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Despite ethnic variation, 11 β-hydroxylase deficiency (11β-OHD) has generally been considered the second most common subtype of congenital adrenal hyperplasia (CAH). We report a high rate of novel mutations in this gene ( CYP11B1 ) in patients from Saudi Arabia. We studied 16 patients with 11β-OHD from 8 unrelated families. DNA was isolated from peripheral blood. The 9 exons and exon-intron boundaries of CYP11B1 were PCR-amplified and directly sequenced. The novel mutations were functionally characterized using subcloning, in vitro mutagenesis, cell transfection and 11-deoxycortisol: cortisol conversion assays. Six mutations were found in these 8 unrelated families. Three of these mutations are completely novel and two have just been recently described as novel mutations from the same population. These include a single nucleotide insertion mutation in codon 18 (c.53_54insT) leading to frameshift and truncation in 4 siblings, a novel mutation (c.1343G>C, p.R448P) in 3 unrelated families, a novel mutation (c.1394A>T, p.H465L) in 2 siblings, a novel mutation (c.617G>T, p.G206V) in 1 patient, and a recently described non-sense novel mutation (c.780G>A, p.W260X) in another patient. Out of the 6 mutations described in this report, only one mutation (p.Q356X) was reported previously. In vitro functional testing of the 3 missense and nonsense novel mutations revealed complete loss of the 11 hydroxylase activity. We conclude that 11 β-OHD in Saudi Arabia has a unique genotype with a high rate of novel mutations. The novel p. R448P mutation is the most common mutation in this highly inbred population. [ABSTRACT FROM AUTHOR]

• Consanguinity rates are high in Saudi Arabia and disorders of sex development (DSD) are common. • This study characterized the molecular genetics of 77 patients from 47 families (44 families are consanguineous) with different DSDs • SRD5A2 and CYP11B1 deficiencies were the most common causes of DSDs • The splice site mutation (c.282-2A>G) was the most common in SRD5A2 • CYP11B1 mutations were mostly novel mutations • Known and novel mutations were found in CYP17A1 , HSD3B2, StAR, NR0B1, HSD17B3, LHCGR and AR. Consanguinity increases the risk of hereditary diseases including disorders of sex development (DSD). There are minimal data on DSD in the highly consanguineous population of Saudi Arabia. This study reports the molecular genetics of a series of patients with different types of DSD. We enrolled 77 patients from 47 families with DSD. DNA was isolated from peripheral leucocytes. Genes of interest were amplified by polymerase chain reaction and subsequently sequenced. Overall, 77 patients from 47 families (44 of them are consanguineous) had a total of 29 mutations; 16 of them were described before and 13 were novel mutations. The most common condition was 5-α reductase (SRD5A2) deficiency (25 patients from 18 families) and the most common mutation was a splice site mutation in intron 1 (c.282-2A>G). The next most common condition was 11-β hydroxylase (CYP11B1) deficiency where 19 patients from 10 families had 8 mutations (7 of them are novel). Other mutations affected CYP17A1 with 2 novel and 2 known mutations in 7 patients; HSD3B2 with 2 known mutations in 11 patients of 4 families; StAR with 1 novel and 1 known mutations in 4 patients; NR0B1 with 1 novel mutation in 2 siblings; HSD17B3 with 1 known mutation in 3 siblings; LHCGR with 1 novel mutation in 2 siblings; and AR with 1 novel and 3 known mutations in 4 unrelated patients. In the highly consanguineous and homogeneous population of Saudi Arabia, SRD5A2 and CYP11B1 deficiencies are common causes of DSDs. Other DSDs occur less frequently but often with novel mutations. [ABSTRACT FROM AUTHOR]