Epidemiology and genetics of neural tube defects: an application of the Utah Genealogical Data Base

The distribution and prevalence of births with neural tube defects in Utah from 1940 to 1979 are analyzed with regard to prevalence rates, secondary sex ratios, seasonality, yearly rates, and time-space clustering. The overall prevalence rate of 1.00 per thousand live births is comparable to that of other populations in the western United States. Analysis of sex ratios indicates a substantially higher proportion of females than males. No significant secular trends or time-space clustering are observed. No seasonality is seen for spina bifida; however, the anencephaly cases are delivered more frequently in the early spring and fall months. Following linkage of the neural tube defect cases to the Utah Genealogical Data Base, application of the genealogical index method shows substantial familial clustering of the disease. The average inbreeding coefficient of the neural tube defect cases is not elevated over that of matched controls. The empirical recurrence risk for the disease is calculated to be 3%, and the heritability estimate is 70%. Likelihood analysis of pedigrees containing spina bifida occulta and spina bifida cystica indicates that they may segregate as an autosomal dominant trait with a penetrance of 75%.