[Prader-Willi syndrome large deletion on two brothers. Is this the exception that confirm the rule?]

Prader-Willi syndrome (PWS), a neuroendocrine disorder could be due to: a large paternally derived chromosome deletion of 15q11-13, to maternal uniparental disomy (UPD), or imprinting mutation (IC); amongst this last group five families, with inherited microdeletion encompassing SNRPN were described; in these families excluded a typical large deletion. Families with more than a child with PWS by classic large deletion have not been published.

We report on a family with three children, 2 of which had typical clinical findings of PWS: mental retardation, hypogonadism, hypotonia, hyperphagia, obesity and also strabismus and synophridia; during pregnancy reduced fetal movement was noted. The Fish probes (SNRPN and D15S10), Methylation specific PCR (MPCR), Southern blot and microsatellite markers confirmed in the PWS brothers a large deletion at least of the area comprising between D15S63 and GABRA5.

No previously described cases in the literature reviewed show for PWS brothers due to a classical deletion. Some possible reasons recurrence in this family could be: at random, germinal mosaicism, or abnormalities at gonadal level environmental factors such as hydrocarbon exposing occupations in fathers of PWS patients as has been referred to by different authors. The latter might be an explanation as the father was working from age of 17 and for over 12 years with paints at shipyards exposed to hydrocarbon and others mutagenic substances. We consider it would be important to bear this case in mind when giving genetic counseling.