Biochemical genetics of neurologic disease

Glucose intolerance in first-degree relatives of patients with Friedreich's ataxia is associated with insulin resistance: evidence for a closely linked inherited trait

Multiple and different genetic defects may be associated with the development of diabetes mellitus. Friedreich's ataxia (FA) is an autosomal recessively inherited neurologic disease associated with a high prevalence of diabetes. We previously demonstrated that patients with FA have insulin resistance prior to the development of overt diabetes mellitus. To determine if insulin resistance is an inherited characteristic in this group, we performed oral glucose tolerance tests (OGTT) on first-degree relatives, 21 parents and 17 siblings, of patients with FA. While fasting concentrations were normal, both glucose and insulin concentrations in response to oral glucose were significantly elevated compared with controls. Corrected insulin responses, CIR = I x 100/G (G-70) (I = insulin, G = glucose), were not different from controls, whereas peripheral insulin activities, A = 10(4)/Ip Gp (p = values of I and G at peak glucose concentration), were significantly decreased (FA, 0.66 +/- 0.11, P less than .001; parents, 0.63 +/- 0.06, P less than .001; siblings, 0.72 +/- 0.09, P less than .01; v controls, 1.52 +/- 0.19), indicating the presence of insulin resistance in patients and first-degree relatives. Multiple discriminant analysis was used to separate patients with FA from controls. The combination of GLUT (sum of glucose values 0 to 3 hours of the OGTT) and CIR achieved significant separation (P less than .0004). Subsequent assignment of the relatives showed that 17 of 18 parents and 11 of 16 siblings (69%) fell in the range of FA, rather than with controls. These data suggest that insulin resistance is an inherited trait in this group.(ABSTRACT TRUNCATED AT 250 WORDS)

Delivery of ultraviolet-inactivated 35S-herpesvirus across an osmotically modified blood-brain barrier

The present studies were undertaken to determine if viral particles can be delivered across the rat blood-brain barrier (BBB). Osmotic BBB modification with intracarotid mannitol (25%) was immediately followed by bolus intracarotid administration of 0.5 ml purified, ultraviolet-inactivated, herpes simplex virus type 1 endogenously labeled with 35S-labeled methionine (2.0 x 10(6) cpm, approximately 5 x 10(8) plaque-forming units/ml). After 60 minutes, intravascular virus was cleared by saline perfusion and the animals were sacrificed. A marked increase (fourfold, p less than or equal to 0.02) in radioactivity was observed in the ipsilateral brain hemisphere when compared to control animals without barrier modification. Administration of intravenous virus immediately after BBB modification displayed no difference in delivery when compared to intracarotid saline-infused controls (without BBB modification) suggesting the importance of a first-pass phenomenon. There were no significant differences in serum concentrations among intracarotid or intravenous groups. These preliminary studies suggest the possibility of delivering viral particles across the BBB with osmotic disruption, which may permit delivery of genetic material in replication-defective viral vectors in the feline model of GM2-gangliosidosis.

Multisystem neuronal degeneration in cocker spaniels

Four young Cocker Spaniels had slowly progressive neurologic signs with ataxia and mental deterioration. Pathologically, the lesions consisted of diffuse nerve cell loss, gliosis, axonal degeneration, and some demyelination in several areas of the brain. Pedigree analysis strongly suggests a hereditary cause for this disease, which is classified as a multisystem neuronal degeneration. This disorder has not been previously reported and has some resemblance to certain degenerative neurologic diseases found in humans. The clinical differential diagnosis includes cerebellar degeneration and lysosomal storage diseases. A definitive diagnosis requires postmortem examination.

Electron microscopy in the diagnosis of lysosomal storage diseases

Lysosomal storage diseases (LSD) affect cells of the conjunctiva in the absence of clinical eye findings. Consequently conjunctiva was added to skin, rectal mucosa, and peripheral blood lymphocytes as a biopsy site for electron microscopic examination in suspected LSD. The abnormally stored substrates in LSD are the result of diminished lysosomal enzyme activity. Although all cells lack the deficient lysosomal enzyme, the quantity of stored material varies with the extent of breakdown of substrate in the cell under normal circumstances. The stored material does not accumulate in all cells and may have a different cellular morphology at different sites. Although no one tissue provides universally diagnostic material for electron microscopy, skin and conjunctiva are optimal for most LSD. Rectal mucosa and peripheral blood lymphocytes are also useful in many cases. Biochemical assays have replaced brain biopsy for diagnosis but these techniques may give equivocal or non-diagnostic results, and in some diseases the enzyme defect remains undefined. Of the 359 biopsies of conjunctiva, skin, rectal mucosa, and lymphocytes we evaluated for LSD and other neurodegenerative diseases, 65 showed abnormal lysosomal storage; in 41 a specific diagnosis was made by biochemical assay or morphology. Ultrastructural examination of tissue from patients with clinically suspected storage disease may disclose pathognomonic alterations or suggest a differential diagnosis even in the absence of clinically evident involvement of the biopsied tissue. Biopsy has particular value in those diseases with incompletely characterized biochemical abnormalities.

CT and MRI in late-onset metachromatic leukodystrophy

A 23-year-old patient suffering from mental deterioration was referred for CT study following her first epileptic fit. The study disclosed generalized atrophy and diffuse symmetric white matter hypodensities. Similar findings were found in her 13-year-old retarded sister. The diagnosis of metachromatic leukodystrophy (MLD) was confirmed by the finding of low arylsulfatase A (ASA) levels in cultured fibroblasts in both sisters. MRI study revealed widespread high intensity signals of T2 nature in the periventricular regions indicating changes in white matter composition.

Glucose intolerance in Friedreich's ataxia: association with insulin resistance and decreased insulin binding

Friedreich's Ataxia (FA) is a neurologic disorder associated with a high prevalence of diabetes mellitus. To assess insulin secretion and insulin resistance, glucose and insulin responses to oral glucose and insulin binding to circulating monocytes and dextran gradient fractionated and unfractionated red blood cells (RBCs) were compared in 11 subjects with FA to 11 age-matched controls. Glucose and insulin responses were elevated from one to three hours after oral glucose in FA. The mean corrected insulin responses were not different while peripheral insulin activity (A) was significantly decreased (1.38 +/- 0.22 v 0.77 +/- 0.16, control v FA, P less than 0.025) indicating the presence of insulin resistance. A significant correlation between the degree of insulin resistance (A) and duration of neurologic symptoms was found (r = .65. P less than 0.025). Resistance to exogenous insulin was confirmed in ten subjects with FA by intravenous insulin tolerance tests (KITT, %/min, 6.25 +/- 0.90 v 3.93 +/- 0.61, P less than .05). Both FA and control groups showed highest insulin binding to fraction A (youngest) RBCs, but no difference was observed between the two groups. However, insulin binding to monocytes was significantly decreased in subjects with FA (% specific binding/10(7) cells/mL, 6.37 +/- 0.71 v 4.51 +/- 0.39, P less than 0.05, control v FA). This was associated with a decrease in apparent receptor affinity. We conclude that FA is associated with insulin resistance, which increases with the duration of neurologic impairment. The insulin binding to monocytes suggests that the insulin resistance may be partially explained by a receptor defect.

Cardiac involvement in Friedreich's ataxia: a clinical study of 75 patients

To establish the prevalence and to characterize the types of cardiac involvement in Friedreich's ataxia, 75 consecutive patients (39 male and 36 female), aged 10 to 66 years (mean 24) were prospectively studied. Electrocardiograms were performed in all patients, vectorcardiograms in 34 and echocardiograms in 58. Electrocardiographic and vectorcardiographic abnormalities occurred in 69 (92%) of the 75 patients. Electrocardiograms revealed ST-T wave abnormalities in 79%, right axis deviation in 40%, short PR interval in 24%, abnormal R wave in lead V1 in 20%, abnormal inferolateral Q waves in 14% and left ventricular hypertrophy (voltage and repolarization criteria) in 16%. Echocardiograms revealed concentric left ventricular hypertrophy in 11%, asymmetric septal hypertrophy in 9% and globally decreased left ventricular function in 7%. Progression from a normal echocardiogram to concentric left ventricular hypertrophy, asymmetric septal hypertrophy or globally decreased left ventricular function was identified in one patient in each category, although the study was not designed for longitudinal follow-up. Two patients died, and necropsy revealed in both a minimally dilated but flabby left ventricle. On the basis of electrocardiographic and vectorcardiographic and echocardiographic data, 95% of patients had one or more disorders. The most common abnormality was segmental myocardial "dystrophy" (electrocardiographic QRS initial force abnormalities), but global left ventricular hypokinesia occurred more often than previously recognized.(ABSTRACT TRUNCATED AT 250 WORDS)

Material prepared from normal brain inhibits migration of leukocytes from Huntington's disease patients

Material inhibiting migration of leukocytes in vitro from Huntington's disease patients, was obtained from human brain removed at autopsy. The active material was present in brainstem, basal ganglia and cerebellum but not in cerebral cortex. It could be recovered at autopsy up to 21.5 h after death, but not from patients who had died following prolonged anoxia. It was susceptible to heating and to freezing and thawing. Its activity was preserved in acid medium to pH 3, and its iso-electric point was around pH 5. Activity was present in the fraction eluted from gel filtration with molecular weight of 1.9 X 10(5). Protein, carbohydrate, lipid and nucleic acid could be identified in the active material, and its activity depended on intact protein and carbohydrate moieties. Sialic acid, although present, did not contribute to antigenicity. Extraction with lipid solvents abolished activity.

Molecular genetics, recombinant DNA techniques, and genetic neurological disease

The molecular defects responsible for Huntington's disease, the spinocerebellar degenerations, myotonic muscular dystrophy, neurofibromatosis, and tuberous sclerosis, among other major dominant inherited diseases of the nervous system, will be identified using the new techniques of molecular genetics. With synthesized nucleic acid segments complementary to portions of the patient's DNA, known as complementary DNA probes, it will be possible to identify and isolate the mutant gene responsible for a particular disease. These events are referred to as gene cloning. In addition, complex genetic regulatory mechanisms involved in cell differentiation during neuroembryogenesis will be elucidated with the application of these strategies. It is important for the clinician to become familiar with the precision and potential of these new methodologies, because they will soon influence significantly the practice of neurology.

Adrenomyeloneuropathy--clinical and biochemical diagnosis

Adrenomyeloneuropathy (AMN) is an X-linked storage disease of very-long-chain fatty acids that presents as primary adrenocortical failure combined with spastic paraparesis and peripheral neuropathy. This disorder was diagnosed in three unrelated adult males. Definitive diagnosis was made by finding elevated very-long-chain fatty acids in plasma and skin biopsy samples. Biochemical characterisation of this disease has elucidated its genetics, clarified its relationship with adrenoleukodystrophy of children and other phenotypic variants, and allowed heterozygote identification, accurate genetic counselling and prenatal diagnosis.

Specific messenger RNA changes in Joseph disease cerebella

Joseph disease is an autosomal-dominant, spinocerebellar degeneration characterized at the biochemical level by elevations in the steady-state levels of several abundant proteins (H, J, and L) in affected brain areas such as the cerebellar cortex. The increased levels of these proteins could either be a consequence of a relative increase in their de novo synthesis or result from altered rates of proteolysis in degenerating brain cells. These alternatives can be distinguished by comparing the in vitro protein-synthetic capacities of the messenger ribonucleic acid populations isolated from cerebellar cortex of control subjects and patients with Joseph disease. Protein H (glial fibrillary acidic protein) is synthesized at detectable levels by all messenger ribonucleic acid isolates, and the levels of its translatable messenger ribonucleic acid are reproducibly increased in ribonucleic acids isolated from cerebellar cortex of patients with Joseph disease as compared with those isolated from cerebellar cortex of control subjects. Thus, the increased level of protein H in Joseph disease is a consequence of an increase in its de novo synthesis and is correlated with the increased number of cerebellar glial cells. In contrast to these results, there is no detectable synthesis of proteins J and L by messenger ribonucleic acid populations isolated from cerebellar cortex of either Joseph disease patients or control subjects, suggesting that the increased levels of these proteins in affected cerebellar cortex are a consequence of posttranslational protein modifications.

Mutagen hypersensitivity in Friedreich's ataxia

Cultured blood lymphocytes from nine patients with Friedreich's ataxia (FrA) and nine matched controls were exposed to a series of graded doses of mitomycin C and ethyl methane sulphonate and examined for the incidence of sister chromatid exchange (SCE). The spontaneous SCE levels did not differ between patients and controls, but the cells from each of the patients showed a significantly enhanced response to the induction of SCE by both mutagens - the patients' cells being up to 50% more sensitive than controls. Cultures from five FrA patients and five controls were analysed to determine the spontaneous incidence of chromosomal aberrations and exposed to a graded series of X-ray doses to measure their response to radiation-induced chromosome damage. The spontaneous aberration incidence in controls did not differ from that found in other control series, but the background incidence of aberrations in cells from the FrA patients was significantly above control levels and appeared to reflect an enhanced response to diagnostic exposure to radionuclides. The FrA cells showed a significantly enhanced in vitro response to chromosome aberration induction by X-rays, the net aberration yields being some 60% greater than those in irradiated controls at doses up to 200 rads. It is concluded that FrA is yet another syndrome which shows hypersensitivity to the induction of chromosome damage by mutagens. Possible factors responsible for this hypersensitivity are discussed and comparisons drawn with ataxia telangiectasia, another autosomal recessive disease characterized by enhanced X-ray sensitivity.

Neurodegenerative diseases of infancy and childhood

The neurodegenerative diseases of infancy and childhood include disorders in which there is progressive loss of neurological function due to structural abnormalities of the central nervous system. Well over six hundred disorders, many of which are rarely seen, can be included in this category. Yet, the conditions represent collectively over one-fourth of all admissions to pediatric neurology services. Five-year samples of admission characteristics of 1218 patients from two medical centers over twenty-two years permit an estimate of the frequency of the neurodegenerative diseases. The six most-encountered diagnoses, in declining order, were: subacute sclerosing panencephalitis; neuronal ceroid lipofuscinosis; tuberous sclerosis with degeneration; West disease, or idiopathic degenerative encephalopathy associated with infantile spasms; Werdnig-Hoffmann disease, and hereditary spastic paraplegia. A classification is offered grouping the neurodegenerative disorders into five major categories: polioencephalopathies, leukoencephalopathies, corencephalopathies, spinocerebellopathies, and diffuse encephalopathies. Disorders in each subgroup may be either genetic or nongenetic. Neurodegenerative diseases have multiple causes, including metabolic, viral, immunopathic, environmental, and epileptogenic. The cause of many remains unknown.

Laboratory diagnosis of inborn errors of metabolism in children

A compendium of tests available to diagnose children with inborn errors of metabolism is presented. It is intended to provide the pediatric pathologist with a rational way of using laboratory tests to investigate a patient who is suspected of having an inborn error of metabolism. It is intended to bridge the gap between the ward and the laboratory by providing a framework for investigations of such children.

Evoked potential abnormalities in the various inherited ataxias

Visual (VEP), brainstem auditory (BAEP), and somatosensory (SEP) evoked potential tests were performed in 45 patients representing ten types of inherited disorders in which ataxia was the most prominent symptom. Comparable VEP abnormalities were present among all types of patients. Normal BAEP tests were recorded in most patients except those with olivopontocerebellar atrophy. SEP results were often more severely abnormal in patients with Friedreich's ataxia. The observations emphasize the similarity in expression of different metabolic-degenerative disorders. When these tests are used clinically, certain features of evoked potentials (especially left-right symmetry) are typical of the inherited ataxias as a group. Few distinguishing features differentiate the individual disorders.

Adrenoleukodystrophy

Adrenoleukodystrophy (ALD) is an X-linked degenerative disease characterized by progressive demyelination and adrenal insufficiency. Several phenotypes are described. In post-mortem tissues there is an accumulation of saturated or mono-unsaturated very long chain fattyacids (VLCFA) in the cholesterol ester fraction of adrenal cortex and cerebral white matter. The accumulated fatty acids are unbranched with carbon chain length between 23 and 32 with most containing 25 or 26 carbons. Determination of VLCFA in readily accessible tissues such as skin fibroblasts and plasma allows for reliable detection of patients and carriers.