Prader-Willi syndrome and Robertsonian translocations involving chromosome 15

A case of Prader-Willi syndrome is presented in which high resolution chromosome analysis revealed not only a familial Robertsonian translocation [t(13q15q)], but also a del(15) (q11.2q13) of the chromosome 15 not involved in the translocation. While there have been numerous reports of Robertsonian translocations involving chromosome 15 in patients with Prader-Willi syndrome, in this case, the Robertsonian translocation was shown to be unrelated to the clinical findings.     

Prader-Willi syndrome in Black females

Reports of Black females with Prader-Willi have been rare. This communication describes two Black females with Prader-Willi syndrome. Chromosome analysis revealed a small deletion of the proximal portion of a chromosome 15 in one case and apparently normal chromosomes in the other.     

一例由染色体不平衡易位t(5;15)导致的Prader-Willi综合征

目的 对1例临床疑似Prader-willi综合征(Prader-Wil syndrome,PWS)的患儿进行遗传学诊断和分型.方法 应用染色体核型分析结合甲基化特异性PCR(methylation-specific PCR,MS-PCR)及短串联重复序列(short tandem repeat,STR)家系连锁分析方法对患儿进行诊断和分子病理学分型.结果 患儿染色体核型为45,XX,der(5)t(5;15)(q35;q13),-15,存在5号与15号染色体之间的不平衡易位;甲基化特异性PCR及STR家系连锁分析方法进一步证实患儿为父源15号染色体不平衡易位导致的15q缺失型Prader-Willi综合征.结论 临床疑似PWS的患儿应进行遗传学检查,以便获得确诊.细胞遗传学及分子遗传学方法的有效结合对于临床诊断、分辨不同病理类型、遗传咨询以及产前诊断都具有积极的作用.     

FISH analysis in Prader-Willi and Angelman syndrome patients

We report on a combined high resolution cytogenetic and fluorescent in situ hybridization study (FISH) on 15 Prader-Willi syndrome (PWS) and 14 Angelman syndrome (AS) patients. High resolution banding showed a microdeletion in the 15q11-q13 region in 7 out of 15 PWS patients, and FISH analysis of the D15S11 and SNRPN cosmids demonstrated absence of the critical region in three additional cases. Likewise 8 out of 14 AS patients were found to be deleted with FISH, using the GABRB3 specific cosmid, whereas only 4 of them had a cytogenetically detectable deletion. © 1995 Wiley-Liss, Inc.     

Sister chromatid exchange in families with Angelman or Prader-Willi syndrome

Using estimation of numbers of sister chromatid exchanges arising in 15q 11 q 13 as a measure, comparisons of the stability of the Prader-Willi syndrome critical region have been made. The groups studied included probands with Prader-Willi or Angelman syndromes either with or without a cytogenetically visible deletion in 15q11q13, their parents, specifically those parents who had passed on the homologue which had become deleted, and a control group. No significant differences were found between any of the four groups, indicating that there was no increase in the instability of the PWSCR region as measured by sister chromatid exchange.     

Unique karyotypes in two patients with Prader-Willi syndrome.

A physical disruption of the Prader-Willi syndrome (PWS) chromosome region is thought to cause PWS. We describe 2 girls with PWS phenotype, who had unique chromosome 15 abnormalities. The first patient showed mosaicism: 45,XX,t(15;15)(qter----p11.1::q11.200----qter)/46,XX,t(15;15)(qter----p1 1.1::q 11.200----qter), +mar. The band 15q11.2 apparently remained intact in the t(15;15) chromosome, and the mar chromosome was considered as r(15) (p11.1q11.1). The second patient had a karyotype of 47,XX,del(15)(q11.200----q11.207), +idic (15)(pter----q11.1::q11.1----pter). The complex breakage and reunion involving the 15q11.2 regions of the father's homologous chromosomes 15 at meiosis appeared to have resulted in the idic(15) and the del(15) chromosomes. These cytogenetic findings suggest that the PWS chromosome region may be localized on the very proximal portion of band 15q11.2.     

Robertsonian (15q;15q) translocation in a child with Angelman syndrome: Evidence of uniparental disomy

A balanced Robertsonian translocation 45,XY,t(15q15q) was detected in a patient with mental retardation, microcephaly, and hypertonia. Deletion of the 15q11q13 region was unlikely based on fluorescence in situ hybridization studies that revealed hybridization of appropriate DNA probes to both arms of the Robertsonian chromosome. Inheritance of alleles from 13 highly polymorphic DNA markers on chromosome 15 showed paternal uniparental isodisomy. The clinical, cytogenetic, and molecular results are consistent with a diagnosis of Angelman syndrome. © 1996 Wiley-Liss, Inc.     

Prader-Willi syndrome associated with inversion of chromosome 15

A boy with Prader-Willi syndrome was found to have an inversion of chromosome 15,[46, XY, inv(15)(p13q13)]. His unaffected father has an apparently identical inversion of chromosome 15 but in addition has a number 14 chromosome with double satellites. This report supports previous indications of a relationship between a "position effect" and the etiology of Prader-Willi syndrome. However, a more complicated explanation is required in view of the cytogenetic findings in the proband's father.     

Fluorescence in-situ hybridisation and molecular studies used in the characterisation of a Robertsonian translocation (13q15q) in Prader-Willi syndrome

A patient with classical Prader-Willi syndrome was found to have a Robertsonian translocation 45,XY,t(13_q15_q)mat. On CBG banding, the translocation chromosome had a large centromere with one primary constriction. Using fluorescence in situ hybridisation, positive signals were obtained with chromosome 13 and chromosome 15 centromere probes, proving that the translocation was dicentric. NOR banding was negative in this chromosome, suggesting that the breakpoints were at 13p11 and 15p11. DNA studies showed that, while there was no deletion involving 15(q11′13), maternal uniparental disomy for chromosome 15 was present. We compare our findings with the five other cases of familial Robertsonian translocation PWS that have been reported.     

Familial translocation t(Y;15)(q12;p11) and de novo deletion of the Prader-Willi syndrome (PWS) critical region on 15q11-q13

We describe a 17-year-old girl with mild Prader-Willi syndrome (PWS) due to 15q11-q13 deletion. The deletion occurred on a paternal chromosome 15 already involved in a translocation, t(Y;15)(q12;p11), the latter being present in five other, phenotypically normal individuals in three generations. This appears to be the first case of PWS in which the causative 15q11-q13 deletion occurred on a chromosome involved in a familial translocation, but with breakpoints considerably distal to those of the familial rearrangement. The translocation could predispose to additional rearrangements occurring during meiosis and/or mitosis or, alternatively, the association of two cytogenetic anomalies on the same chromosome could be fortuitous. Am. J. Med. Genet. 70: 222–228, 1997. © 1997 Wiley-Liss, Inc.     

Maternal disomy and Prader-Willi syndrome consistent with gamete complementation in a case of familial translocation (3;15) (p25;q11.2)

Maternal uniparental disomy (UPD) for chromosome 15 is responsible for an estimated 30% of cases of Prader-Willi syndrome (PWS). We report on an unusual case of maternal disomy 15 in PWS that is most consistent with adjacent-1 segregation of a paternal t(3;15)(p25;q11.2) with simultaneous maternal meiotic nondisjunction for chromosome 15. The patient (J.B.), a 17-year-old white male with PWS, was found to have 47 chromosomes with a supernumerary, paternal der(15) consisting of the short arm and the proximal long arm of chromosome 15, and distal chromosome arm 3p. The t(3;15) was present in the balanced state in the patient's father and a sister. Fluorescent in situ hybridization analysis demonstrated that the PWS critical region resided on the derivative chromosome 3 and that there was no deletion of the PWS region on the normal pair of 15s present in J.B. Methylation analysis at exon alpha of the small nuclear ribonucleoprotein-associated polypeptide N (SNRPN) gene showed a pattern characteristic of only the maternal chromosome 15 in J.B. Maternal disomy was confirmed by polymerase chain reaction analysis of microsatellite repeats at the gamma-aminobutyric acid receptor beta3 subunit (GABRB3) locus. A niece (B.B.) with 45 chromosomes and the derivative 3 but without the der(15) demonstrated a phenotype consistent with that reported for haploinsufficiency of distal 3 p. Uniparental disomy associated with unbalanced segregation of non-Robertsonian translocations has been reported previously but has not, to our knowledge, been observed in a case of PWS. Furthermore, our findings are best interpreted as true gamete complementation resulting in maternal UPD 15 and PWS. Am. J. Med. Genet. 78:134–139, 1998. © 1998 Wiley-Liss, Inc.     

Prader-Willi syndrome in two siblings: one with normal karyotype, one with a terminal deletion of distal Xq

Two sibs, a 13-year-old girl and an 11-year-old girl, with typical clinical features of the Prader-Willi syndrome (PWS) are reported. High-resolution chromosome analysis showed the normal karyotype in the elder sister, and 46,X,del(X)(pter----q26.1:) in the younger sister. But an interstitial deletion of 15q was not detected in either of the cases. PWS is most probably an etiologically heterogeneous syndrome consisting of two subgroups, with partial deletion and non-deletion of chromosome 15, respectively.     

Exclusion mapping of the Cohen syndrome gene from the Prader-Willi syndrome locus

Karyotype and DNA analyses using DNA probes were carried out in a family with the Cohen syndrome. Two affected brothers had normal chromosomal constitutions. A major deletion or duplication of genomic DNA fragments hybridized with the DNA probes, pML34 at D15S9 locus and pTD3-21 at D15S10 locus, assigned on 15q11-q12 was not detected in the patients. In addition, a linkage of the syndrome to D15S9 and D15S10 loci was not observed in the family. These data suggest that a gene for the Cohen syndrome is excluded from the 15q11-q12 region, on which a gene for the Prader-Willi syndrome is assigned, and that the Cohen syndrome is distinctly different from the Prader-Willi syndrome, although clinical manifestations of the Cohen and the Prader-Willi syndromes are very similar.     

High-resolution cytogenetic studies in patients with Prader-Willi syndrome

We investigated 24 patients with Prader-Willi syndrome by the high-resolution banding technique. Their history and clinical findings were also examined in some detail. Twelve had interstitial deletion of 15q; del(15) (q11.2q13) in 11 cases and del(15) (q11.2q12) in one case. Six revealed normal karyotypes at about 500-850 bands per haploid-set level. In an additional six cases, no deletion was detected. However, we took the results as tentative, as the observed karyotypes were at the 400-bands level. During the course of this study, it was realized that a small deletion in the proximal 15q could be easily overlooked when a mitotic spread around 400-bands or less per haploid-set level was used. There was no distinct difference in the clinical features of patients with interstitial deletion and those with a normal karyotype. Two cases in the latter group lacked some of the typical features of the former group, e.g. poor fetal vigor, neonatal feeding difficulty, hypotonia, and delayed motor development.     

Cytogenetic and molecular studies in the Prader-Willi and Angelman syndromes: An overview

The majority of patients with Angelman syndrome and Prader-Willi syndrome have a cytogenetic and molecular deletion of chromosome 15q11q13 with the primary difference being in the parental origin of deletion. Our current understanding of the cytogenetics and molecular genetics of these 2 clinically distinct syndromes will be discussed in this review. © 1993 Wiley-Liss, Inc.     

Methylation PCR analysis of Prader-Willi syndrome,Angelman syndrome,and control subjects

We report on a relatively large survey of Prader-Willi syndrome, Angelman syndrome, and control subjects with the newly described methylation polymerase chain reaction (PCR) method to determine its usefulness for molecular diagnosis. Sixty-one Prader-Willi syndrome (PWS) individuals (26 men and 35 women), 9 Angelman syndrome (AS) patients (5 men and 4 women), and 58 other individuals were studied with methylation PCR following sodium bisulfite treatment of genomic DNA. In addition, multiple tissues, including fetal tissue, were studied from several individuals to determine the effects of various tissues on methylation PCR results. The expected methylation PCR result was observed in each case. This PCR-based assay evaluates the methylation status of the CpG island of the SNRPN gene and allows for rapid molecular diagnosis of PWS or AS with less labor than Southern hybridization for methylation analysis. The PCR results were identical to those achieved by Southern hybridization in those individuals studied. Am. J. Med. Genet. 80:263–265, 1998. © 1998 Wiley-Liss, Inc.     

Prader-Willi syndrome in a child with XYY

We report a 26-month-old boy with XYY syndrome, with the complication of Prader-Willi syndrome (PWS) due to uniparental maternal disomy of chromosome 15. To our knowledge, this is the first case of XYY syndrome and PWS. Clinical findings were fully compatible with the diagnostic criteria for PWS. Molecular analysis revealed a maternal heterodisomy of chromosome 15, indicating that non-disjunction of chromosome 15 had occurred at maternal meiosis I, and that the non-disjunction of chromosome Y and of chromosome 15 had occurred independently. Received: May 10, 1999 / Accepted: June 22, 1999     

Isochromosome 15q of maternal origin in two Prader-Willi syndrome patients previously diagnosed erroneously as cytogenetic deletions

Since our previous report on two Prader-Willi syndrome (PWS) patients with t(15q;15q) (Niikawa and Ishikiriyama; Hum Genet 69:22–27,1985) was erroneous, we report here new data and a corrected interpretation. Reexamination of the parental origin of their t(15q;15q) using polymorphic DNA markers that are mapped to various regions of 15q documented no molecular deletions at the 15q11-q13 region in either patient. Both patients were homozygous at all loci examined and their haplotypes on 15q coincided with one of those in their respective mothers. These results indicate that the presumed t(15q;15q) in each patient was actually an isochromosome 15q producing maternal uniparental disomy, consistent with genomic imprinting at the PWS locus. © 1994 Wiley-Liss, Inc.     

Perinatal and first year follow-up of patients with Prader-Willi syndrome: normal size of hands and feet

Four patients with Prader-Willi syndrome, diagnosed in the neonatal period and followed during the first year of life, are reported. There were three males and one female. All four patients presented with hypotonia and distinct craniofacial dysmorphism. Prometaphase chromosome analysis showed interstitial deletion of 15q in all of them. The placentae and umbilical cords were examined in three of the patients and found normal. Electromyography done in the neonatal period suggested primary myopathy. Height, weight and head circumference were normal at birth in all patients. Hand and foot measurements showed normal size at birth and during the first year of life.