Cholesterol is not merely a structural lipid; it is a critical and a morphogen . Its deficiency explains the majority of the syndromic features.
The Pathophysiology of Smith-Lemli-Opitz Syndrome: From Cholesterol Deficiency to Clinical Dysmorphology Fisiopatologia De Smith Thier
At the molecular level, SLOS is caused by pathogenic variants in the DHCR7 gene located on chromosome 11q13.4. This gene encodes the enzyme (also known as 7-dehydrocholesterol reductase). This enzyme catalyzes the final step of cholesterol biosynthesis: the reduction of the double bond at the C7-C8 position of 7-dehydrocholesterol (7-DHC) to produce cholesterol. Cholesterol is not merely a structural lipid; it
| System | Pathophysiology | Clinical Manifestation | | :--- | :--- | :--- | | | Shh deficiency → abnormal ventral patterning; cholesterol lack → poor myelination. | Microcephaly, agenesis of corpus callosum, cerebellar hypoplasia, intellectual disability, autism, self-injurious behavior. | | Craniofacial | Shh deficiency → impaired midline fusion. | Broad nasal tip, ptosis, micrognathia, cleft palate, bifid uvula. | | Limb | Aberrant Shh gradient in zone of polarizing activity (ZPA). | 2-3 toe syndactyly (pathognomonic), postaxial polydactyly, short thumbs. | | Gastrointestinal | Lack of cholesterol → smooth muscle dysmotility; Shh deficiency → abnormal gut looping. | Severe gastroesophageal reflux, pyloric stenosis, Hirschsprung disease (5-7% of cases). | | Genitourinary | Impaired androgen synthesis (cholesterol precursor for all steroids). | Hypospadias, cryptorchidism, ambiguous genitalia in 46,XY males; uterus didelphys in females. | | Skin/Adnexa | Abnormal sterol composition in keratinocyte membranes. | Photosensitivity (due to 7-DHC accumulation), dry skin, syndactyly of toes. | This gene encodes the enzyme (also known as