Clinical and Molecular Findings in Two PatientsWith Russell-Silver Syndrome and UPD7:Comparison With Non-UPD7 Cases

L.E. Bernard,1 M.S. Penaherrera,2 M.I. Van Allen,1 M.S. Wang,2 S-L. Yong,1 F. Gareis,3 S. Langlois,1and W.P. Robinson2*1Department of Medical Genetics, British Columbia’s Children’s Hospital2BC Research Institute for Children’s and Women’s Health, Vancouver, British Columbia, Canada3Department of Endocrinology, Children’s Hospital, Oakland California

The clinical presentation of prenatal andpostnatal growth deficiency, triangularface, relative macrocephaly, and body asym-metry is frequently diagnosed as Russell-Silver syndrome (RSS). Maternal uniparen-tal disomy (UPD) of chromosome 7 was re-ported previously in a small subset ofindividuals with RSS phenotype or primor-dial growth retardation. The primary pur-pose of this study was to identify RSS pa-tients with UPD7 and determine whether ornot they present phenotypic findings thatdistinguish them from RSS patients withoutUPD7. UPD7 testing was performed in 40 pa-tients with unexplained growth retarda-tion, including 21 patients with a diagnosisof RSS. In addition, a subset of patients wasscreened with markers spanning chromo-some 7 to detect potential microdeletions orsegmental uniparental disomy. Two of theRSS cases were identified to have maternalUPD7; no cases with deletion or partial UPDwere detected. Together with previouslypublished studies, UPD7 was identified in11/120 (9%) of individuals with classical RSSphenotype. Our patients with UPD7 andthose previously published had a classicalRSS phenotype and were not clinically dis-tinguishable from other children diagnosedwith RSS. Am. J. Med. Genet. 87:230–236,1999. © 1999 Wiley-Liss, Inc.

KEY WORDS: Silver-Russell syndrome;Russell-Silver syndrome; uni-parental disomy; short stat-ure

INTRODUCTION

Uniparental disomy (UPD) is the inheritance of bothhomologs from one parent. The presence of UPD canplay a significant role in the clinical phenotype due toimprinting, the differential expression of genes de-pending on parent-of-origin (see Ledbetter and Engel[1995] for review). In some isolated cases, UPD mayalso result in homozygosity for a recessive mutation forwhich only one parent is a carrier.

Evidence that chromosome 7 has one or more mater-nally imprinted regions containing growth-relatedgene(s) was first suggested by three reports of individu-als with maternal isodisomy for chromosome 7 whowere ascertained because they had an autosomal re-cessive disease for which only the mother was a car-rier [Spence et al., 1988; Voss et al., 1989; Spotila etal., 1992]. All three of these individuals had signifi-cant unexplained postnatal growth failure but noother major anomalies. An additional case with unipa-rental isodisomy for paternal 7p and maternal 7q(46,XX,i(7p),i(7q)) was ascertained on amniocentesisand also showed postnatal, but not prenatal, growthrestriction [Eggerding et al., 1994]. Further support fora maternally imprinted region on chromosome 7 influ-encing growth was provided by a report of confinedplacental mosaicism for trisomy 7 with maternal UPD7in the baby [Langlois et al., 1995]. Because this caseinvolved maternal heterodisomy for the entire chromo-some, the postnatal growth restriction present was un-likely to be caused by homozygosity for a recessive mu-tation. The prenatal growth deficiency could have beencaused by either an imprinting effect of UPD7 or to thepresence of trisomy 7 in the placenta. Only one case ofpaternal UPD7 has been reported [Hoglund et al.,1994]. This patient was ascertained because of congen-ital chloride diarrhea and had no other abnormal find-

Contract grant sponsor: Medical Research Council of Canada.Dr. Bernard and Dr. Penaherrera contributed equally to this

manuscript.*Correspondence to: Dr. Wendy Robinson, University of British

Columbia Department of Medical Genetics, BC Research Insti-tute for Children’s and Women’s Health, Room 3086, 950 W 28thAvenue, Vancouver, BC, Canada,V5Z 4H4.E-mail: wendyr@unixg.ubc.ca

Received 25 March 1999; Accepted 11 August 1999

American Journal of Medical Genetics 87:230–236 (1999)

© 1999 Wiley-Liss, Inc.

ings except mild high-frequency sensorineural hearingloss, suggesting that lack of a maternal copy of chro-mosome 7 is not associated with any imprinting abnor-malities.

Russell-Silver syndrome (RSS) is characterized byprenatal and postnatal growth deficiency, relative mac-rocephaly, and a characteristic facial Gestalt. The roleof UPD7 in the pathogenesis of RSS was first studiedby Kotzot et al. [1995] by screening for UPD7 in 25patients with RSS and 10 patients with unexplainedprimordial growth retardation. Of four maternal UPD7cases identified in this group of 35 patients, three hadclassical RSS. The remaining UPD7 patient had shortstature and multiple signs of RSS and the commentwas made by the authors that some clinicians wouldcharacterize this individual as having RSS. These re-sults were confirmed by two additional studies thatfound maternal UPD7 in a combined total of 6 of 74patients with RSS [Preece et al., 1997; Eggerman et al.,1997].

A maternally imprinted gene PEG1/MEST wasmapped to human chromosome region 7q32 [Riesewijket al., 1997]. This gene is expressed from the paternalbut not the maternal allele in human embryos and pla-centa but biparental expression is observed in bloodlymphocytes. It was suggested that this could be a can-didate gene for the imprinting effects associated withmaternal (mat) UPD7, although its potential functionis not yet clear [Nishita et al., 1996]. Riesewijk et al.[1998] showed no evidence for a major role of (PEG1/MEST) in RSS, based on the results of mutationscreening and methylation analysis of the 58 region ofthe gene in 49 patients with RSS and nine patientswith primordial growth retardation (PGR). Studies ofthe mouse homologue (Mest/Peg1) by targeted muta-genesis in embryonic stem cells (ES) showed that pa-ternal transmission activates the targeted allele lead-ing to embryonic growth retardation and reduced post-natal survival rates in mutant progeny. Moreover,abnormal maternal behavior and impaired placento-phagia was also seen in Mest-deficient females [Lefeb-vre et al., 1998].

The primary purpose of this study was to identifyfurther matUPD7 patients to help identify phenotypicfindings that might be predictive of matUPD7. Mater-nal UPD7 screening was performed in 40 patients re-ferred because of unexplained short stature. A diagno-sis of RSS was made in 21 of these. Other syndromesassociated with UPD, such as Prader-Willi (PWS), An-gelman (AS), and Beckwith-Wiedemann (BWS) syn-dromes, can also be caused by deletions or duplicationsinvolving the critical imprinted region on the samechromosome [Elliott and Maher, 1994; Knoll et al.,1989]. In addition, UPD associated with BWS is typi-cally segmental, that is, only the terminal portion ofthe 11p arm shows uniparental inheritance with theremainder of the chromosome showing biparental in-heritance [Henry et al., 1993]. Therefore, we also testednumerous additional markers spanning chromosome 7in a subset of our patient population to look for similarmicrodeletions or segmental UPD.

MATERIALS AND METHODSStudy Population

Patients were identified initially either by review ofmedical charts of RSS patients previously seen at theBritish Columbia Provincial Medical Genetics Pro-gramme or by physician referral. Detailed clinical in-formation was not available on four cases referred asbeing RSS from outside British Columbia. Charts fromthe remaining 36 cases were reviewed by one of us(MVA), and the patient was given a diagnosis of RSS ifhe/she did not have any other disorder and met thefollowing criteria: 1) prenatal growth deficiency (lowbirth weight); 2) postnatal growth deficiency (> 2 stan-dard deviations below the mean (STD BTM)); and 3)facial Gestalt including triangular facies, relative mac-rocephaly, broad forehead, small chin, and smallmouth with down-turned corners and thin upper lip. Adiagnosis of RSS was confirmed in 21 of these cases,two of whom were sibs (49a and b).

RSS patients may also have other more variablemanifestations including asymmetry, D5 clinodactyly,cafe-au-lait macules, feeding dysfunction, hypospadias,delayed closure of the anterior fontanelle, delayed boneage, and excess sweating on head and upper trunk.Because these traits are variable, their presence pro-vided additional support for the diagnosis, but theirabsence did not rule out the diagnosis.

Molecular Analysis

DNA analysis was performed using microsatellitemarkers spanning chromosome 7 (Table I). In all cases,two markers were required to be informative for exclu-sion of UPD7 with at least one informative marker oneach arm of the chromosome. Numerous additionalmarkers were tested in 11 of the RSS and 9 of the“short stature” patients to try and screen for potentialsmall deletions or duplications. Markers on the q-armwere predominantly used because the report of Eggerd-ing et al. [1994] suggests that an imprinted “RSS” genemust lie on 7q. Furthermore, the maternally imprintedgene PEG1/MEST was mapped to human chromosome7q32 near to D7S649 [Kobayashi et al., 1997]. D7S649and a number of markers more distal on the q-armwere also tested for the purpose of detecting potentialcases of segmental UPD resulting from a somatic re-combination event. This would lead to isodisomy onlyfor markers mapping between the recombination eventand the telomere. Both isodisomy and a deletion can beexcluded if a marker is heterozygous in the patient. Aduplication is considered unlikely but cannot be accu-rately excluded if a marker is heterozygous and there isno obvious difference in dosage between the two alleles.

Marker order was determined from the Genome Da-tabase integrated chromosome 7 map version 3 avail-able online at http://cedar.genetics.soton.ac.uk/pub/and, in part, the Genethon 1994 Chromosome 7 linkagemap [Gyapay et al., 1994]. Paternity was checked forthe UPD7 patients using microsatellite markers fromchromosomes 2, 4, 12, and 15. Primers were obtainedfrom Research Genetics or were synthesized usingprimer sequences available through the Genome Data-Base. Polymerase chain reactions (PCR) were per-

UPD7 in Two Russell-Silver Patients 231

formed using standard conditions. The PCR productswere run on 6% polyacrylamide and 50% urea sequenc-ing gels. Bands were visualized by silver staining.

RESULTSMolecular Results

DNA microsatellite markers spanning chromosome 7were typed in each family to determine if the patienthad UPD for all or part of chromosome 7 (Table I). Intwo cases (RSS-4 and RSS-8), maternal DNA was notavailable. However, inheritance at $ 17 markers wasconsistent with a paternal contribution, making mater-nal UPD7 highly unlikely. In one additional case (RSS-14), paternal DNA was not available but maternalUPD7 could be excluded by the presence of nonmater-nal alleles in the child. Two of 21 patients with a diag-nosis of RSS (case RSS-11 and RSS-44) were found tohave maternal UPD for chromosome 7. RSS-11 washomozygous for all markers typed, including thosenear the centromere (Table I). These results suggest apostzygotic duplication of chromosome 7 as the mostlikely origin for the UPD. Paternity was tested in thisfamily using highly informative microsatellite markersfrom chromosomes other than 7, including: D2S172,D3S1766, D12S88, D15S1043, D15S165, and D17S807.

Inheritance at each of these markers was consistentwith paternity. Maternal heterodisomy was observedin RSS-44 for D7S507 D7S669 and D7S515, and isodi-somy was observed at D7S691 and D7S495 indicatingthat the extra maternal chromosome 7 originatedfrom a meiotic error following normal meiosis I recom-bination (Table I). Inheritance at D4S398, D4S424,D15S541, and D15S165 was consistent with paternity.

No evidence for lack of maternal or paternal trans-mission (indicative of a deletion) nor any apparent dos-age differences between alleles in heterozygous pa-tients (indicative of a duplication) were observed forany of the markers tested in the remaining patients.Specifically, heterozygosity was observed in 11 non-UPD7 patients for D7S649 (the remainder being eithernot typed or uninformative). Segmental UPD of distal7q (D7S649 or distal) was excluded in 27 cases of eitherconfirmed RSS or unexplained short stature (the re-mainder not being examined for markers in this region)(Table I). As only a subset of cases will be informativefor any given marker, an increase in homozygosity inpatients as compared with parents can help indicate ifany particular marker is deleted in a substantial pro-portion of patients [Morrow et al., 1995]. As shown inTable I, there were no significant differences in hetero-zygosity between patients and parents for any marker.

TABLE I. Summary of Molecular Data For Mother (m), Patient (p), and Father (f) in Two matUPD7 Cases (RSS-11 and RSS-44), and Heterozygosity for Chromosome 7 Markers in

Non-UPD7 Patients (RSS and Unexplained Short Stature) and Their Parents

Markertested

femaleb

Geneticdistance

(cM)Chromosome

locationRSS-11m,p,f

RSS-44m,p,f

Non-UPD

PatientsNo. het/total

(%)

ParentsNo. het/total

(%)

D7S531 7 p22.3 bb,bb,ab 9/16 (56%) 10/28 (36%)D7S517 9 p22.3 ab,aa,cca 10/13 (77%) 14/22 (64%)D7S513 26 p21.3 bb,bb,ab 22/27 (81%) 35/55 (64%)D7S664 32 p21.1 ac,aa,ab 9/16 (56%) 20/29 (69%)D7S507 37 ac,ac,bba 1/1 (100%) 1/1 (100%)D7S460 bb,bb,ab bb,bb,aca 0 0D7S528 73 p15.2 3/3 (100%) 4/5 (80%)D7S485 75 p15.1 3/3 (100%) 5/5 (100%)D7S691 82 p12.3 ab,bb,bb bc,bb,aca 10/14 (71%) 16/26 (62%)D7S645 103 q11.21 5/6 (83%) 10/11 (91%)D7S2476 108 4/5 (80%) 7/9 (78%)D7S613 109 q11.21 5/6 (83%) 7/11 (64%)D7S669 119 q11.21 ac,cc,bc bd,bd,aca 14/14 (100%) 20/28 (71%)D7S440 123 q11.22 4/6 (67%) 10/12 (83%)D7S524 130 q11.23 bc,bb,ab 11/20 (55%) 25/37 (68%)D7S558 142 q21.13 bb,bb,ab 16/22 (73%) 24/40 (60%)COL1A2 144 q22.1 ab,bb,aaa 12/17 (71%) 20/31 (65%)D7S515 150 q22.1 ab,bb,aaa ad,ad,bca 14/18 (78%) 24/31 (77%)D7S796 153 q22.2 bc,bb,aca 17/18 (94%) 29/34 (85%)D7S501 160 q31.1 ab,bb,cda 14/18 (78%) 26/36 (72%)D7S799 166 q bb,bb,aca 17/18 (94%) 29/31 (94%)D7S480 168 q31.3 cd,cc,aba 15/19 (79%) 25/35 (71%)D7S649 176 q32.1 aa,aa,bba 11/20 (55%) 18/37 (49%)D7S800 186 q ab,aa,cda 11/20 (55%) 20/36 (56%)D7S495 196 q34 bc,bb,ab bc,cc,aba 16/22 (73%) 34/42 (81%)D7S498 208 q35 ab,aa,ab 13/19 (68%) 22/35 (63%)D7S505 215 q36.1 bc,bb,ab 16/20 (80%) 20/34 (59%)D7S483 217 q36.2 ab,bb,bb 12/14 (93%) 18/24 (75%)D7S637 234 q36.3 ab,bb,aaa 8/19 (42%) 18/37 (49%)D7S550 236 q36.3 ab,aa,bba 10/14 (71%) 18/26 (69%)

aNonpaternal inheritance verified with these markers.bFemale genetic distance from pter (cM).

232 Bernard et al.

Clinical Findings in UPD7 Cases

Patient RSS-11 was born at 36 weeks of gestation toa 26-year-old (G3P2) woman. The pregnancy was com-plicated by in utero growth retardation presenting inthe third trimester. Delivery was by Caesarian sectionbecause of late decelerations associated with a tightnuchal cord wrapped twice around the neck. Birthweight was 1,974 g (3th centile), length 43.2 cm (3th

centile) (Table II), and placenta was small at 300 g(expected 400–500 g). OFC was not available. Neona-tally she required gavage feedings, had no recordedhypoglycemia, and had poor weight gain. She was re-admitted at age 2 months for failure to thrive, but aspecific cause was not identified. There was a history ofa heart murmur without apparent structural malfor-mation of the heart.

She had persistence of relative macrocephaly and

TABLE II. Size and Growth of RSS Patients Compared With Standardized Growth Curves*

SexGestation(weeks) Age at exam.

Weight in kg(STD BTM)

(weeks 50th%)c

Length in cm(STD BTM)

(weeks 50th%)c

OFC in cm(STD BTM)

(weeks 50th%)c

UPD7RSS-11 F 36 Birth 1.97 (−1.7) (33) 43.2 (−2.2) (32) —

2 yr 4 mo 8.3 (−3.3) 77.5 (−3.0; −8.8b) 49.5 (0.8)7 yr 14 (−3.1) 110 (−1.9; −6.3b) 52.5 (0.8)8 yr 9 mo 19 (−1.3) 119 (−1.7; −6.6b) 53 (0.9)

RSS-44 M 41.5 Birth 2.44 (−2.1) (35.5)a 44.5 (−4.1) (33.5) 34 (−1.3) (37.5)1 yr 5.61 (−4.5) 63.6 (−4.7) —1 yr 6 mo 5.64 (−5.1) 68.7 (−4.5) —2 yr 7.5 (−3.9) 77.7 (−2.8) —3 yr 1 mo 7.6 (−4.4) 80.5 (−4.0) —

UPD7-excludedRSS-1 F 41 Birth 2.04 (−2.9) (34)a 47 (−2.7) (36) 33 (−2.5) (35.5)

1 yr 1 mo 6.1 (−3.8) 67.6 (−2.8) 44 (−1.2)1 yr 9 mo 8.1 (−3.1) 80.5 (−1.5; −4.2b) 47 (−0.7)

RSS-3 M 34 Birth 1.62 (−2.0) (31.5) 42.5 (−1.3) (31.5) 32 (0.9) (34.5)3 yr 2 mo 8.2 (−4.1) 78.7 (−4.3; −10.6b) 49.3 (−0.9)4 yr 11.8 (−2.5) 93 (−2.0; −6.5b) 50.5 (−0.5)

RSS-4 M — Birth 0.681 — —10 yr 9 mo 18.6 (−1.8) 118.8 (−3.5) 52.6 (−0.3)

RSS-5 M 38 Birth 2.24 (−2.5) (34.5) 48.3 (−0.9) (37) —3 yr 3 mo 11.5 (−2.2) 86 (−2.6) 49.2 (−1.0)

RSS-8 M 36 Birth 2.31 (−0.6) (35) 45.7 (−0.6) (34.5) —4 yr 7 mo 11.7 (−2.9) 93 (−2.7) 49.2 (−1.6)

RSS-12 M 36 Birth 1.44 (−3.4) (30.5)a 39.5 (−4.6) (30.5) 33 (0.2) (36)11 mo 5.4 (−4.2) 63.9 (−4.3) 45.3 (−0.6)

RSS-15 M 36–37 Birth 1.87 (−2.0) (33) 45 (−1.0) (34) —1 yr 7 mo 8.2 (−3.0) 73.4 (−3.1) 47 (−0.8)2 yr 6 mo 10.0 (−2.5) 80.9 (−3.0) 48 (−0.7)

RSS-16 M — 2 yr 9.6 (−2.4) 78.3 (−2.6) 48.5 (−0.4)RSS-18 M 40 Birth 1.50 (−4.3) (30.5) 35 (−8.3) (26.5)a —

1 yr 9 mo 7.6 (−3.4) 71.8 (−3.4) 43.7 (−3.0)2 yr 4 mo 8 (−3.8) 76.5 (−3.7) 45 (−3.1)

RSS-21 F 30 Birth 0.970 (−2.6) (26.5) 34 (−4.0) (25.5) 26 (0.9) (28.5)3 yr 9 mo 9.7 (−3.7) 84.1 (−3.5) 46 (−3.1)

RSS-22 M 40 Birth 2.34 (−2.5) (35)a 49 (−1.2) (37) 33.5 (−1.1) (37)1 yr 1 mo 6.28 (−3.9) 68.5 (−2.9) 41.5 (−3.2)3 yr 7 mo 11 (−2.7) 88.1 (−2.5) 45.7 (−3.7)

RSS-29 M 34 Birth 1.06 (−4.3) (27)a 34 (−6.0) (26)a 27.5 (−2.4) (30.5)8.5 mo 5.0 (−3.7) 56.9 (−6.0) 41 (−2.7)

RSS-35 M 36 Birth 2.24 (−0.8) (34.5) — —9 yr 5 mo 19.97 (−1.3) 121.9 (−1.6) 50.6 (−1.3)

RSS-36 M 36 Birth 1.6 (−3.0) (31) 42 (−3.0) (32) 31.3 (−1.4) (33)9 yr 3 mo 17.5 (−1.7) 123.6 (−1.3) 52.4 (0.0)

RSS-37 M 32 Birth 0.85 (−3.6) (26)a — 29.5 (0.2) (32)RSS-39 F 40 Birth 1.63 (−4.0) (31.5)a 38.1 (−6.8) (29) —RSS-42 M 34–36 Birth 1.29 (−2.5) (30) — 31.5 (−0.6) (33)

10 mo 6.26 (−2.5) 67.5 (−2.0) 44.8 (−0.5)RSS-49a M 40 Birth 2.0 (−3.2) (34) 38 (−6.8) (30) 34 (−0.6) (38)

9 yr 6 mo 16.9 (−1.8) 108 (−3.9) 52.5 (0.05)RSS-49b F 37 Birth 2.24 (−1.4) (34.5) 42 (−3.3) (32) —

11 yr 11 mo 33.5 (−0.4) 137 (−1.5) 55.5 (1.2)

*n.d., not determinable as gestational age was unknown.aLess than 3rd centile (−3 SD) expected for gestational age.bSecond figure is STD-BTM corrected for parental heights.cGiven for birth measurements only.

UPD7 in Two Russell-Silver Patients 233

growth retardation postnatally (−3 STD below themean at age 2 years 4 months, << 5th centile) (TableII), which is striking in view of the parental heightsbeing > 95th centile. Endocrinology evaluation did notidentify a hormonal cause for her short stature. Growthhormone stimulation studies were normal. Bone agewas delayed; studies done at chronological age 4 yearswere consistent with age 2 years. Development of grossmotor skills was delayed compared with her other sibsbut was within the normal range. She has selectivelearning disabilities, in particular delays in expressivemore than receptive speech. At age 9 years, she is inthe 2nd grade in a regular classroom with a resourceroom and a special aide. There are concerns about shortattention span, dyslexia, speech, reading, and simplemath skills. Social skills are normal for age and thereare no behavior concerns. Formal IQ testing has notbeen done. Other pertinent clinical information in-cludes enamel hypoplasia of the primary and second-ary teeth. There is a leg length discrepancy of 1.5 cmbut no other evidence of body asymmetry.

On examination of patient RSS-11 at age 7 years,height was 110 cm (5th centile), weight was 14.0 kg (<5th centile), and head circumference was 52.5 cm (50thcentile). A photograph of patient RSS-11 at age 7 isshown in Figure 1. At age 8 years 9 months, height was119 cm (<5th centile), weight was 19 kg, and OFC was53.0 cm (50th centile). She has relative macrocephalywith bright platinum hair, triangular face, frontalbossing, and no apparent asymmetry of the face. Pal-

pebral fissures are up-slanting, inner canthal distanceis 2.8 cm, palpebral fissure length is 3.0 cm, pupils arenormal. Nose measures 3.5 cm and is normally formed.Midface is prominent, and there are dimples in hercheeks. Philtrum measures 0.9 cm being somewhatshort, and the philtral ridges are flattened. There is athin upper lip. Palate is normal. There is enamel hy-poplasia of anterior incisors and molars. Chin ispointed with a dimple at the tip. Neck and chest arenormal. Lungs are clear to auscultation. Cardiac statusis normal without murmurs. Abdomen is soft withouthepatosplenomegaly. Genitalia are normal. There isbrachyclinodactyly of the 5th fingers and there aredimples at the shoulders and a sacral dimple. There isno body asymmetry except for a persistent leg lengthdiscrepancy noted at age 4. There is no scoliosis. Thereare multiple cafe-au-lait spots and a small nevus on theleft leg. Neurological status is normal.

Patient RSS-44 was born by Caesarean section at41.5 weeks of gestation, weighed 2,440 g (<5th centile),and length was 44.5 cm (<5th centile) at birth. This wasthe first child of the 20-year-old mother and 24-year-old father. Parents are above average height (167 cmand 180 cm, respectively). At age 5 months, a gavagetube was inserted because of concerns of poor feeding.At examination at age 1 year, weight was 5.6 kg andlength 63.6 cm. He appeared thin with no subcutane-ous fat and relative macrocephaly, triangular face,prominent forehead, and marked 5th finger clinodac-tyly. Neither cardiac abnormalities nor abdominal or-ganomegaly was noted. External genitalia were nor-mal. He had a single lower incisor. Scalp hair, nails,and skin pigmentation were reported as normal. At age3 years 1 month, height was 80.5 cm (<<5th centile)and weight 7.6 kg (<<5th centile) (Table II).

Clinical Findings in All RSS Patients

After review of the medical records by a clinical ge-neticist (MVA), 21 patients were given a diagnosis ofRSS (patients 49a and 49b are sibs). Height, weight,and head circumference at birth and at the oldest avail-able age on each RSS patient are shown in Table II. Ofthose patients for whom measurements were availableat birth, eight had very low birth weight (with one ormore measurements more than 3 standard deviationsbelow the mean (STD BTM) expected for gestationalage), whereas the rest were small for gestational age[Usher and McLean, 1969]. When compared with stan-dard growth curves [Smith, 1977], 16/21 patients hadvery short stature (at least 2.5 STD BTM) at the mostrecent examination. At the oldest available age, thisincludes three patients (RSS-01, 03, and 11) that had aheight between 1 and 2 STD BTM. However, all threeof these patients had tall parents (RSS-01 mother 171cm, father 183 cm; RSS-03 mother 173 cm, father 183cm; and RSS-11 mother 183 cm, father 188 cm). A cor-rection for expected height given the mean parentalheight indicated that all three had significant shortstature (at least 4 STD BTM) (Table II). A summary ofadditional clinical findings is shown in Table III.Fig. 1. Patient RSS-11 at age 7 years.

234 Bernard et al.

DISCUSSION

During the course of this study, we identified twopatients with UPD7. In one case (RSS-11), all chromo-some 7 markers tested were homozygous, which sug-gests a mitotic duplication of the maternal chromosome7 early in development, although a meiosis II errorfollowing meiosis I without recombination cannot beexcluded. Heterozygosity for some markers in the sec-ond case (RSS-44) is consistent with a maternal meioticnondisjunction event leading to transmission of an ex-tra chromosome 7. In either case, the paternal chromo-some may have been lacking in the sperm or lostshortly after fertilization. Considering our results andpreviously published cases ascertained through RSS(11 cases) or unexplained growth retardation (onecase), five cases showed complete isodisomy and sevenpartial or complete heterodisomy for maternal chromo-some 7 [Eggerman et al., 1997; Kotzot et al., 1995;Preece et al., 1997]. This ratio is similar to the fre-quency of meiotic (17/27) and somatic (10/27) origins oftrisomy 7 ascertained through spontaneous abortions[Robinson et al., 1999].

Our patients with UPD7 had classical RSS, as hasbeen reported for previously identified UPD7/RSScases [Eggerman et al., 1997; Kotzot et al., 1995; Preece

et al., 1997]. RSS-11 at age 9 years was somewhattaller than expected for RSS (−1.7 STD BTM). How-ever, both of her parents are tall, and when a meanparental height was incorporated into her expectedheight at age 9 years, she was significantly small (−6.6STD BTM). This patient also had enamel hypoplasiaand mild developmental delay, particularly of expres-sive speech. RSS-44, also with UPD, was too young toevaluate for speech development. Of the 15 previouslyreported cases of maternal UPD7 and one case of ma-ternal isodisomy for 7q, psychomotor retardation wasreported in two and speech delay in one, whereasenamel hypoplasia was not noted [Spence et al., 1988;Voss et al., 1989; Spotila et al., 1992; Kotzot et al.,1995; Langlois et al., 1995, Eggerding et al., 1994; Eg-germann et al., 1997; Preece et al., 1997]. Althoughclinical data were sparse in some of the previous pub-lications, there does not yet appear to be any specificclinical findings, which identify patients with UPD7from among those classified with RSS. Enamel hypo-plasia is common in Williams syndrome, which is as-sociated with a deletion of 7q11.23 and the presence ofthis defect in the present case could possibly be due tohomozygosity for a recessive gene in this region.

In our study, we detected two cases of UPD7 in 21

TABLE III. Additional Clinical Features of Russell-Silver Patients*

Relativemacrocephaly

Triangularfacies

Frontalbossing

Lateclosure

of anteriorfontanelle

Small mouth,down-turnedcorners, thin

upper lipD5

clinodactylyAsym-metry

Café-au-lait

macules

Delayedboneage

Develop-mentaldelay Other

UPD7RSS-11 + + + N/A N/A + + + + + Teeth enamel

hypoplasiaRSS-44 + + N/A N/A + N/A − − −

Non-UPD7RSS-1 + N/A + + + + − + − +RSS-3 + + + − N/A − N/A N/A − N/A Placental sub-chorion

hematomaRSS-4 + − + N/A − + + − + − HemihypertrophyRSS-5 + + + N/A N/A + − − + + Seizures/coleithiasesRSS-8 + + N/A N/A N/A + − − + N/A HypospadiasRSS-12 + N/A + + + + − − N/A + Conductive hearing

lossRSS-15 + N/A N/A N/A N/A N/A N/A N/A + N/A Tongue tiedRSS-16 + + N/A N/A N/A + − N/A − + Hypotonia, motor

delay, hipdisplasia,abnormal digits

RSS-18 N/A + N/A N/A N/A + − − − N/ARSS-21 + + N/A N/A N/A + − − + N/A Placental sub-

chorion hematoma;pectus excavatum

RSS-22 N/A N/A N/A N/A + + − + N/A N/ARSS-29 + + + N/A N/A + + N/A N/A N/A Hypospadias, edema

of lower limbs,renal tubularacidosis

RSS-35 + + N/A N/A N/A + − + + − Esotropia, arthritisRSS-36 + + N/A + N/A + + − + − Mediastinal ganglio-

neuroblastomaRSS-37 + + N/A N/A N/A + N/A − − −RSS-39 + + N/A N/A N/A + N/A − + −RSS-42 + + N/A + + − + − N/A + Hypospadias, left

hypoplastic kidneyRSS-49a + + + N/A − + + − − − Ichthyosis vulgaris/

sweating whileeating

RSS-49b + + + N/A − + + + − −

*N/A, data not available; +, feature present; −, feature absent.

UPD7 in Two Russell-Silver Patients 235

patients with classical RSS. This proportion is similarto that of previous reports [Kotzot et al, 1995; Egger-mann et al., 1997; Preece et al., 1997]. UPD7 was iden-tified in 11/120 (9%) individuals with a confirmed RSSphenotype. The cause of the remaining cases probablyis heterogeneous. Although we did not detect any evi-dence of microdeletions or microduplications, it is im-possible to fully “cover” the whole chromosome, andonly a small number of patients was informative forany given marker. As other syndromes associated withUPD (Prader-Willi syndrome, Angelman syndrome,and Beckwith-Wiedemann syndrome) have also beenassociated with microdeletions or duplications withinthe involved chromosome, as well as imprinting muta-tions and point mutations within imprinted genes,these all remain mechanisms to consider in the re-maining group of patients.

ACKNOWLEDGMENTS

We thank the patients and their families for partici-pating in this study and the following geneticists forreferring patients: Drs. Barbara McGillivray, JanFriedman, Patrick MacLeod, Suzanne Lewis, MarkStephan, R. Rothstein, L. Clarke, B. Blumberg, AnnStembridge, and Kristyne Stone. Technical assistanceprovided by Fabiana Bernasconi and Brian Kuchinka.L.E.B. was supported by a fellowship from the MedicalResearch Council of Canada.

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