Current concepts in genetics. Lysosomal storage diseases

Diagnosis of inherited metabolic disorders affecting the nervous system

Knowledge of the molecular causes for genetic diseases that affect the nervous system is rapidly expanding. Especially striking has been the finding in several autosomal dominant neurodegenerative disorders that unstable expansions of trinucleotide repeats are responsible for the genetic disorder and that the length of the repeat can be correlated with the age of onset and the severity of symptoms. Phenotypic heterogeneity in many disorders associated with enzyme deficiencies can often be linked to the amount of residual enzyme activity occurring with different gene mutations. Making a specific diagnosis of a neurological disorder associated with genetically determined metabolic defects requires access to a laboratory that can assist in arranging for appropriate testing to be carried out. In some disorders such as the aminoacidurias diagnostic metabolic studies can be performed in hospital clinical chemistry laboratories. In others, such as the lysosomal storage diseases, a laboratory that carries out special lipid analyses and white blood cell enzyme assays will be necessary. DNA mutational analyses are becoming commercially available for diagnosing many disorders such as mitochondrial diseases and those conditions associated with expanded trinucleotide repeats. It may be necessary to contact individual research laboratories when confronted with a disorder that has been newly discovered or that is very rare. A computerised directory of specialised laboratories that perform disease specific testing for genetic disorders should be useful in choosing the appropriate diagnostic or research laboratory.

Review: the cerebrohepatorenal syndrome of Zellweger, morphologic and metabolic aspects

The cerebrohepatorenal syndrome of Zellweger (CHRS) is remarkable not only for a distinctive combination of congenital anomalies, but also for an unusual variety of profound metabolic disturbances. After a discussion of the clinical diagnosis of CHRS, abnormalities in the metabolism of peroxisomes, mitochondria, iron, pipecolic acid, glycogen, bile acids, and organic acids are discussed and related to the clinical and other biochemical findings in the syndrome. Attention is also drawn to syndromes with biochemical or clinical abnormalities similar to those of CHRS. Although the biochemical findings indicate major abnormalities in oxidative metabolism, the primary defect remains obscure.

Peripheral hemodynamics in patients with Fabry's disease

Altered vasomotor activity has been reported as a clinically prominent feature of Fabry's disease (angiokeratoma corporis diffusum universale). While symptomatic cardiovascular involvement occurs eventually in most patients with this disorder, little is known concerning the effect of Fabry's disease on peripheral hemodynamics. Peripheral hemodynamics in the extremities and digits were studied in eight patients with Fabry's disease by means of segmental and venous occlusion pneumoplethysmography and thermal probes, and the results obtained were compared with those of 10 normal subjects. Forearm vascular resistance in Fabry's disease patients was significantly higher (p less than 0.01) than that in normal subjects. Forearm venous capacitance in Fabry's disease was significantly lower (p less than 0.01). Segmental pulse volume amplitudes showed no significant difference in any segments (upper arm, wrist, thigh, above and below knee, and the calf) between the two groups. Finger and toe blood flow, finger and toe pulse volume, and temperature in the resting state were all significantly less (p less than 0.01, p less than 0.05: p less than 0.01, p less than 0.01: p less than 0.05, p less than 0.05, respectively) than those in normal subjects. Finger and toe blood flow and pulse volume after vasodilation procedures were significantly less (p less than 0.05, p less than 0.01: p less than 0.05, p less than 0.01, respectively) than those in normal subjects despite equal elevation of digital temperature obtained after vasodilation in both groups. These findings indicate the presence of vasoconstrictive process in both resistance vessels and capacitances vessels in cutaneous and skeletal muscular beds. A limited response in the cutaneous circulation to vasodilation procedures also was seen. These data suggest the possibility that latent enhanced sympathoadrenal discharge as well as the accumulation of glycolipid in the autonomic nervous system and vessel walls plays an important role in the disturbed pathophysiology of this disorder.

Brain biopsies for neurodegenerative disease in children

Brain biopsies for neurodegenerative disease performed at The Hospital for Sick Children, Toronto, over a 12-year period (1964 to 1976) were reviewed. Of 64 biopsies, major histologic abnormalities with diagnostic or prognostic significance comprised 39% of the total cases, minor abnormalities represented 13%, and 48% appeared normal. The procedure failed to provide prognostic assistance in 41%. With the advent for newer diagnostic techniques (enzyme assays and muscle, skin, peripheral nerve, rectal, and appendix biopsies) for neurodegenerative disease in childhood, a much lower yield is noted (15 to 20%). Only two progressive degenerative childhood conditions remain in which cerebral tissue is necessary for diagnosis--Alexander disease and Canavan spongy degeneration.

Hypersialyloligosacchariduria in mucolipidoses: a method for diagnosis

A method is described for the detection of abnormal oligosaccharides in a small (5 ml) volume of urine, employing filtration on a Bio Gel P-6 column, determination of neutral sugar and bound sialic acid, and determination of creatinine content. With this method increased urinary excretion of sialic acid-rich oligosaccharides has been detected in nine patients with mucolipidoses (five cases of mucolipidosis II and four patients of mucolipidosis, with beta-galactosidase deficiency). The filtration patterns of oligosaccharides in mucolipidoses were clearly distinguishable from those in other inborn errors of metabolism. Total excreted oligosaccharides were increased 5--30-fold in these patients; mucolipidosis II, 640--1350 microgram neutral sugar/mg creatinine; control 54 +/- 20 microgram neutral sugar/mg creatinine. The oligosaccharides consisted of three sialic acid-rich fractions and were common in both types of mucolipidosis. Our data indicate that hypersialyoligosacchariduria is the main biochemical feature of both types of mucolipidosis.

An unusual case of phospholipidosis

We present the results of a structural, histochemical and lipid-chromatographic study of tissues obtained at postmortem from an unusual case of phospholipidosis. A previous biopsy of the appendix and liver (Elleder et al., 1975a) had revealed a predominance of phosphoglyceride storage, principally of lysobisphosphatidic acid (LBPA) postmortem material showed that this lipid was stored exclusively in central neurons. In the spleen and the lymph node, however, sphingomyelin (SP) was shown, histochemically and chromatographically, to be the main lipid stored. Total sphingomyelinase (SPase) activity in the appendix was reduced to about 50% of normal. Neuroaxonal dystrophy (NAD) and a conspicuous discrepancy between the degree of distension of some neurons and their lipid content deserve special mention. The case is contrasted with classical sphingomyelinosis; the complexity of the Niemann-Pick group of diseases is discussed as an indication of the difficulties of classification of any atypical case.

Enzyme replacement therapy for adenosine deaminase deficiency and severe combined immunodeficiency

To evaluate their role as a form of replacement therapy, frozen irradiated red blood cells were administered to a child with adenosine deaminase deficiency associated with severe combined immunodeficiency disease. In vitro lymphocyte responses to mitogens and allogeneic cells were restored. Subsequently, a "thymus shadow" appeared, and immunoglobulin synthesis was demonstrated. Frozen irradiated plasma, which alone had no effect on lymphocytes numbers or responses, promoted lymphocytosis when given with frozen irradiated red blood cells. The patient received the transfusions with or without irradiated plasma at four-week intervals and remained free of infection for 17 months. The patient's lymphocyte adenosine triphosphate levels were elevated before therapy, which consistently reduced them without altering the lymphocyte adenosine deaminase activity. Enzyme replacement therapy may provide a way to treat patients with adenosine deaminase deficiency associated with severe combined immunodeficiency disease who do not have histocompatible bone-marrow donors.

Parkinsonism and levodopa: a five-year experience

Seventy parkinsonian patients were treated continuously with levodopa for five years. During the first year, sixty-three patients (90 per cent) improved. After five years, however, only thirty-seven patients remained improved while thirty-three patients (48 per cent) experienced progressive disease. Complications of treatment, albeit nonfatal, increased in frequency during the five-year interval. The reason for early improvement and subsequent deterioration of parkinsonian symptoms and signs in spite of levodopa therapy remains unexplained. It suggests that Parkinson's disease may not be simply a striatal dopamine deficiency syndrome and that treatment with levodopa is more than replacement therapy.