A 2-month-old male child is presented with microcephaly (head size smaller than normal), micrognathia (abnormally small lower jaw), ptosis (drooping eyelids), a small upturned nose, cleft palate, and ambiguous genitalia. Following biochemical analysis it is determined that the infant has highly elevated levels of 7-dehydrocholesterol in his tissues. These findings are indicative of which of the following disorders?

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Quizplus · Accepted Answer

Smith-Lemli-Opitz syndrome is characterized by elevated levels of 7-dehydrocholesterol due to a defect in cholesterol biosynthesis, and the symptoms described match this condition.  Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive disorder resulting from a defect in cholesterol synthesis. The defect resides in the terminal enzyme of the cholesterol biosynthesis pathway, namely 7-dehydrocholesterol reductase. Defects in this gene result in increased levels of 7-dehydrocholesterol and reduced levels (15%-27% of normal) of cholesterol in SLOS patients. The clinical spectrum of SLOS is very broad, ranging from the most severe form manifesting as a lethal malformation syndrome, to a relatively mild disorder that encompasses behavioral and learning disabilities. A frequent observation in SLOS infants is poor feeding and postnatal growth failure. There are distinct craniofacial anomalies associated with SLOS, which include microcephaly (head size smaller than normal), micrognathia (abnormally small lower jaw), ptosis (drooping eyelids), a small upturned nose, and cleft palate or bifid uvula. Male infants with SLOS exhibit genital abnormalities that range from a small penis to ambiguous genitalia or gender reversal. Abnormalities in limb development are common in SLOS patients and include short thumbs, postaxial polydactyly, and single palmar creases. In addition, the most common clinical finding in SLOS patients is syndactyly (fusion of digits) of the second and third toes. This latter limb deformity is found in over 95% of SLOS patients.

A 2-Month-Old Male Child Is Presented with Microcephaly (Head Size