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Biomedical subjects

M J Mahoney

Publications and source records attributed to M J Mahoney.

At least 163 records · Page 9Linked to original sources
PubMed1976

Organic acidemias.

Inherited organic acidemias are a group of metabolic disorders currently being described and investigated as gas-liquid chromatography is applied to unexplained diseases of infancy and childhood. Common clinical presentations include attacks of ketoacidosis, unexplained metabolic acidosis, failure of normal development, seizures, and other neurologic abnormalities. Hyperglycinemia, hyperammonemia, and hypoglycemia are other laboratory findings frequently present. Diagnosis depends on examination of urine, and sometimes blood, by gas-liquid chromatography to measure concentrations of organic acids and organic acid derivatives. Prognosis in many cases is excellent if diagnosis is made promptly and the metabolic acidosis can be reversed. Recovery from neurologic deficits has frequently been seen. Long-term therapy is generally dependent on restricting precursors of the toxic organic acid which builds up as a consequence of the enzyme deficiency. If there is some enzyme activity retained or if alternate metabolic pathways exist, success with therapy is likely.

Acidosis, Renal Tubular↗
PubMed1975

Prenatal therapy of a patient with vitamin-B12-responsive methylmalonic acidemia.

Methylmalonic acidemia due to deficient synthesis of 5'-deoxyadenosylcobalamin was discovered in a mid-term fetus by culture of amniotic-fluid cells. Elevated concentrations of methylmalonic acid were also found in amniotic fluid and maternal urine. Treatment during the last nine weeks of gestation with large doses of vitamin B12 given to the mother reversed the increasing maternal excretion of methylmalonic acid, which was 23 mug per milligram of creatinine at 31 weeks' gestation. Just before delivery, the mother was excreting 5 mug, two to three times normal. At birth the methylmalonic acid content of the baby's urine (67 mug per milligram of creatinine) and serum (2.0 mug per milliliter) was only moderately elevated, and serum vitamin B12 concentration was very high. Acid levels rose in serum and urine in response to oral protein loading, but subsided after vitamin B12 administration. The infant is developing normally on a restricted protein diet alone at present. Prenatal therapy of methylmalonic acidemia is possible with large amount of vitamin B12 administered to the mother.

Amino Acid Metabolism, Inborn Errors↗
PubMed1975

Fetal blood drawing.

A small sample of fetal blood suitable for studies of haemoglobin synthesis was obtained from a placental vessel under endoscopic visualisation in 23 of 26 patients in whom the procedure was attempted prior to second-trimester abortion. Fetal blood loss, calculated in 23 cases, was between 0-2 ml. and 2-5 ml., and fetal blood-volume depletion varied from 0-5% to 15%. No short-term ill-effects were demonstrated in mother or fetus in any of 16 patients in whom the injection of aborti-facient was postponed for between 16 and 24 hours after the procedure.

Abortion, Therapeutic↗
PubMed1975

Methylmalonicacidemia: biochemical heterogeneity in defects of 5'-deoxyadenosylcobalamin synthesis.

We measured the synthesis of 5'-deoxyadenosylcobalamin (AdoCbl) in fibroblast extracts from patients with inherited methylmalonicacidemia due to deficient activity of the cobalamin-dependent holoenzyme, methylmalonyl-CoA mutase (EC 5.4.99.2). Previous studies with intact fibroblasts from patients whose holoenzyme deficiency was secondary to abnormal cobalamin metabolism had defined two phenotypes, one in which whole cells failed to accumulate AdoCbl and a second in which they failed to accumulate both AdoCbl and the second cobalamin coenzyme, methylcobalamin. With a broken cell assay of AdoCbl synthesis in cell extracts and the cell lines are named cbl A mutants; the other class shows severe deficiency of AdoCbl synthesis and the cell lines are named cbl B mutants. We define cbl C mutants as those in which both AdoCbl and methylcobalamin fail to accumulate in intact cells. The assay for AdoCbl synthesis is thought to measure two enzymatic activities, cob(II)alamin reductase (EC 1.6.99.9) and cob(I)alamin adenosyltransferase (EC 2.5.1.17). Subcellular fractionation studies place this combined activity in mitochondria.

Amino Acid Metabolism, Inborn Errors↗
PubMed1975

Genetic complementation in heterokaryons of human fibroblasts defective in cobalamin metabolism.

Inherited methylmalonicacidemia due to deficiency of methylmalonyl-CoA mutase (methylmalonyl-CoA CoA-carbonylmutase; EC 5.4.99.2) activity results from at least three classes of biochemically distinct defects affecting cobalamin (Cbl: vitamin B12) metabolism (cbl A, cbl B, and cbl C mutants) and a fourth class producing a defective mutase apoenzyme. We have obtained genetic evidence in support of this biochemical heterogeneity, using heterokaryons prepared by Sendai-virus-mediated cell fusion. Nine fibroblast lines from patients with defective Cbl metabolism (4 cbl A, 3 cbl B, and 2 cbl C), two from patients with defective mutase apoenzyme, and two from controls were fused in pairwise combinations and tested for functional mutase holoenzyme using a radioautographic procedure which detects [14C]propionate incorporation into trichloroacetic-acid-precipitable material in fibroblast monolayers in situ. Each of the mutants incorporates negligible radioactivity compared to control cells. Activity is also negligible when different mutants are mixed without virus or when homokaryons are produced by self-fusion. Heterokaryons produced by fusing members of each of the four mutant classes with representatives of any other class recover the ability to incorporate [14C]propionate to levels comparable to those of control cells. However, heterokaryons produced between members of the same class fail to complement in all cases. We conclude that the mutants with defective Cbl metabolism (cbl A, cbl B, cbl C) comprise three complementation groups, that a fourth group corresponds to mutase apoenzyme deficiency, and that all four classes of mutations are recessively inherited.

Amino Acid Metabolism, Inborn Errors↗
PubMed1975

Prenatal diagnosis of methylmalonic aciduria.

Prenatal diagnosis using amniocentesis was sought in two midtrimester pregnancies, each at risk for a different type of inherited methylmalonic aciduria. In one pregnancy a normal fetus was diagnosed from studies of cultured amniotic fluid cells and the diagnosis confirmed after the baby was born. In the second pregnancy a fetus with a methylmalonyl-CoA mutase apo enzyme defect was found. The diagnosis was based on cultured cell studies and supported by an elevation of methylmalonate in both amniotic fluid and maternal urine. Confirmatory studies were obtained using cultured cells from the aborted fetus. At the present time, assays of cultured amniotic fluid cells are imperative for firm diagnosis. With more experience, quantities of amniotic fluid and maternal urine methylmalonate may prove sufficient if differentiation among the various types of methylmalonic aciduria is not required.

Abortion, Legal↗
PubMed1975

Heme synthetase deficiency in human protoporphyria. Demonstration of the defect in liver and cultured skin fibroblasts.

The final step in heme biosynthesis is chelation of porphyrin with Fe++ catalyzed by the mitochondrial enzyme heme synthetase. We have employed a sensitive radiochemical assay for this enzyme, using 59Fe and deuteroporphyrin or protoporphyrin as substrates. In this method iron is maintained in the ferrous state, oxygen is excluded from the incubation system, and labeled heme product is extracted into ethyl acetate. This assay has been used to measure the activity of heme synthetase in homogenates of liver, obtained by needle biopsy, and in sonicates of human skin fibroblasts, cultured in vitro. In addition, activity of the first enzyme of the heme synthetic pathway, delta-aminolevulinic acid synthetase, has been measured in fibroblast lysates. Lysates of fibroblasts from eight patients with protoporphyria had activities of delta-aminolevulinic acid synthetase which did not differ significantly from those of eight normal fibroblast lines, whereas activity of heme synthetase, with either deuteroporphyrin or protoporphyrin as substrate, was markedly decreased in sonicates of skin fibroblasts from these patients, the mean being 8% of control with deuteroporphyrin and 14% with protoporphyrin as substrate. In homogenates of liver from five patients with protoporphyria, activity of heme synthetase was also significantly less than that found in six patients without prophyria, the mean being 13% of control with protoporphyrin as substrate. These results provide evidence that decreased activity of heme synthetase is the basic defect in the heme synthetic pathway in protoporphyria. This deficiency is probably responsible for protoporphyrin accumulation and hence the biochemical and clinical features observed in protoporphyria.

5-Aminolevulinate Synthetase↗