A patient with the Smith-Lemli-Opitz Syndrome may be classified based on the level of 7-dehydrocholesterol reductase (DHCR7) activity, which correlates with the clinical severity.

Clinical Features

DHCR7 Activity


less severe malformations

mild to moderate reduction

Type I

severe malformations, often with stillbirth or neonatal death

markedly reduced to none

Type II


A patient with Type II disease may be a:

(1) homozygote for a single severe mutation

(2) compound heterozygote with two severe mutations


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