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Biomedical subjects

B R Powell

Publications and source records attributed to B R Powell.

26 records · Page 2Linked to original sources
PubMed1990

Deletion mapping of Aland Island eye disease to Xp21 between DXS67 (B24) and Duchenne muscular dystrophy.

Aland Island Eye Disease (AIED) is an X-linked form of ocular hypopigmentation--also known as Forsius-Eriksson, or type 2, ocular albinism--in which affected males demonstrate subnormal visual acuity, protanomalous red-green colorblindness, axial myopia, astigmatism, hypoplasia of the fovea, and hypopigmentation of the fundus. A patient has previously been described who, in addition to AIED, manifested a contiguous gene syndrome which included congenital adrenal hypoplasia (AHC), glycerol kinase deficiency (GKD), and Duchenne muscular dystrophy (DMD). In the present paper report we report the molecular genetic analysis of his deletion. Initially, multiplex polymerase-chain-reaction amplification was used to screen for a DMD-locus deletion which was then further characterized, using DMD cDNA and genomic probes, via Southern blot analysis. The deletion includes the region encompassed by probes C7 (DXS28) and DMD cDNA 8. Probes B24 (DXS67) and DMD cDNA 5b-7 show normal hybridization patterns and appear to flank the deletion, while the DMD cDNA 8 detects a junction fragment. Molecular genetic techniques have mapped the deletion in this patient to the subbands Xp21.3-21.2, between DXS67 and DMD.

Albinism, Ocular↗
PubMed1990

3-Hydroxy-3-methylglutaryl-CoA lyase deficiency as detected by radiochemical assay in cell extracts by thin-layer chromatography, and identification of three new cases.

In this rapid radiochemical assay for 3-hydroxy-3-methylglutaryl-coenzyme A lyase (I) activity in cell extracts, DL-3[glutaryl-3-14C]hydroxy-3-methylglutaryl-coenzyme A is used as substrate and the radiochemical product, [3-14C]acetoacetic acid, is converted to the more stable [3-14C]-3-hydroxybutyric acid in the presence of added NADH and 3-hydroxybutyrate dehydrogenase. Substrate and product are separated and quantified by thin-layer chromatography on cellulose (solvent system: butanol/water/formic acid, 77:13:10 by vol). All reagents for the assay are commercially available. No detailed column chromatography or spectrophotometry is required. Thus the assay is suited for any clinical laboratory. Using this procedure, we studied cultured fibroblasts or lymphocytes isolated from whole blood from five patients in whom the urinary organic acid profile was suggestive of deficiency of I. Three patients had less than or equal to 18% of control I activity in fibroblast or lymphocyte extracts. The other two had activity within the normal range. In one of the latter cases, urinary excretion of three of the characteristic acids disappeared with age, and 3-hydroxyisovaleric acid excretion was within normal limits. The other case presented with urinary excretion of moderate amounts of all four metabolites and the characteristic absence of urinary ketone bodies. Evidently, confirmatory enzyme studies should be undertaken, even when the profile of urinary organic acids appears definitive for this deficiency.

Cells, Cultured↗
PubMed1989

Aland Island eye disease (Forsius-Eriksson syndrome) associated with contiguous deletion syndrome at Xp21. Similarity to incomplete congenital stationary night blindness.

We report the ophthalmological findings of a 6-year-old boy who has features of both Aland Island eye disease (also called Forsius-Eriksson ocular albinism) and incomplete congenital stationary night blindness, as defined by Miyake, leading us to suspect that they are the same entity. This child has a deletion of part of band 21 of the short arm of the X chromosome (Xp21) and three other X-linked disorders: congenital adrenal hypoplasia, glycerol kinase deficiency, and Duchenne type muscular dystrophy. The electroretinogram showed negative scotopic and abnormal photopic waveforms that were similar, if not identical, to the electroretinographic findings in both Aland Island eye disease and X-linked incomplete congenital stationary night blindness. Because of this similarity and the defective dark adaptometry that has been reported in patients with this disorder, we believe that Aland Island eye disease is more appropriately classified as a form of congenital night blindness than as a form of ocular albinism. From our case and review of the literature, Aland Island eye disease and incomplete congenital stationary night blindness appear indistinguishable. If further studies confirm that the disorders are the same, we recommend use of the term Aland Island eye disease or Forsius-Eriksson-Miyake syndrome. We also recommend that the gene symbols CSNB1 and CSNB2 be used for complete congenital stationary night blindness and Aland disease, respectively.

Adolescent↗
PubMed1989

Metabolic myopathies: evaluation by graded exercise testing.

Exertional muscle pain and fatigue are common complaints; some patients with these symptoms have a metabolic myopathy. We have performed graded exercise testing with analysis of expired ventilation on 13 individuals with various kinds of metabolic myopathies. Their results differed from normal and reflected the underlying biochemical abnormality. Patients with disorders of the mitochondrial electron transport chain demonstrated marked limitations in aerobic metabolism and a greatly reduced maximum oxygen consumption. During intense exertion, normal individuals increase carbon dioxide generation due to buffering of lactic acid. This did not occur in patients with McArdle disease, in whom the respiratory exchange ratio (carbon dioxide production/oxygen consumption) did not rise above 1.0 at maximum exercise. These results indicated a deficit in anaerobic metabolism. Pyruvate dehydrogenase complex allows pyruvate produced from carbohydrate metabolism to enter the citric acid cycle. Patients with this enzyme deficiency showed an initially normal pattern followed by an abrupt cessation in carbohydrate dependent aerobic metabolism at higher work loads. During high-intensity exercise, progressive anaerobic metabolism was not accompanied by additional oxygen consumption. Finally, results from a patient with carnitine palmitoyl transferase deficiency revealed an early dependence on carbohydrate metabolism. The ventilatory threshold occurred at a low percentage of maximal oxygen consumption, reflecting the limited availability of lipid substrates for aerobic metabolism. Detection of some muscle metabolic abnormalities can be made on small biopsy specimens. However, definitive diagnosis of the defect nearly always requires studies on fresh or frozen muscle tissue obtained by an open biopsy. The decision on how the tissue should be processed and which metabolic studies should be performed frequently needs to be made before the biopsy is obtained. Thus, a noninvasive method to initially characterize patients with potential metabolic disorders is useful. Exercise testing with expired gas analysis can indicate the presence of a metabolic myopathy and results can then be used to direct the appropriate biochemical evaluations.

Adolescent↗
PubMed1982

An X-linked syndrome of diarrhea, polyendocrinopathy, and fatal infection in infancy.

We have studied a patient from a family in which 17 male infants died in the first years of life. The clinical characteristics of this disorder were established from information from eight patients. The features included diarrhea, diabetes mellitus, hemolytic anemia, eczematoid rashes, and exaggerated responses to viral illnesses, combined with pathologic evidence of autodestruction of endocrine glands, insulitis, and thyroiditis with thyroid autoantibodies in one patient. When tested, B-lymphocyte cell function, T cell numbers, polymorphonuclear leukocyte chemotaxis, and complement concentrations were normal. Lymphocyte stimulation with phytohemagglutinin was low in one to two affected males and delayed skin test anergy was noted in another, raising the question of a T-lymphocyte cell abnormality. The basic genetic mechanism is unknown, but involvement of an immune response locus on the X chromosome, dysfunction of which is responsible for overactivity of the autoimmune system, is postulated.

Adult↗
PubMed1976

Rehabilitation performance and adjustment in stroke patients: a study of social class factors.

In a prospective follow-up study comparing the adjustment of hemiplegics in rehabilitation programs in a public institution (N = 100) and a private university facility (N = 105) measures were taken one month after admission and 18-24 months after discharge. Initially, the groups differed in social profiles (social class, ethnicity, marital status), incidence of secondary medical conditions and attitudes, including expectancies and F scale and sick role questionnaire. They did not differ in performance and motivation on the programs. At follow-up treatment. Many more went to nursing homes. Implications for rehabilitation programs are presented.

Activities of Daily Living↗
PubMedDate not supplied

Duchenne/Becker muscular dystrophy: correlation of phenotype by electroretinography with sites of dystrophin mutations.

The dark-adapted electroretinogram (ERG) of patients with Duchenne and Becker muscular dystrophy (DMD/BMD) shows a marked reduction in b-wave amplitude. Genotype-phenotype studies of mouse models for DMD show position-specific effects of the mutations upon the phenotype: mice with 5' defects of dystrophin have normal ERGs, those with defects in the central region have a normal b-wave amplitude associated with prolonged implicit times for both the b-wave and oscillatory potentials, and mice with 3' defects have a phenotype similar to that seen in DMD/BMD patients. The mouse studies suggest a key role for the carboxyl terminal dystrophin isoform, Dp260, in retinal electrophysiology. We have undertaken a systematic evaluation of DMD/BMD patients through clinical examination and review of the literature in order to determine whether the position-specific effects of mutations noted in the mouse are present in man. We have found that, in man, a wider variation of DMD defects correlate with reductions in the b-wave amplitude. Individuals with normal ERGs have mutations predominantly located 5' of the transcript initiation site of Dp260. Our results suggest that the most important determinant in the ERG b-wave phenotype is the mutation position, rather than muscle disease severity. Forty-six per cent of patients with mutations 5' of the Dp260 transcript start site have abnormal ERGs, as opposed to 94% with more distal mutations. The human genotype-phenotype correlations are consistent with a role for Dp260 in normal retinal electrophysiology and may also reflect the expression of other C-terminal dystrophin isoforms and their contributions to retinal signal transmission.

Dystrophin↗