What is Smith-Lemli-Opitz syndrome (SLOS)?

Updated: Jan 27, 2021
  • Author: Robert D Steiner, MD; Chief Editor: Luis O Rohena, MD, MS, FAAP, FACMG  more...
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Smith-Lemli-Opitz syndrome (SLOS) is a multiple congenital anomaly (MCA)/intellectual disability (ID) syndrome caused by a defect in cholesterol synthesis. [1] An autosomal recessive genetic condition, it results from a deficiency of the enzyme 3 beta-hydroxysterol-delta 7-reductase (7-dehydrocholesterol-delta 7-reductase [DHCR7] EC, the final enzyme in the sterol synthetic pathway that converts 7-dehydrocholesterol (7DHC) to cholesterol. Smith-Lemli-Opitz syndrome is usually suspected clinically, but biochemical studies (and/or genetic studies) are necessary for diagnosis. Currently, no treatment has proven effective long-term for patients with the syndrome. [2]

Affected individuals usually have low plasma cholesterol levels and invariably have elevated levels of cholesterol precursors, including 7DHC. The most severely affected individuals (those with the condition formerly referred to as Smith-Lemli-Opitz syndrome type II) have multiple congenital malformations and are often miscarried or stillborn or die in the first weeks of life. Dysmorphic facial features, microcephaly, second-toe and third-toe syndactyly, other malformations, and intellectual disability (ID) are typical. Mildly affected individuals may have only subtle dysmorphic features and, often, learning and behavioral disabilities.

See the image below.

Child with Smith-Lemli-Opitz syndrome. Child with Smith-Lemli-Opitz syndrome.

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