Editor—Cri du chat syndrome (CdCS) is one of the more common deletion syndromes, involving the short arm of chromosome 5, with an incidence of 1 in 50 000 live births. Classically, patients with this syndrome present with microcephaly, a round face, hypertelorism, micrognathia, prominent nasal bridge, epicanthic folds, hypotonia, and severe psychomotor retardation. Infants also exhibit a high pitched cry similar to the mewing of a cat, which is usually considered diagnostic for this syndrome.1 2 Recently, genotype-phenotype studies in CdCS led to the identification of two separate chromosomal regions, hemizygosity for which is associated with specific phenotypes.3 A deletion of 5p15.3 results in the manifestation of a cat-like cry4, while a deletion of 5p15.2 results in the presentation of the other major clinical features of the syndrome.5 Moreover, a region for speech delay in 5p15.3 has been identified.6

From a review of 331 published cases, Niebuhr2 estimated that most CdCS cases are the result of de novo deletions (about 80%), some derive from a familial rearrangement (12%), and only a few show other rare cytogenetic aberrations, such as mosaicism (3%), rings (2.4%), and de novo translocations (3%). Chromosomal mosaicism in CdCS has been described involving a cell line with a 5p deletion and a cell line with a normal karyotype.2 7

We describe the first three reported cases of mosaic de novo 5p anomalies involving two rearranged cell lines in CdCS out of 80 (3.75%) patients from the Italian Register of CdCS8analysed in a large study of correlation between 5p deletion and phenotypic effect (Cerruti Mainardi et al, manuscript in preparation).

Patient 1 was the first female child of healthy, unrelated parents. At birth the mother was 29 and the father 31 years old. The pregnancy was …