reach puberty, develop secondary sex characteristics and menstruate at the usual time. The genital tract is usually normal in females, except for a report of a bicornuate uterus. In males, testes are often small, but spermatogenesis is thought to be normal. Exceptionally, some with Cri du chat are very high-functioning and do not seem very different from developmentally typical individuals, with mostly the exception of mild learning difficulties, and do not have speech difficulties, although they may have milder facial features and a high-pitched voice due to their condition. Genetics Cri du chat syndrome is due to a partial deletion of the short arm of chromosome number 5, also called "5p monosomy" or "partial monosomy." Approximately 90% of cases result from a sporadic, or randomly occurring, de novo deletion. The remaining 10–15% are due to unequal segregation of a parental balanced translocation where the 5p monosomy is often accompanied by a trisomic portion of the genome. These individuals may have more severe disease than those with isolated monosomy of 5p. A recent study suggests this may not be the case where a trisomy of chromosome 4q is involved. Most cases involve total loss of the most distal 10–20% of the material on the short arm. Fewer than 10% of cases have other rare cytogenetic aberrations (e.g., interstitial deletions, mosaicisms, rings and de novo translocations). The deleted chromosome 5 is paternal in origin in about 80% of de novo cases. Loss of a small region in band 5p15.2 (cri du chat critical region) correlates with all the clinical features of the syndrome with the exception of the catlike cry, which maps to band 5p15.3 (catlike critical region). The results suggest that 2 noncontiguous critical regions contain genes involved in this condition's cause. Two genes in these regions, Semaphorine F (SEMA5A) and delta catenin (CTNND2), are potentially involved in cerebral development. The deletion of the telomerase reverse transcriptase (hTERT) gene localized in 5p15.33 may contribute to the phenotypic changes in cri du chat syndrome as well. Diagnosis Diagnosis is based on the distinctive cry and accompanying physical problems. These common symptoms are quite easily observed in infants. Affected children are typically diagnosed by a doctor at birth. Genetic counseling and genetic testing may be offered to families with individuals who have cri du chat syndrome. Prenatally the deletion of the cri du chat related region in the p arm of chromosome 5