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Biomedical subjects

L Arbour

Publications and source records attributed to L Arbour.

At least 19 recordsLinked to original sources
PubMed2005

Submicroscopic deletions and duplications in individuals with intellectual disability detected by array-CGH.

Intellectual disability (ID) affects about 3% of the population (IQ < 70), and in about 40% of moderate (IQ 35-49) to severe ID (IQ < 34), and 70% of cases of mild ID (IQ 50-70), the etiology of the disease remains unknown. It has long been suspected that chromosomal gains and losses undetectable by routine cytogenetic analysis (i.e., less than 5-10 Mb in size) are implicated in ID of unknown etiology. Array CGH has recently been used to perform a genome-wide screen for submicroscopic gains and losses in individuals with a normal karyotype but with features suggestive of a chromosome abnormality. In two recent studies, the technique has demonstrated a approximately 15% detection rate for de novo copy number changes of individual clones or groups of clones. Here, we describe a study of 22 individuals with mild to moderate ID and nonsyndromic pattern of dysmorphic features suspicious of an underlying chromosome abnormality, using the 3 Mb and 1 Mb commercial arrays (Spectral Genomics). Deletions and duplications of 16 clones, previously described to show copy number variability in normal individuals [Iafrate et al., 2004; Lapierre et al., 2004; Schoumans et al., 2004; Vermeesch et al., 2005] were seen in 21/22 subjects and were considered polymorphisms. In addition, three subjects showed submicroscopic deletions and duplications not previously reported as normal variants. Two of these submicroscopic changes were of de novo origin (microdeletions at 7q36.3 and a microduplication at 11q12.3-13.1) and one was of unknown origin as parental testing of origin could not be performed (microduplication of Xp22.3). The clinical description of the three subjects with submicroscopic chromosomal changes at 7q36.3, 11q12.3-13.1, Xp22.3 is provided.

Chromosome Aberrations↗
PubMed2005

Prenatally detected trisomy 20 mosaicism.

BACKGROUND: Trisomy 20 is one of the more common mosaic trisomies detected on amniocentesis and presents with a normal outcome in over 90% of reported cases. Trisomic cells are almost never confirmed in newborn blood and are only rarely found in other fetal or placental samples. Nonetheless, some abnormal outcomes have been reported, including unexplained fetal demise, intrauterine growth restriction, and multiple congenital anomalies. Because of the lack of molecular studies on such cases, it is unknown whether the origin of trisomy or presence of uniparental disomy (UPD) could have some influence on outcome. METHODS: We present data on six cases of trisomy mosaicism, two detected by chorionic villous sampling (CVS) and four by amniocentesis (AF), submitted to our laboratory for molecular studies. RESULTS AND CONCLUSIONS: A meiotic origin of the trisomy could be confirmed in only one of these cases. In addition, uniparental disomy was excluded in all four cases for which parents were available for testing. The four cases with low levels of trisomy in amniotic fluid (0%, 10%, 11%, and 12%) were associated with a normal outcome. The remaining two cases of trisomy 20 had high levels of trisomy in amniotic fluid (96% and 58%) and had abnormal outcomes (developmental delay in one and stillbirth with IUGR and severe oligohydramnios in the other). Including previously published cases, there is a clear association with the level of trisomy and outcome, with only 4% abnormal outcomes when <40% trisomic cells were detected. Higher levels of trisomy were also observed in male fetuses as compared to female fetuses (p = 0.01); however, there were no sex differences in frequency of abnormal outcomes.

Adult↗
PubMed2005

Recurrent trisomy 21: four cases in three generations.

Recurrent trisomy 21: four cases in three generations. While gonadal mosaicism can lead to recurrence of trisomy 21 (T21) for a single couple, the recurrence of free T21 in multiple members of a single pedigree has rarely been reported. We present an unusual pedigree with four cases of Down syndrome (DS) with free T21 were born to four separate women related through three generations of one family. The mothers were aged 18, 21, 29, and approximately 30 years at the time of the births. Using microsatellite markers, we excluded most of chromosome 21, excepting two small regions within 21q11.1 and 21q22.3, as being shared among the mothers of the DS children. However, two members of the pedigree, including one DS mother with a normal G-banded karyotype, carried supernumerary alleles at markers 2503J9TG, D21S369, and D21S215, which span the region from 21pter to 21q11.1. Fluorescence in situ hybridization using a centromeric probe hybridizing to chromosomes 13 and 21 did not reveal a novel location, ruling out a cryptic centromeric translocation between chromosome 21 and any chromosome other than chromosome 13. The level of meiotic recombination on chromosome 21 was unusually high in this family as well. We hypothesize that a cryptic rearrangement within the highly repetitive region of 21q11.1 is present in this family, disrupting pairing and leading to an increased risk of non-disjunction of chromosome 21 in this family.

Child↗
PubMed2004

Heart defects and other malformations in the Inuit in Canada: a baseline study.

OBJECTIVES: Birth defects occur in all ethnic groups, remaining an important world-wide cause of perinatal and infant morbidity. This contributes greatly to an excess of health care dollars allocated to the care and repair of those affected. This is especially true when those affected live in remote geographical locations. STUDY DESIGN: A chart review of 2567 live births of children of Inuit parents residing in Arctic Quebec (Nunavik) and on Baffin Island (Nunavut) between 1989 and 1994 (five years) was carried out compared to rates of anomalies of the Alberta Congenital Anomalies Surveillance System (ACASS). RESULTS: Birth defects were higher in the Inuit sample in nearly every major ICD-9 category with the exception of neural tube defects, eye anomalies and chromosome abnormalities. (Total: 99.7/1000 Vs 51.5/1000; OR 1.93 95% CI 1.7-2.3). Congenital heart defects were significantly increased 22.9/1000 Vs 5.6/1000, with an OR of 4.18 (95% CI 3.2-5.4) in the ICD-9 category 745. In particular, ventricular septal defects (VSDs) and atrial septal defects (ASDs) (OR 4.9 CI 3.5-6.9 and 4.6 CI 2.9-7.2) were frequent. CONCLUSIONS: A high rate of heart defects was an important contributor to the nearly two times rate of total birth defects in the Inuit compared to the ACASS. Further study should be carried out to determine the contributing factors. Genetic predisposition to specific heart defects, and a diet low in folate and vitamin A are considerations. The use of alcohol may exacerbate vitamin status in pregnancy. Optimizing vitamin status in the periconceptional period may reduce the rate of birth defects.

Canada↗
PubMed2002

Prenatal diagnosis of apparently isolated unilateral multicystic kidney: implications for counselling and management.

Cases where initial prenatal diagnosis was made of isolated unilateral multicystic kidney (UMCK) were reviewed to determine appropriate counselling and management strategies. For the 73 cases, chromosome abnormalities, pregnancy complications and family histories were reviewed. In addition, subsequently diagnosed birth defects, and pediatric medical and surgical outcomes were available for 54 cases. Of those with outcome information available renal/genital-urinary tract abnormalities were diagnosed subsequently in 33% and non-renal abnormalities in 16% of cases. Of the non-renal abnormalities, congenital heart defects were most frequent (7%). One chromosome abnormality, a trisomy 21, was present among 32 cases where karyotypes were known (3%). Amniotic fluid volume abnormalities were present in 11 cases but not predictive of associated anomalies, with the exception of one case where polyhydramnios accompanied multiple malformations consistent with VATER association. A family history of structural renal anomalies was reported in 11 cases (20%). There were 14 cases of partial or complete involution (25%), including two cases of complete prenatal involution of the cystic kidneys. No long-term associated morbidity such as hypertension or malignancy was present in our cohort. Based on our study and corroborating literature, amniocentesis should be offered to women when a seemingly isolated UMCK is detected on routine prenatal ultrasound. Furthermore, a detailed ultrasound with careful assessment of the fetal heart and contralateral kidney is indicated at diagnosis and during the third trimester to assess for further evidence of structural abnormalities, as well as amniotic fluid volume abnormalities. Careful assessment of the newborn is indicated with appropriate speciality referral as required.

Abnormalities, Multiple↗
PubMed2001

Recurrent trisomy 15 in a female carrier of der(15)t(Y;15)(q12;p13).

We report on a female carrier of der(15) t(Y;15)(q12;p13) who had two pregnancy losses with trisomy 15 and one with tetraploidy. Molecular analysis showed that both non-disjunction events resulting in the trisomy 15 pregnancies occurred in maternal meiosis I. This finding raises the possibility that there may be an increased risk for trisomy 15 in some carriers of unbalanced t(Y;15) which, if followed by trisomic zygote rescue, may lead to uniparental disomy (UPD).

Abortion, Habitual↗
PubMed1999

Genetic polymorphisms in methylenetetrahydrofolate reductase and methionine synthase, folate levels in red blood cells, and risk of neural tube defects.

Folic acid administration to women in the periconceptional period reduces the occurrence of neural tube defects (NTDs) in their offspring. A polymorphism in the gene encoding methylenetetrahydrofolate reductase (MTHFR), 677C-->T, is the first genetic risk factor for NTDs in man identified at the molecular level. The gene encoding another folate-dependent enzyme, methionine synthase (MTR), has recently been cloned and a common variant, 2756A-->G, has been identified. We assessed genotypes and folate status in 56 patients with spina bifida, 62 mothers of patients, 97 children without NTDs (controls), and 90 mothers of controls, to determine the impact of these factors on NTD risk. Twenty percent of cases and 18% of case mothers were homozygous for the MTHFR polymorphism, compared to 11% of controls and 11% of control mothers, indicating that the mutant genotype conferred an increased risk for NTDs. The risk was further increased if both mother and child had this genotype. The MTR polymorphism was associated with a decreased O.R. (O.R.); none of the cases and only 10% of controls were homozygous for this variant. Red blood cell (RBC) folate was lower in cases and in case mothers, compared to their respective controls. Having a RBC folate in the lowest quartile of the control distribution was associated with an O.R. of 2.56 (95% CI 1.28-5.13) for being a case and of 3.05 (95% CI 1.54-6.03) for being a case mother. The combination of homozygous mutant MTHFR genotype and RBC folate in the lowest quartile conferred an O.R. for being a NTD case of 13.43 (CI 2.49-72.33) and an O.R. for having a child with NTD of 3.28 (CI 0.84-12.85). We propose that the genetic-nutrient interaction--MTHFR polymorphism and low folate status--is associated with a greater risk for NTDs than either variable alone.

5-Methyltetrahydrofolate-Homocysteine S-Methyltran↗
PubMed1999

Intrauterine exposure to clomiphene and neonatal persistent hyperplastic primary vitreous.

A 4-year-and-10-month-old girl was diagnosed shortly after birth with persistent hyperplastic primary vitreous (PHPV). Her mother took clomiphene 100 mg daily for approximately 4 weeks and discontinued the drug once she had a positive pregnancy test. The exact time of gestation was not clear. Clomiphene is an estrogen antagonist effective in the treatment of anovulation. Various ocular side effects have been described in women taking the drug, including decreased vision, mydriasis, flashing lights, central scotoma, photophobia, diplopia, allergic reactions, retinal vasospasms, detachment posterior vitreous, and possibly posterior subcapsular cataracts. These occur in 1.5-10% of patients taking clomiphene. The potential effects of clomiphene on the fetus have been investigated in five animal studies. Cataracts were observed in fetal mice and rats, but not in monkeys. In humans, a case of congenital retinal aplasia was described. The possibility of clomiphene-induced congenital PHPV should be considered, especially in pregnant women who are taking a high and prolonged dose.

Animals↗
PubMed1999

Discordant measures of androgen-binding kinetics in two mutant androgen receptors causing mild or partial androgen insensitivity, respectively.

We have characterized two different mutations of the human androgen receptor (hAR) found in two unrelated subjects with androgen insensitivity syndrome (AIS): in one, the external genitalia were ambiguous (partial, PAIS); in the other, they were male, but small (mild, MAIS). Single base substitutions have been found in both individuals: E772A in the PAIS subject, and R871G in the MAIS patient. In COS-1 cells transfected with the E772A and R871G hARs, the apparent equilibrium dissociation constants (Kd) for mibolerone (MB) and methyltrienolone are normal. Nonetheless, the mutant hAR from the PAIS subject (E772A) has elevated nonequilibrium dissociation rate constants (k(diss)) for both androgens. In contrast, the MAIS subject's hAR (R871G) has k(diss) values that are apparently normal for MB and methyltrienolone; in addition, the R871G hAR's ability to bind MB resists thermal stress better than the hAR from the PAIS subject. The E772A and R871G hARs, therefore, confer the same pattern of discordant androgen-binding parameters in transfected COS-1 cells as observed previously in the subjects' genital skin fibroblasts. This proves their pathogenicity and correlates with the relative severity of the clinical phenotype. In COS-1 cells transfected with an androgen-responsive reporter gene, trans-activation was 50% of normal in cells containing either mutant hAR. However, mutant hAR-MB binding is unstable during prolonged incubation with MB, whereas normal hAR-MB binding increases. Thus, normal equilibrium dissociation constants alone, as determined by Scatchard analysis, may not be indicative of normal hAR function. An increased k(diss) despite a normal Kd for a given androgen suggests that it not only has increased egress from a mutant ligand-binding pocket, but also increased access to it. This hypothesis has certain implications in terms of the three-dimensional model of the ligand-binding domain of the nuclear receptor superfamily.

Amino Acid Sequence↗
PubMed1999

Proposed model for interaction between residents and residency training programs, and pharmaceutical industry.

Medical residents in training are as much targets of pharmaceutical-industry marketing as are physicians in practice. This interaction is often subtle and takes the form of sponsorship of meals at academic events, support for conference travel, books, and items such as pens and notepads. Most residency programs direct little time towards training in ethics and the critical analysis of pharmaceutical-industry marketing. We propose a model for the relationship between residents and residency programs, and the pharmaceutical industry that addresses the need for such interaction to be viewed in light of the patient-centered ethic of professional conduct and the ideal of unbiased medical practice. A committee of residents at different levels of training and two staff physicians received the mandate to examine this issue. The committee developed a set of guidelines and a proposed schema for the handling of funds from pharmaceutical companies (still not implemented). Each residency program would develop a common fund for money donated by pharmaceutical companies. This fund would be administered by a committee with defined priorities. The presence of residents on this committee under staff preceptorship would serve as a springboard for education on the subject. Guidelines for acknowledgement of sponsorship, solicitation of funds, gifts for care of patients, ongoing education, and the wider applicability of these proposals were also developed. Residents' interaction with the pharmaceutical industry during training could have lifelong influence on medical practice. We hope that our model will promote critical appraisal of the potential risks and benefits of this interaction.

Advertising↗
PubMed1998

Confirmation of FWT1 as a Wilms' tumour susceptibility gene and phenotypic characteristics of Wilms' tumour attributable to FWT1.

A susceptibility gene for Wilms' tumour (WT), designated FWT1, was previously mapped to chromosome 17q12-q21 by linkage analysis of a single family. We now confirm the existence of this gene by analysis of additional cases in the original family (3-point LOD score=5.69), and by detecting strong evidence of linkage to this region in an unrelated pedigree with seven cases of WT (3-point LOD score=2.56). Analysis of 11 smaller WT families confirms that there is genetic heterogeneity in familial WT, as three families exhibit strong evidence against linkage to FWT1. One of these was subsequently found to have a predisposing WT1 mutation. However, the other two families show evidence against both FWT1 and WT1, suggesting that at least one further familial WT gene exists. Analysis of the phenotype of 16 WT cases from the families linked to FWT1 demonstrates that they present at a significantly older age and a significantly later stage than both sporadic WT and the six cases from two families unlinked to either FWT1 or WT1. The results confirm the role of FWT1 in susceptibility to WT, provide strong evidence for genetic heterogeneity in familial WT and suggest there are phenotypic differences between familial WT due to FWT1, familial WT due to other genes and non-familial WT.

Chromosomes, Human, Pair 17↗
PubMed1997

The familial Wilms' tumour susceptibility gene, FWT1, may not be a tumour suppressor gene.

A familial Wilms' tumour susceptibility gene, known as FWT1, has recently been localised to chromosome 17q12-q21 by genetic linkage analysis. Four Wilms' tumours from a family showing strong evidence of linkage to FWT1 were examined for allele loss using polymorphic microsatellite markers on chromosome 17q. In three tumours no loss of heterozygosity was observed. In the remaining case, loss of heterozygosity was detected at all markers analysed. However, the alleles lost in this Wilms' tumour were those segregating with the disease in the family. This is in contrast to the usual pattern observed in familial cancer syndromes, where the allele lost in tumours arising in gene carriers is the wild type inherited from the non mutation carrying parent. Taken together with previous data indicating that LOH on chromosome 17q is rare in sporadic Wilms' tumour, the results suggest that FWT1 is not a tumour suppressor gene. Moreover, loss of alleles linked to the disease and the implied absence of the mutated susceptibility gene in one tumour, suggests that a mutation in FWT1 may be necessary for the initiation of some familial Wilms' tumours but subsequently the maintenance of the neoplastic phenotype becomes independent of the FWT1 mutation.

Alleles↗
PubMed1997

An autosomal dominant form of familial persistent hyperinsulinemic hypoglycemia of infancy, not linked to the sulfonylurea receptor locus.

Persistent hyperinsulinemic hypoglycemia of infancy (PHHI), a rare disorder due to defective negative feedback regulation of insulin secretion by low glucose levels, is often familial. Most cases are recessively inherited, and mutations of the sulfonylurea receptor gene (SUR) or the closely linked KIR6.2 gene have been found in several families. Both of these genes encode components of the potassium channels responsible for glucose-regulated insulin release. However, in some families recessive PHHI is not linked to the SUR-KIR6.2 locus, suggesting genetic heterogeneity. We report here a French Canadian kindred with hypoglycemia in five first cousins. All five patients had documented hypoglycemia, and all responded well to diazoxide. In two, inappropriately elevated insulin levels during hypoglycemia were documented. This familial clustering strongly suggests the existence of an autosomal dominant form of PHHI. By preliminary linkage analysis, we tested the possibility of a dominant negative SUR or KIR6.2 mutant. The insulin (INS) and glucokinase (GCK) genes were also tested as additional candidates. Microsatellite markers closely linked to each gene were used, and large negative Lod scores were obtained at the known recombination fractions between all three genes studied and the corresponding marker. We conclude that mutation of a gene other than SUR or KIR6.2 is responsible for the dominant PHHI in this family, and this gene cannot be INS or GCK. We propose that a genome-wide search for this gene is important for elucidating this rare disorder and, more importantly, for determining its potential impact on understanding noninsulin-dependent diabetes mellitus and on the effort to develop bioengineered beta-cells for transplantation.

ATP-Binding Cassette Transporters↗
PubMed1996

Glutathione deficiency as a complication of methylmalonic acidemia: response to high doses of ascorbate.

A 7-year-old boy with deficient activity of methylmalonyl coenzyme A mutase (mut-methylmalonic acidemia) was seen in severe metabolic crisis. After hemodialysis and clearance of toxic metabolites, severe lactic acidosis persisted with multiorgan failure. Glutathione deficiency was noted and high-dose ascorbate therapy (120 mg/kg) commenced. Glutathione deficiency may contribute to the lactic acidosis observed during decompensation in patients with methylmalonic acidemia.

Acidosis, Lactic↗
PubMed1996

Evidence for a familial Wilms' tumour gene (FWT1) on chromosome 17q12-q21.

Wilms' tumour (WT) is one of the most common solid tumours of childhood, occurring in 1 in 10,000 children and accounting for 8% of childhood cancers. It is believed to result from malignant transformation of abnormally persistent renal stem cells (nephrogenic rests) which retain embryonic differentiation potential. Although WT is usually sporadic, approximately one percent occur in families in which susceptibility appears to be inherited as an autosomal dominant trait with incomplete penetrance. Predisposition to other cancers or to the developmental abnormalities associated with sporadic WT is not usually apparent in WT families. The WT1 gene at 11p13 (ref.2), and additional genes on chromosomes 11p15 (ref. 3) and 16q (ref. 4) have been implicated in the development of WT but are not responsible for familial WT. We have carried out a genome linkage search in a large Canadian family with seven confirmed cases of WT. Our results provide strong evidence for the localisation of a familial WT predisposition gene, FWT1, to an 18-centimorgan (cM) interval on chromosome 17q12-q21.

Child↗
PubMed1996

Multifactorial inheritance of non-syndromic macrocephaly.

OBJECTIVE: To reevaluate previous claims that non-syndromic macrocephaly is usually inherited as an autosomal dominant trait. DESIGN: Head size was measured in the parents and sibs of children with non-syndromic macrocephaly. OUTCOME MEASURES: If autosomal dominant inheritance is involved, the frequency distribution should be bimodal. RESULTS: Head circumference of parents and sibs of the macrocephalic probands had a mean significantly greater than the population norm, and a unimodal distribution. Probands with psychomotor impairment had bigger heads, and more had a history of birth difficulty, than did unimpaired probands. CONCLUSIONS: The usual genetic basis for non-syndromic macrocephaly is multifactorial with a polygenic genetic basis, rather than autosomal dominant. Risk of recurrence appears to be much lower than if it would be on the assumption of autosomal dominant inheritance. Macrocephaly in a parent or sib of an unborn child may present a risk for birth injury to that child. A larger series of patients will be necessary to resolve this question.

Adult↗