Family studies in Prader-Willi syndrome

Clinical, cytogenetic and molecular studies have been undertaken in the families of 52 probands with Prader-Willi syndrome. The maternal age at the birth of a proband with a deletion in 15p11q13 was on average 8 years less than that of the mothers of probands with uniparental disomy (UPD), the paternal age was on average 7 years less. Seven probands with UPD were all female, as were 7 patients who had neither a detectable chromosomal abnormality nor UPD. Cytogenetic and molecular polymorphisms in proximal chromosome 15 indicated that for probands with a 15q11q13 deletion, inheritance of both the maternal and the intact paternal homologue is random in their unaffected sublings. Pigmentation studies suggest that probands who have a deletion in 15q11q13 have lighter colouring than other family members implying that D15S12 may not be imprinted.