Louis Dallaire

Fluorometric assay of neuraminidase with a sodium (4-methylumbelliferyl-α-d-N-acetylneuraminate) substrate

Abstract This report describes the preparation of a sodium (4-methylumbelliferyl-α- d -N-acetylneuraminate) substrate and its use in a sensitive fluorometric assay of neuraminidase (EC 3.2.1.18) from Vibrio cholerae, cultured fibroblasts, and human leucocytes. V. cholerae neuraminidase showed maximum activity at pH 4.6 and an apparent Km of 1.5 m m and was activated by CaCl2 and inhibited by ethylenediaminetetraacetate, NaCl, and N-acetylneuraminic acid. The inhibition by N-acetylneuraminic acid was competitive (Ki = 6.1 m m ). Cultured fibroblast and leucocyte neuraminidases showed maximum activity between pH 4.2 and 4.4 and apparent Km values of 0.13 and 0.22 m m , respectively. Neuraminidase activity was considerably reduced in cultured fibroblasts of patients with mucolipidosis types I, II, and III.

Neurologic Crises in Hereditary Tyrosinemia

Hereditary tyrosinemia results from an inborn error in the final step of tyrosine metabolism. The disease is known to cause acute and chronic liver failure, renal Fanconis syndrome, and hepatocellular carcinoma. Neurologic manifestations have been reported but not emphasized as a common problem. In this paper, we describe neurologic crises that occurred among children identified as having tyrosinemia on neonatal screening since 1970. Of the 48 children with tyrosinemia, 20 (42 percent) had neurologic crises that began at a mean age of one year and led to 104 hospital admissions. These abrupt episodes of peripheral neuropathy were characterized by severe pain with extensor hypertonia (in 75 percent), vomiting or paralytic ileus (69 percent), muscle weakness (29 percent), and self-mutilation (8 percent). Eight children required mechanical ventilation because of paralysis, and 14 of the 20 children have died. Between crises, most survivors regained normal function. We found no reliable biochemical marker for the crises (those we evaluated included blood levels of tyrosine, succinylacetone, and hepatic aminotransferases). Urinary excretion of delta-aminolevulinic acid, a neurotoxic intermediate of porphyrin biosynthesis, was elevated during crises but also during the asymptomatic periods. Electrophysiologic studies in seven patients and neuromuscular biopsies in three patients showed axonal degeneration and secondary demyelination. We conclude that episodes of acute, severe peripheral neuropathy are common in hereditary tyrosinemia and resemble the crises of the neuropathic porphyrias.

Clinical heterogeneity in cobalamin C variant of combined homocystinuria and methylmalonic aciduria

We describe two patients with methylmalonic aciduria and homocystinuria (Cbl C). The disorder was not diagnosed in patient 1 until 4 1/2 years of age; he had a history of fatigue, anorexia, delirium, and spasticity. Moderate megaloblastic bone marrow changes were observed, and there was hyperreflexia of the lower limbs. His condition improved clinically with hydroxycobalamin therapy. Patient 2 was hospitalized at 6 weeks of age because of lethargy and poor feeding. She was found to have macrocytosis. Despite an initial good clinical response to hydroxycobalamin, she developed a striking pigmentary retinopathy. Methylmalonic aciduria persisted in both patients, and homocystinuria persisted in patient 1 despite therapy. The diagnosis of Cbl C disease has been confirmed in both patients by biochemical studies of cultured fibroblasts, including complementation studies. The differences in age of onset and clinical findings together with the similar biochemical findings in these two patients demonstrate the heterogeneity of phenotypic expression in patients with apparently identical abnormalities of vitamin B12 metabolism.

Prenatal detection of intestinal obstruction: deficient amniotic fluid disaccharidases in affected fetuses

Amniotic fluid samples from four fetuses with intestinal obstructions (two anal imperfora‐tions, one duodenal atresia and one multiple intestinal atresia) were deficient in disaccha‐ridase activities. These results indicate that disaccharidase assay in amniotic fluid can be used as a rapid and simple test for the prenatal detection of fetal intestinal obstructions.

Monozygotic twins with 45,X/46,XY mosaicism discordant for phenotypic sex

We report on two sets of monozygotic twins (MZTs) discordant for phenotypic sex ascertained at birth when the female twin was noted to have signs of the Ullrich-Turner syndrome. Cytogenetic investigations on the female of the first pair showed 45,X/46,XY mosaicism in lymphocytes but fibroblasts grown from two skin biopsies at separate sites and from gonadal tissue showed only 45,X cells. The male showed mosaicism in both blood lymphocytes and skin fibroblasts. In the second family, both twins also showed mosaicism in lymphocytes. The female had a 45,X karyotype in fibroblasts from skin and gonadal tissue, but in contrast to the first family, the male twin had a normal male karyotype in fibroblasts from skin biopsy and from connective tissue adjacent to the vas deferens. Discordant phenotypic sex in monozygotic twins is rare. As in our cases, the nine previously reported sets of MZTs all had mosaicism for sex chromosome abnormalities. A mitotic error leading to the loss of a Y chromosome prior to, accompanying, or following the twinning process would account for the reported combinations of karyotypes.

Dicarboxylic aminoaciduria: an inborn error of amino acid conservation.

A 38-month-old apparently healthy male has been followed for three years because of a massive glutamic and aspartic aminoaciduria detected shortly after birth in a neonatal screening program. Amino acid clearance studies revealed the presence of renal wastage of dicarboxylic amino acids. Intestinal transport and in vitro oxidation of dicarboxylic amino acids were found to be intact. Clinical and metabolic data obtained on a previously described patient and the present case suggest that some patients with dicarboxylic aminoaciduria might have a selective renal conservation defect without clinical abnormalities, whereas others might demonstrate an additional defect in intestinal transport associated with fasting hypoglycemia.

The syndrome of retardation with urogenital and skeletal anomalies in siblings

2. Pinsky, L., and DiGeorge, A. M.: A familial syndrome of facial and skeletal anomalies associated with genital abnormality in the male and normal genitals in the female, J. PEDIAT. 66: 1049, 1965. 3. Gibson, R.: A case of the Smith-Lemli-Opitz syndrome of multiple congenital anomalies in association with dysplasia epiphysialis punctata, Canad. M. A. J. 92: 574, 1965. 4. Meskln, L. H., Gorlin, R. J., and Isaacson, R. J.: Abnormal morphology of the soft palate. I. The prevalence of cleft uvula, Cleft Palate J. 1: 342, 1964. 5. Lowry, R. B., Miller, J. R., and Maclean, J. R.: Personal communication. 6. Uchida, I. A., Miller, J. R., Soltan, H., et al.: Personal communication. 7. Walker, N. F.: The use of dermal configurations in the diagnosis of mongolism, J. PEDlAr. 50: 19, 1957.

Frequencies of chromosomal abnormalities at amniocentesis: Over 20 years of cytogenetic analyses in one laboratory

Prenatal diagnosis of chromosomal disorders has been performed for more than 20 years, mainly for advanced maternal age. Chromosomal abnormality rates derived from second trimester amniocentesis have mainly come from a collection of small-scale studies from North America and Western Europe. Accurate risk estimates for chromosomal abnormalities are important tools for the physician or obstetrician who would need to make referrals to a prenatal genetic center. This paper presents amniocentesis rates of clinically significant cytogenetic abnormalities for various indications, including advanced maternal age, previous chromosomal abnormality, parental structural rearrangement and a family history of aneuploidy as defined in the text. These data come from a Canadian prenatal diagnosis laboratory with more than 20 years experience in second trimester cytogenetic analysis. They show that the overall frequency of chromosomal abnormalities for advanced maternal age (> or = 35 years) is 1.79%. In this group, 21% of all abnormalities are structural rearrangements (including markers) and less than half of all abnormalities are trisomy 21. The advanced maternal age specific risk of aneuploidies at second trimester is 1.24%. Recurrence risk for aneuploidy after a previous one is 1.29%. However, it is much higher (4.84%) for women of > or = 35 years. When a parents brother, sister, nephew or niece is affected, the risk of occurrence of aneuploidies (0.24%) is not elevated. When there is a balanced translocation in one of the parents, the overall risk is 10.2% for unbalanced translocations and 37.3% for balanced translocations.

Developmental patterns of intestinal disaccharidases in human amniotic fluid

A close relationship exists between relative disaccharidase activities (maltase, sucrase, trehalase, palatinase, turanase, lactase, and cellobiase) in amniotic fluid and corresponding jejunal mucosa of five human fetuses (16 to 21 weeks of gestation) suggesting that these intestinal enzymes pass into amniotic fluid. Serial determination of disaccharidase activities in amniotic fluid samples collected between 10 and 42 weeks of gestation showed maximum mean activities at 14 to 17 weeks of gestation and a rapid drop to less than 12 per cent maximum values at about 22 weeks. This drop is probably caused by combined effects of decreased extrusion rate of intestinal disaccharidases and increased reabsorption of the enzymes in swallowed amniotic fluid with fetal development.

Club foot, an adverse outcome of early amniocentesis: disruption or deformation?

An association between the occurrence of club foot and early amniocentesis has been reported. The largest of these randomised studies was the Canadian Early and Mid-Trimester Amniocentesis Trial. Data describing the neonatal outcome, focusing on this association, are presented. Possible mechanisms for the association and the implications for the development of club foot are discussed.