subject III:2 show type II PFE with slightly more eruptionpotential of the distal-most affected tooth on the right side. Similar to his sister (subject III:4), hehas a unilateral pattern of PFE with a Class I relationship on the unaffected side (left).

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Sequences were compared to wild type PTH1R (ac-cession NM_000316.2) from GenBank release GRCh37by using the BLAST algorithm.14 For our study, previ-ously reported single nucleotide polymorphisms andsynonymous substitutions in the coding region wereignored.

RESULTS

Pedigree analysis by visual inspection (Fig 1) sug-gested an autosomal dominant inheritance with variableexpressivity of PFE. For all examined persons, therewas a complete absence of systemic disorders, and stat-ure was within normal limits but varied as expected ac-cording to population norms. Two affected familymembers were classified as PFE type I (subjects III:3and II:2); 2 were type II (subjects III:2 and III:4). In

the family, the severity varied greatly. For example,the pretreatment records of subject III:4 showeda much less severe manifestation of PFE with only uni-lateral involvement (Fig 2, A-C). Subjects III:4 and III:2(Fig 3) had previously been diagnosed with ankylosisrather than PFE, since the more severe classic appear-ance of PFE was lacking (only 2 or 3 affected teeth in1 quadrant). This is in contrast to their full sibling, sub-ject III:3 (Fig 4), whose pretreatment photos showeda severe bilateral open bite that included the caninesthrough the second molars. Subject II:2 (Fig 5, A-C)was similar in severity to her son (subject III:3). Inthis family, an identical genetic diagnosis (see next sec-tion) was an equalizing element; although the clinicaldiagnoses were disparate between affected members,the resultant orthodontic failure was the same.

Fig 4. A-C, In subject III:3, pretreatment records show a bilateral posterior open bite and a significantClass III molar relationship. Type I PFE, with the distal-most teeth affected more severely, is evident.D-F, Final orthodontic result after orthognathic surgery to correct the skeletal and dental Class III mal-occlusion shows that the severe bilateral posterior open bite was not significantly improved.

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Clinical and cephalometric evaluation of verticaland sagittal relationships showed that affected personswere rarely Class II skeletal or dental and more likelyClass III. Cosegregation of Class III malocclusion andPFE traits was observed. Specifically, 2 subjects af-fected with PFE were also diagnosed as Class III skele-tal; subject I:2 was not affected with PFE but had a ClassIII malocclusion. In the 2 subjects with PFE and ClassIII, orthognathic surgery was required to correct theClass III sagittal relationship. Furthermore, these per-sons with a Class III skeletal relationship had a more se-vere posterior lateral open bite. Analysis of the clinicalpretreatment and posttreatment records also showedthat, despite the clinical severity of the PFE phenotype,treatment with a continuous archwire resulted in thesame outcome: failure to erupt. The response to treat-ment was often intrusion of the adjacent teeth (Fig 2,F), creating a more severe malocclusion than beforeorthodontic treatment.

Direct sequencing of PTH1R from the 9 participants(5 affected, 4 unaffected) showed the cosegregation ofa novel mutation with the PFE phenotype. Mutationalanalysis of PTH1R showed a heterozygous alteration,c.1353-1 G . A, which resulted in a putative splice-site mutation and skipping of exon 15 (Fig 6). This mu-tation, which is predicted to cause loss of function of thePTH1R protein, segregated in an autosomal dominantfashion with the phenotype. Absence of the alterationin subjects I:1 and I:2 ruled out an autosomal recessivemode of inheritance. The c.1353-1 G . A mutation

appeared in subject II:2 (her sibling, II:3, was unavail-able for testing but was reported to have a similar erup-tion disorder) and 3 of her children, subjects III:2, III:3,and III:4. Sequence data from the unaffected subjects(I:1, I:2, and III:5) showed no alterations of PTH1R.Functional studies are currently underway to specifi-cally determine the consequence of this sequence alter-ation in the PTH1R gene.

DISCUSSION

Our pedigree and clinical analysis findings furtherconfirm that PFE is an inherited disorder, and that the in-heritance can be autosomal dominant with variable ex-pressivity. We ruled out autosomal recessive inheritancein this family, since we found 1 of 2 scenarios: (1) themutation occurred as a new, spontaneous mutation ina founder, or (2) when 2 generations were affected,only 1 parent carried the PTH1R mutation. Moreover,autosomal recessive mutations of the PTH1R genehave been reported in the literature with severe formsof dwarfism; this form is often lethal and results in deathshortly after birth.15-17 It has been proposed that, in thecase of BOCD, autosomal recessive mutations ofPTH1R most likely result in a complete lack of func-tional PTH receptors. Hence, the skeletal abnormalitiesseen in BOCD are explained by a lack of functional PTHreceptors; conversely, autosomal dominant mutations inPFE result in reduced gene dosage with some functionalprotein remaining.

Fig 5. Pretreatment records including A, lateral cephalometric and B, panoramic radiographs of sub-ject II:2 show unilateral type I PFE with a Class III dental and skeletal relationship. C-E, Posttreatmentrecords after orthognathic surgery to advance the maxilla show correction in the sagittal dimension,but the posterior open bite remains.

Fig 6. Representative electropherogram of the PTH1R sequence segregating the PFE phenotype.Pairwise alignment using bioinformatic tools using GenBank indicate that a heterozygous alteration,c.1353-1 G.A, caused a putative splice-site mutation and skipping of exon 15 and resulted in loss offunction of the PTH1R protein. All affected subjects carried this mutation.

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One characteristic of BOCD is mandibular hypopla-sia, presumably caused by condylar cartilage hypopla-sia in affected persons. Since 2 subjects with PFE alsohad Class III skeletal patterns, the Class III skeletal pat-terns could have been the result of growth disturbancesin the cartilaginous nasal capsule, leading to maxillaryhypoplasia rather than exuberant mandibular growth.

Hence, patients with PFE might allow an opportunityto study the genetic and epigenetic factors associatedwith localized intramembranous bone growth and an at-tempt to relate those findings to more generalized endo-chondral skeletal growth disorders.

The finding that both mild and severe cases carriedthe same mutation in 1 family challenged previous

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diagnoses of ankylosis for isolated unerupted teeth. Inthis family, 2 affected members had been diagnosedwith ankylosis, determined by bone sounding. Becauseour evaluation found that all family members had PFE,it shows a need to establish better diagnostic tools to dis-tinguish between ankylosis and PFE. Alternatively, per-haps these 2 conditions belong to the same biologicspectrum and are effectively the same disorder. Futurestudies that explore the molecular and cellular eventsof ankylosis vs PFE will help to elucidate the pathwaysthat contribute to normal eruption. When either MFE ordelayed eruption is ruled out, the orthodontist would bewise to use a genetic analysis to improve the orthodonticmanagement of PFE patients.

It is still unclear why highly variable clinical expres-sivity is observed in PFE, with some persons affected bi-laterally and others affected unilaterally in the samefamily. Likewise, there is no apparent explanation forwhy the posterior dentition is preferentially affected.We speculated that similar to other patterning genes thatare involved in tooth development (eg, MSX1, DLX2,PAX9), the PTH1R gene product acts in a temporally-and spatially-specific manner, affecting the posterior vsanterior segments of the alveolus and corresponding teeth.

The discovery of a gene that is responsible for PFEdoes not eliminate the likelihood that additional genes,yet to be discovered, are also responsible for this condi-tion. Similar to tooth agenesis and other craniofacialdisorders, many genes in critical pathways interactwith PTH1R. Although the recent report of autosomaldominant mutations in PTH1R makes this gene an idealcandidate gene for analysis of an eruption failure pheno-type,9 future research should address these questions:what is the specific role of PTH1R in the spectrum oferuption failure phenotypes, and are additional genesresponsible for familial eruption failure?

CONCLUSIONS

Although molecular studies in mice have signifi-cantly advanced our understanding of the cellular andmolecular pathways involved in tooth eruption, its spe-cific genetic and cellular determinants and their rela-tionships to clinical disorders are still poorlyunderstood.18 By taking advantage of the geneticknowledge by the identification of PTH1R, we can be-gin to understand these determinants and avoid unnec-essary procedures such as futile attempts to extrudeteeth orthodontically, thereby sparing PFE patients ex-cessive costs and protracted treatment times. Additionalgenotype and phenotype studies of PFE will also aid indetermining whether affected persons (carrying muta-tions in PTH1R or other yet unidentified genes) might

respond to orthodontic forces. To date, there are onlya few anecdotal cases of successful extrusion of teeth af-fected with PFE. We hope that, with the identification ofadditional genes involved in abnormal tooth eruption,we will someday elucidate the genetic basis of severalcritical biologic aspects that underlie all clinical ortho-dontics: (1) normal tooth eruption, (2) normal dentoal-veolar growth and development, (3) tissue behavior innormal physiologic tooth drift, (4) tissue reaction to or-thodontic tooth movement, and (5) variability in re-sponse to orthodontic treatment. The ultimate goal ofgenetic research in orthodontics is to shift the emphasisin diagnosis and treatment planning from a wholly phe-notypic or clinical perspective to greater considerationof a patient’s genotype.

Since we now have no mechanotherapeutic meansfor modifying dentoalveolar growth in PFE, any attemptat early orthodontic intervention for these patients is fu-tile. Once growth is complete, several multidisciplinarytreatment strategies can partially solve the severe poste-rior open-bite malocclusions that are characteristic ofthis disorder. Single-tooth or multiple-tooth osteoto-mies or selective extractions followed by implants canoften lead to a functioning occlusion. Thus, the advan-tage of making an early diagnosis of PFE is that it allowsa clinician the peace of mind to merely observe and doc-ument the unfavorable growth changes that willinevitably take place. This treatment-planning recom-mendation is meant to be in sharp contrast to an expost facto diagnosis of PFE after unsuccessful ortho-dontic extrusion of the teeth. The disadvantage of a ther-apeutic diagnosis (early orthodontic interventionparticularly with a continuous archwire) is that it can ac-tually make the situation worse. Thus, the best treatmentfor an accurately established early diagnosis of PFE isinitially no treatment but reserving the multidisciplinaryoptions for affected patients for a later time after thecompletion of growth.

We thank the family and the dentists who partici-pated in this study; Jaerim Lee, Kevin Tsui, and KimThompson for preparing the data; Warren McCullomfor formatting the graphics; and Richard Youngbloodfor editing the manuscript.

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