Prader-Willi syndrome: Methylation study or fluorescence in situ hybridization first.

Prader–Willi syndrome (PWS) is neurogenetic disorder involving the imprinting mechanism at 15q11–13 region. We report a 4-year-old girl who was referred to our laboratory to be investigated for clinical obesity, mental deficiency and respiratory problems. The patient was born for non-consanguineous and healthy biological parents. After normal pregnancy, the patient was delivered by cesarean section at full term, with a birth weight of 2500 g, and the height and head circumference were unknown. In neonatal stage, she presented severe hypotonia with feeding problems. Her developmental progress was delayed. She walked and developed speech at the age of 3 years. Since the age of 3 years, she presented severe dental problems. Methylation study had confirmed the diagnosis, and for detecting etiology, fluorescence in situ hybridization using probes for small nuclear ribonucleoprotein polypeptide N (SNRPN), which map inside the chromosomal region 15q11–15q13, was necessary to confirm the 15q11–15q13 deletion of paternal chromosome 15, which is the predominant genetic defect in PWS. In conclusion, we report this case with an objective to reinforce the necessity of analysis of DNA methylation within the 15q11–13 region, which is an important tool for the correct diagnosis among children presenting with neonatal hypotonia, mental deficiency and obesity.

A combination of five short tandem repeats of chromosome 15 significantly improves the identification of Prader-Willi syndrome etiology in the Argentinean population

Prader-Willi syndrome (PWS) is a multisystemic disorder caused by the loss of expression of paternally transcribed genes in the PWS critical region of chromosome 15. Various molecular mechanisms are known to lead to PWS: deletion 15q11-q13 (75% of cases), maternal uniparental disomy (matUPD15) (23%) and imprinting defects (2%). FISH and microsatellite analysis are required to establish the molecular etiology, which is essential for appropriate genetic counseling and care management. We characterized an Argentinean population, using five microsatellite markers (D15S1035, D15S11, D15S113, GABRB3, D15S211) chosen to develop an appropriate cost-effective method to establish the parental origin of chromosome 15 in nondeleted PWS patients. The range of heterozygosity for these five microsatellites was 0.59 to 0.94. The average heterozygosity obtained for joint loci was 0.81. The parental origin of chromosome 15 was established by microsatellite analysis in 19 of 21 non-deleted PWS children. We also examined the origin of the matUPD15; as expected, most of disomies were due to a maternal meiosis I error. The molecular characterization of this set of five microsatellites with high heterozygosity and polymorphism information content improves the diagnostic algorithm of Argentinean PWS children, contributing significantly to adequate genetic counseling of such families.

Estudo clínico, citogenético e molecular nas síndromes de Prader-Willi e Angelman / Clinical, cytogenetical and molecular studies in Prader-Willi and Angelman syndromes

A Síndrome de Prader-Willi (SPW) e a Síndrome de Angelman (SA) säo doenças neurogenéticas consideradas como exemplos do fenômeno de impressäo genômica, em seres humano, estando relacionadas com alteraçöes envolvendo a regiäo cromossômica 15q11-13. As alteraçöes genéticas predominantes, na SPW, säo deleçöes na regiäo 15q11-13, de origem paterna e dissomia uniparental materna e, na SA, encontram-se deleçöes na regiäo 15q11-13 materna e dissomia uniparental paterna. Estudamos 5 pacientes com suspeita clínica de SPW e 4 pacientes com suspeita clínica de SA, atendidos no Setor de Genética Médica do Hospital das Clínicas da FMRP-USP, com o objetivo de estabelecer o diagnóstico clínico e etiológico nessa amostra. Para isso, utilizamos citogenética convencional, estudo de metilaçäo por Southern blotting com a sonda KB17 (ilha CpG do gene SNRPN), após digestäo com as enzimas de restriçäo Xba I e Not I, e análise de polimorfismos de repetiçäo (CA)n por PCR, usando os primers 196 e IR4-3R. Dos 9 pacientes avaliados, todos tiveram avaliaçäo citogenética convencional normal. Foram confirmados molecularmente 1 caso de SPW por deleçäo nova, 1 caso de SPW por dissomia uniparenteal materna e 1 caso de SPW em que a causa genética näo pode ser esclarecida pela análise de polimorfismo com os primers usados. Foram confirmados, molecularmente, 2 casos de SA, ambos por deleçäo nova na regiäo 15q11-13 e, 1 caso de SA, cuja clínica é extremamente sugestiva, teve resultado molecular normal, podendo-se sugerir uma mutaçäo de ponto no gene responsável pela SA.

Síndrome de Prader-Willi / Prader-Willy Syndrome

A Síndrome de Prader-Willi é uma doença rara, congênita, que acomete 1 a cada 15 mil nascimentos, caracterizada por hipogonadismo, hiperfagia com obesidade mórbida, baixa estatura, retardo mental, fácies dismórfica, sendo originada de uma anormalidade no braço longo do cromossomo 15 no locus 15q 11-13 de origem paterna. Relata-se caso de Síndrome de Prader-Willi, com revisäo da literatura, apresentando características clínicas, genéticas, dietéticas, metabólicas e tratamento