Recent advances in the molecular genetics of congenital and acquired primary adrenocortical failure.
IntroductionIn recent years there have been many advances in ourunderstanding of the molecular pathogenesis of both congenitaland acquired adrenocortical failure (autoimmune or otherwise).As well as providing some fascinating insights into adrenalgland development and steroid hormone biosynthesis, therecognition of these various distinct disorders, either at aclinical or molecular genetic level, often has implications forthe management of the patient and their immediate family. In thispaper, we review the salient clinical and molecular features of thevarious causes of primary adrenocortical failure (Table 1).Genetics of autoimmune Addison’s diseaseAutoimmune Addison’s disease (AAD) is a chronic disorder ofthe adrenal gland, characterized by insufficiency of adrenocor-tical hormones due to autoimmune destruction of steroidogenicadrenocortical cells (Oelkers, 1996). The cytochrome P450enzymes involved in steroidogenesis, including 21-hydroxylase(Baumann-Antczak et al., 1992; Winqvist et al., 1992), 17-hydroxylase (Krohn et al., 1992) and side chain cleavageenzyme (Winqvist et al., 1993) have been identified as primaryautoantigens in AAD. With the overall decrease in theprevalence of tuberculosis, AAD has emerged as the mostcommon cause of primary adrenal failure in developedcountries (Nerup, 1974; Kong & Jeffcoate, 1994). Nevertheless,AAD is a relatively rare endocrinopathy; recent epidemiologi-cal studies showing an estimated prevalence in the generalEuropean population of about 100 per million (Kong J Laureti et al., 1999).The results of human leucocyte antigen (HLA) typing, takentogether with the clinical heterogeneity of presentation anddifferent modes of inheritance, have suggested distinctpathogenic bases for different forms of AAD. Thus, AADmay occur in isolation, as a manifestation of the autoimmunepolyendocrinopathy type 1 syndrome (APS1), or as part of theautoimmune polyendocrinopathy type 2 (APS2) syndrome(Table 1) (Spinner et al., 1968; Neufeld et al., 1981; Maclaren& Riley, 1986).Autoimmune polyendocrinopathy type 1 syndrome: amonogenic autoimmune disorderIn the autoimmune polyendocrinopathy type 1 (APS1)syndrome, which is also known as the autoimmune poly-endocrinopathy, candidiasis and ectodermal dystrophy(APECED) syndrome, AAD occurs in association withautoimmune hypoparathyroidism, chronic mucocutaneous can-didiasis and other organ-specific autoimmune disorders. Theseinclude type 1 diabetes, primary gonadal failure, perniciousanaemia, chronic active hepatitis and hypothyroidism (Neufeldet al., 1981; Ahonen et al., 1990). The age of onset of AAD inAPS1 is typically between 11 and 15years, although othermanifestations of APS1 (e.g. hypoparathyroidism and candi-diasis) are likely to present at an earlier age. APS1 is amonogenic disorder with autosomal recessive inheritance,affecting both sexes with equal prevalence (Ahonen, 1985),and is rare in most populations. However, because of foundereffects, it is relatively common in the Finnish population andIranian Jews with estimated prevalences of 1/25000 and 1/9000, respectively (Ahonen, 1985; Zlotogora & Shapiro, 1992).Initial genetic studies of APS1 focused on HLA, and noassociation of this disorder with any specific HLA haplotypehas been found (Neufeld et al., 1981; Maclaren & Riley, 1986;Aaltonen et al., 1993; Huang et al., 1996). The gene underlyingAPS1 was subsequently localized on chromosome 21q22 bylinkage analysis (Aaltonen et al., 1994) and identified bypositional cloning (Finnish-German APECED consortium,1997; Nagamine et al., 1997). This gene, designated auto-immune regulator-1 (AIRE-1), encodes a 545 amino acidprotein that has two plant homeodomain (PHD)-type zinc-finger motifs, suggesting a role as a transcription factor(Finnish-German APECED consortium, 1997; Nagamine etal., 1997). AIRE-1 mRNA is expressed in lymphoid tissuesincluding thymus, lymph node and spleen, and possibly also inother tissues including the adrenal cortex (Finnish-GermanAPECED consortium, 1997; Nagamine et al., 1997), whichsuggests that it may have an important role in the developmentof a normal immune response.
Read more
145
