A deletion of the long arm of chromosome 15 (usually involving bands 15q11-q12) has been seen in approximately 50% of Prader-Willi syndrome (PWS) patients. However, 14 patients with non-PWS (or atypical PWS) phenotype with 15q deletion indicate great clinical variability. A deletion was found in a propositus with a de novo translocation [45,XY,-15,-22,+rec(15;22)(22pter → 22q13.2::15q14 → 15qter)], who had anomalies not normally observed in PWS patients. Activities of several enzymes mapped to the involved chromosomes were studied in the patient and control individuals. A 50% decrease in the level of arylsulfatase-A confirmed a small deletion in 22q(22q13.2 → qter), and additional studies localized more precisely the loci for α-mannosidase (cytoplasmic) and β-galactosidase.
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