Prader-Willi syndrome and a deletion/duplication within the 15q11-q13 region

Prader-Willi syndrome (PWS) is characterised by infantilehypotonia, feeding difficulties, hypogonadism, smallhands and feet, mental deficiency, obesity in early childhood, a particular facial appearance, and a paternally derived 15q11-q13 deletion (approximately 4 million bp in size) in about 70 % of subjects, maternal disomy 15 (both 15s from the mother) in 25 % of subjects, or an imprinting muta-tion in 2-5 % of subjects.1–4 PWS syndrome is considered to be the most common genetic cause of marked obesity in humans.1 Two breakpoint clusters have been reported centromeric to locus ZNF127 with the most proximal breakpoint (BP1) accounting for 44 % of cytogenetic deletions while 56 % of deletions occur at the second proximal breakpoint (BP2).5 6 The second breakpoint (BP2) lies between loci D15S541/S542 and D15S543 and breakpoint BP1 is proximal to D15S541/ S542.5 6 A third breakpoint (BP3) is distally located within the