CYP21/C4 gene organisation in Italian 21-hydroxylase deficiency families

Novel rapid molecular diagnosis methods for comprehensive genetic analysis of 21-hydroxylase deficiency

BACKGROUND

Molecular analysis of the CYP21A2 gene is highly important for understanding the aetiology of 21-hydroxylase deficiency (21-OHD). The aim of this study was to use a novel approach named CNVplex, together with the SNaPshot assay and direct sequencing, to identify CYP21A2 mutations efficiently and comprehensively. Targeted CYP21A2 mutation analysis was performed in 113 patients and 226 parents. Large rearrangements of CYP21A2 were characterized by CNVplex; twenty prevalent mutations, including nine common micro-conversions and eleven high-frequency mutations reported in the literature, were detected by SNaPshot; and rare mutations were investigated by direct sequencing.

RESULTS

Among the 113 21-OHD patients, 95.6% of the affected alleles were detected accurately by SNaPshot and CNVplex. Prevalent mutations were detected in 69.5% of the alleles; 62.4% of alleles contained pseudogene-derived micro-conversions, 1.8% contained nonpseudogene-derived mutations, and 5.3% contained complex variations resulting from multiple recombinations between CYP21A2 and CYP21A1P. Large rearrangements were identified in 27.0% of the alleles, including five types (CH-1, CH-3, CH-4, CH-5 and CH-8) of chimeric CYP21A1P/CYP21A2 genes. Two novel CYP21A2 haplotypes and four de novo CYP21A2 mutations were characterized. A rare haplotype with a c.955 C > T mutation in the duplicated CYP21A2 gene was found in 0.9% of the probands and 33.3% of the parents. In addition, four parents were also diagnosed with 21-OHD.

CONCLUSION

CNVplex and SNaPshot appear to be highly efficient and reliable techniques for use in a molecular diagnosis laboratory, and combined with direct sequencing based on locus-specific PCR, they might constitute a definitive way to detect almost all common and rare 21-OHD-related alleles.

Multiplex ligation-dependent probe amplification (MLPA) assay for the detection of CYP21A2 gene deletions/duplications in congenital adrenal hyperplasia: first technical report

BACKGROUND

More than 90% of the cases of Congenital Adrenal Hyperplasia (CAH) are associated with mutations in 21-hydroxylase gene (CYP21A2). Up to now, large CYP21A2 rearrangements have been mainly detected by Southern blot analysis, although more rapid methods have been alternatively proposed. In this paper, we report the use of a multiplex ligation-dependent probe amplification (MLPA) method for easy and rapid detection of deletions/duplications in the CYP21A2 gene.

METHODS

We collected 18 CAH Italian patients previously analyzed by gene sequencing and Southern blot technique. In addition, a prenatal diagnosis study was performed.

RESULTS

Of the 7 known subjects with CYP21A2 deletions and 2 with gene duplications previously characterized in our laboratory, all were successfully identified by the MLPA analysis. In the prenatal diagnosis study, the MLPA assay was able to identify the presence of a CYP21A2 gene duplication in the fetus, as well in other two family members.

CONCLUSION

MLPA analysis represents a simple, rapid and sensitive tool for the detection of CYP21A2/CYP21A1P deletions/duplications in CAH molecular diagnosis. Compared to Southern blot, MLPA may be considered a high throughput analysis, allowing the simultaneous study of several samples in the same experiment and the investigation of both gene (CYP21A2) and pseudogene (CYP21A1P) in each patient.

A simple and robust quantitative PCR assay to determine CYP21A2 gene dose in the diagnosis of 21-hydroxylase deficiency

BACKGROUND

Correct diagnosis of 21-hydroxylase deficiency (21OHD) requires the identification of CYP21A2 gene deletions and CYP21A1P/CYP21A2 chimeric genes, which are disease-causing alleles, and gene duplications, which can lead to false-positive 21OHD allele results. Because lack of suitable CYP21A2 dosage assessment methods hampers correct 21OHD diagnosis, we developed a new assay based on the relative quantification of the CYP21A2 gene using the DSP gene as a reference.

METHODS

The assay to determine CYP21A2 copy number is based on real-time PCR. The method also detects the presence of the CYP21A1P/CYP21A2 chimeric gene. We used a duplex PCR to coamplify the DSP gene, included as an internal control, along with CYP21A2. The difference in threshold cycles between CYP21A2 and DSP genes (DeltaCt) was used to assess CYP21A2 copy number.

RESULTS

The DeltaCt values obtained from 24 samples used to set up the method clearly differentiated 3 nonoverlapping intervals, which corresponded to the number of CYP21A2 copies: -1.35 to -0.25 defined 2 gene copies, +0.20 to +2.00 defined 1 copy, and -2.50 to -1.50 defined 3 copies. With these intervals we were able to assess the gene copy number in 24 additional samples.

CONCLUSIONS

This new method for gene copy assessment detects homozygous and heterozygous CYP21A2 gene deletions, CYP21A1P/CYP21A2 chimeric genes, and gene duplications. Moreover, the method is robust, fast, and easy to use in a molecular diagnosis laboratory. This method together with CYP21A2 gene sequencing can provide a definitive system for the detection of almost all, common as well as rare, 21OHD alleles.

Characterisation of CAH alleles with non-radioactive DNA single strand conformation polymorphism analysis of the CYP21 gene

The major cause of congenital adrenal hyperplasia (CAH), a common recessive genetic disease, is the deficiency of steroid 21-hydroxylase (21OH), a microsomal enzyme encoded by the CYP21 gene. Although several CAH causing mutations have been identified in the CYP21 gene of patients with 21OH deficiency, genotyping of the 21OH locus is quite complex because of the high frequency of gene conversion and the presence of multiple mutations on single CAH alleles. In order to perform the complete characterisation of the CYP21 gene coding region more simply, we developed a highly sensitive, non-radioactive method allowing DNA single strand conformation polymorphism (DNA-SSCP) analysis. This method was applied to the characterisation of all the exons and intron-exon junctions of the CYP21 gene in five patients affected by the simple virilising form and one affected by the salt wasting form. In all samples showing SSCP signals, direct sequence analysis showed the presence of more than one single sequence variant. In particular, four mutations which are already known to cause the disease, 16 polymorphisms, and one newly identified C to T transition at position 849 were detected. A random sequence analysis, performed on 31 out of 81 exons showing a normal SSCP pattern, shows the method to be highly sensitive: no sequence variant was detected, thus confirming the validity of this non-radioactive DNA-SSCP analysis in characterising the CYP21 gene in patients with steroid 21OH deficiency. Notwithstanding the complete characterisation of all exons and exon/intron junctions of the CYP21 gene, no complete genotype/phenotype correlation was found in the panel of patients analysed, thus suggesting that characterisation of CAH alleles must be extended to outside the coding region of the CYP21 gene, most probably into the promoter region.

Screening of CYP21 gene mutations in 129 French patients affected by steroid 21-hydroxylase deficiency

The frequency of 12 different mutations of the steroid 21-hydroxylase gene (CYP21) was investigated in 129 French patients affected by congenital adrenal hyperplasia (CAH) due to steroid 21-hydroxylase deficiency. Eighty-nine percent of the CAH chromosomes were characterized. The most frequent mutations were a C-G substitution in intron 2, the deletion of the CYP21 gene and a T-A substitution in exon 4 in the severe form of the disease, and a G-T substitution in exon 7 in the nonclassic form. The correlation between the genotypes and the clinical forms of the disease showed marked variation in the phenotype from a single genotype, suggesting that individual variation and undetected additional mutations on the same CAH chromosome accounted for the phenotype. In 65 informative meioses of CAH families, no de novo mutation was found.

Adrenocorticotrophin stimulation and HLA polymorphisms suggest a high frequency of heterozygosity for steroid 21-hydroxylase deficiency in patients with Turner's syndrome and their families

OBJECTIVE

Following the chance observation of congenital adrenal hyperplasia in a patient with Turner's syndrome we decided to evaluate the incidence of 21-hydroxylase deficiency (21-OHD) in patients with Turner's syndrome and in their relatives.

SUBJECTS

Fifty-two patients with Turner's syndrome (mean age +/- SD 14.7 +/- 5.6 years) and 26 relatives were studied.

MEASUREMENTS

17-Hydroxyprogesterone (17-OHP) serum levels before and after i.m. administration of 0.25 mg of ACTH(1-24) were evaluated in patients with Turner's syndrome and relatives. In Turner patients basal testosterone and dehydroepiandrosterone concentrations were determined. The results of ACTH tests were analysed according to HLA class I and II alleles of subjects.

RESULTS

The baseline 17-OHP was in the range of the classical form of 21-OHD in one Turner patient, who had severe clitoral enlargement since birth. In 11 patients the stimulated 17-OHP serum level was higher than in normal controls and similar to that found in 21-OHD heterozygous subjects. Clitoral enlargement was significantly more frequent in patients with high stimulated 17-OHP levels (P < 0.001). The frequency of heterozygous-type responses was higher in Turner subjects (1:4.6) than in the Italian population (1:47 for the classic form and 1:9.5 for the non-classic form of the disease). In our patients the frequencies of HLA antigens and haplotypes, usually associated with 21-OHD, were different compared to the controls. HLA-B8, which is negatively associated to 21-OHD, was less frequent in Turner patients than in controls and absent in those with an elevated 17-OHP level. HLA-B14, B22 and B35 were more frequent, though not significantly so, in Turner patients than in controls and even more so in the group with an elevated 17-OHP level. The same investigations performed in 26 relatives of the Turner patients showed a high frequency of carriers of 21-OHD and three subjects with the cryptic form of the disease.

CONCLUSIONS

Although in the literature there are only two reports of the association of Turner's syndrome and 21-OHD, on the basis of our experience this association was more frequent, in the Italian population. Since some of the typical signs of 21-OHD (short final stature, varying degrees of virilization, menstrual irregularities, amenorrhoea, infertility) in patients with Turner's syndrome could also be attributed to the chromosomal abnormality, it is therefore more difficult to diagnose 21-OHD in Turner subjects. Adrenal function should be assessed, at least in the presence of clitoral enlargement, in patients with Turner's syndrome, particularly if their karyotype does not contain a Y chromosome. The hypothesis of the presence of cryptic Y chromosome material in these patients should also be considered.