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      Incidence of Classical 21-Hydroxylase Deficiency and Distribution of CYP21A2 Mutations in Estonia

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          Aims: To determine the incidence of classical 21-hydroxylase deficiency (21-OHD) in Estonia from 1978 to 2004, and describe their phenotype and genotype. Methods: All Estonian endocrinologists informed us about their patients with 21-OHD. The diagnosis was confirmed in 20 patients, who were all screened for 8 common mutations of the CYP21A2 gene. Results: The 27-year period incidence was 1:25,500. The incidence from 1992 was 1:16,100, which more accurately reflects the real situation in Estonia. The salt-wasting form (SW) was diagnosed in 14 (7 males) and the simple virilizing form in 6 patients (1 male). The median age at diagnosis of the SW form was 30 days in males and 2 days in females. The investigation of 34 unrelated alleles showed that a common deletion/conversion was the most frequent mutation in our group (7/34). Six other mutations were present: p.Ile172Asn (5/34), 8-bp deletion (3/34), intron-2 splice mutation (3/34), p.Arg356Trp (3/34), p.Gln318X (3/34) and a small conversion (2/34). Mutations in 8 alleles remained uncertain. Conclusions: The incidence of classical 21-OHD in Estonia in 1992–2004 was 1:16,100. The genotype of our patients is similar to those from other Caucasian populations. The relatively late age at diagnosis and the skewed female:male ratio supports the need for newborn screening for 21-OHD.

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          Most cited references 12

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          Disease expression and molecular genotype in congenital adrenal hyperplasia due to 21-hydroxylase deficiency.

          Genotyping for 10 mutations in the CYP21 gene was performed in 88 families with congenital adrenal hyperplasia due to 21-hydroxylase deficiency. Southern blot analysis was used to detect CYP21 deletions or large gene conversions, and allele-specific hybridizations were performed with DNA amplified by the polymerase chain reaction to detect smaller mutations. Mutations were detected on 95% of chromosomes examined. The most common mutations were an A----G change in the second intron affecting pre-mRNA splicing (26%), large deletions (21%), Ile-172----Asn (16%), and Val-281----Leu (11%). Patients were classified into three mutation groups based on degree of predicted enzymatic compromise. Mutation groups were correlated with clinical diagnosis and specific measures of in vivo 21-hydroxylase activity, such as 17-hydroxyprogesterone, aldosterone, and sodium balance. Mutation group A (no enzymatic activity) consisted principally of salt-wasting (severely affected) patients, group B (2% activity) of simple virilizing patients, and group C (10-20% activity) of nonclassic (mildly affected) patients, but each group contained patients with phenotypes either more or less severe than predicted. These data suggest that most but not all of the phenotypic variability in 21-hydroxylase deficiency results from allelic variation in CYP21. Accurate prenatal diagnosis should be possible in most cases using the described strategy.
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            Transferability of tag SNPs in genetic association studies in multiple populations.

            A general question for linkage disequilibrium-based association studies is how power to detect an association is compromised when tag SNPs are chosen from data in one population sample and then deployed in another sample. Specifically, it is important to know how well tags picked from the HapMap DNA samples capture the variation in other samples. To address this, we collected dense data uniformly across the four HapMap population samples and eleven other population samples. We picked tag SNPs using genotype data we collected in the HapMap samples and then evaluated the effective coverage of these tags in comparison to the entire set of common variants observed in the other samples. We simulated case-control association studies in the non-HapMap samples under a disease model of modest risk, and we observed little loss in power. These results demonstrate that the HapMap DNA samples can be used to select tags for genome-wide association studies in many samples around the world.
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              CYP21 gene mutation analysis in 198 patients with 21-hydroxylase deficiency in The Netherlands: six novel mutations and a specific cluster of four mutations.

              Congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency is one of the most common autosomal recessive disorders. The aim of this study was to assess the frequencies of CYP21 mutations and to study genotype-phenotype correlation in a large population of Dutch 21-hydroxylase deficient patients. From 198 patients with 21-hydroxylase deficiency, 370 unrelated alleles were studied. Gene deletion/conversion was present in 118 of the 370 alleles (31.9%). The most frequent point mutations were I2G (28.1%) and I172N (12.4%). Clustering of pseudogene-derived mutations in exons 7 and 8 (V281L-F306 + 1nt-Q318X-R356W) on a single allele was found in seven unrelated alleles (1.9%). This cluster had been reported before in two other Dutch patients and in two patients in a study from New York, but not in other series worldwide. Six novel mutations were found: 995-996insA, 1123delC, G291R, S301Y, Y376X, and R483Q. Genotype-phenotype correlation (in 87 well documented patients) showed that 28 of 29 (97%) patients with two null mutations and 23 of 24 (96%) patients with mutation I2G (homozygous or heterozygous with a null mutation) had classic salt wasting. Patients with mutation I172N (homozygous or heterozygous with a null or I2G mutation) had salt wasting (2 of 17, 12%), simple virilizing (10 of 17, 59%), or nonclassic CAH (5 of 17, 29%). All six patients with mutation P30L, V281L, or P453S (homozygous or compound heterozygous) had nonclassic CAH. The frequency of CYP21 mutations and the genotype-phenotype correlation in 21-hydroxylase deficient patients in The Netherlands show in general high concordance with previous reports from other Western European countries. However, a cluster of four pseudogene-derived point mutations on exons 7 and 8 on a single allele, observed in almost 2% of the unrelated alleles, seems to be particular for the Dutch population and six novel CYP21 gene mutations were found.

                Author and article information

                Horm Res Paediatr
                Hormone Research in Paediatrics
                S. Karger AG
                April 2008
                21 January 2008
                : 69
                : 4
                : 227-232
                aDepartment of Paediatrics, University of Tartu, Tartu, Estonia, and bNational Genetics Reference Laboratory, St Mary’s Hospital, Manchester, UK
                113023 Horm Res 2008;69:227–232
                © 2008 S. Karger AG, Basel

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                Page count
                Tables: 2, References: 21, Pages: 6
                Original Paper


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