American Journal of Medical Genetics 2000; 91: 298-304

Phenotypic heterogeneity of growth and psychometric intelligence in Prader-Willi syndrome: variable expression of a contiguous gene syndrome or parent-child resemblance?
Malich S, Largo R, Schinzel A, Molinari L, Eiholzer U.

Phenotypic variability in children with Prader-Willi syndrome (PWS) was investigated with respect to variable expression of the contiguous gene syndrome and trait variance. In a prospective study, parent/child resemblance of anthropometric and psychometric measures was analyzed in 22 children with PWS (11 females and 11 males; 18 deletions, 4 uniparental disomy (UPD)) and in a control group (88 females and 88 males). The average child-midparent Z-score difference for height in females was -1.9 and in males -0.9, head circumference -1.7 and -1.0, and body mass index (BMI) 2.3 and 2.7, respectively. Intellectual performance of females and males was, on average, -2.7 and -2.6 below maternal performance. Range and standard deviation were moderately increased for height and head circumference, doubled for BMI, and unchanged for IQ. Parent/child correlations for anthropometric and psychometric measurements in the study group did not significantly differ from those of the control group. Exceptions were higher correlations between mothers and daughters for height (P < 0.05) and BMI (P < 0.01), and lower correlations for head circumference between midparent values and daughters (P < 0.05) than in the control group. In conclusion, parent-child resemblance in growth and intellectual development among children with PWS was found to be comparable to that noted in the normal population, indicating a strong determination by trait variance. Children with PWS differed significantly with respect to a lower trait level and — with the exception of IQ — a larger variability. The latter may indicate a variable expression of the contiguous gene syndrome. Am. J. Med. Genet. 91:298–304, 2000.