[Familial oculo-cutaneous hypopigmentation of dominant transmission due to a disorder in melanocyte formation. Association of Prader-Willi syndrome with a chromosome abnormality in one of the subjects involved].

Four members of a Swiss family were affected with oculo-cutaneous hypopigmentation of dominant transmission which differed from the previously described cases of dominant oculo-cutaneous albinism by its ultrastructure. The hypopigmentation described here is characterized by the formation of numerous, but very small, melanosomes. Melanocytic tyrosinase activity was normal in light microscopy. However, on electron microscopy, tyrosinase activity was strong in premelanosomes of stage I only, and decreased rapidly in the later stages. One of the affected members also presented a Prader-Willi syndrome and a chromosomal anomaly, both being probably unrelated to the pigmentary disorder.