Ethnic and National Differences in Congenital Adrenal Hyperplasia Incidence: A Systematic Review and Meta-Analysis

Background: Congenital adrenal hyperplasia (CAH) is an autosomal recessive genetic disorder that causes defects in the adrenal cortex enzymes that impair the biosynthesis of cortisol, aldosterone, or both. The most common type is the 21-hydroxylase enzyme deficiency in approximately 95% of cases resulting from CYP21A2 gene mutations or deletions. Objectives: This study aimed to systematically review the national differences in CAH incidence and analyze the pooled results to determine disparities and whether ethnicity can predispose people to develop CAH. Methods: PubMed, Scopus, and LILACS were used to achieve results until June 22, 2018. Study eligibility criteria included availability of full-text; English, Spanish, or Portuguese languages; incidence or number of new cases; and number of live births or sample population. Only the classic CAH type (salt-wasting and simple-virilizing) was considered, and no distinction was made between the enzyme deficiency types. Results: This study summarizes the findings of 58 studies and 31 countries (from 1969 to 2017), in which the overall CAH incidence was 1:9,498 (95% confidence interval: 1:9,089, 1:9,945). Countries from the Eastern Mediterranean and Southeast Asia revealed the highest CAH incidence. The lowest incidence was reported in countries of the Western Pacific of Asia. No remarkable difference was observed in the Hispanics/Latino and White groups. However, they manifested a higher incidence of CAH than people identified as Black or of African descent. Published studies on CAH incidence in the sub-Saharan African region and parts of Europe were insufficient. Conclusions: This study highlights the at-risk population for CAH and regions that need monitoring for CAH. The highest CAH incidence could be attributed to higher consanguinity, less genetic diversity, or other genetic causes since CAH is an inherited genetic disorder. Cultural practices in some places regarding consanguineous unions or geographic isolation may directly affect the incidence. Newborn screening for CAH may be unavailable in many developing countries, thereby affecting the actual CAH incidence. Therefore, healthcare workers should be trained to recognize CAH at an early stage to reduce its complications and mortality.