DHCR7 and Smith-Lemli-Opitz syndrome: It is noteworthy that deficiency of 7-dehydrocholesterol reductase (DHCR7), the terminal enzyme in cholesterol biosynthesis, is the genetic cause of Smith-Lemli-Opitz syndrome (SLOS) which is an autosomal recessive disorder characterized by pre- and post-natal growth retardation, distinct facial anomalies, microcephaly, and mental retardation [73], [74].