Genetic features:
(1) The phenotypic frequency is around 1 in 25,000 to 50,000, while the frequency of occult microdeletions is higher.
(2) Most cases are caused by de novo deletions, with a few cases due to malsegregation of a balanced translocation in one of the parents.
(3) The critical region for the phenotype is at 5p15 (p15.2 to p15.3)
Newborn features:
(1) catlike, mewing cry due to a congenital laryngeal defect
(2) microcephaly
(3) round, moonlike facies
(4) hypertelorism
(5) epicanthal folds
(6) broad nasal bridge
(7) muscular hypotonia
(8) strabismus
Other findings:
(1) cardiac malformations
(2) failure to thrive and severe developmental delay
(3) mental retardation and slow language development
