Incidence of Smith-Lemli-Opitz syndrome in Canada: Results of three-year population surveillance

OBJECTIVES: To determine the incidence and point prevalence of Smith-Lemli-Opitz syndrome (SLOS) in Canada; to determine the percentage of mild cases of SLOS; and to determine the age of diagnosis of mildly affected patients. SLOS is a treatable genetic condition that may be difficult to diagnose in its mildest form because of nonspecific clinical markers (two- to three-toe webbing, short upturned nose, and micrognathia). STUDY DESIGN: More than 2000 Canadian pediatricians and pediatric specialists were surveyed monthly for 36 months through a standing national surveillance program. A clinical identification form was designed to identify patients with SLOS or its phenocopies. Clinical information was obtained on all reported cases; suggested cases were investigated by biochemical or molecular analysis. RESULTS: Thirty-five of 86 reports of suggested SLOS were confirmed SLOS. Twelve infants with SLOS were born during the surveillance period, and two additional infants with SLOS were diagnosed prenatally. Twenty-one infants with SLOS were born before the onset of surveillance. CONCLUSIONS: The minimum incidence of SLOS in Canada is 1 in 70,358 live births. The minimum prevalence of SLOS is approximately 1 in 950,000. Eighteen percent of patients were mildly affected; the mean age of diagnosis of mildly affected patients was 5.3 years.