The opposite condition, microcephaly, may be caused by failure of the brain to develop or by intrauterine infection, drug toxicity, or brain trauma.
Inadequate growth of brain: Microcephaly (abnormal smallness of head), and hydrocephalus (abnormal buildup of cerebrospinal fluid in the head).
Commonly, the fore-brain fails to divide into lobes or hemispheres (holoprosencephaly), and the entire head is unusually small (microcephaly).
Infants with cri du chat also typically have low birth weight, slow growth, a small head (microcephaly), and poor muscle tone (hypotonia).
They also have unusual facial features, poor muscle tone (hypotonia), small head size (microcephaly), and mental retardation.
Microcephaly (small head size) is common.