Asunto(s)
Intercambio Genético/genética , Eliminación de Gen , Proteínas Recombinantes de Fusión/genética , Esteroide 21-Hidroxilasa/genética , Tenascina/genética , Niño , Rotura Cromosómica/genética , Deleción Cromosómica , Análisis Mutacional de ADN , Femenino , Haplotipos/genética , Humanos , Complejo Mayor de Histocompatibilidad/genética , Masculino , Linaje , Polimorfismo Genético/genética , Proteínas/genética , Seudogenes/genética , Mapeo RestrictivoRESUMEN
Steroid 21-hydroxylase deficiency is caused by defectiveness of the CYP21 gene. Such defects have presumably originated from interactions with the nearby CYP21P pseudogene during evolution. We studied these mechanisms by comparing the genetic variability of CYP21, CYP21P, and CYP21P/CYP21 hybrids (resulting from large-scale rearrangements) at eight mutation sites in a group of Dutch steroid 21-hydroxylase deficiency patients, their family members, and controls. The most common CYP21 defect in patients with salt-losing steroid 21-hydroxylase deficiency was a splice junction mutation in intron 2. The most common defect in the simple virilising form of the disease was ile72 --> asn. CYP21P showed considerable sequence variation in its central and 3' sections; the 5' section was constant. A single nucleotide (T) insert in exon 7 was found in all CYP21P genes. During the course of evolution, this was probably the third defect introduced into CYP21P after the splice junction mutation in intron 2 and the 8 bp deletion in exon 3. Gene conversions introducing CYP21-like sequences contribute to CYP21P variability. Such an event has occurred de novo in one family. A comparison of CYP21 and CYP21P mutations on the same chromosome shows that at least some of the small-scale gene conversions that supposedly transfer defects to CYP21 involve interaction between homologous chromosomes. The majority of the putative CYP21P-CYP21 transitions in hybrid genes appears to occur in a distinct zone that lies 5' of nucleotide 2108, which is further downstream than previously hypothesised. The other transitions lie upstream of nucleotide 999. Apparent 'large-scale' CYP21-CYP21P gene conversions lead to hybrid genes that are very similar to those found in CYP21 deletions, so these haplotypes have probably resulted from a meiotic double unequal crossover.
Asunto(s)
Hiperplasia Suprarrenal Congénita , Esteroide 21-Hidroxilasa/genética , Mapeo Cromosómico , Complemento C4/genética , Salud de la Familia , Genes/genética , Variación Genética , Haplotipos , Humanos , Mutación , Países Bajos , Seudogenes/genéticaRESUMEN
Aldosterone and cortisol were found in plasma samples from two patients with salt-losing congenital adrenal hyperplasia caused by steroid 21-hydroxylase deficiency. One patient had a CYP21 gene deletion on one chromosome and a mutation causing erroneous mRNA splicing on the other. The other patient had a CYP21 gene deletion on one chromosome and a large scale conversion of CYP21 to CYP21P on the other. All CYP21P-like genes in these patients were defective, since they carried a deleterious 8 bp deletion in the third exon. After HPLC purification of the patients' plasma samples, cortisol was no longer detectable in the radioimmunoassay, but aldosterone levels were still within or slightly above the normal reference range. Aldosterone dropped to very low levels after steroid replacement therapy had taken effect. In at least one of these patients, the genetic defect rules out normal functioning of the adrenocortical steroid 21-hydroxylase, which implies involvement of an alternative enzyme system.
Asunto(s)
Hiperplasia Suprarrenal Congénita , Hiperplasia Suprarrenal Congénita/metabolismo , Aldosterona/biosíntesis , Esteroide 21-Hidroxilasa/genética , Hiperplasia Suprarrenal Congénita/genética , Aldosterona/sangre , Preescolar , Cromatografía Líquida de Alta Presión , Análisis Mutacional de ADN , Eliminación de Gen , Prueba de Histocompatibilidad , Humanos , Hidrocortisona/sangre , Lactante , Masculino , Mutación , Renina/sangreRESUMEN
Two steroid 21-hydroxylase genes are normally present within the human major histocompatibility complex near the genes encoding the fourth component of complement (C4A and C4B). Steroid 21-hydroxylase is encoded by the CYP21 gene, while the highly homologous CYP21P gene is a pseudogene. We studied steroid 21-hydroxylase and complement C4 haplotypes in 33 Dutch patients (29 families) suffering form classical congenital adrenal hyperplasia (CAH) and in their 80 family members, and also in 55 unrelated healthy controls, using 21-hydroxylase and complement C4 cDNA probes. Eleven different haplotypes, defined in terms of gene deletions, gene duplications, conversions of CYP21 to CYP21P, and "long" and "short" C4 genes, were found. In 23% of the patients' haplotypes, the CYP21 gene was deleted; in 12%, it was converted into a CYP21P pseudogene. In the remaining 65%, the defect was apparently caused by a mutation not detectable by this method. The most common haplotype (with one CYP21 and one CYP21P gene) was significantly more often observed in patients with simple virilizing CAH than in those with salt-losing CAH. Comparison of the 21-hydroxylase haplotypes found in CAH patients from several countries shows evidence for considerable genetic variation between the groups studied.
Asunto(s)
Hiperplasia Suprarrenal Congénita/genética , Complemento C4/genética , Haplotipos , Esteroide 21-Hidroxilasa/genética , Femenino , Humanos , Complejo Mayor de Histocompatibilidad , Masculino , Países BajosRESUMEN
We studied the configuration of the complement C4/CYP21 (steroid 21-hydroxylase) region of the human major histocompatibility complex in patients suffering from congenital adrenal hyperplasia (CAH) and in the general population in The Netherlands, using C4 and CYP21 probes and the restriction enzymes TaqI and Bg/II. We found a rare TaqI 3.9-kb restriction fragment in the mother of a CAH patient, and present evidence that this polymorphism is caused by an additional restriction site in the first intron of a complement C4 gene.
Asunto(s)
Complemento C4/genética , Intrones/genética , Polimorfismo de Longitud del Fragmento de Restricción , Hiperplasia Suprarrenal Congénita/genética , Southern Blotting , ADN/análisis , Desoxirribonucleasas de Localización Especificada Tipo II , Femenino , Humanos , Masculino , Hibridación de Ácido Nucleico , Seudogenes , Esteroide 21-Hidroxilasa/genéticaRESUMEN
The adrenogenital syndrome (AGS) is usually caused by steroid 21-hydroxylase deficiency. Two steroid 21-hydroxylase genes are present within the major histocompatibility complex (MHC) on chromosome 6: an active gene (CYP21) and a pseudogene (CYP21P). Several types of mutations have been described; these mutations can be categorized as gene deletions, gene duplications, gene conversions and smaller mutations inside the gene. Some of these cause a defect in the CYP21 gene, possibly resulting in 21-hydroxylase deficiency. Apart from the intrinsic scientific value of these results, the methods applied become increasingly important in diagnostics.
Asunto(s)
Hiperplasia Suprarrenal Congénita/genética , Esteroide 21-Hidroxilasa/genética , Deleción Cromosómica , Cromosomas Humanos Par 6 , Sondas de ADN , Genes MHC Clase I/genética , Humanos , Complejo Mayor de Histocompatibilidad/genética , Mutación , Polimorfismo de Longitud del Fragmento de RestricciónRESUMEN
The adrenogenital syndrome (AGS) is a relatively common inherited metabolic disease, generally caused by a deficiency of the adrenocortical enzyme steroid 21-hydroxylase. This results in an insufficient biosynthesis of several important steroid hormones such as cortisol and aldosterone, and, on the other hand, in a strongly increased production of androgens (testosterone). In girls, virilization of the external genitals is usually seen. In some patients, severe salt loss occurs shortly after birth, and a life-threatening crisis may develop. Mild variants of the disease have also been described. Steroid 21-hydroxylase is encoded by a gene within the HLA complex on the short arm of chromosome 6. HLA typing thus allows the study of the hereditary transmission of several forms of the AGS. In addition, molecular biology at present opens new perspectives to fundamental and clinical genetic research.