Genetics of primary aldosteronism

Secondary arterial hypertension: improvements in diagnosis and management in the last 10 years

The diagnosis and management of secondary hypertension has improved in the last decade as a result of the advances in the acknowledgment of some physiopathologic mechanisms and mainly by the development of new diagnostic methods. Furthermore, the treatment of some types of secondary hypertension may be solved by noninvasive techniques. Hypertension of renal and renovascular origin, coarctation of the aorta, primary hyperaldosteronism, and adrenal medullary tumors are analyzed. The main results of some relevant studies on diagnostic and treatment of those diseases are presented. Also, some experimental methods are mentioned, taking into account the possibility of clinical use in the near future.

Primary aldosteronism: learning from the study of familial varieties

Primary aldosteronism (PAL) has been traditionally regarded as a rare cause of hypertension and not worth looking for in the absence of hypokalemia. However, the availability of the aldosterone/renin ratio as a screening test and its application to a wider population of hypertensives has resulted in a marked increase in detection rate, suggesting that PAL is common, with most patients being normokalemic. The spectrum of PAL has been expanded further by the study of familial varieties, in which family screening efforts have permitted the recognition of earlier, sometimes even pre-clinical, stages of disease. Familial hyperaldosteronism type I(FH-I) In FH-I, inheritance of a 'hybrid' 11beta-hydroxylase/aldosterone synthase gene causes adrenocorticotrophic hormone (ACTH)-regulated aldosterone and 'hybrid steroid' (18hydroxy-cortisol and 18-oxo-cortisol) overproduction. Genetic testing, by Southern blot or polymerase chain reaction-based techniques, has greatly facilitated detection, being more convenient and more reliable than dexamethasone suppression testing, and has led to a fuller appreciation of the marked phenotypic variability in this disorder. The demonstration of excessive, abnormally regulated aldosterone production in normotensive subjects with FH-I suggests that absence of hypertension in such individuals cannot merely be attributed to lack of expression of the hybrid gene. Determinants of hypertension severity may include patient gender, gender of affected parent, degree of hybrid gene expression, and interactions with other genetic and environmental factors. Detailed biochemical studies, including analyses of aldosterone/PRA/cortisol 'day-curve' levels, have led to a fuller understanding of aldosterone regulation both before and in response to glucocorticoid treatment in this condition, and prompted a re-examination of current approaches to treatment Unless ACTH is completely suppressed by glucocorticoid treatment, the hybrid gene dominates over the wild-type aldosterone synthase genes in terms of aldosterone production, both in untreated and treated FH-I. This may in part be due to an abnormality affecting the functional expression of the 'wild-type' genes. Demonstration of persisting hybrid gene expression in patients rendered normotensive by very low doses of glucocorticoids suggests that currently recommended doses, aimed at normalizing aldosterone regulation (rather than blood pressure), may be too high, and may therefore place patients at unnecessary risk of developing Cushingoid side effects. Familial hyperaldosteronism type II (FH-II) Like FH-I, FH-II is associated with hyperaldosteronism and probable autosomal dominant inheritance. Unlike FH-I, hyperaldosteronism in FH-II is not dexamethasone suppressible, and is not associated with the hybrid gene mutation. Detection of adrenal mass lesions, which are frequently (17 of 57 patients in the Greenslopes Hospital series) responsible for PAL in FH-II, does not help to differentiate FH-II from FH-I, since mass lesions may also be common in that condition (detected in seven of 21 patients). Biochemically and morphologically, FH-II is indistinguishable from apparently non-familial PAL, and demonstrates similar variability even among individuals of the same family. In one informative family available for linkage analysis, FH-II does not segregate with either the AT1 gene or the CYP11B2 gene, or any other genetic defect in the chromosome 8q21-8qtel region. A genome-wide search is in progress. As has already occurred in FH-I, the elucidation of underlying genetic mutations in FH-II is likely to facilitate early detection, thereby helping to broaden its spectrum and to permit close follow-up and appropriately timed institution of specific therapy, and wider detection among patients with hypertension of potentially curable or specifically treatable forms.

Primary aldosteronism

The basic clinical pathophysiology of primary aldosteronism (PAL) was described by Conn in terms of autonomous production of aldosterone, secondary suppression of renin and development of hypertension with hypokalaemic alkalosis. Conn recognised a normokalaemic form of the syndrome and suggested that it might masquerade as essential hypertension and be not uncommon. This was hotly disputed at the time, and normokalaemic PAL considered rare until recently, and, as a consequence, overlooked. The advent of a simple screening test, the aldosterone-renin ratio, led to recognition that normokalaemic forms are not uncommon. In fact, PAL may be the commonest specifically treatable and potentially curable form of hypertension so far identified. In all patients with PAL confirmed by lack of suppressibility ("autonomy") of aldosterone production, Familial Hyperaldosteronism Type I (FH-I, glucocorticoid-remediable hyperaldosteronism, reviewed elsewhere in this issue) should first be excluded by dexamethasone suppression or genetic testing. Capable of causing fatal stroke in young people affected by this dominantly inherited disorder, it can be reversed by doses of glucocorticoids such as dexamethasone which partially suppress endogenous ACTH without producing "steroid" side-effects. The remaining varieties of PAL may eventually also be shown to have a genetic basis, but are currently treated either by excision of a solitary aldosterone-secreting tumour or by antagonism of aldosterone's action in the renal tubule. It is possible that both adrenal cortices are genetically predisposed to overproduction of aldosterone in all varieties of PAL, whether because of anomalous regulation of aldosterone secretion or because of a tendency towards hyperplasia and neoplasia. Aldosterone-producing adenomas (APA's) can be divided into two main subtypes based on morphology and biochemical behaviour. The first subtype to be morphologically and biochemically characterised is composed predominantly of fasciculata-like cells and is unresponsive to angiotensin II (ALL-U-APA). The more recently characterised subtype is composed predominantly of glomerulosa-like cells, is responsive to angiotensin II (AII-R-APA) and could previously have been misdiagnosed as bilateral hyperplasia. The renin gene is often overexpressed in the second variety of adenoma, and in surrounding non-tumorous cortex, and the two subgroups show different allelic frequencies for RFLP's of the constitutive renin gene and the constitutive ANP gene locus. Unilateral, solitary, benign adrenal cortical adenomas producing aldosterone (APA's) represent a potentially surgically curable form of hypertension. Adrenal venous sampling (AVS) should always be performed because APA's are biochemically recognisable by adrenal venous steroid measurement before they are identifiable by computerised tomography or scintigraphy, and adrenal masses seen on CT may not be responsible for PAL. The secretory activity of adrenal masses must therefore be established by AVS before surgical removal. Discovery of an adrenal mass on CT requires formulation of a plan, whether or not it is found to be secreting hormones in excess. Independently of the treatment of the patient's hypertension, an apparently nonfunctioning adrenal mass ("incidentaloma") should be removed if 2.5 cm or more in diameter, because of the risk of cancer. Smaller masses require long-term follow-up. Primary aldosteronism not lateralising on AVS should be treated with low dose spironolactone, or with amiloride. For any such patients intolerant of medical treatment, laparoscopic removal of the adrenal showing higher production of aldosterone on AVS is an option worthy of consideration.The resultant reduction in mass of tissue autonomously secreting aldosterone should improve hypertension, as aldosterone productions falls below a critical level, and may even be curative in the short, medium or long term, depending on the rate of growth and activity of au

Hybrid gene or hybrid steroids in the detection and screening for familial hyperaldosteronism type I

1. Early diagnosis of Familial Hyperaldosteronism Type I (FH-I, glucocorticoid-suppressible hyperaldosteronism) in asymptomatic, affected individuals is essential if death from stroke is to be prevented. 2. In 21 patients with FH-I (presence of the causative hybrid 11 beta-hydroxylase/aldosterone synthase gene confirmed by Southern blot testing), various biochemical parameters were compared as possible screening tests. Hypokalaemia and elevated plasma aldosterone each detected only two (10%) of the affected individuals. 3. Plasma renin activity 19 (90%) and aldosterone/renin ratio 18 (86%) were more reliable but not free from false negatives. 4. Levels of the urinary 'hybrid' steroid, 18-oxocortisol, were elevated (P < 0.01) in all 15 patients tested (138.2 +/- 17.4 micrograms/g creatinine, range 41.6 +/- 281.0 micrograms/g) with no overlap when compared with 11 normals (9.7 +/- 1.3 micrograms/g, range 2.8-17.4 micrograms/g). 5. We conclude that measurement of urinary 'hybrid' steroids is probably the most rapid and reliable biochemical screening test currently available for FH-I, with confirmation dependent on demonstration of the hybrid gene by genetic techniques.