Steroid 21-hydroxylase gene polymorphism in Addison's disease patients

Exploring antigenic variation in autoimmune endocrinopathy

Autoimmune disorders develop owing to a misdirected immune response against self-antigen. Genetic studies have revealed that numerous variants in genes encoding immune system proteins are associated with the development of autoimmunity. Indeed, many of these genetic variants in key immune receptors or transcription factors are common in the pathogenesis of several different autoimmune conditions. In contrast, the proclivity to develop autoimmunity to any specific target organ or tissue is under-researched. This has particular relevance to autoimmune endocrine conditions, where organ-specific involvement is the rule. Genetic polymorphisms in the genes encoding the targets of autoimmune responses have been shown to be associated with predisposition to several autoimmune diseases, including type 1 diabetes, autoimmune thyroid disease and Addison's disease. Mechanistically, variations leading to decreased intrathymic expression, overexpression, different localisation, alternative splicing or post-translational modifications can interfere in the tolerance induction process. This review will summarise the different ways genetic variations in certain genes encoding endocrine-specific antigens (INS, TSHR, TPO, CYP21A2, PIT-1) may predispose to different autoimmune endocrine conditions.

Relation between HLA and copy number variation of steroid 21-hydroxylase in a Swedish cohort of patients with autoimmune Addison's disease

OBJECTIVE

Autoantibodies against the adrenal enzyme 21-hydroxylase is a hallmark manifestation in autoimmune Addison's disease (AAD). Steroid 21-hydroxylase is encoded by CYP21A2, which is located in the human leucocyte antigen (HLA) region together with the highly similar pseudogene CYP21A1P. A high level of copy number variation is seen for the 2 genes, and therefore, we asked whether genetic variation of the CYP21 genes is associated with AAD.

DESIGN

Case-control study on patients with AAD and healthy controls.

METHODS

Using next-generation DNA sequencing, we estimated the copy number of CYP21A2 and CYP21A1P, together with HLA alleles, in 479 Swedish patients with AAD and autoantibodies against 21-hydroxylase and in 1393 healthy controls.

RESULTS

With 95% of individuals carrying 2 functional 21-hydroxylase genes, no difference in CYP21A2 copy number was found when comparing patients and controls. In contrast, we discovered a lower copy number of the pseudogene CYP21A1P among AAD patients (P = 5 × 10-44), together with associations of additional nucleotide variants, in the CYP21 region. However, the strongest association was found for HLA-DQB1*02:01 (P = 9 × 10-63), which, in combination with the DRB1*04:04-DQB1*03:02 haplotype, imposed the greatest risk of AAD.

CONCLUSIONS

We identified strong associations between copy number variants in the CYP21 region and risk of AAD, although these associations most likely are due to linkage disequilibrium with disease-associated HLA class II alleles.

CYP21A2 polymorphisms in patients with autoimmune Addison's disease, and linkage disequilibrium to HLA risk alleles

OBJECTIVE

Steroid 21-hydroxylase, encoded by CYP21A2, is the major autoantigen in autoimmune Addison's disease (AAD). CYP21A2 is located in the region of the HLA complex on chromosome 6p21.3, which harbours several risk alleles for AAD. The objective was to investigate whether CYP21A2 gene variants confer risk of AAD independently of other risk alleles in the HLA loci.

DESIGN

DNA samples from 381 Norwegian patients with AAD and 340 healthy controls (HC) previously genotyped for the HLA-A, -B, -DRB1, and -DQB1 and MICA loci were used for genotyping of CYP21A2.

METHODS

Genotyping of CYP21A2 was carried out by direct sequencing. Linkage of CYP21A2 to the HLA loci was assessed using UNPHASED version 3.0.10 and PHASE version 2.1.

RESULTS

Heterozygotes of the single-nucleotide polymorphisms (SNPs) rs397515394, rs6467, rs6474, rs76565726 and rs6473 were detected significantly more frequently in AAD patients compared with HC (P<0.005), but all SNPs were in a linkage disequilibrium (LD) with high-risk HLA-DRB1 haplotypes. rs6472C protected against AAD (odds ratio=0.15, 95% CI (0.08-0.30), P=3.8×10(-10)). This SNP was not in an LD with HLA loci (P=0.02), but did not increase protection when considering the effect of HLA-DRB1 alleles. Mutations causing congenital adrenal hyperplasia were found in heterozygosity in <1.5% of the cases in both groups.

CONCLUSION

Genetic variants of CYP21A2 associated to AAD are in LD with the main AAD risk locus HLA-DRB1, and CYP21A2 does not constitute an independent susceptibility locus.

Autoimmune Addison disease: pathophysiology and genetic complexity

Autoimmune Addison disease is a rare autoimmune disorder with symptoms that typically develop over months or years. Following the development of serum autoantibodies to the key steroidogenic enzyme, 21-hydroxylase, patients have a period of compensated or preclinical disease, characterized by elevations in adrenocortocotropic hormone and renin, before overt, symptomatic adrenal failure develops. We propose that local failure of steroidogenesis, causing breakdown of tolerance to adrenal antigens, might be a key factor in disease progression. The etiology of autoimmune Addison disease has a strong genetic component in man, and several dog breeds are also susceptible. Allelic variants of genes encoding molecules of both the adaptive and innate immune systems have now been implicated, with a focus on the immunological synapse and downstream participants in T lymphocyte antigen-receptor signaling. With the exception of MHC alleles, which contribute to susceptibility in both human and canine Addison disease, no major or highly penetrant disease alleles have been found to date. Future research into autoimmune Addison disease, making use of genome-wide association studies and next-generation sequencing technology, will address the gaps in our understanding of the etiology of this disease.

Cellular immunity and immunopathology in autoimmune Addison's disease

Autoimmune adrenocortical failure, or Addison's disease, is a prototypical organ-specific autoimmune disorder. In common with related autoimmune endocrinopathies, Addison's disease is only manageable to a certain extent with replacement therapy being the only treatment option. Unfortunately, the available therapy does not restore the physiological hormone levels and biorhythm. The key to progress in treating and preventing autoimmune Addison's disease lies in improving our understanding of the predisposing factors, the mechanisms responsible for the progression of the disease, and the interactions between adrenal antigens and effector cells and molecules of the immune system. The aim of the present review is to summarize the current knowledge on the role of T cells and cellular immunity in the pathogenesis of autoimmune Addison's disease.

Predisposition for de novo gene aberrations in the offspring of mothers with a duplicated CYP21A2 gene

CONTEXT

Although CYP21A2 de novo mutations are assumed to account for 1 to 2% of congenital adrenal hyperplasia (CAH) alleles and CYP21 genotyping has been done worldwide, there are only a few well-documented cases of CYP21A2 de novo mutations. The majority of these are deletions resulting from unequal crossings over owing to misalignment of homologous chromosomes during meiosis. Whereas so far, only heterozygous deletions of the CYP21A1P pseudogene were seen as premutations for de novo aberrations, the present report addresses such a predisposing role for parental duplicated CYP21A2 genes.

SUBJECTS AND METHODS

As part of routine diagnostic procedures, CYP21 genotyping has been performed in two unrelated female CAH index patients and in their clinically asymptomatic parents and siblings.

RESULTS

Both patients have inherited the paternal Intron2splice mutation and have harbored a de novo gene aberration (large deletion and I271N/exon 4) on their maternal haplotype. Surprisingly, both mothers were carriers of rare duplicated CYP21A2 haplotypes carrying CAH alleles, which were not detected in the daughters. Among 133 CAH alleles that were detected in patients and that could be traced to the respective family members by genotyping, these two de novo aberrations (representing 1.5% of 133 traced CAH alleles) were the only ones identified.

CONCLUSION

Because both de novo CYP21A2 gene aberrations so far identified in our laboratory occurred in the gametes of mothers carrying rare duplicated CYP21A2 haplotypes, we hypothesize that duplicated CYP21A2 genes could predispose for de novo mutations in the offspring, which is of relevance for prenatal CYP21 genotyping and genetic counseling.

[Primary adrenal insufficiency in adults: 150 years after Addison]

Thomas Addison first described, 150 years ago, a clinical syndrome characterized by salt-wasting and skin hyperpigmentation, associated with a destruction of the adrenal gland. Even today, over a century after Addison's report, primary adrenal insufficiency can present as a life-threatening condition, since it frequently goes unrecognized in its early stages. In the 1850s, tuberculous adrenalitis was present in the majority of patients, but nowadays, autoimmune Addison's disease is the most common cause of primary adrenal insufficiency. In the present report, we show the prevalence of different etiologies, clinical manifestations and laboratorial findings, including the adrenal cortex autoantibody, and 21-hydroxylase antibody in a Brazilian series of patients with primary adrenal insufficiency followed at Divisão de Endocrinologia da Universidade Federal de São Paulo (UNIFESP) and at Faculdade de Medicina de Ribeirão Preto-USP (FMRP-USP).

Adrenal autoimmunity: results and developments

Autoimmune Addison's disease (autoimmune adrenalitis) often occurs in autoimmune polyendocrinopathy syndromes APS1 (APECED) and APS2. Although the genetic background and etiology of the two syndromes is remarkably different, they both result in a similar autoimmune destruction of the adrenal cortex. Recently, the defective gene in APS1, AIRE (autoimmune regulator) was identified, whereas in APS2, the major genetic factor remains to be found in the human major histocompatibility complex haplotype (HLA) region. In addition to the genetic factors, the recent findings in genetics and immunity leading to the pathogenesis of adrenal autoimmunity in polyendocrinopathy syndromes are discussed.

Doença de addison de etiologia auto-imune

A doença de Addison de etiologia auto-imune é uma endocrinopatia rara e potencialmente fatal, que pode ocorrer de forma isolada ou como parte das síndromes poliglandulares auto-imunes (SPA) dos tipo I e II. Auto-anticorpos anti-cortex adrenal são considerados marcadores imunológicos sensíveis do processo auto-imune destrutivo, podendo identificar indivíduos na fase pré-clínica da doença. A enzima 21-hidroxilase (citocromo P450c21) representa o principal antígeno adrenocortical, embora outros citocromos P450 (17a-hidroxílase e colesterol desmolase) possam, também, desencadear a resposta auto-imune, principalmente na SPA do tipo I e na doença de Addison associada à falência ovariana precoce. O papel dos auto-anticorpos anti-P450c21 na patogênse da falência adrenal ainda não está bem estabelecido, assim como aquele dos anticorpos anti-receptor do ACTH.