Analysis of chromosome breakage in the Prader-Labhart-Willi syndrome

Analysis of chromosome breakage with mitomycin C (MMC) and folate‐deficient culture conditions was undertaken on 18 Prader‐Labhart‐Willi syndrome (PLWS) patients (10 with 15q12 deletion [5 females, 5 males; x̄ age = 17.9 yr, range of 0.3 to 40 yr] and 8 without deletion [2 females, 6 males; x̄ age = 18.6 yr, range of 7 to 26 yr]), 21 PLWS parents with an average age of 39.2 yr and a range of 25 to 70 yr (12 fathers [8 fathers of PLWS children with the 15q12 deletion and 4 fathers of PLWS children with normal chromosomes] and 9 mothers [4 mothers of PLWS children with the 15q12 deletion and 5 mothers of PLWS children with normal chromosomes]), and age‐matched control individuals. There was no difference between PLWS patients and control individuals in the number of chromosome and chromatid aberrations in cells grown at 48 and/or 96 hr in either 20 ng/ml or 50 ng/ml of MMC or between the PLWS parents and control individuals in cells grown in 50 ng/ml MMC for 96 hr, although a small increase (P < 0.05) in chromosome breakage was found in cells from the total PLWS parental group compared with control individuals exposed for 48 hr in 50 ng/ml MMC. There was also no significant difference in chromosome fragile site frequency in cells grown in folate‐deficient culture conditions in PLWS patients, their parents, or controls. The average sister chromatid exchange (SCE) frequencies observed in PLWS subgroups (deletion vs. nondeletion), their parents or control individuals were not significantly different. No clustering of chromosome/chromatid breaks or SCEs identified in the proximal long arm was found when compared with the middle or distal long arm regions of the D group chromosomes.