Familial Prader-Willi syndrome: Case report and a literature review

Prader-Willi syndrome (PWS) is a neurobehavioural disorder arising through a number of different genetic mechanisms. All involve loss of paternal gene expression from chromosome 15q11q13. Although the majority of cases of PWS are sporadic, precise elucidation of the causative genetic mechanism is es sential for accurate genetic counselling as the recurrence risk varies acco rding to the mechanism involved. A pair of siblings affected by PWS is desc ribed. Neither demonstrates a microscopically visible deletion in 15q11q13 or maternal disomy. Methylation studies at D15S63 and at the SNRPN locus co nfirm the diagnosis of PWS. Molecular studies reveal biparental inheritance in both siblings with the exception of D15S128 and D15S63 where no paterna l contribution is present indicating a deletion of the imprinting centre. F amily studies indicate that the father of the siblings carries the deletion which, he has inherited from his mother. The recurrence risk for PWS in hi s offspring is 50%.