Functional analysis of four CYP21 mutations from spanish patients with congenital adrenal hyperplasia.

Deleterious mutations in the CYP21 (steroid 21-hydroxylase) gene cause congenital adrenal hyperplasia (CAH). These mutations usually result from recombinations between CYP21 and an adjacent pseudogene, CYP21P, including deletions and transfers of deleterious mutations from CYP21P to CYP21 (gene conversions). Additional rare mutations that are not gene conversions account for 5-10% of 21-hydroxylase deficiency alleles. Recently, four novel CYP21 point mutations leading to amino acid changes were identified in a population of 57 Spanish families with CAH. A nonsense mutation, K74X, was also identified. The enzymatic activities of 21-hydroxylase mutants G90V, G178A, G291C, and R354H were examined in transiently transfected CHOP cells using progesterone and 17alpha-hydroxyprogesterone as substrates. The G90V, G291C, and R354H mutations effectively eliminated 21-hydroxylase activity. However, the G178A mutant retained significant activity when 17alpha-hydroxyprogesterone was the substrate. These results correlate well with the identification of G90V, G291C, and R354H in patients with severe "salt-wasting" disease and G178A in a patient with the milder simple virilizing form.     

Molecular analysis of the CYP21 gene and prenatal diagnosis in families with 21-hydroxylase deficiency in northeastern Iran

OBJECTIVES: A rapid and convenient approach for the detection of the most common CYP21 gene mutations in patients with congenital adrenal hyperplasia (CAH) with classical forms of 21-hydroxylase deficiency was used. In addition, a new semiquantitative strategy for the detection of del8-bp was designed. These procedures were used for prenatal diagnosis and genotype-phenotype correlation in northeastern Iran. Design: Molecular analysis of the CYP21 gene for the detection of the 9 most common mutations (CYP21gene deletion, P30L, i2g, del-8bp, I172N, E6 cluster, V281L, Q318X and R356W) was performed on 30 CAH patients and for prenatal diagnosis in 2 cases. METHODS: Restriction fragment length polymorphism, amplification-created restriction sites, allele-specific polymerase chain reaction (PCR) and semiquantitative PCR were performed. RESULTS: We characterized 90% of the CAH chromosomes. The most frequent mutations in the CYP21 gene were del-CYP21 (25%), I172N (22%) and i2g (15%). Unlike in other ethnic groups, there was no R356W mutation, however, a higher rate of del-8bp (10%) was found in our population. Wealso found 6 complex alleles in our patients. For 2 families prenatal CYP21 gene analysis resulted in the diagnosis of healthy fetuses and termination of dexamethasone treatment in the 15th week of gestation. Genotype-phenotype correlation was observed. The rate of homozygosity (50%) was greater than the predicted values due to the higher rate of parental consanguinity in our population. CONCLUSIONS: These molecular procedures proved to be sensitive and rapid for the detection of the most common mutations of the CYP21 gene and prenatal diagnosis. Increased 17-hydroxyprogesterone, found in neonatal CAH screening, can be confirmed by these mutation analyses.     

Steroid 21-hydroxylase gene mutational spectrum in 50 Tunisian patients: Characterization of three novel polymorphisms

Congenital adrenal hyperplasia (CAH) is an autosomal recessive disease of steroid biosynthesis in humans. More than 90% of all CAH cases are caused by mutations of the 21-hydroxylase gene (CYP21A2), and approximately 75% of the defective CYP21A2 genes are generated through an intergenic recombination with the neighboring CYP21A1P pseudogene. In this study, the CYP21A2 gene was genotyped in 50 patients in Tunisia with the clinical diagnosis of 21-hydroxylase deficiency. CYP21A2 mutations were identified in 87% of the alleles. The most common point mutation in our population was the pseudogene specific variant p.Q318X (26%). Three novel single nucleotide polymorphism (SNP) loci were identified in the CYP21A2 gene which seems to be specific for the Tunisian population. The overall concordance between genotype and phenotype was 98%. With this study the molecular basis of CAH has been characterized, providing useful results for clinicians in terms of prediction of disease severity, genetic and prenatal counseling.     

Structure-based analysis of five novel disease-causing mutations in 21-hydroxylase-deficient patients

Congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency is the most frequent inborn error of metabolism, and accounts for 90-95% of CAH cases. The affected enzyme, P450C21, is encoded by the CYP21A2 gene, located together with a 98% nucleotide sequence identity CYP21A1P pseudogene, on chromosome 6p21.3. Even though most patients carry CYP21A1P-derived mutations, an increasing number of novel and rare mutations in disease causing alleles were found in the last years. In the present work, we describe five CYP21A2 novel mutations, p.R132C, p.149C, p.M283V, p.E431K and a frameshift g.2511_2512delGG, in four non-classical and one salt wasting patients from Argentina. All novel point mutations are located in CYP21 protein residues that are conserved throughout mammalian species, and none of them were found in control individuals. The putative pathogenic mechanisms of the novel variants were analyzed in silico. A three-dimensional CYP21 structure was generated by homology modeling and the protein design algorithm FoldX was used to calculate changes in stability of CYP21A2 protein. Our analysis revealed changes in protein stability or in the surface charge of the mutant enzymes, which could be related to the clinical manifestation found in patients.     

Three novel mutations in Japanese patients with 21-hydroxylase deficiency

OBJECTIVE: This study analyzed the mutation of 21-hydroxylase deficiency (21-OHD) in 36 unrelated Japanese patients with congenital adrenal hyperplasia (CAH). METHODS: All the exons of the functional CYP21 gene (CYP21A2) were analyzed by polymerase chain reaction (PCR) and PCR direct sequencing. RESULTS: Apparent gene deletions and conversions were present in 23.6% of the 72 CAH alleles, in which the most frequent mutation was the IVS2-13 A/C>G (27.8%), followed by I172N (26.3%), consistent with the frequencies reported for other countries. Previously described mutations were not present in three unrelated cases. Sequence analysis of the complete functional CYP21A2 gene revealed three, not yet described mutations that represent a common pseudogene sequence. These three putative novel mutations are located in exon 1 (M1I), in exon 5 (1210-1211insT), and in exon 3 (R124H). CONCLUSIONS: In this study, we have identified three putative novel mutations. It remains to be determined whether these three mutations are responsible for the significant number of as yet uncharacterized CAH patients in Japan.     

Diversity of the CYP21P-like gene in CYP21 deficiency

More than 90% of cases of congenital adrenal hyperplasia (CAH) are caused by mutations of the CYP21 gene. The occurrence of defective CYP21 genes, including 15 mutations, has been attributed to intergenic recombination of DNA sequences from CYP21P, and shows no influence on the RP1-C4A-CYP21P-XA-RP2-C4BCYP21- TNXB gene locus on chromosome 6p21.3. However, multiple gene deletions in this region produce at least three categories of gene arrangements: (a) C4A-CYP21P/CYP21-TNXB, in which there is a CYP21P/CYP21 fusion gene; (b) C4A-XCYP21-TNXB, where XCYP21 indicates that the CYP21 gene contains mutations of IVS2 (-12A/C>G and 707-714delGAGACTAC); and (c) C4A-CYP21P-TNXA/TNXB, in which the TNX A and B genes are fused. Among them, seven different structures of the CYP21 haplotype were found at these three loci. Formation of the C4A-CYP21P/CYP21-TNXB locus produced four distinct CYP21P/CYP21 chimeras. The C4A-XCYP21-TNXB locus contained the IVS2 mutation -12A/C>G and 707-714delGAGACTAC from the XCYP21 gene; and two kinds of TNXA/TNXB hybrids were found in the C4A-CYP21P-TNXA/TNXB locus. The seven different CYP21 alleles produced 3.2 kb Taq I fragments caused by deletion of the RP2-XA-C4B locus. Therefore, production of a 3.2-kb CYP21 allele shows diversity, but is not a unique feature of the CYP21P gene. Most of these gene arrangements probably exist in the C4A-XCYP21-TNXB and C4A-CYP21P/CYP21-TNXB gene loci. The existence of the C4A-CYP21P-TNXA/TNXB locus might not be common in CAH patients with 21-hydroxylase deficiency.     

CYP21 mutations in Brazilian patients with 21-hydroxylase deficiency

Congenital adrenal hyperplasia caused by 21-hydroxylase deficiency is a common autosomal recessive disorder resulting from mutations in the 21-hydroxylase (CYP21) gene. To develop a strategy to screen for the most commonly occurring CYP21 mutations in Brazil, we performed molecular genotype analysis on 73 children with CAH representing 71 unrelated families. The techniques used for CYP21 molecular genotype analysis were: restriction fragment length polymorphism, single-strand conformational polymorphism, allele-specific oligonucleotide hybridization, allele-specific polymerase chain reaction amplification, and heteroduplex analyses. Mutations were identified on all but eight affected alleles. The intron 2 splicing mutation was the most frequently identified mutation. Screening for the most common mutations detected at least one mutation on 132/142 (93%) alleles. Multiple CYP21 mutations were detected on 16.2% of alleles. The high frequency of multiple mutations on a single allele emphasizes the importance of thorough and accurate molecular genotype analysis of the complex CYP21 locus.     

Analysis of the association of HLA-DQ1 alleles with mutation of the 21-hydroxylase gene in patients with congenital adrenal hyperplasia

In 96 patients with congenital adrenal hyperplasia (CAH) and 50 healthy donors from northwestern Russia the distribution of the HLA-DQA1 alleles and the mutation spectrum and frequency at the CYP21B gene were examined. In the patients with nonclassical (NC) CAH, the distribution of the HLA-DQA1 polymorphic alleles was similar to that in the population sample. In the patients with the salt-wasting form of the disease a statistically significant decrease of the *0401 or *501 major allele frequency was observed. The prevalence of certain HLA-DQA1 genotypes, namely, HLA5, HLA3, and HLA4, was observed in the patients with the NC, salt-wasting (SW), and simple virilizing CAH, respectively. Each clinical group was characterized by a specific spectrum of clinically valuable mutations. An association between the CYP21B mutations most frequently found in case of SW and SV CAH (delB, I2splice, and I172N) and certain HLA-DQA1 alleles was demonstrated. The necessity of more precise clinical diagnostics of the NC CAH cases along with detailed examination of this group for determination of the major mutations typical of the NC CAH cases from northwestern Russia is discussed.     

Pro-453 to Ser mutation in CYP21 is associated with nonclassic steroid 21-hydroxylase deficiency.

Steroid 21-hydroxylase deficiency is the leading cause of impaired cortisol synthesis in congenital adrenal hyperplasia (CAH), with the nonclassic form (NC) comprising approximately 1% of the Caucasian population. The structure of the CYP21 gene was studied in 13 unrelated NC-CAH patients, three affected siblings, and 55 blood donors using polymerase chain reaction. In addition to the Leu-281 and Leu-30 mutations previously associated with NC-CAH, the finding of a Pro-453 to Ser mutation in exon-10 of CYP21 in the NC-CAH patients is reported. Ser-453 was found in 46.2% of unrelated NC-CAH patients, but only 7.7% and 3.6% of salt-wasting CAH patients and blood donors, respectively. In contrast to the Leu-281 and Leu-30 mutations, Ser-453 has not been previously detected in the CYP21 pseudogene (CYP21P) and, therefore, has not likely arisen by gene conversion.     

Investigation of CYP21A2 mutations in Turkish patients with 21-hydroxylase deficiency and a novel founder mutation

Congenital adrenal hyperplasia (CAH) is a group of autosomal recessively inherited disorders characterized by impaired production of adrenal steroids. Approximately 95% of all CAH are caused by mutations of the CYP21A2 that encodes 21-hydroxylase. In this study, mutation analyses of CYP21A2 were performed in 48 CAH patients from 45 Turkish families with the clinical diagnosis of 21-hydroxylase deficiency (21OHD). While in 39 (86.7%) of 21OHD patients, disease causing CYP21A2 mutations were identified in both alleles, in two 21OHD patients CYP21A2 mutations were identified only in one allele. In four patients, mutation was not detected at all. In total, seventeen known and one novel, disease causing CYP21A2 mutations were observed. Among identified mutations, previously described c.293-13C/A>G, large rearrangements and p.Q319X mutations were the most common mutations accounting for 33.3%, 14.4% and 12.2% of all evaluated chromosomes, respectively. In six families (13.3%) a novel founder mutation, c.2T>C (p.M1?), inactivating the translation initiation codon was found. This mutation is not present in pseudogene CYP21A1P and causes the classical form of the disease in six patients. In addition, depending on the nature of the rearrangements CYP21A1P/CYP21A2 chimeras were further classified as CH^c/d, and CH-1^c was shown to be the most prominent chimera in our study group. In conclusion, with this study we identified a novel founder CYP21A2 mutation and suggest a further classification for CYP21A1P/CYP21A2 chimeras depending on the combination of junction site position and whether it is occurred as a result of deletion or conversion. Absence of disease causing mutation of CYP21A2 in ten of screened ninety chromosomes suggests the contribution of regulatory elements in occurrences of CAH due to the 21OHD.     

Mutation-haplotype analysis of steroid 21-hydroxylase (CYP21) deficiency in Finland. Implications for the population history of defective alleles

Congenital adrenal hyperplasia (CAH) due to steroid 21-hydroxylase deficiency is a common inherited defect of adrenal steroid hormone biosynthesis. Unusually for genetic disorders, the majority of mutations causing CAH apparently result from recombinations between the CYP21 gene encoding the 21-hydroxylase enzyme and the closely linked, highly homologous pseudogene CYP21P. The CYP21 and CYP21P genes are located in the major histocompatibility complex class III region on chromosome 6p21.3. We analyzed the mutations and recombination breakpoints in the CYP21 gene and determined the associated haplotypes in 51 unrelated Finnish families with CAH. They represent no less than half of all CYP21 deficiency patients in Finland. The results indicate the existence of multiple founder mutation-haplotype combinations in the population of Finnish CAH patients. The three most common haplotypes constituted half of all affected chromosomes; only one-sixth of the haplotypes represented single cases. Each of the common haplotypes was shown consistently to carry a typical CYP21 mutation and only in some cases was additional variation observed. Surprisingly, comparisons with previous published data revealed that several of the frequent mutation-haplotype combinations in Finland are in fact also found in many other populations of patients of European origin, thus suggesting that these haplotypes are of ancient origin. This is in clear contrast to many reports, including the present one, where a high frequency of de novo mutations in the CYP21 gene has been reported. In addition, two unique sequence aberrations in CYP21 (W302X and R356Q), not known to exist in the CYP21P pseudogene, were detected. Received: 5 September 1996 / Revised: 11 November 1996     

Mutational analysis in Lebanese patients with congenital adrenal hyperplasia due to a deficit in 21-hydroxylase

Molecular defects in the gene encoding steroid 21-hydroxylase (CYP21) result in impairment of adrenal steroid synthesis in patients affected with autosomal-recessive congenital adrenal hyperplasias (CAH). In this study, we report on the molecular screening of six point mutations, large deletions, gene conversion events and duplications in 25 unrelated Lebanese families affected by CAH due to steroid 21-hydroxylase. The methods used (PCR-digestion and southern blot) allowed the detection of 96% of the disease chromosomes. In classical forms, the most frequent mutation was the splice site mutation in intron 2 accounting for 39% of the disease alleles. Gene conversion events accounted for 14% of the alleles, but no large deletions were found. In nonclassical forms, the V281L mutation in exon 7 represent 86% of the tested alleles. Genotype-phenotype correlations were as expected: Delta 8nt, Q318X and gene conversion correspond to SW forms, whereas the intron 2 splice site mutation may give either SW or SV forms; the V281L mutation was responsible for nonclassical forms. The spectrum of mutations underlines the genetic diversity of the Lebanese population. No correlation could be drawn out between mutations and some specific religious communities, except for the Delta 8nt mutation, which is present only in the Christian Maronite group. Molecular study of the CYP21 gene might constitute a good support for clinicians, especially in consanguineous families, for whom we could provide genetic counselling.     

Low frequency of deletion alleles in patients with steroid 21-hydroxylase deficiency in a Mexican population

Steroid 21-hydroxylase deficiency is caused by mutations in the CYP21 gene. Approximately 95% of mutant alleles are generated by recombination events between the acitve gene CYP21 and its highly homologous pseudogene, CYP21P. Deletion alleles are generated by unequal crossing over, while point mutations are the result of gene conversion events. Deletions account for 20–25% of the 21-hydroxylase deficiency alleles in most populations studied. We have looked for deletions among 53 unrelated Mexican patients with steroid 21-hydroxylase deficiency and found that deletions represent less than 1% of the disease alleles. These findings suggest that nearly all mutant alleles in our patient population contain point mutations and that the low representation of deletion alleles among clinically diagnosed patients may be due to missing detection of salt wasters, mainly males, who may die during the neonatal period. Received: 17 November 1995 / Revised: 29 February 1996, 12 April 1996     

Identification of four novel mutations in the CYP21 gene in congenital adrenal hyperplasia in the Chinese

Congenital adrenal hyperplasia (CAH) is a common autosomal recessive disorder mainly caused by defects in the steroid 21-hydroxylase (CYP21) gene. We have analyzed CYP21 gene sequences in 65 CAH families in Taiwan. All ten exons of the CYP21 gene were analyzed by differential polymerase chain reaction followed by single-strand conformation polymorphism electrophoresis and the amplification-created restriction site method. About 95% (123 chromosomes) contain mutations due to conversion of DNA sequences into its neighboring homologous pseudogene, CYP21P. Four novel mutations representing 5% of the total chromosomes have also been identified. The mutations were confirmed by sequencing an aberrant DNA fragment. These four mutations included a base change of the splicing donor site at intron 2 from GT to AT, a base substitution of C to T at codon 316, deletion of ten bases (TCCAGCTCCC) at codons 330–333 of exon 8, and duplication of 16 bases (CCTGGATGACACGGTC) at codons 393–397 of exon 9. The loss of the splicing donor site at intron 2 and the premature stop at codon 316 may result in aberrant splicing to reduce enzyme activity and a truncated protein with no enzyme activity, respectively. Likewise, both the duplication and the deletion forms create a frameshift and premature stop during translation. The resulting proteins lack the heme-binding domain and hence are expected to lose enzymatic activity. Since these mutations are not found in the neighboring CYP21P pseudogene, gene conversion should not be the cause of these novel mutations. Received: 20 April 1998 / Accepted: 30 May 1998     

A new DNA diagnostic system for the detection of human <Emphasis Type="Italic">CYP21</Emphasis> gene mutations associated with adrenal cortex hyperplasia

Congenital Adrenal Hyperplasia (CAH) is one of the most widespread severe autosomal recessive hereditary diseases. CAH is caused by the impaired biosynthesis of the key human hormones cortisol and aldosterone and is accompanied by the excess synthesis of androgens. Over 90% of CAH cases are caused by a deficiency of the steroid 21-hydrohylase (P450c21). The degree of damage in this enzyme is responsible for the severity of the clinical manifestation of CAH from potentially lethal to mild symptoms. Various mutations of the gene encoding this enzyme are the main source of the reduced activity of the steroid-21-hydrolase. The location of the highly homological pseudogene CYP21P in close proximity to the functional gene impedes the DNA diagnostics of CAH. To detect the eight most frequent CYP21 gene mutations associated with CAH, we developed a new real-time PCR-based system of DNA diagnostics using new allele-specific primers and TaqMan probes for the analyzed mutations. The method was primarily tested on artificial DNA templates, where the analyzed mutations were introduced by site-directed mutagenesis. Then, it was tested on DNA samples from 43 patients with clinical and biochemical manifestations of CAH; seven patients were used as a control. Two mutant alleles were detected in two different individuals: the nonsense Q318X and the missense V281L mutations.     

Defective,deleted or converted CYP21B gene and negative association with a rare restriction fragment length polymorphism allele of the factor B gene in congenital adrenal hyperplasia

Summary Defects in the enzyme, steroid 21-hydroxylase, result in congenital adrenal hyperplasia (CAH), a common autosomal recessive disorder of cortisol biosynthesis. The gene encoding this protein (CYP21B) and a closely linked pseudogene (CYP21A) have been mapped in the HLA complex on chromosome 6p, adjacent to the complement genes C4B and C4A, about 80 kb from the factor B gene. Molecular analyses of patients with CAH have shown that the cause of the defect may be either a deletion, a point mutation or a conversion of the active gene. Linkage of the disease to HLA has previously been studied by several groups. We have analyzed DNAs from patients with classical and non-classical CAH and from their family members, by probing with CYP21, C4 and BF cDNAs. In 70% of the CAH haplotypes studied, the defective CYP21B gene was indistinguishable from its structurally intact corresponding gene in Southern blot analysis, and presumably bore point mutations. In the remaining chromosomes, evidence for gene conversions, deletions and various deleterious mutations of the CYP21B gene is given. Moreover, our linkage studies show that a polymorphic TaqI cleavage site in the factor B gene, recently described by us, may be a new and useful genetic marker, because we found this TaqI restriction site only in unaffected haplotypes carrying functional CYP21B genes and, therefore, in negative association with the defective CYP21B gene.     

Analysis of the Association between the HLA-DQA1 Alleles and the Steroid 21-Hydroxylase Gene Mutations in the Patients with Congenital Adrenal Hyperplasia

In 96 patients with congenital adrenal hyperplasia (CAH) and 50 healthy donors from northwestern Russia the distribution of the HLA-DQA1 alleles and the mutation spectrum and frequency at the CYP21B gene were examined. In the patients with nonclassical (NC) CAH, the distribution of the HLA-DQA1 polymorphic alleles was similar to that in the population sample. In the patients with the salt-wasting form of the disease a statistically significant decrease of the *0401 or *0501major allele frequency was observed. The prevalence of certain HLA-DQA1 genotypes, namely, HLA5, HLA3, and HLA4, was observed in the patients with the NC, salt-wasting (SW), and simple virilizing CAH, respectively. Each clinical group was characterized by a specific spectrum of clinically valuable mutations. An association between theCYP21B mutations most frequently found in case of SW and SV CAH (delB, I2splice, and I172N) and certain HLA-DQA1alleles was demonstrated. The necessity of more precise clinical diagnostics of the NC CAH cases along with detailed examination of this group for determination of the major mutations typical of the NC CAH cases from northwestern Russia is discussed.     

Identification of molecular defects causing congenital adrenal hyperplasia by cloning and differential hybridization of polymerase chain reaction-amplified 21-hydroxylase (CYP21) genes.

Congenital adrenal hyperplasia (CAH), one of the most common autosomal recessive disorders, is caused primarily by defects in the gene encoding steroid 21-hydroxylase, CYP21B. The molecular diagnosis of CAH, important for prenatal diagnosis, carrier detection, and a better understanding of the various clinical CAH forms, is complicated by the close proximity of a highly similar pseudogene, CYP21A, containing (and probably donating, by gene conversion-like events) most of the defects underlying CAH. In this study, we describe an efficient strategy to identify molecular defects causing CAH: polymerase chain reaction-amplified CYP21 loci are cloned and hybridized to a set of oligonucleotides, allowing rapid and allele-specific identification of all known CYP21B mutations relevant to 21-hydroxylase function. Possible new mutations can be identified by subsequent nucleic acid sequencing provided they reside within the cloned CYP21B fragment (from the TATA box to the 8th of the 10 CYP21B gene exons). Using this method, the CYP21B gene mutations of a heterozygous carrier and 25 CAH patients have been identified by oligonucleotide hybridization. All disease haplotypes seem to have been generated by recombinational events involving the CYP21A pseudogene. In 5 individuals, these data were subsequently verified by nucleic acid sequencing. The procedure can be used for diagnostic applications and may facilitate identification of new CYP21B defects.     

Distribution of deletions and seven point mutations on CYP21B genes in three clinical forms of steroid 21-hydroxylase deficiency

To characterize mutations in the CYP21B gene that are responsible for congenital adrenal hyperplasia (CAH), DNA samples from 91 French patients have been studied by allelic-specific oligonucleotide hybridization and Southern blot analysis. Seven sites mostly found in the CYP21A pseudogene and deletions of the functional CYP21B gene have been screened. Gene conversions involving small DNA segments accounted for 57% of the tested mutations and probably cause 74% of the mutations responsible for the disease. Complete deletion of the CYP21B gene accounted for 18% of the CAH mutations in the whole sample and for 21% in the classical form of the disease. Three mutations were found associated with specific clinical forms of the disease: a G-C substitution in the seventh exon was associated with the late-onset form of the disease, and both an 8-bp depletion in the third exon and complete deletion of CYP21B were associated with the salt-wasting form.     

Analysis of the spectra of mutational damage of the 21-hydroxylase gene in patients with adreno-genital syndrome

The spectrum of mutations in the steroid 21-hydroxylase gene (CYP21B) and the frequency of 11 mutations among 66 patients with different forms of congenital adrenal hyperplasia (CAH) were analyzed by means of PCR amplification. Each of the CAH forms was characterized by specific spectrum of diagnostically important mutations. The salt-losing (SL) form of the disease was most frequently associated with gene deletion (39%) and the 668-13C-G mutation in the second intron (23.5%), whereas the majority of simple virilizing (SV) CAH cases were associated with the 1172N mutation in exon 4 (22%), gene deletion (16.5%), and the 668-13C-G mutation (16.5%). Mutations in the steroid 21-hydroxylase gene were detected in 70% of the chromosomes from the patients with the SL and SV forms of CAH, and only in 1.3% of the chromosomes from the patients with the nonclassic (NC) form. A total of 78 mutant chromosomes from the NC CAH patients were examined, and only one case of a gene deletion in the heterozygous state was revealed. In the individuals examined, the V281L and P30L mutations described in the NC CAH patients from other populations were not detected. This result can be explained either by the fact that NC CAH cases in Russia are associated with other major mutations, or by difficult clinical diagnosis questionable CAH cases.