Smith-Lemli-Opitz syndrome involves a deficiency in which enzyme?

Smith-Lemli-Opitz syndrome is caused by a deficiency in the enzyme known as 7-dehydrocholesterol reductase, which is encoded by the DHCR7 gene. This enzyme plays a crucial role in the biosynthesis of cholesterol by catalyzing the final step in the cholesterol production pathway, which converts 7-dehydrocholesterol into cholesterol. When this enzyme is deficient, it leads to impaired cholesterol synthesis and an accumulation of 7-dehydrocholesterol, resulting in the clinical manifestations associated with Smith-Lemli-Opitz syndrome, such as developmental delays, physical malformations, and behavioral issues.

Understanding the role of DHCR7 provides critical insight into how genetic mutations in this gene lead to the observed symptoms. The other options refer to different enzymes or genes with distinct functions unrelated to Smith-Lemli-Opitz syndrome. For example, CYP21A2 is involved in steroidogenesis and is associated with congenital adrenal hyperplasia, while AR refers to the androgen receptor which is not directly related to this syndrome. Thus, recognizing the specific enzyme deficiency tied to the clinical features can aid in the diagnosis and management of the syndrome.