Smith-Lemli-Opitz Syndrome
Patient Information
Characteristics
Background and History
This is a malformation disorder named after the three authors who first described it in 1964. It is a disorder of cholesterol synthesis and the clinical features are many with considerable variation among individuals.
Clinical Correlations
Most individuals have some growth and mental delay. They often exhibit irritable and hyperactive behavior and some have autistic features. They are sometimes described as ‘floppy’ babies and are often short in length. The brain may be small and underdeveloped. The jaw is small, and cleft palate, extra digits, a short nose, and ambiguous genitalia may be present. Many organ systems, including the heart, lungs, kidneys, gastrointestinal tract have one or more malformations. The eyes are prominent and the upper lids appear to droop. Cataracts and underdevelopment of the optic nerves have been noted in some cases.
Genetics
Inheritance
This is an autosomal recessive disorder with a horizontal pattern of inheritance. It is caused by a gene mutation that results in impaired cholesterol synthesis.
Pedigree
Autosomal recessive
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.
Diagnosis and Prognosis
Those most severely affected may be miscarried or stillborn. Newborns with this disorder often appear ill at birth and infant mortality is high as a result of multiple organ malformations. There is considerable variation in severity of symptoms, however, and many children live longer. The diagnosis may be made by a pediatrician but often other specialists contribute as well. Dietary supplementation of cholesterol has been found beneficial in some patients.
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