Cases reported "Prader-Willi Syndrome"

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1/15. Syndromal obesity due to paternal duplication 6(q24.3-q27).

    The likelihood of a paternally expressing imprinted gene in chromosome region 6(q23-24) has been highlighted by cases of transient neonatal diabetes mellitus (TNDM) in which paternal uniparental disomy (UPD) for chromosome 6 or paternal duplication 6(q23-qter) was detected. We present the case of a 38-year-old man with moderate to severe intellectual delay, short stature, small hands and feet, eye abnormality, small mouth, and obesity (without hyperphagia) beginning in mid-childhood. The perinatal and neonatal histories were normal. The patient had a duplication within 6q. fluorescence in situ hybrisation studies were performed with single and dual hybridisations using a chromosome 6 library probe, short and long arm subregional probes, 6q23-24, 6q25.3-6qter locus-specific probes, and a 6q telomere probe. The hybridisation results defined an inverted duplication of 6q24.3 to 6q27. DNA studies with microsatellite markers from 6p and 6q showed regular biparental inheritance of chromosome 6 and confirmed that the duplication was paternal in origin. Our patient appears to be the first one known to have paternal duplication of chromosome area 6(q24-q27) who did not have TNDM as an infant. He has remained nondiabetic, although obesity, without hyperphagia, has been a constant problem since its onset in mid-childhood.
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2/15. Duplication within chromosome region 15q11-q13 in a patient with similarities to prader-willi syndrome confirmed by region-specific and band-specific fish.

    We report on a patient presenting with mental retardation and obesity and a proximal duplication of chromosome 15. The patient shared some clinical signs with prader-willi syndrome. With a region-specific paint, generated by microdissection, a duplication in region 15q11.2-q13 was shown to be present. Subsequently, FISH with probes localized to chromosome region 15q11.2-q12 and microsatellite analysis was used to characterize this chromosome aberration further and an insertion duplication within the region frequently deleted in Prader-Willi and angelman syndrome was demonstrated.
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3/15. Familial interstitial 570 kbp deletion of the UBE3A gene region causing Angelman syndrome but not prader-willi syndrome.

    angelman syndrome (AS) is a disorder of psychomotor development caused by loss of function of the imprinted UBE3A gene. Since the paternal UBE3A copy is regularly silent, only mutations inactivating the maternal copy cause AS. Among 1,272 patients suspected of AS, we found one with an isolated deletion of the UBE3A gene on the maternally inherited chromosome. Initial dna methylation testing at the SNURF-SNRPN locus in the patient revealed a normal pattern. The deletion was only detected through allelic loss at microsatellite loci D15S1506, D15S122, and D15S210, and confirmed with fluorescence in situ hybridization (FISH) using bacterial artificial chromosome (BAC) probes derived from the loci. It extends approximately 570 kilobase pairs (kbp), encompassing the UBE3A locus, and is flanked by loci PAR/SN and D15S986. The deletion is familial, and haplotype studies suggest that a great grandfather of the index patient already carried this deletion, and that it causes AS when inherited through the female germline but not prader-willi syndrome (PWS) when paternally inherited. Our findings support the hypothesis that the functional loss of maternal UBE3A gene activity is sufficient to cause AS and that the deleted region does not contain genes or other structures that are involved in PWS. Finally, this case highlights that methylation tests can fail to detect some familial AS cases with a recurrence risk of 50%.
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4/15. A further case of a prader-willi syndrome phenotype in a patient with angelman syndrome molecular defect.

    angelman syndrome (AS) and prader-willi syndrome (PWS) are distinct human neurogenetic disorders; however, a clinical overlap between AS and PWS has been identified. We report on a further case of a patient showing the PWS phenotype with the AS molecular defect. Despite the PWS phenotype, the dna methylation analysis of SNRPN revealed an AS pattern. Cytogenetic and FISH analysis showed normal chromosomes 15 and microsatellite analysis showed heterozygous loci inside and outside the 15q11-13 region. The presence of these atypical cases could be more frequent than previously expected and we reinforce that the dna methylation analysis is important for the correct diagnosis of severe mental deficiency, congenital hypotonia and obesity.
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5/15. prader-willi syndrome with an unusually large 15q deletion due to an unbalanced translocation t(4;15).

    prader-willi syndrome (PWS) is a neurobehavioral disorder caused by deletions in the 15q11-q13 region, by maternal uniparental disomy of chromosome 15 or by imprinting defects. Structural rearrangements of chromosome 15 have been described in about 5% of the patients with typical or atypical PWS phenotype. An 8-year-old boy with a clinical diagnosis of PWS, severe neurodevelopmental delay, absence of speech and mental retardation was studied by cytogenetic and molecular techniques, and an unbalanced de novo karyotype 45,XY,der(4)t(4;15)(q35;q14),-15 was detected after GTG-banding. The patient was diagnosed by SNURF-SNRPN exon 1 methylation assay, and the extent of the deletions on chromosomes 4 and 15 was investigated by microsatellite analysis of markers located in 4qter and 15q13-q14 regions. The deletion of chromosome 4q was distal to D4S1652, and that of chromosome 15 was located between D15S1043 and D15S1010. Our patient's severely affected phenotype could be due to the extent of the deletion, larger than usually seen in PWS patients, although the unbalance of the derivative chromosome 4 cannot be ruled out as another possible cause. The breakpoint was located in the subtelomeric region, very close to the telomere, a region that has been described as having the lowest gene concentrations in the human genome.
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6/15. Unique maternal deletion of 15q in a patient with some symptoms of prader-willi syndrome.

    BACKGROUND: Human chromosome 15q11-q13 is a critical region for prader-willi syndrome (PWS) and angelman syndrome (AS) and most of the genes are under the condition of imprinting mechanism. PWS results from the loss of expression of paternally expressed genes and AS of maternally expressed genes. In this study molecular studies about a patient with congenital anomalies and mental retardation are analyzed. methods: Highly polymorphic microsatellite markers were analyzed by PCR. These markers exist within 15q11-q13 and distal to 15q13. RESULTS: Only the maternal D15S986 locus within 15q11-q13 was deleted and other markers were biallelic. CONCLUSIONS: The result of maternal small region deletion in this patient is different from the typical PWS with paternal chromosome deletion and it suggests that nearby the deleted region there exists a gene (genes) which is not imprinted but needs biallelic expression.
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7/15. The impact of imprinting: prader-willi syndrome resulting from chromosome translocation, recombination, and nondisjunction.

    prader-willi syndrome (PWS) is most often the result of a deletion of bands q11.2-q13 of the paternally derived chromosome 15, but it also occurs either because of maternal uniparental disomy (UPD) of this region or, rarely, from a methylation imprinting defect. A significant number of cases are due to structural rearrangements of the pericentromeric region of chromosome 15. We report two cases of PWS with UPD in which there was a meiosis I nondisjunction error involving an altered chromosome 15 produced by both a translocation event between the heteromorphic satellite regions of chromosomes 14 and 15 and recombination. In both cases, high-resolution banding of the long arm was normal, and FISH of probes D15S11, SNRPN, D15S10, and GABRB3 indicated no loss of this material. Chromosome heteromorphism analysis showed that each patient had maternal heterodisomy of the chromosome 15 short arm, whereas PCR of microsatellites demonstrated allele-specific maternal isodisomy and heterodisomy of the long arm. SNRPN gene methylation analysis revealed only a maternal imprint in both patients. We suggest that the chromosome structural rearrangements, combined with recombination in these patients, disrupted normal segregation of an imprinted region, resulting in uniparental disomy and PWS.
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8/15. prenatal diagnosis of uniparental disomy 15 following trisomy 15 mosaicism.

    Maternal uniparental disomy 15 (UPD15), responsible for approximately 25 per cent of prader-willi syndrome cases, is usually caused by maternal meiosis I non-disjunction associated with advanced maternal age. These cases may initially be detected as mosaic trisomy 15 during routine prenatal diagnostic studies. In such cases, PCR (polymerase chain reaction) microsatellite analysis of uncultured cells makes prospective prenatal diagnosis for UPD15 possible with results available in 2-4 days. We have performed molecular analyses on a series of seven cases of mosaic trisomy 15 identified in amniotic fluid (AF, n = 3) or chorionic villus samples (CVS, n = 4) from patients initially referred for advanced maternal age or abnormal triple screen. In all cases, the maternal ages were > or = 35 years and maternal meiosis I non-disjunction was documented as the cause of the trisomy in all informative cases (n = 5). Of the three case with mosaic trisomy 15 at amniocentesis, two showed the presence of the trisomy in the fetus. Molecular analysis showed one case with maternal UPD15 in the euploid cell line and one case with biparental inheritance. Both of these families elected to terminate the pregnancies based on the presence of true fetal mosaicism. In the third case, low-level trisomy 15 mosaicism in the amniotic fluid was not confirmed in a follow-up amniotic fluid sample and molecular analysis indicated biparental inheritance in the fetus. For the four trisomy 15 mosaics detected at CVS, molecular analysis was performed on direct amniotic fluid cell lysates for prospective diagnosis of UPD at 14-16 weeks' gestation. Follow-up cytogenetic analysis of the amniotic fluid in all four cases was normal, indicating confined placental mosaicism. Molecular analysis showed one of these four cases to have maternal heterodisomy 15. Based on the likelihood of prader-willi syndrome due to maternal UPD15, the couple chose to terminate the pregnancy. The total of two of seven cases of trisomy 15 mosaicism resulting in UPD15 is consistent with the theoretical expectation of one-third and indicates a high risk of UPD in such pregnancies. Therefore, UPD testing should be offered in all cases of mosaic trisomy 15 encountered in CVS or amniocentesis.
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9/15. A 5-year-old white girl with prader-willi syndrome and a submicroscopic deletion of chromosome 15q11q13.

    We report on a 5-year-old white girl with prader-willi syndrome (PWS) and a submicroscopic deletion of 15q11q13 of approximately 100-200 kb in size. High resolution chromosome analysis was normal but fluorescence in situ hybridization (FISH), Southern hybridization, and microsatellite data from the 15q11q13 region demonstrated that the deletion was paternal in origin and included the SNRPN, PAR-5, and PAR-7 genes from the proximal to distal boundaries of the deletion segment. SNRPN and PW71B methylation studies showed an abnormal pattern consistent with the diagnosis of PWS and supported the presence of a paternal deletion of 15q11q13 or an imprinting mutation. Biparental (normal) inheritance of PW71B (D15S63 locus) and a deletion of the SNRPN gene were observed by microsatellite, quantitative Southern hybridization, and/or FISH analyses. Our patient met the diagnostic criteria for PWS, but has no reported behavior problems, hyperphagia, or hypopigmentation. Our patient further supports SNRPN and possibly other genomic sequences which are deleted as the cause of the phenotype recognized in PWS patients.
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10/15. Familial translocations involving 15q11-q13 can give rise to interstitial deletions causing Prader-Willi or angelman syndrome.

    A de novo interstitial deletion of 15q11-q13 is the major cause of prader-willi syndrome (PWS) and angelman syndrome (AS). Here we describe two unrelated PWS patients with a typical deletion, whose fathers have a balanced translocation involving the PWS/AS region. Microsatellite data suggest that the deletion is the result of an unequal crossover between the derivative chromosome 15 and the normal chromosome 15. We conclude that familial translocations involving 15q11-q13 can give rise to interstitial deletions causing PWS or AS and that prenatal diagnosis in such families should include fluorescence in situ hybridisation or microsatellite studies or both.
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