Variability in a family with an insertion involving 5p

Cri-du-chat syndrome is due to a partial deletion of the short arm of chromosome 5 and comprises a catlike cry, minor facial anomalies, growth delays, and psychomotor retardation. We identified a family with an insertion involving chromosome areas 5p and 16q. Four relatives are balanced carriers and have a normal phenotype, 5 have inherited the insertion in an unbalanced form with 2 resulting in partial trisomy of 5p and 3 in partial monosomy of 5p. The 3 individuals show a variable phenotype with respect to mental delay and some of the findings of cri-du-chat syndrome. The extent of the 5p deletion in this family was determined using previously mapped markers. The deletion in this family was informative for further refining the phenotypic map for the cri-du-chat syndrome. This family demonstrates the importance of performing phenotype-genotype correlation studies based on the presence rather than the absence of abnormalities.