ACTA ENDOCRINOLOGICA (BUC)

Prader-Willi syndrome (PWS) is commonly caused by the absence of the paternal contribution for imprinted genes in chromosomes 15q11.\r\nWe present a case of a 16 years-old girl with hypotonia, feeding difficulties, failure to thrive and strabismus during infancy followed by hyperphagia, early-onset obesity with insulin-dependent diabetes mellitus and necrobiosis lipoidica diabeticorum, short stature, hypogonadotropic hypogonadism and some of the facial characteristics of individuals with PWS. Routine Giemsa banded chromosomes were obtained from peripheral blood lymphocytes. Karyotype analysis showed a mosaic triple X (46,XX/47,XXX). Using\r\nmethylation studies of the PWS critical region (SNRPN locus) and by polymorphic microsatellite analysis, the existence of microdeletion of the critical area on paternal\r\nchromosome 15 was shown in white blood cells. Mosaicism for triple-X was observed in other three reported patients with PWS but in all of these reported cases an uniparental maternal heterodisomy for chromosome 15 was described. The X chromosome mosaicism in our case is presumed to have arisen postzygotically. The findings in our patient provide evidence that these two chromosomal anomalies are not related and had occurred together coincidentally. Genetic counseling for this family should consider these two conditions separately and provide separate recurrence\r\nrisks for each.