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Biomedical subjects

J T Clarke

Publications and source records attributed to J T Clarke.

At least 91 records · Page 5Linked to original sources
PubMed1991

Multiple sulfatase deficiency with early severe retinal degeneration.

We report an unusual case of multiple sulfatase deficiency in which neurodegeneration was accompanied by early, severe visual impairment associated with prominent pigmentary retinopathy, suggesting a diagnosis of neuronal ceroid-lipofuscinosis. The levels of arylsulfatases A, B, and C, heparan N-sulfatase, N-acetylgalactosamine-6-sulfate sulfatase, and iduronate-2-sulfate sulfatase were all markedly decreased in cultured skin fibroblasts. Screening tests for mucopolysacchariduria were consistently negative; however, thin-layer chromatographic analysis of isolated urinary glycosaminoglycans showed increased amounts of heparan sulfate.

Child↗
PubMed1991

Arteriopathy and coarctation of the abdominal aorta in children with mucopolysaccharidosis: imaging findings.

Eight children with mucopolysaccharidosis I (MPS I), representing 33% of all children with MPS I seen at our institution during an 18-year period, developed hypertension. Five of these hypertensive children also exhibited symptoms of aortic coarctation. The radiographic evaluation of four of these children with MPS I (three with Hurler syndrome, MPS I H, and one with Scheie disease, MPS I S) and arteriopathy affecting the thoracic aorta, abdominal aorta, and visceral and renal arteries is presented. Hypertension developed in all four children before they were 4 years old; three had differences between upper- and lower-extremity blood pressures. Irregular narrowing of the abdominal aorta with either multiple minor asymmetric wall lesions (n = 2) or abrupt concentric narrowing (n = 2) was present in all children as shown by aortography (n = 3), sonography (n = 3), MR imaging (n = 2), and/or autopsy (n = 1). A variety of other vessels also were involved, including the ascending aorta (n = 1) and vertebral (n = 1), axillary (n = 1), intercostal (n = 2), lumbar (n = 2), mesenteric (n = 3), renal (n = 2), and iliac arteries (n = 3). Autopsy in one child demonstrated thickened heart valves, narrowing of the coronary arteries, and irregularity of the aorta due to deposition of mucopolysaccharide material within the intima. Our series demonstrates various facets of the arteriopathy of MPS I as shown by sonography, MR imaging, and angiography.

Angiography↗
PubMed1991

Hunter disease (mucopolysaccharidosis type II) associated with unbalanced inactivation of the X chromosomes in a karyotypically normal girl.

The mechanism of profound generalized iduronate sulfatase (IDS) deficiency in a developmentally delayed female with clinical Hunter syndrome was studied. Methylation-sensitive RFLP analysis of DNA from peripheral blood lymphocytes from the patient, using MspI/HpaII digestion and probing with M27 beta, showed that the paternal allele was resistant to HpaII digestion (i.e., was methylated) while the maternal allele was digested (i.e., was hypomethylated), indicating marked imbalance of X-chromosome inactivation in peripheral blood lymphocytes of the patient. Similar studies on DNA from maternal lymphocytes showed random X-chromosome inactivation. Among a total of 40 independent maternal fibroblast clones isolated by dilution plating and analyzed for IDS activity, no IDS- clone was found. Somatic cell hybrid clones containing at least one active human X chromosome were produced by fusion of patient fibroblasts with Hprt- hamster fibroblasts (RJK88) and grown in HAT-ouabain medium. Methylation-sensitive RFLP analysis of DNA from the hybrids showed that of the 22 clones that retained the DXS255 locus (M27 beta), all contained the paternal allele in the methylated (active) form. No clone was isolated containing only the maternal X chromosome, and in no case was the maternal allele hypermethylated. We postulate from these studies that the patient has MPS II as a result of a mutation resulting in both the disruption of the IDS locus on her paternal X chromosome and unbalanced inactivation of the nonmutant maternal X chromosome.

Animals↗
PubMed1991

Sequence of DNA flanking the exons of the HEXA gene, and identification of mutations in Tay-Sachs disease.

The rapid identification of mutations causing Tay-Sachs disease requires the capacity to readily screen the regions of the HEXA gene most likely to be affected by mutation. We have sequenced the portions of the introns flanking each of the 14 HEXA exons in order to specify oligonucleotide primers for the PCR-dependent amplification of each exon and splice-junction sequence. The amplified products were analyzed, by electrophoresis in nondenaturing polyacrylamide gels, for the presence of either heteroduplexes, derived from the annealing of normal and mutant DNA strands, or single-strand conformational polymorphisms (SSCP), derived from the renaturation of single-stranded DNA. Five novel mutations from Tay-Sachs disease patients were detected: a 5-bp deletion of TCTCC in IVS-9; a 2-bp deletion of TG in exon 5; G78 to A, giving a stop codon in exon 1; G533 to T in exon 5, producing the third amino acid substitution detected at this site; and G to C at position 1 of IVS-2, expected to produce abnormal splicing. In addition, two mutations, (G1496 to A in exon 13 and a 4-bp insertion in exon 11) that have previously been reported were identified.

Alleles↗
PubMed1991

The management of otolaryngological problems in the mucopolysaccharidoses: a retrospective review.

The mucopolysaccharidoses are rare, genetically transmitted metabolic disorders that affect children early in life. These potentially life-threatening diseases almost invariably involve the auditory apparatus and the upper respiratory tract. Thus, the otolaryngologist is frequently involved in the care of these patients. This paper presents a 10-year retrospective review of the management of these patients at the Hospital for Sick Children. Data concerning auditory and upper respiratory pathology are presented. Results indicate that persistent serous otitis, sensorineural hearing loss, and upper respiratory obstruction leading to sleep apnea, are frequent findings in these patients. Specific recommendations are made with regard to appropriate otolaryngologic intervention in children affected with these diseases.

Adenoidectomy↗
PubMed1990

Screening for carriers of Tay-Sachs disease among Ashkenazi Jews. A comparison of DNA-based and enzyme-based tests.

BACKGROUND AND METHODS: The prevention of Tay-Sachs disease (GM2 gangliosidosis, type 1) depends on the identification of carriers of the gene for this autosomal recessive disorder. We compared the enzyme-based test widely used in screening for Tay-Sachs disease with a test based on analysis of DNA. We developed methods to detect the three mutations in the HEXA gene that occur with high frequency among Ashkenazi Jews: two mutations cause infantile Tay-Sachs disease, and the third causes the adult-onset form of the disease. DNA segments containing these mutation sites were amplified with the polymerase chain reaction and analyzed for the presence of the mutations. RESULTS: Among 62 Ashkenazi obligate carriers of Tay-Sachs disease, the three specific mutations accounted for all but one of the mutant alleles (98 percent). In 216 Ashkenazi carriers identified by the enzyme test, DNA analysis showed that 177 (82 percent) had one of the identified mutations. Of the 177, 79 percent had the exon 11 insertion mutation, 18 percent had the intron 12 splice-junction mutation, and 3 percent had the less severe exon 7 mutation associated with adult-onset disease. The results of the enzyme tests in the 39 subjects (18 percent) who were defined as carriers but in whom DNA analysis did not identify a mutant allele were probably false positive (although there remains some possibility of unidentified mutations). In addition, of 152 persons defined as noncarriers by the enzyme-based test, 1 was identified as a carrier by DNA analysis (i.e., a false negative enzyme-test result). CONCLUSIONS: The increased specificity and predictive value of the DNA-based test make it a useful adjunct to the diagnostic tests currently used to screen for carriers of Tay-Sachs disease. Although some false positive results may be desirable on an enzyme-based test that is used in screening, the DNA test allows precise definition of the carrier state for the known mutations.

Alleles↗
PubMed1990

First trimester prenatal diagnosis of Tay-Sachs disease using the sulfated synthetic substrate for hexosaminidase A.

Uncultured and cultured embryonic trophoblastic tissue obtained by chorionic villus sampling (CVS) displays enzyme activity towards 4-methylumbelliferyl-2-acetamido-2-deoxy-beta-D-glucopyranosyl-6-sulfate (MUGS), a specific substrate for Hexosaminidase A (Hex A), the enzyme deficient in Tay-Sachs disease (TSD). Specific activity is comparable to that found in cultured amniocytes and fibroblasts. The enzyme activity has a pH optimum of 4.1 and an apparent Km of 6 x 10(-4) mol/L. Thirteen pregnancies in eight families at risk for TSD were monitored by CVS using MUGS as the Hex A substrate. Four fetuses were proven affected by enzyme analysis of fetal tissues and cultured fetal fibroblasts obtained at the time of termination of the pregnancies. Nine fetuses were judged to be unaffected. Eight babies were clinically normal while the other pregnancy is continuing. The use of MUGS as substrate for Hex A makes prenatal diagnosis by CVS of families at risk for TSD simple, direct and accurate.

Cells, Cultured↗
PubMed1990

Hunter disease (mucopolysaccharidosis type II) in a karyotypically normal girl.

A female child of healthy, unrelated parents presented at 12 months of age with a history of moderately severe developmental delay, macrocephaly, dysmorphic facies, hypotonia, hepatosplenomegaly, mild generalized dysostosis multiplex, mucopolysacchariduria (dermatan and heparan sulfates), and Alder-Reilly bodies in peripheral blood leukocytes. Iduronate sulfatase activity in plasma was markedly depressed: 0.11 units/ml/h (normal, 1.75 +/- 0.56, N = 6). Analyses of arylsulfatases A, B, and C, heparan N-sulfatase, alpha-mannosidase, beta-mannosidase, beta-glucuronidase, beta-hexosaminidase, beta-galactosidase, and alpha-fucosidase activities in plasma, leukocytes, and/or cultured skin fibroblasts were all normal. Urinary sulfatide excretion was also within normal limits. Karyotypes of peripheral blood leukocytes and cultured skin fibroblasts were normal. Serum iduronate sulfatase activities in the parents were in the normal range (father, 1.63 units/ml/h; mother, 1.25 units/ml/h). The results of analyses of restriction fragment length polymorphisms (RFLP) of DNA from cultured skin fibroblasts with the use of probes for loci extending from Xpter to Xq28 showed X chromosome heterozygosity and confirmed the paternal origin of one of the X chromosomes. Studies on sulfur-35 uptake in mixed fibroblast cultures showed cross-correction of [35S]-glycosaminoglycan accumulation between cells from the patient and normal cells or cells from a patient with Hurler disease; however, there was no cross-correction between cells from the patient and those from boys affected with classical Hunter disease. This represents only the second confirmed case of Hunter disease reported in a karyotypically normal girl.

Arylsulfatases↗
PubMed1990

Caprine beta-D-mannosidosis: characterization of a model lysosomal storage disorder.

Interest in using caprine beta-D-mannosidosis as a model to evaluate bone marrow transplantation in the treatment of human lysosomal storage disorders provided the stimulus for characterization of beta-D-mannosidase in selected goat tissues and induction of hemopoietic chimerism in the goat. Total beta-D-mannosidase activity was measured with the use of 4-methylumbelliferyl beta-D-mannopyranoside as substrate. Residual activity in mutant liver was 52% of control but no activity was detectable in mutant kidney or brain tissue. Normal adult goat liver contained two forms of beta-D-mannosidase, a nonlysosomal form (52%) with a broad pH range for optimum activity (4.5-8.0) and a lysosomal form (48%) with a pH optimum of 5.5. Residual enzyme in mutant liver consisted entirely of the nonlysosomal form. Normal adult thyroid, kidney and brain contained two major lysosomal isoenzymes with pIs 5.5 and 5.9 and traces of a minor isoenzyme with pI 5.0. Normal liver contained three isoenzymes with similar pIs; however, an isoenzyme with pI 5.0 predominated. In 60-day fetal liver lysosomal isoenzymes predominated and only trace amounts of nonlysosomal isoenzyme were detectable. Total hepatic beta-D-mannosidase activity increased towards adult levels during the last 90 days of gestation as a result of increasing nonlysosomal isoenzyme activity. Intraperitoneal injection of fetal liver cells into 60-day goat fetuses resulted in sustained hemopoietic chimerism in surviving kids without evidence of graft-versus-host-disease. These results suggest that transplantation of normal fetal liver cells into preimmunocompetent goat fetuses affected with beta-D-mannosidosis is feasible and may provide an alternative strategy for evaluation of postnatal bone marrow transplantation in the treatment of human lysosomal storage disorders.

Animals↗
PubMed1989

Induction of hemopoietic chimerism in the caprine fetus by intraperitoneal injection of fetal liver cells.

Intraperitoneal injection of allogeneic liver cells from 43-day-old male fetuses into normal 60-day female goat fetuses resulted in persistent hemopoietic chimerism in surviving recipients without clinical evidence of graft-versus-host disease. Transplantation of normal fetal liver cells into preimmunocompetent goat fetuses affected with beta-D-mannosidosis may provide an alternative strategy for evaluating hemopoietic stem cell transplantation in the treatment of human lysosomal storage diseases.

Animals↗
PubMed1989

Marked clinical difference between two sibs affected with juvenile metachromatic leukodystrophy.

In a child with enzymatically and histopathologically proven metachromatic leukodystrophy (MLD), the disease pursued a course typical of juvenile MLD characterized by neurological degeneration beginning at age 9 years and ending in death at age 18. A younger brother of the patient was found to have profound deficiency of arylsulfatase A in leukocytes and to excrete five- to 20-fold greater-than-normal amounts of sulfatide in the urine. He was completely free of symptoms attributable to MLD until age 16 when he developed acute cholecystitis caused by sulfatide accumulation in the gallbladder. Results of detailed neurological examination at age 21 years were normal; formal psychometric assessment showed a full-scale IQ of 105 (Wechsler). Studies on cultured skin fibroblasts from the brother showed defects in arylsulfatase A activity, measured with the use of synthetic and natural substrates, and in radiolabeled sulfatide turnover. Cellulose acetate gel electrophoresis of fibroblast extracts from the patient showed no detectable arylsulfatase A isozyme under conditions that clearly distinguished pseudo-arylsulfatase A deficiency from classical MLD. Biochemically, the patient was indistinguishable from patients with classical MLD; on the other hand, his clinical course is dramatically more benign than that of his sister who was affected with severe MLD.

Adolescent↗
PubMed1989

Tay-Sachs disease carrier screening: follow-up of a case-finding approach.

In order to determine the status of Tay-Sachs disease carrier identification in Toronto, Canada, since a change was made in 1978 from testing in the context of large-scale community clinics (up to 1,200 individuals tested in 1 day) to a case-finding approach to screening, a sample of area Jews was surveyed by questionnaire. The results indicated that a trend has developed for individuals at risk to delay testing until pregnancy when carrier detection is technically more difficult and the time available for retesting and organizing prenatal diagnosis is limited. If the trend continues, the full potential of chorionic villus sampling (CVS) for the prenatal diagnosis of the disease will be difficult to realize.

Adolescent↗
PubMed1987

The excitation of the far ultraviolet electroglow emissions on Uranus, Saturn, and Jupiter.

We propose that the diffuse FUV emissions of H and H2 in excess of photoelectron excitation observed from the sunlit atmospheres of Uranus, Saturn, and Jupiter are produced by electric field acceleration of photoelectrons and ions locally in the upper atmospheres. This in situ acceleration is required to satisfy the many observational constraints on the altitude distribution, exciting particle energy, and total input energy requirements of the electroglow mechanism. We further suggest that a primary mechanism leading to this acceleration is an ionospheric dynamo, which is created in the same manner as the Earth's dynamo. The calculated altitude of charge separation by the neutral wind drag on ions across magnetic field lines is consistent with the observed peaks in electroglow emissions from the Voyager ultraviolet spectrometer limb scan data on both Saturn (near the homopause) and Uranus (just above the homopause). This dynamo action therefore appears to initiate the acceleration process, which must have the form of field-aligned potentials to accelerate the magnetized electrons. We propose that these field-aligned potentials are due to anomalous resistivity, which results from sufficiently high field-aligned currents in the ionosphere to generate plasma instabilities and therefore runaway electrons and ions above some critical lower initial energy. There are multiple candidate processes for inducing these currents, including polarization in the equivalent F regions and inner magnetospheric convection, and each of these processes should exhibit latitudinal structure. The acceleration of low-energy electrons in an H2 atmosphere preferentially results in FUV radiation and further ionization, whereas electron acceleration in a nitrogen/oxygen atmosphere such as the Earth's is dominated by elastic scattering and thus results in electric currents. Individual electron and proton collisions with H2 molecules will result in excitation, ionization, and heating, so that considerable enhancement of the ionospheric density and heating of the upper atmosphere will accompany the FUV emission.

Electrons↗
PubMed1987

Properties and prenatal ontogeny of beta-D-mannosidase in selected goat tissues.

beta-D-Mannosidase activity in selected normal adult, neonatal and foetal goat tissues and in tissues from animals affected with caprine beta-mannosidosis was examined with the use of 4-methylumbelliferyl beta-D-mannopyranoside as substrate. The enzyme in normal adult thyroid, kidney and brain exhibited a sharp unimodal pH optimum at pH 5.0, whereas the enzyme in both normal adult and mutant liver exhibited broad pH ranges of activity (pH 4.5-8.0). No residual enzyme was detectable in mutant kidney or brain; in contrast, residual activity in mutant liver was 52% of that in a neonatal control. Concanavalin A-Sepharose 4B (Con A-Sepharose) fractionation of normal adult liver beta-D-mannosidase resolved the enzyme into an unbound (non-lysosomal) from (52%) with a broad pH range of activity (pH 4.5-8.0) and a bound (lysosomal) form (48%) with a sharp pH optimum of 5.5. The enzyme in mutant liver consisted entirely of the unbound (non-lysosomal) form. Beta-D-Mannosidase activity in normal adult thyroid, kidney and brain was resolved by chromatofocusing into two major isoenzymes, with pI 5.5 and 5.9, and traces of a minor isoenzyme, with pI 5.0. In normal adult liver the enzyme was also resolved into three isoenzymes with similar pI values; however, that with pI 5.0 predominated. The predominant form of the enzyme in 60-day-foetal liver was bound by Con A, exhibited a unimodal pH optimum (5.0) and was resolved into two isoenzymes, with pI 5.4 and 5.8; only traces of an isoenzyme with pI 5.0 were detectable. Total hepatic beta-D-mannosidase activity increased progressively towards adult values during the last 90 days of gestation as a result of increasing non-lysosomal isoenzyme activity (pI 5.0). Lysosomal beta-D-mannosidase was shown to occur in all normal goat tissues studied as multiple isoenzymes, which are genetically and developmentally distinct from the non-lysosomal isoenzyme occurring predominantly, if not exclusively, in liver.

Animals↗