Genetic microcephaly includes multiple syndromes that usually have normal chromosomal studies but are presumed to have a genetic origin on the basis of a positive family history, or proven to have a genetic origin on the basis of DNA testing. Some patients considered to have genetic microcephaly may show chromosomal abnormalities when prometaphase chromosome studies are performed. Nevertheless, these patients are still classified as having a genetic microcephaly because a normal prometaphase chromosomal study does not exclude their diagnosis. When a genetic syndrome is diagnosed, the family should be referred to a geneticist for counseling. The following are the most common genetic syndromes.

Brachmann-de Lange Syndrome
Neonates with Brachmann-de Lange syndrome have typical facies. They are microcephalic, with bushy eyebrows and synophrys, long curly eyelashes, depressed nasal bridge, upturned nose, long philtrum, thin upper lip, and down-turned angle of the mouth. In addition to characteristic facial features, neonates with Brachmann-de Lange syndrome may have flexion contracture of the elbows, hypoplastic nipples and umbilicus, low-set thumb, brachydactyly or syndactyly of the second and third toes, hallux valgus, and sometimes absence of the third toe. Prometaphase chromosome studies should be done in all neonates with Brachman-de Lange syndrome. A duplication of the q26-q27 band region of chromosome 3 is present in some patients with Brachman-de Lange syndrome.

Williams Syndrome
The diagnosis of Williams syndrome is based on the typical facies and cardiac abnormalities. The facies is characterized by prominent lips and subcutaneous tissue around the eyes. The irises are often blue and have a stellate pattern. Neonates with Williams syndrome may also present with cardiac abnormalities with or without the characteristic facies. The cardiac abnormalities include supravalvular aortic stenosis, valvular aortic stenosis, aortic stenosis, coarctation of the aorta, and pulmonary stenosis. Musculoskeletal malformations, including arthrogryposis, may occur. Hypercalcemia is usually present. The diagnosis may be established by fluorescent in situ hybridization studies. Inherited and sporadic cases show deletion of chromosome subunit 7q11.23.5. Most cases are sporadic. Williams syndrome is a connective tissue disorder. The 7q11 site constitutes the elastin gene.