A blind prometaphase study of Prader-Willi syndrome: frequency and consistency in interpretation of del 15q.

Controversy continues to exist concerning the proportion of individuals with Prader-Willi syndrome who have a chromosome 15 deletion and concerning the reliability with which a cytogenetic service laboratory can accurately perform the appropriate analysis. Blind prometaphase cytogenetic study of 13 individuals from a Prader-Willi syndrome clinic and seven controls has revealed that approximately 70% of accurately diagnosed clinically typical patients with this disorder have an evident deletion of at least 15q12. Blind analysis of panels of chromosome 15 pairs from all cases in this study by the directors of four independent cytogenetic service laboratories demonstrated substantial interobserver consistency in interpretation of results. The possibility of euploid mosaicism for del 15q was investigated, but remains unresolved.