There is a worldwide incidence of approximately 1:15,000 live births for classical CAH owing to 21-hydroxylase deficiency. (38) The prevalence in specific populations based on newborn screening results are 1:10,000 – 1: 23,000 in the United States and Europe (38-41), 1:18,000 in Japan (42), and 1:23,000 in New Zealand. (43)

Nonclassical 21 hydroxylase deficiency has a much higher frequency than the classical forms of CAH. (44, 45) Nonclassical 21 hydroxylase deficiency has an ethnic specific frequency of 1:27 for Ashkenazi Jews, 1:53 for Hispanics, 1:63 for Yugoslavs, 1:333 for Italians, and 1 in 100 in a diverse Caucasian population. The ethnic specific frequency of nonclassical CAH indicates that it may be the most frequent monogenic disease in humans (Figure 4) and may be the commonest cause of reduced fertility.

Figure 4. Frequency of nonclassical and classical 21-hydroxylase deficiency in comparison with other autosomal recessive disease incidences. Speiser #2056]