Disease relevance of CYP21A1P

• Phenotype and genotype correlation of the microconversion from the CYP21A1P to the CYP21A2 gene in congenital adrenal hyperplasia [1].
• The most frequent (> 20% of chromosomes) cause of salt wasting adrenal hyperplasia in Russia is a chimeric CYP21A-CYP21B gene with normal copy of a pseudogene which results from gene conversion in chromosome with B14-DQA1 0101/0102 haplotype [2].
• To identify other potential nonclassic alleles, we used recombinant vaccinia virus to express two mutant enzymes carrying the mutations Pro-30----Leu (normally present in CYP21P) and Ser-268----Thr (considered a normal polymorphism of CYP21) [3].
• RESULTS: AC-A and SC-A were positive in all sera; among antibodies to adrenal CYP enzymes, only CYP21-A were present in all the patients with Addison's disease of short-medium duration (<15 years) [4].

High impact information on CYP21A1P

• DNA sequence analysis suggests that the mutation arose by a microconversion event involving exchange of up to 390 nucleotides between maternal CYP21A and CYP21B genes [5].
• More than two hundred characterized 21-hydroxylase deficiency alleles appear to result exclusively from sequence exchanges involving the 21-hydroxylase gene (CYP21B) and a closely related pseudogene (CYP21A) [5].
• More than 90% of these mutations result from intergenic recombinations between CYP21 and the closely linked CYP21P pseudogene [6].
• An analyses of the RCCX structures in 22 salt-losing, congenital adrenal hyperplasia patients revealed a significant increase in the monomodular structure with a long C4 gene linked to the pseudogene CYP21A, and bimodular structures with two CYP21A, which are likely generated by recombinations between heterozygous RCCX length variants [7].
• Gene conversions and unequal crossovers between CYP21 (steroid 21-hydroxylase gene) and CYP21P involve different mechanisms [8].

Chemical compound and disease context of CYP21A1P

• Single-nucleotide polymorphisms in intron 2 of CYP21P: evidence for a higher rate of mutation at CpG dinucleotides in the functional steroid 21-hydroxylase gene and application to segregation analysis in congenital adrenal hyperplasia [9].

Biological context of CYP21A1P

• Since it is unlikely that the term 'large-scale gene conversion' describes a mechanism that actually occurs between the CYP21A2 and CYP21A1P genes, we propose the discontinuation of that terminology [10].
• A tandemly duplicated gene designated CYP21A1P (21A), which lies 30 kilobases upstream, contains several point mutations and an 8-base pair deletion so that it cannot encode P450c21 protein; as a result, it is generally considered to be a pseudogene [11].
• We concluded that the 6.2-kb TaqI fragments of the CYP21A2 haplotype may lead to an incorrect result in the analysis between CYP21A2 and CYP21A1P [12].
• The 3.7- and 3.2-kb fragments produced by TaqI digestion are respective crucial markers of the CYP21A2 and CYP21A1P genes for the analysis of the RCCX module in chromosome 6p21 [12].
• During the course of genetic analysis of CYP21A2, we found that misgenotyping of CAH by PCR-based method is possible if both alleles of a CAH patient were deletion mutations and at least one of them carried a CYP21A1P-CYP21A2 fusion gene [13].

Anatomical context of CYP21A1P

• After transiently transfecting the plasmid constructs into mouse adrenocarcinoma Y1 cells, mouse testis Leydig tumor MA10 cells and human liver tumor HepG2 cells, our results showed that sequences located within the -13943/-13174 and -3278/-2586 regions upstream from the CYP21P had suppression effects on the promoter activity of human CYP21 [14].
• The CYP21 gene is located along with the CYP21P pseudogene in the human leukocyte antigen major histocompatibility complex region on chromosome 6 [15].

Associations of CYP21A1P with chemical compounds

• Thus, 2 of 15 chromosomes do not carry deletions and may represent gene conversions; 13 of 15 chromosomes studied have a deletion of approximately equal to 30 kb, leaving behind the C4A gene and a single CYP21A-like gene [16].
• However, the large size (approximately 30 kb) of the individual CYP21 + C4 repeat units together with the difficulty in identifying reliable CYP21A- and CYP21B-specific markers has prevented direct monitoring of gene organization on individual haplotypes by conventional Southern analyses [17].
• CONCLUSION: These data suggest that these CpG dinucleotides are more frequently mutated in CYP21 than in CYP21P, and that several mutations at CpG dinucleotides in the coding regions of CYP21 might result from CpG instability rather than the more usually proposed mechanism of gene conversion [9].
• RESULTS: Intron 2 of CYP21P contains frequent SNPs around nucleotide 398 and nucleotide 509, which can be typed by PCR/restriction enzyme digestion with HaeIII [9].

Physical interactions of CYP21A1P

• All eight chimeric CYP21 genes coupled with HLA-Bw47 in five unrelated patients had the CYP21A-CYP21B sequence transition within the same gene region (+1375 to +1993) [18].

Regulatory relationships of CYP21A1P

• In most cases the CYP21-inactivating point mutations are transferred by apparent gene conversions from CYP21P to CYP21 [19].

Other interactions of CYP21A1P

• Hybridization with specific oligonucleotide probes showed that in all 13 cases this remaining CYP21 gene carried an 8-base-pair deletion, typical of CYP21A, that prevents synthesis of a functional protein [16].
• Sequences promoting the transcription of the human XA gene overlapping P450c21A correctly predict the presence of a novel, adrenal-specific, truncated form of tenascin-X [20].
• In the present experiments we cultured primary human adrenocortical cells in defined medium and used RNase protection assays to examine whether there might be a selective increase in the relative abundance of CYP21P transcripts under any of the various regulatory factors known to affect expression of 21-hydroxylase [21].
• All patients with the G424S mutation presented CYP21P and C4A gene deletions and human leukocyte antigen DR17 on the same haplotype, suggesting a linkage disequilibrium and a probable founder effect [22].

Analytical, diagnostic and therapeutic context of CYP21A1P

• Sequence analysis revealed that this allele carried two missense mutations, R339H and P453S, neither of which has been previously observed in CYP21A or CYP21B [23].
• It has been demonstrated that one reaction for PCR amplification of the CYP21 gene and the chimeric CYP21P/CYP21 gene using mixed primers in combination with nested PCR and single-strand conformation polymorphism is considered highly efficient and accurate for molecular diagnosis of CAH due to 21-hydroxylase deficiency [24].
• 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 [25].
• Densitometry of the autoradiographs was used to determine the ratio of the copy-number of the 21-hydroxylase gene (CYP21B) to the copy-number of its pseudogene (CYP21A) [26].
• However, the diagnosis of classic 21-hydroxylase deficiency was obtained by Southern blotting studies, showing that she was homozygous for the 30-kb deletion, including the 3' end of CYP21P pseudogene, the C4B gene, and the 5' end of the functional CYP21 gene [27].

References