Smith-Lemli-Opitz syndrome (ORPHA:818)
Smith-Lemli-Opitz syndrome (SLOS) is characterized by multiple congenital anomalies, intellectual deficit, and behavioral problems.
Epidemiology
SLOS is most common in central and northern Europe with an estimated incidence of around 1/ 20,000 to 1/ 40,000 births.
Clinical description
The disease is present at birth, but may be detected in later childhood or adulthood in mild forms. Patients present with growth retardation and intellectual deficit. Behavioral problems include multiple autistic traits, hyperactivity, self-injurious behavior and sleep disturbances. The structural brain anomalies may include hypoplasia or absence of the corpus callosum, and holoprosencephaly. Microcephaly (80% of cases), bitemporal narrowing, ptosis, a broad nasal bridge, short nasal root, anteverted nares (90% of cases), a small chin, and micrognathia are common craniofacial features. Occasionally, cataract, strabismus, and nystagmus are observed. Other clinical features include cleft palate or bifid uvula (1/3 of patients), photosensitivity, rhizomelia and postaxial polydactyly of the hands or feet, syndactyly of the 2nd and 3rd toes (95% of cases), and short and proximally placed thumbs. Genital anomalies (small penis, hypospadias, ambiguous genitalia) are frequent in males (70% of cases). Cardiovascular anomalies (atrial and ventricular septal defects, patent ductus arteriosus, atrioventricular canal) can be present. Gastrointestinal anomalies including poor feeding, gastroesophageal reflux, pyloric stenosis, malrotation, and colonic aganglionosis are frequent.
Etiology
SLOS is due to an inborn error of cholesterol synthesis and is caused by mutations in the DHCR7 gene (11q13.4) leading to deficiency of the enzyme 3 beta-hydroxysterol-delta 7-reductase that converts 7-dehydrocholesterol (7DHC) to cholesterol.
Diagnostic methods
Diagnosis is based on the detection of elevated 7DHC levels in plasma or tissues. Mutation analysis confirms the diagnosis. Imaging studies (CT, MRI, echocardiogram) may be performed to detect malformations.
Differential diagnosis
he differential diagnosis includes lathosterolosis, desmosterolosis, Dubowitz syndrome, Cornelia De Lange syndrome, oculo-digito-esophago-duodenal syndrome, Noonan syndrome, Pallister-Hall syndrome, trisomy 13 and trisomy 18 (see these terms), and pseudotrisomy 13.
Antenatal diagnosis
Prenatal diagnosis may be suspected at fetal ultrasonography and should be confirmed by analysis of amniotic fluid or chorionic villous samples, measurements of 7DHC content and mutation analysis if DHCR7 mutations have already been identified in the family.
Genetic counseling
Transmission is autosomal recessive.
Management and treatment
Management is symptomatic and most patients are treated with dietary cholesterol supplementation. Treatment trials are underway investigating combined treatment with cholesterol supplementation and a HMG CoA reductase inhibitor (simvastatin). Surgery is proposed in case of secondary problems due to malformations.
Prognosis
Prognosis depends on the severity of the disease and on the associated malformations. Heart disease and brain malformations may be lethal. Some individuals live into adulthood. Mildly affected individuals may be able to live and work in a group home setting.

                            Last update: 
                            November 2009


                            - Expert reviewer(s): 
                            Dr Simona BIANCONI  - Dr Forbes PORTER