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.
Chromosome breakage analysis with Mitomycin C (MMC) and sister chromatid exchanges (SCE) were obtained on 10 computer operators with computer exposure for a minimum of 3 hours per day for 4 years and 10 control subjects matched for age and personal lifestyle. No difference was found between the two groups in the total number of chromatid and chromosome aberrations in cells grown at 48 and/or 96 hours in Mitomycin C (20 or 50 ng/ml-final concentration). The average number of SCE per cell in approximately 30 cells from each person was 6.4 ± 1.1 (mean ± standard deviation) for the computer operators and 9.2 ± 1.6 for the controls. This difference was significant (p <.001). The replicative index was significantly higher (p<.01) in computer operators than in control subjects. The number of SCE appeared not to be influenced by the years of computer exposure. Additional studies with larger sample sizes will be needed to identify if significant differences exist in cell kinetics and sister chromatid exchanges in individuals employed as computer operators.
Plasma immunoreactive beta-melanocyte-stimulating hormone (beta-MSH) levels, which actually represent the combined concentrations of beta-lipotropin (beta-LPH) and gamma-LPH in normal individuals, were measured in 12 patients (6 males and 6 females with an average age of 16.8 years, range 4 months to 27 years) with the Prader-Labhart-Willi syndrome (PLWS). Five patients were previously identified with high-resolution analysis as having the 15q chromosomal deletion, whereas 7 patients had normal chromosomes. Hypopigmentation was observed in all 5 patients with the 15q deletion. Of the 7 individuals with normal chromosomes, two were hypopigmented and 5 had normal pigmentation. Fasting (6 to 12 hours) plasma samples were analyzed for immunoreactive beta-MSH in the 12 PLWS individuals. Plasma immunoreactive beta-MSH (LPH) levels were within the normal range in all 12 individuals. There was no significant difference in the plasma immunoreactive beta-MSH concentrations between patients who did and did not have the chromosomal deletion or in those who were or were not hypopigmented. Thus, a decrease in circulating plasma immunoreactive beta-MSH (LPH) does not appear to be the cause of the hypopigmentation observed in some patients with PLWS.
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