back to the list

Smith-Magenis Syndrome, Microdeletion 17p11.2

SMS

Clinical Features

The Smith-Magenis syndrome is a dysmorphy syndrome (brachycephaly, mid face hypoplasia, short broad hands) with a moderate to severe mental retardation, retardation of growth and speech delay. Patients show a stereotypical and autoagressive behaviour including and reduced pain susceptability. Many SMS patients suffer from impairment of the circadianic rhythm with severe insomnia. 68 % show amblyacousia, 65 % scoliosis, 52 % ventricular megaly, 37 % distinctive cardiac and renal features,  especially doubling of the ureter and 23% show low levels of immunoglobulins.

Genetic Information

Smith-Magenis syndrome is a "contiguous gene-syndrome" (CGS) cytogentically characterised by an interstitial microdeletion in the short arm of chromosome 17 (17p11.2, partial monosomy 17p11.2) caused by an unequal crossover in the germ line of one of the parents which also may causea duplication of sequences in 17p11.2 (Potocki-Lupski syndrome).

Patients with a duplication show a milder form of the syndrome.

Mutations of the RAI1 gene are found in up to 5% of deletion negative patients.

Prevalence

1 : 25 000

Diagnostic