The cri-du-chat syndrome is a contiguous gene syndrome that results from a 
deletion of the short arm of chromosome 5 (5p). Patients present with a cat-like 
cry at birth, which is usually considered diagnostic of this syndrome. 
Additional features of the syndrome include failure to thrive, microcephaly, 
hypertelorism, epicanthal folds, hypotonia, and severe mental retardation. We 
report on four families in which patients with 5p deletions have only the 
characteristic cat-like cry, with normal to mildly delayed development. The 
precise locations of the deletions in each family were determined by FISH using 
lambda phage and cosmid clones. All of the deletion breakpoints map distal to a 
chromosomal region that is implicated with the facial features and severe mental 
and developmental delay in the cri-du-chat syndrome. DNA clones mapping in the 
chromosomal region associated with the cat-like cry feature will be useful 
diagnostic tools. They will allow for the distinction between 5p deletions that 
will result in the severe delay observed in most cri-du-chat syndrome patients 
and those deletions that result in the isolated cat-like cry feature, which is 
associated with a better prognosis.