Plasma renin activity and aldosterone in familial dysautonomia

Familial dysautonomia

Familial dysautonomia (FD) is a neurodevelopmental genetic disorder within the larger classification of hereditary sensory and autonomic neuropathies, each caused by a different genetic error. The FD gene has been identified as IKBKAP. Mutations result in tissue-specific expression of mutant IkappaB kinase-associated protein (IKAP). The genetic error probably affects development, as well as maintenance, of neurons because there is neuropathological and clinical progression. Pathological alterations consist of decreased unmyelinated and small-fiber neurons. Clinical features reflect widespread involvement of sensory and autonomic neurons. Sensory loss includes impaired pain and temperature appreciation. Autonomic features include dysphagia, vomiting crises, blood pressure lability, and sudomotor dysfunction. Central dysfunction includes emotional lability and ataxia. With supportive treatment, prognosis has improved greatly. About 40% of patients are over age 20 years. The cause of death is usually pulmonary failure, unexplained sudden deaths, or renal failure. With the discovery of the genetic defect, definitive treatments are anticipated.

Hyper- and hypoaldosteronism

Aldosterone participates in blood volume and serum potassium homeostasis, which in turn regulate aldosterone secretion by the zona glomerulosa of the adrenal cortex. Autonomous aldosterone hypersecretion leads to hypertension and hypokalemia. Improved screening techniques have led to a re-evaluation of the frequency of primary aldosteronism among adults with hypertension, recognizing that normokalemic cases are more frequent than was previously appreciated. The genetic basis of glucocorticoid remediable aldosteronism has been elucidated and adequately explains most of the pathophysiologic features of this disorder. A new form of familial aldosteronism has been described, familial hyperaldosteronism type II; linkage analysis and direct mutation screening has shown that this disorder is unrelated to mutations in the genes for aldosterone synthase or the angiotensin II receptor. The features of aldosterone hypersecretion may be due to non-aldosterone-mediated mineralocorticoid excess. These include two causes of congenital adrenal hyperplasia (11 beta-hydroxylase deficiency and 17 alpha-hydroxylase deficiency), the syndrome of apparent mineralocorticoid excess (AME) due to 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) deficiency, primary glucocorticoid resistance, Liddle's syndrome due to activating mutations of the renal epithelial sodium channel, and exogenous sources of mineralocorticoid, such as licorice, or drugs, such as carbenoxolone. The features of mineralocorticoid excess are also often seen in Cushing's syndrome. Hypoaldosteronism may lead to hypotension and hyperkalemia. Hypoaldosteronism may be due to inadequate stimulation of aldosterone secretion (hyporeninemic hypoaldosteronism), defects in adrenal synthesis of aldosterone, or resistance to the ion transport effects of aldosterone, such as are seen in pseudohypoaldosteronism type I (PHA I). PHA I is frequently due to mutations involving the amiloride sensitive epithelial sodium channel. Gordon's syndrome (PHA type II) is due to resistance to the kaliuretic but not sodium reabsorptive effects of aldosterone for which the genetic basis is still unknown. This review aims to provide a survey of the clinical disorders of aldosterone excess and deficiency and their clinical management, with a focus on primary aldosteronism and isolated aldosterone deficiency.

Renal disease in familial dysautonomia

A study of renal disease in familial dysautonomia identified excess glomerulosclerosis in 10 or 13 autopsied and biopsied patients. Sympathetic nerve terminals could not be found on renal vessels in biopsied tissue; they were invariably demonstrable in controls. Altered renovascular responsivity to systemic hypotension in familial dysautonomia may lead to ischemia and subsequent sclerosis of glomeruli. Review of 79 living outpatients showed that clinically overt renal disease was rare in familial dysautonomia. Nevertheless, frequent observations of elevations of serum creatinine concentrations (32% of patients) and blood urea concentrations (76% of patients) indicated a high prevalence of abnormality. An association was found between hypotension and renal dysfunction.

Sodium, renin, aldosterone, catecholamines, and blood pressure in diabetes mellitus

Interrelations among plasma renin activity (PRA), aldosterone and cortisole levels, 0lood volume, exchangeable sodium, urinary catecholamines, and blood pressure were studied in 35 normal subjects and 60 age-matched non-azotemic patients with diabetes mellitus (60% with hypertension, 15% with orthostatic hypotension). Basal PRA, plasma aldosterone, cortisol, blood volume, plasma potassium, and urinary electrolytes were comparable in diabetic and normal subjects. Diabetic patients, however, had a 10% increase in body sodium (P less than 0.01), and 8% of them showed normal postural PRA responses and subnormal aldosterone responses; 22% had subnormal PRA and normal aldosterone responses, and 17% had subnormal responses of PRA and aldosterone. Non-PRA-related aldosterone responses could not be explained by ACTH or electrolytes. Orthostatic decreases in blood pressure correlated (P less than 0.01) with both catecholamine excretion and basal PRA. This suggests that in diabetes mellitus, body sodium is increased. Basal PRA and plasma aldosterone are usually normal, but their postural responses are frequently impaired. Absent aldosterone responses, despite normal PRA responsiveness, may reflect an adrenal abnormality or an ineffective form of renin. Marked postural aldosterone stimulation, unrelated to PRA, ACTH, or electrolytes, points to a potent unknown factor in aldosterone control. Low levels of free peripheral catecholamines and PRA may be complementary factors contributing to postural hypotension.

Pathologic hypofunction of the renin-angiotensin-aldosterone system

The literature now contains reports of many cases of aldosterone deficiency. Usually, the presenting features are persistent hyperkalemia and tendencies to serious urinary sodium loss and hypotension. A classification of defects leading to pathologic hypofunction of the renin-angiotensin-aldosterone system (RAAS hypofunction) is presented, with emphasis on idiopathic hyporeninemia (probably the most common). Criteria for diagnosis are (1) normal adrenal glucocorticoid function, (2) low aldosterone excretion under basal and stimulated conditions, and (3) renal tubular responsiveness to exogenous mineralocorticoid. The condition is effectively managed with mineralocorticoid replacement therapy and should be considered in the presence of unexplained persistent hyperkalemia, hyponatremia, or postural hypotension.