No abstract

The adrenoleukodystrophies refer to three genetically distinct disorders all characterized by the accumulation of very long-chain fatty acids. In this paper we will review the biochemical aspects of these leukodystrophies with particular emphasis on the methods used to measure very long-chain fatty acid levels in plasma and their reliability. Furthermore, we will concentrate on the primary defect in the X-linked form of adrenoleukodystrophy.

Profiles of saturated very-long-chain (> C22) fatty acids were studied in plasma, fibroblasts, erythrocytes, platelets, and leukocytes of patients affected by peroxisomal disorders such as Zellweger syndrome, X-linked adrenoleukodystrophy (X-ALD), and classic rhizomelic chondrodysplasia punctata (RCDP) and in controls. In Zellweger patients, the concentration of hexacosanoic acid (C26:0) and the C26:0/C22:0 ratio are greatly increased in plasma and fibroblasts. However, the plasma concentration of docosanoic acid (C22:0) is greatly decreased. Also in platelets, leukocytes, and to a lesser extent erythrocytes, the C26:0 concentrations and both the C26:0/C22:0 and C24:0/C22:0 ratios are greatly increased. The C24:0/C22:0 ratio is significantly increased in plasma, platelets, and leukocytes, but not in erythrocytes. In X-ALD, the C26:0 concentration and the C26:0/C22:0 and C24:0/C22:0 ratios are significantly increased in plasma, fibroblasts, platelets, and leukocytes, but the erythrocytes show substantial overlap in the 5-90% ranges between controls and patients. In RCDP, slightly increased C26:0 and C26:0/C22:0 ratios are found in erythrocytes, platelets, and leukocytes, but not in plasma and fibroblasts. We conclude that plasma and fibroblasts are the specimens of choice for biochemical diagnosis of Zellweger syndrome and X-ALD, respectively. The slight increase in C26:0 in blood cells of RCDP patients suggests a decreased flux of very-long-chain fatty acids through the peroxisomal beta-oxidation pathway in liver in this genetic disorder.

The Smith-Lemli-Opitz syndrome is a genetic disorder characterized by typical clinical features including reduced myelination of both brain and peripheral nervous system and defective cholesterol biosynthesis. In patients this results in very low cholesterol concentrations and accumulation of cholesterol precursors in plasma, tissues, cultured cells and faeces. We now show that the cholesterol concentration in CSF of Smith-Lemli-Opitz patients is markedly decreased and that 7- and 8-dehydrocholesterol concentrations are highly increased in comparison to controls. Moreover, dietary treatment of patients with cholesterol seems not to affect CSF cholesterol concentration.