American Journal of Medical Genetics 132A:164–170 (2005)

Recurrent Adjacent-2 Segregation of a Familialt(14;21)(q11.2;q11.2): Phenotypic Comparison of twoBrothers and a Paternal Aunt Inheriting the der(14)Emily Chen,1* Michele A. Choe,2 William D. Loughman,3 Susan Covert,3 Sheila Bitts,4

Amy Rowe,3 Linda Beischel,5 and John P. Johnson5

1Department of Genetics, Kaiser Permanente Medical Group, Oakland, California2Department of OB/Gyn, Loyola University Medical Center, Maywood, Illinois3Department of Genetics, Children’s Hospital Oakland, Oakland, California4Genzyme, Pasadena, California5Department of Genetics, Shodair Hospital, Helena, Montana

A 14-year-old boy was referred for a geneticsevaluation after high-resolution chromosomeanalysis showed a small amount of extra materialin the proximal long arm of chromosome 21. Fiveyears prior, his karyotype analysis was inter-preted as normal with a variant chromosome 21.The patient has short palpebral fissures, strabis-mus, flat antihelices of the ears, long thumbs withbilaterally absent interphalangeal creases, prox-imal bilateral 3/4 syndactyly, small testes, hypo-tonia, mental retardation, and speech problems.He has significant depression and behavioralproblems including hyperactivity, aggression,and impulsivity. His 8-year-old brother has moresevere behavioral disturbances and depression,but less significant mental retardation. A paternalaunt has mental retardation, is unusually docile,and appears similar to our patient. Chromosomeanalysis and fluorescence in situ hybridization(FISH) whole chromosome paint of chromo-some 21 showed that the patient’s father carriesa ‘‘cryptic’’ balanced translocation, 46,XY,t(14;21)(q11.2;q11.2), as does the patient’s paternalgrandmother. Uniparental disomy studies usingseven informative polymorphic nucleotide repeatmarkers from 14q and 21q confirmed biparentalinheritance of the number 14 and 21 chromosomesfor each brother, and indicate that they and thepaternal aunt, all of whom inherited the der(14),are monosomic for proximal 21q and trisomic forproximal 14q. These karyotypes arose through anadjacent-2 segregation in the father on two occa-sions, and from the paternal grandmother on oneoccasion. This family is an example of recurrentmalsegregation with translocations involving theacrocentrics. � 2004 Wiley-Liss, Inc.

KEY WORDS: chromosomes 14 and 21; recipro-cal translocation; adjacent-2 seg-regation; mental retardation

INTRODUCTION

Chromosome analysis is a routine part of the evaluation ofany child with unusual physical findings and mental retarda-tion [Aase, 1990].With continuing improvement in techniques,it is useful to periodically re-evaluate a child’s karyotype usingthe latest molecular genetic and molecular cytogenetic techni-ques. The patient we describe was originally studied in 1990.This study showed that he had a normal 46,XY karyotype withan apparently variant chromosome 21. Upon re-evaluation,this variant 21 was thought to be a derivative chromosome 14and further family studies were pursued. We present clinicaland laboratory studies from this patient and two affectedrelatives.

CLINICAL REPORTS

See family pedigree (Fig. 1), showing three affectedmembers.

Patient 1

The propositus (III:2) is a 21-year-old Caucasian male. Atbirth, he weighed 2,863 g (5%), was 48.3 cm long (3%), and had

Fig. 1. Pedigree of family: individuals III:2, III:3, and II:1 have speechand developmental problems, with associated minor anomalies.

*Correspondence to: Emily Chen, Department of Genetics,Kaiser Permanente Medical Group, 280 West MacArthur Blvd.,Oakland, CA 94611. E-mail: emily.chen@kp.org

Received 16 July 2003; Accepted 19 December 2003

DOI 10.1002/ajmg.a.30511

� 2004 Wiley-Liss, Inc.

anOFCof 33 cm (10%).At 6months of age, hewasnoted tohavehypotelorism, epicanthal folds, hypotonia, and developmentaldelay. He sat at 6 months, walked at 1 year, toilet trained at4 years, said single words at 7 years and sentences at 10 yearsof age. At 14½ years of age, his weight was 41 kg (10%), height151 cm (5%), OFC 53.5 cm (30%) (Fig. 2). Interpupillarydistance was 5.5 cm (30%) and palpebral fissure length was2.5 cm (<3%). Ears had flat antihelices and small lobules. Hehad inverted nipples. Fingers were long and thin with 3/4proximal syndactyly bilaterally. Thumbs were long withabsent interphalangeal creases bilaterally. Feet had higharches. The first toes were deviated medially and the feet haddecreased plantar creases. Penis, testes, and scrotum werehypoplastic and he had surgery for cryptorchidism. Neuro-logically, he had poor fine motor control, overall hypotonia,decreased reflexes, andataxia.Hehadanunsteadygait and toewalked. Speech was inarticulate. He was hyperactive, impul-sive, emotionally labile, and aggressive. Previous diagnosticstudies including chromosomes, DNA fragile X, fluorescence insitu hybridization (FISH) for Angelman syndrome, urineorganic acids, somatomedin C, FSH, LH, testosterone, prolac-tin, boneagefilms,EMG,andnerve conduction studieswereallnormal.HeadMRIat age 9 years showedquestionable cerebralatrophy. He has resided in a group home for the last 14 years.Management of his behavior with medications has been achallenge. On last evaluation at age 19 years 9 months he wasnoted to have motor apraxia (tongue and hands), mildarticulation disorder, and ADHD.

Patient 2

This is the younger brother (III:3) (by exactly 6 years)of Patient 1. At 9 years of age he had a weight 31.5 kg(75th centile), height of 130 cm (25th centile), andOFC 55.5 cm(98th centile). He had short palpebral fissures (2.5 cm; 3%),strabismus requiring two surgeries, protruding, cupped ears,high palate, crowded teeth, thin upper lip (Fig. 3). Handcreases were superficial, and he had 4th and 5th finger clino-dactyly and overlapping toes. Testes were retractile. He had asuperficial sacral dimple.

Developmental concerns began at 1 year of age. Behavioralproblems such as short attention span, outbursts, verbal abusewere of later onset compared to his brother; however, he even-tually tried over 30 medications as an attempt to improve hisbehavior, which is still amajor problem. Compared to his olderbrother, his coordination is better. He has an easier time

learning, more of a sense of humor, and is more attentive. Hestarted speaking at a normal age but has some articulationproblems.He can read about 70words.He resides in a separateresidential home. He throws things, hurts others, and needsconstant supervision. He has difficulty distinguishing rightfromwrong.Hismother feels that his behavior is under control50–75% of the time.

Physical examination findings which are similar betweenthe brothers include: short palpebral fissures, mildly dysplas-tic ears, chronic otitis media, superficial hand creases,especially at interphalangeal joints. The boys are also similarin the way that their speech articulation is poor. They bothhave ADHD, severe behavioral problems, difficulties withmotor planning, and are tactilely defensive.

Patient 3

This is the paternal aunt (II:1) of Patients 1 and 2. She is now50 years old. By report and photographs, she has some facialresemblance (Fig. 4) to Patient 1. She has long, slender fingerswith normal thumb creases. She is less delayed than eitherpatients 1 or 2. She reads signs, writes in cursive, attends asheltered workshop, lives semi-independently, and is docilewithout hyperactivity. She is, however, unable to accuratelycount money and has inarticulate speech. She too resides in aresidential home.

CYTOGENETIC STUDIES

Using high resolution cytogenetic analysis of culturedperipheral blood lymphocytes, GTG, CBG, and Ag/NORstaining were performed using standard protocols. Patient 1(III:2) and his brother, Patient 2 (III:3), both have a malekaryotype with a small amount of additional chromosomalmaterial in the proximal long arm of one chromosome 21q.

The father, II:2, carries the same unusual chromosome 21(Fig. 5A). NORandC-bandingwere not informative. FISHwas

Fig. 2. III:2. Patient 1: Note narrow facies, short palpebral fissures.

Fig. 3. III:3. Patient 2: He has short palpebral fissures and protrudingears.

Recurrent Adjacent-2 Segregation 165

performed on a previously GTG-banded slide with a digox-igenin-labeled whole chromosome paint 21 (wcp 21) (Oncor,Gaithersberg, MD) and detected with fluorescein-conjugatedanti-digoxigenin Fab fragments (2 mg/ml) (Boehringer Man-nheim, Indianapolis, IN) as described [Tung et al., 2001]. FISHwith awcp21 showed no signal on the proximal long arm of the‘‘variant 21’’ and a small region of signal on the proximal longarm of a D group chromosome (Fig. 5B and C). Based on theGTG and FISH analyses, the paternal karyotype was inter-preted as 46,XY,t(14;21)(q11.2;q11.2), with the ‘‘variant 21’’chromosome being the der(14).

III:1 and II:3 have normal blood karyotypes.The paternal grandmother (I:2) has the same cytogenetic

findings as II:2, and the paternal aunt (II:1) has the samecytogenetic findings as III:2 and III:3 (results not shown).

AdditionalFISHanalysis ofPatient 1with theD14Z1/D22Z1(Oncor) probe showed a positive hybridization signal on athird G group-size chromosome (Fig. 5D). FISH with a wcp 14(Cambio, Cambridge, UK) showed a positive hybridizationsignal on the proximal arm of this G group-size chromosome(Fig. 5E). These analyses confirm that Patient 1 inherited theder(14) chromosome. Therefore, the brothers III:2 and III:3have an unbalanced karyotype, 46,XY,der(14)t(14;21)(q11.2;-q11.2)pat. ish der(14)(D14Z1/D22Z1þ, wcp14þ, wcp21þ) andare partially trisomic for proximal 14q and partially mono-somic for proximal 21q. The paternal aunt has the sameunbalanced translocation.

DNA STUDIES

DNA samples were obtained from II:2 and II:3, the parents,and from the two affected boys III:2 and III:3. Samples wereamplified by the polymerase chain reaction using primers

supplied by Research Genetics, Inc., for the markers listedin Table I. The positions of the markers on the relevantchromosomes (14 and 21) were taken from composite geneticmaps available on the NCBI Entrez website (www.ncbi.nlm.nih.gov/). Amplification products were labeled by incor-poration of fluorescent d-nucleotides, and were analyzed byhigh-resolution capillary electrophoresis (ABI 310). Inheri-tance was studied comparing alleles in family members, andhaplotypes and phase were arbitrarily inferred for III:2.Crossovers are interpreted for III:3. Results are shown inTable I and Figure 6. The largest allele in the family is calledallele 1. Trisomywas inferred by presence of three alleles or bythe presence of a second allele of approximately twice the sizeexpected, as assessed quantitatively using ABI Gene Scansoftware (see Fig. 7). Where only one allele was observed, thepresence ofmonosomy or deletionwas also inferred baseduponthe peak area of the allele.

Results show that both boys (III:2 and III:3) are deleted for apaternal allele atmarkersD21S1437andD21S1436, both closeto the centromere. For the markers D14S742 and D14S1280,also near the centromere, the boys have either three alleles(III:2), or a duplicated allele (III:3). This results from inheri-tance of the father’s normal chromosome 14, and in place of anormal 21 from father, the translocated chromosome 14,whichcontains a long segment of chromosome 21 (indicated ‘‘21’’ inFig. 8).

DISCUSSION

Wepresent this family as an example of recurrent adjacent-2segregation of a subtle, ‘‘cryptic’’ reciprocal translocationinvolving two acrocentric chromosomes. The resulting pheno-types from inheritance of this apparently identical unbalancedrearrangement are variable. The unbalanced segregationappears to producemental retardation and speech articulationproblems. In the boys, with paternal inheritance, the unba-lanced translocation is also associated with behavior problemsincluding hyperactivity, impulsivity, and aggression. Physicalfindings include short palpebral fissures, dysplastic ears,decreased palmar and plantar crease formation, genitalanomalies, long, slender fingers, and abnormal feet. Thesefindings are likely to be associated with 14q11.2 trisomy and21q11.2 monosomy.

The new diagnosis in this family supports the practice ofrepeating chromosome analysis at high resolution in a childwith mental retardation and unusual physical features of un-known etiology or considering the use of subtelomeric FISHprobes. In this case, a ‘‘variant’’ chromosome 21 was laterproven to be abnormal by FISH studies.

Any attempt to explain recurrence of the adjacent-2malsegregation in this family is speculative. Alternate segre-gation of balanced translocations is the normal and most fre-quent outcome, and is expected in the majority of gametes,resulting in normal or carrier children. Of the outcomes frommalsegregation, adjacent-1 transmission is most likely, whichresults in inheritance of chromosomes with two differentcentromeres [Gardner and Sutherland, 1996]. Adjacent-2 seg-regation products inmany species are often not viable, and thissegregation is rare, observed in about 3–4% of unbalancedhuman progeny resulting from parents with translocations[Duckett and Roberts, 1981]. The percentage is dependentboth on size of the chromosome segments involved, and onhow chiasma formation and terminalization progress [de Boer,1979]. Most adjacent-2 malsegregations have involved chro-mosome 9 and an acrocentric, or two acrocentrics, withmaternal inheritance [Jalbert and Sele, 1979].

Both sexes in this family, in at least two generations,have transmitted the sameabnormal karyotype fromadjacent-2 segregation. In this particular translocation, adjacent-1

Fig. 4. II:1. Paternal aunt: she resembles III-2 and III-3.

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nondisjunction would result in proximal 21q trisomy, pre-sumably viable, with proximal 14q monosomy, perhapsinviable. Unbalanced outcomes from 3:1 nondisjunction wouldcreate trisomy14(21), clearly lethal, or trisomy21(14), perhapsa possible outcome involving the proximal trisomy 14 as inthese patients, combined with trisomy of the entire distal longarm of chromosome 21, likely resulting in most findings ofDown syndrome. However, these latter outcomes are the leastlikely.Other outcomes, suchasmonosomy14 or 21, are also notexpected to occur.Whenadjacent-2 inheritance is observed in a

family such as this one, observation of other unbalanced out-comes is generally excluded; in addition, quadrivalents withshort centric fragments apparently predispose to adjacent-2nondisjunction [Jalbert et al., 1980]. Adjacent-2 nondisjunc-tion is also likely to be recurrent [Jalbert andSele, 1979]. In onefamily with a t(13;18), both types of unbalanced adjacentnondisjunction were observed, resulting in trisomy 18p in onechild and monosomy 18p in another [Cotton et al., 1993]. Areview by Duckett and Roberts [1981], refers to 20 transloca-tion families in the literature, with 10 having recurrences of

Fig. 5. A: Partial karyotype and ideogram of the balanced paternal translocation.B: Partial GTG-bandedmetaphase from the father (II:2).C: FISHwitha wcp21 of the samemetaphase as (B) showing a region of nonhybridization on the proximal long arm of the der(14) and hybridization on the proximal longarm of the der(21) chromosome.D: FISHwith aD14Z1/D22Z1 showed signal on an additional chromosome fromPatient 1(III:2), consistentwith inheritanceof the der(14). E: FISH with a wcp 14 showed signal on the der(14) chromosome from Patient 1 (III:2).

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adjacent-2 segregation. In the 20 translocation familiesreviewed, 19 involved at least once acrocentric chromosome,with 6 involving 2 acrocentrics, 8 involving chromosome 9and an acrocentric, and the only one without acrocentric in-volvement was a translocation between chromosome 9 and X.

One of the families described [Laurent et al., 1973] had at(14;21), resulting in anunbalanced femalewith trisomy 14q12and monosomy of chromosome 21 proximal to band q22,similar to the results in the family described here. The pro-positus was 3 months old when described, and had been small

TABLE I. Chromosome 14 and 21 Marker Inheritance

Marker Location Mbp cM II:2 (Father) II:3 (Mother) III:2 (Patient 1) III:3 (Patient 2)

D14S1280 14q 24.65 25.87 2,3 1,3 1,2,3a 2,3,3a

D14S597 14q NA 28.01 1,2 1,1 1,1 1,1D14S297 14q 30.52 31.75 1,2 1,1 1,2 1,2D14S306 14q NA 44.06 1,2 3,3 2,3 2,3D14S587 14q NA 55.82 2,3 1,4 1,2 3,4D14S610 14q 86.20 95.89 2,2 1,2 1,2 1,2D21S1436 21q 20.26 13.05 2,2 1,2 1,-b 2,-b

D21S1437 21q 20.57 13.05 1,3 1,2 1,-b 2,-b

D21S1435 21q NA 27.14 2,3 1,2 1,3 2,3D21S1270 21q 27.40 30.63 1,3 2,3 1,3 3,3D21S1440 21q 38.06 36.77 1,3 2,3 1,2 2,3D21S156 21q 39.26 NA 1,2 2,2 2,2 1,2D21S1446 21q 46.89 57.77 1,1 2,2 1,2 1,2

cM, centiMorgans (Marshfield) taken from www.ncbi.nlm.nih.gov/genome/sts; Mbp, megabasepairs (Sequence Map) taken from www.ncbi.nlm.nih.gov/genome/sts; NA, not available.aTrisomic with three alleles or duplication of the ‘‘3’’ allele.bMonosomic with deletion of the paternal allele or reduced intensity.

Fig. 6. Inheritance of chromosomes 14 and 21: Translocated chromo-somes 14 shown in solid and 21 in hatched. Note reciprocal translocation ofproximal long arms of these chromosomes in the father, II:2. The affectedsons III:2 and III:3 have inherited the derivative chromosome 14 (T),containing a deletion of proximal 21q and presence of proximal 14q,

centromere, and short arm, and have inherited the normal chromosome 14(N), resulting in an unbalanced karyotype. Numbers next to the chromo-somes are alleles formarkers as listed in the table, withhaplotypes as showninferred from in III-2,with crossovers shown for theproband’s brother III:3.

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for gestational age, showed poor postnatal growth, had a largemouth with long upper lip and flattened philtrum, and showedsignificant joint contractures of the hands.

When chromosome 21 is involved, and a potential unba-lanced outcome includes partialmonosomy 21, adjacent-2 non-disjunction is not rare, occuring in 9 of 35 families withchromosome 21 translocations [Huret et al., 1995]. Therefore,partial proximal chromosome 21 monosomy is apparentlyviable.

Human sperm studies show somewhat different resultsfor adjacent-2 nondisjunction, demonstrating the results ofsegregation by FISH or after in vitro fertilization of hamstereggs. In a review of 31 such studies by Martin and Spriggs[1995], adjacent-2 nondisjunction was observed in 25 of 31translocations, at an overall frequency of 11%, being the secondrarest abnormal outcome, but observed in as high as 31% ofsegregants in a t(16;19).

In conclusion, adjacent-2 nondisjunction is not an uncom-mon result of meiosis in carriers of translocations involvingacrocentric chromosomes, especially if they are transmit-ted through females. The results of malsegregation in suchfamilies can be difficult to resolve without FISH or molecularstudies, as in this report.

ACKNOWLEDGMENTS

We thank Mountain States Regional Genetics ServicesNetwork for support of our molecular methods development(J.P.J., L.B.). We also thank Ann Parker, M.D. for clinicalinformation, Jeff Shaw, M.S. for helping with computergraphics, and Philip D. Cotter, Ph.D. for his expertise on theFISH studies.

REFERENCES

Aase J. 1990. Diagnostic dysmorphology. New York: Plenum PublishingCorporation. 18p.

Cotton C, CumminsM, Smith A. 1993. Alternate, adjacent 2 and 3:1 meioticsegregation products from a balanced t(13;18)(q212;q11) carrier. ClinGenet 44:193–195.

De Boer P. 1979. Proximal chiasma localization within an interstitialchromosome segment, a likely correlate of adjacent-2 segregation of

Fig. 7. Allelic inheritance assessed on theABI 310 Inheritance of three alleles in III:2 forD14S1280and of a duplicatedpaternal allele in III:3.Duplicatedalleles for both sibs with D14S742. Deletion of the paternal allele for D21S1437 in III:3 and for D21S1436 in III:2.

Fig. 8. Meiotic segregation of the paternal balanced translocation: fromthe quadrivalent formed by attempted pairing of homologues, adjacent-2segregation results in inheritance of chromosomes containing the samecentromerebut different long arms.Data are shown formeiosis in individualII:2, and the adjacent segregation of two chromosome 14 centromeres leadsto trisomy for marker D14S1280, and monosomy for proximal 21q markersD21S1436 andD21S1437, as demonstrated in individual III:2. In the figure,II:2 and III:2 refer to individuals in the pedigree in Figure 1.

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