Five mutations at the PAH locus account for almost 90% of PKU mutations in French-Canadians from eastern Quebec.
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Base Sequence↗
Biomedical subjects
C Laberge
Publications and source records attributed to C Laberge.
DNA sampling and informed consent.
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California↗
HIV infection among Quebec women giving birth to live infants.
This is the first anonymous unlinked seroprevalence study in Canada to use serum samples from newborns to determine the seroprevalence rate of human immunodeficiency virus (HIV) infection among childbearing women. Of the 68,808 samples tested 42 were confirmed as positive, for an overall crude seroprevalence rate of 6.1 per 10,000 live births (95% confidence interval [CI] 4.4 to 8.3), or 1 woman in 1638. Women who lived on Montreal island had an overall rate of 17.9 per 10,000 live births (95% CI 12.2 to 25.4), or 1 woman in 559. We observed a significant association between revenue index and seroprevalence; the rates were as high as 46.4 per 10,000 live births (95% CI 18.7 to 95.3), or 1 woman in 216, for Montreal island postal code areas with revenue indexes 20% or more below the provincial median. Extrapolation of the data suggested that 56 women with HIV infection gave birth to a live infant during 1989 in Quebec. Even though attempts to generalize the data from childbearing women to women of childbearing age have an inherent conservative bias, the results of our study suggest that 988 women (95% CI 713 to 1336) aged 15 to 44 years in Quebec had HIV infection in 1989. The actual number is likely substantially higher. The need for well-designed, creative interventions to prevent further HIV transmission to women is evident. Planning for the provision of medical and psychosocial services sensitive to specific needs of women who are already infected should start immediately.
Adolescent↗
Tight linkage of creatine kinase (CKMM) to myotonic dystrophy on chromosome 19.
The myotonic dystrophy (DM) gene is localized to the proximal long arm of chromosome 19. There have been reports of tight linkage to a number of chromosome 19 markers, including APOC2 and creatine kinase muscle type (CKMM), but they did not establish orientation of the 2 markers to DM. We screened several large multi-generational DM families for linkage to a series of chromosome 19 markers including CKMM. CKMM is tightly linked to DM in these data with z(theta) = 28.41; theta = 0.01. Analysis of cross-over data indicates CKMM is on the same side and closer to DM than APOC2. Thus, CKMM is a useful probe for carrier detection studies in presymptomatic individuals as well as for prenatal diagnosis.
Chromosome Mapping↗
Recurrent mutation, gene conversion, or recombination at the human phenylalanine hydroxylase locus: evidence in French-Canadians and a catalog of mutations.
The codon 408 mutation (CGG----TGG, Arg----Trp) in exon 12 of the phenylalanine hydroxylase (PAH) gene occurs on haplotype 1 in French-Canadians; elsewhere this mutation (R408W) occurs on haplotype 2. A CpG dinucleotide is involved. The finding is compatible with a recurrent mutation, gene conversion, or a single recombination between haplotypes 2 and 1. A tabulation of 20 known mutations at the PAH locus reveals three instances of putative recurrent mutation.
Alleles↗
Different molecular basis for fumarylacetoacetate hydrolase deficiency in the two clinical forms of hereditary tyrosinemia (type I).
Hereditary tyrosinemia is characterized by a deficiency of the enzyme fumarylacetoacetate hydrolase (FAH; E.C.3.7.1.2), the last enzyme in the catabolic pathway of tyrosine. FAH was purified from rat and human liver and was used to immunize rabbits. Specific antibodies were used to probe protein extracts of livers and other tissues of normal and tyrosinemic patients. No immunoreactive FAH band was observed on immunoblots of liver, kidneys, and lymphocytes from patients presenting with the acute form of hereditary tyrosinemia. Patients with the chronic form had immunoreactive FAH at a level approximately 20% of normal liver values, which was correlated with the measured enzymatic activity. Immunoblot analysis of aborted fetal tissues revealed normal FAH immunoreactivity in normal liver and kidneys. No FAH immunoreactivity was found in liver and kidneys of tyrosinemic fetuses. The presence of FAH immunoreactivity in normal fetal tissues suggests that deficient FAH activity in tyrosinemia is not simply related to a developmentally regulated expression of the enzyme. By this immunoblot assay, FAH was detected in most human tissues, with maximal immunoreactivity in liver and kidneys and with only trace amounts in chorionic villi and cultured amniocytes. These data confirm that the primary defect in the acute form of hereditary tyrosinemia is an absence of FAH. Moreover, these data suggest that both clinical forms of the disease have a different molecular basis.
Amino Acid Metabolism, Inborn Errors↗
Fumarylacetoacetase measurement as a mass-screening procedure for hereditary tyrosinemia type I.
Fluorometric quantitative tyrosine determination on dried-blood spots is the primary neonatal screening test used for tyrosinemia type I (HT) in the province of Quebec. Succinylacetone determination on these same spots is used as the complementary test when the tyrosine level is higher than a given threshold. This procedure has proved to be less discriminant over the past few years because of changes in newborn feeding and because of early discharge of newborns from the nursery. We have developed an enzyme-linked immunosorbent assay (ELISA) to measure the deficient enzyme in HT in dried-blood spots. Fumarylacetoacetase (FAH) (E.C.3.7.1.2) was measured retrospectively by an ELISA on 25 dried-blood samples from proven patients with HT and prospectively in 72,000 specimens received in the neonatal screening program. In this pilot project, FAH was measured first, and, if necessary, succinylacetone was determined as the complementary test. All 25 samples from proven patients and specimens from four other patients detected in the pilot study have shown almost complete absence of FAH in dried-blood samples. At a cutoff level of 12.5% of normal adult blood spotted on the same type of paper, only 30 other cases disclosed FAH levels low enough to warrant succinylacetone measurement but had no detectable succinylacetone. The false-positive rate is thus 1:2,400 with this primary ELISA. However, blood transfusion in newborns prior to blood collection on filter paper may yield false-negative tests, since FAH is present in erythrocytes of normal donors.(ABSTRACT TRUNCATED AT 250 WORDS)
Amino Acid Metabolism, Inborn Errors↗
Oral loading of homogentisic acid in controls and in obligate heterozygotes for hereditary tyrosinemia type I.
Homogentisic acid (HGA) (50 mg/kg) was given orally to 22 obligate heterozygotes for hereditary tyrosinemia type 1 (HT) and to 11 controls. After 1 h the mean +/- standard error (SE) plasma level of HGA was 30.42 +/- 1.41 micrograms/ml in carriers and 19.29 +/- 1.62 in controls. Mean +/- SE fasting delta-amino-levulinate dehydratase (delta-ALD) was 40.05 +/- 1.79 m microM/min/g Hb in carriers, much lower than the 60.81 +/- 5.11 found in controls. After 3 h this difference in levels of delta-ALD remained, with mean +/- SE values of 25.70 +/- 2.89 m microM/min/g Hb in carriers, compared with 48.83 +/- 5.37 in controls. Three-hour mean +/- SE excretion of fumarylacetone "equivalent" [FAc] in urine in carriers, 51.597 +/- 5.580 micrograms/mg/creatinine, was significantly higher than the 27.941 +/- 5.916 in controls. Three-hour excretion of succinylacetone "equivalent" [SAc] was also significantly higher in the urine of carriers. FAc in 3-h urine was identified by thin-layer chromatography and confirmed by gas chromatography/mass spectrometry. Multivariate stepwise discriminant analysis showed that the inclusion order of significant variables was as follows: HGA levels at 1 hr, fasting level of delta-ALD, residual level of HGA at 3 h, and 3-h excretion of [FAc]. Non-significant variables were HGA tolerance, levels of delta-ALD at 3 h, sex, and 3-h excretion of [SAc].(ABSTRACT TRUNCATED AT 250 WORDS)
Amino Acid Metabolism, Inborn Errors↗
HIV-2 detected in newborn study--Quebec.
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Enzyme-Linked Immunosorbent Assay↗
DNA sampling and informed consent.
Standard consent forms for blood and tissue sampling are inadequate for DNA sampling. However, creating new and separate forms for each type of activity associated with DNA analysis (banking, linkage analysis and genetic diagnosis) tends to dissociate the participant from what is essentially a medical continuum. Furthermore, DNA sampling involves the sharing of samples and data among centres. To ensure patient control throughout this multifaceted process, we have developed an integrated approach to obtaining consent for DNA sampling at each level of participation. Movement from one level to another is reflected in the choices offered to participants. This inclusive approach is based on the underlying principle of informed consent, namely the respect for individuality, confidentiality and freedom of choice. This approach should help practitioners of medical genetics recognize the medical context of DNA sampling.
Canada↗
Prospective ascertainment of complete and partial serum biotinidase deficiency in the newborn.
We screened 163,000 newborn filter-paper blood samples for serum biotinidase deficiency (McKusick 25326) and found 15 probands: three had complete deficiency (incidence 18.4 cases per million live births, 95% confidence interval 4-54 cases per million); the others had partial deficiency. The positive predictive value of the test for either form of biotinidase deficiency was 9.86%. We found seasonal variation in biotinidase activity in filter-paper blood samples. The cost per test was Can.$0.27 (1987 dollar value) and per case of complete deficiency ascertained, $15,500. Family studies indicated that complete serum biotinidase deficiency is a homozygous phenotype and partial deficiency is the heterozygous form. Homozygous cases were treated with biotin and have shown no clinical manifestations (55 patient-months of observation). None of the heterozygotes (n = 42, age 3 months - 62 years) has clinical manifestations. The number of heterozygotes found by screening was much less than predicted probably because the screening test detects mainly the samples with very low (outlier) biotinidase activity. The variant allele(s) for biotinidase deficiency was more common in French Canadians than in other ethnic groups in Quebec; there was no evidence of regional clustering or founder effect.
Amidohydrolases↗
Myotonic dystrophy in Quebec: geographical distribution and concept of genetic homogeneity.
The geographical distribution relative to place of residence of patients with myotonic dystrophy (MD) and admitted to a Quebec hospital during a five year period (1980-1984) is presented and discussed. The sample consists of 72 males and 68 females of varying ages over 10 years. Analysis of the data shows a North Shore distribution of patients in a cline from Saguenay-Lac-St-Jean, through Québec City and to Montréal. However, a low prevalence is apparent on the South Shore, east of Québec City, for which an historical and genealogical explanation are discussed. This geographic distribution favours the hypothesis of genetic homogeneity for the MD gene in the Québec population. A stronger second argument comes from genealogical studies of 10 families sampled from the Chicoutimi Muscular Dystrophy Clinic. Genealogical paths traced to ancestors who founded Charlevoix for these 10 families go back to a cluster of 25 founders, one of whom must have been the carrier of the MD gene. The probative third argument for genetic homogeneity comes from the allelic distribution of the apolipoprotein E (ApoE) gene in the Québec City, Saguenay and in families with MD. The ApoE locus is on chromosome 19 and closely linked to MD. In MD-affected individuals there is a linkage disequilibrium for the epsilon 4 allele while non-MD members of these families show allelic frequencies not differing significantly from the control population.(ABSTRACT TRUNCATED AT 250 WORDS)
Adolescent↗
Hypertriglyceridemia and lower LDL cholesterol concentration in relation to apolipoprotein E phenotypes in myotonic dystrophy.
Plasma lipid, lipoprotein levels and apolipoprotein apo E phenotypes were determined in 70 patients with myotonic dystrophy (MyD) and 81 controls. Marked differences were noticed in the apo E phenotype frequencies between the two groups. Plasma triglycerides and VLDL cholesterol were higher in MyD than controls, but only the latter was related to differences in the apo E phenotypes between two groups. Accordingly, the ratio of VLDL cholesterol/plasma triglycerides was increased significantly in MyD, suggesting accumulation of intermediary density particles due to lower affinity of E2 containing lipoproteins for lipoprotein cell receptors. The LDL cholesterol concentration was lower in MyD than controls and was related to differences in the apo E phenotype frequencies between the two groups. These results indicate increased removal of LDL particles in the apo E2 phenotypes, perhaps due to upregulation of LDL (B, E) receptor activity. Plasma cholesterol and HDL cholesterol concentrations were similar in both groups. Another feature of the study was lower levels of plasma cholesterol, triglycerides, VLDL and LDL cholesterol in the homozygous E4:E4 phenotype. These results suggest increased clearance rate of both VLDL and LDL particles and support the concept that apo E4-containing lipoproteins have higher in vivo affinity for ape E and/or B, E receptors.
Adolescent↗
Myotonic dystrophy: linkage with apolipoprotein E and estimation of the gene carrier status with genetic markers.
The genes for myotonic dystrophy (MD) and for apolipoprotein E (ApoE) belong to a chromosome 19 synthenic group of markers. A familial linkage analysis between MD and ApoE was performed using the J Ott LIPED program (IBM PC/XT, April 1984) to estimate the genetic distance between these 2 genes. Of a total of 136 individuals in 11 MD families, 81 were confirmed to be affected by the disease and 41 were asymptomatic. ApoE phenotypes were determined in 115 of these 122 individuals. No recombinant was observed out of 74 meioses which were informatives for both MD and the ApoE isoproteins. A global maximal lod score Z of 19.00 was obtained at the recombination fraction theta = 0. The upper theta value at the confidence interval corresponding to the peak lod score (Z max) - 1 was 0.03. This suggests that the loci for MD and ApoE are at a distance of 0 to 0.03 Morgan. Since ApoE and apolipoprotein C2 (ApoC2) have been shown by others to be about 40 kb apart, our data are therefore consistent with the distance estimate of 0.02 Morgan reported between MD and ApoC2. The D19S19 (LDR152) polymorphic DNA sequence is also tightly linked to MD on chromosome 19. The segregation of ApoE isoproteins and of ApoC2 and D19S19 DNA polymorphism was utilized for evaluating the probability for individuals at risk of inheriting the disease gene in MD families. Data are presented on 3 families to emphasize the usefulness of genetic markers to estimate the MD gene carrier status of asymptomatic individuals and also for those presenting a partial syndrome. The limitations of such approach are also discussed.
Apolipoproteins E↗
Novel PKU mutation on haplotype 2 in French-Canadians.
We analyzed DNA from nine French-Canadian probands from eastern Quebec province; all had hyperphenylalaninemia (phenylketonuria [PKU] or non-PKU forms) caused by mutations at the phenylalanine hydroxylase locus. Analysis of RFLP haplotypes and mutations revealed a novel mutation, an A-to-G transition (met----val) in codon 1 (the translation-initiation codon). It occurred on 5 of the 18 mutant chromosomes and was associated each time with haplotype 2. A proband homozygous for this mutation had the PKU phenotype. In other probands, the codon 1 mutation was inherited once with the splice junction mutation in exon 12 (on haplotype 3), conferring PKU, and was inherited twice with a mutation on haplotype 1, conferring PKU in one proband and non-PKU hyperphenylalaninemia in the other. The other five probands carried mutations, conferring PKU, on the following haplotype combinations: 1/3 (twice), 1/9, 3/4, and 1/1. The mutations on haplotypes 1, 4, and 9 are not yet characterized. This preliminary study reveals a novel PKU mutation and considerable genetic heterogeneity at the phenylalanine hydroxylase locus in French-Canadians.
Exons↗
A study on the inheritance of thyroxine-binding globulin (TBG) deficiency from data obtained in 13 families detected by a neonatal screening program.
Thirteen families with thyroxine-binding globulin deficiency, detected through probands screened by the Quebec Network of Genetic Medicine, were investigated. These families were divided into two groups, depending on whether hemizygous males had low or undetectable serum thyroxine-binding globulin levels. Five families belonged to the low (hypo-TBGnemic) type while the remaining 8 families belonged to the absent (a-TBGnemic) type. On pedigree analysis, 10 families satisfied the requirements for an X-linked co-dominant mode of transmission. Three families, 2 a-TBGnemic and 1 hypo-TBGnemic, did not satisfy these requirements and three hypotheses had to be put forward to explain these situations: an autosomal recessive mode of transmission, a spontaneous mutation, or an extreme lyonisation of the defective X. Since the thyroxine-binding globulin gene has been localized to the X-chromosome, the two latter explanations appear to be the most plausible.
Female↗
Feasibility of chemical screening of urine for neuroblastoma case finding in infancy in Quebec.
Neuroblastoma is the most common fatal solid tumour of childhood. Studies in Japan suggest that screening urine at 6 months for tumour-derived metabolites greatly improves early case finding and prognosis. The incidence rate of neuroblastoma in Quebec is at least 1 per 10,330 live births, higher than that of all other diseases responding to early treatment except congenital hypothyroidism screened for in the Quebec Network of Genetic Medicine. The feasibility of chemical screening of urine for elevated levels of homovanillic acid and vanillylmandelic acid in Quebec was assessed. The cost-effectiveness of screening 100,000 infants per year would be high (cost-benefit ratio 2.4), with a net saving of about $280,000 and eight lives per year. The estimated cost of adding neuroblastoma screening to the existing urine metabolite screening program is $70,700. The apparent sensitivity of the proposed test is 0.859 and the rate of false-positive results about 0.1%, both acceptable values. The attitude of potential participants toward the present urine screening program and the addition of a "tumour test" was positive. The results indicate that a pilot study of neuroblastoma screening in Quebec could be undertaken.
Attitude to Health↗
A new probe for the diagnosis of myotonic muscular dystrophy.
Myotonic muscular dystrophy (DM) is the most common muscular dystrophy, affecting adults as well as children. It is inherited as an autosomal dominant trait and is characterized by variable expressivity and late age-of-onset. Linkage studies have established the locus on chromosome 19. In order to identify tightly linked probes for diagnosis as well as to define in detail the DM gene region, chromosome 19 libraries were constructed and screened for restriction fragment length polymorphisms tightly linked to DM. A genomic clone, LDR152 (D19S19), was isolated that is tightly linked to DM; recombination fraction = 0.0 (95% confidence limits 0.0-0.03); lod score, 15.4.
Adult↗