Search PubMed⌕ Search

Biomedical subjects

A D Sadovnick

Publications and source records attributed to A D Sadovnick.

At least 37 records · Page 2Linked to original sources
PubMed2002

Segmental linkage disequilibrium within the dopamine transporter gene.

The dopamine transporter gene (DAT) has been implicated in a variety of disorders, including bipolar disorder, attention-deficit hyperactivity disorder, cocaine-induced paranoia, Tourette's syndrome, and Parkinson's disease. As no clear functional polymorphism has been identified to date, studies rely on linkage disequilibrium (LD) to assess the possible genetic contribution of DAT to the various disorders. A better understanding of the complex structure of LD across the gene is thus critical for an accurate interpretation of the results of such studies, and may facilitate the mapping of the actual functional variants. In the process of characterizing the extent of variation within the DAT gene, we have identified a number of single nucleotide polymorphisms (SNPs) suitable for LD studies, 14 of which have been analyzed, along with a 3' repeat polymorphism, in a sample of 120 parent-proband triads. Calculations of pairwise LD between the SNPs in the parental haplotypes revealed a high degree of LD (P < 0.00001) in the 5' (distal promoter through intron 6) and 3' (exon 9 through exon 15) regions of DAT. This segmental LD pattern is maintained over approximately 27 kb and 20 kb in these two regions, respectively, with very little significant LD between them, possibly due to the presence of a recombination hotspot located near the middle of the gene. These analyses of the DAT gene thus reveal a complex structure resulting from both recombination and mutation, knowledge of which may be invaluable to the design of future studies.

Dopamine Plasma Membrane Transport Proteins↗
PubMed2002

A multigenerational family with multiple sclerosis.

We report a family with 15 individuals affected with multiple sclerosis present in three and possibly four generations. The segregation of multiple sclerosis within this pedigree is consistent with an autosomal dominant mode of inheritance with reduced penetrance. The clinical characteristics of the affected individuals are indistinguishable from those seen in sporadic multiple sclerosis with respect to sex ratio, age at onset, onset symptom, MRI and clinical course. Eleven of 14 cases (78.6%) were positive for the known multiple sclerosis-associated major histocompatibility complex (MHC) Class II HLA DRB1*15 allele. Parametric linkage analysis gave a non-significant LOD score of 0.31 (theta; = 0.33) for the DRB1 gene. However, among 11 affected children with at least one DRB1*15 bearing parent, all 11 out of 11 received at least one copy of this known susceptibility allele. A transmission disequilibrium test analysis was significant for the DRB1*15 allele within this single family; P = 0.0054. The inheritance pattern in this family suggests the presence of a single major locus responsible for multiple sclerosis susceptibility, with DRB1 acting as an important modifier. This family could be an important resource for the identification of a multiple sclerosis susceptibility gene.

Adolescent↗
PubMed2001

Screening for PS1 mutations in a referral-based series of AD cases: 21 novel mutations.

BACKGROUND: Mutations in the presenilin-1 gene (PS1) account for a majority of patients with early-onset familial AD. However, the clinical indications and algorithms for genetic testing in dementia are still evolving. METHODS: The entire open reading frame of the PS1 gene was sequenced in a series of 414 consecutive patients referred for diagnostic testing, including 372 patients with AD and 42 asymptomatic persons with a strong family history of AD. RESULTS: Forty-eight independent patients screened had a PS1 mutation including 21 novel mutations. In addition, 3% of subjects (11/413) had a known polymorphism, the Glu318Gly substitution. The majority of the mutations were missense substitutions but there were three insertions and Delta exon 10 mutation. With six exceptions (codons 35, 178, 352, 354, 358, and 365) most of the mutations occurred at residues conserved in the homologous PS2 gene or in PS1 of other species. CONCLUSIONS: Eleven percent of a referral-based series of patients with AD can be explained by coding sequence mutations in the PS1 gene. The high frequency of PS1 mutations in this study indicates that screening for PS1 mutations in AD is likely to be successful, especially when directed at patients with a positive family history with onset before 60 years (90% of those with PS1 mutations were affected by age 60 years). This will also have significance for the secondary identification of at-risk relatives who might be candidates for future prophylactic therapies for AD.

Adult↗
PubMed2001

Evidence of linkage with HLA-DR in DRB1*15-negative families with multiple sclerosis.

The importance of the HLA-DR locus to multiple sclerosis (MS) susceptibility was assessed in 542 sib pairs with MS and in their families. By genotyping 1,978 individuals for HLA-DRB1 alleles, we confirmed the well-established association of MS with HLA-DRB1*15 (HLA-DRB1*1501 and HLA-DRB5*0101), by the transmission/disequilibrium test (chi2=138.3; P<.0001). We obtained significant evidence of linkage throughout the whole data set (mlod=4.09; 59.9% sharing). Surprisingly, similar sharing was also observed in 58 families in which both parents lacked the DRB1*15 allele (mlod=1.56; 62.7% sharing; P=.0081). Our findings suggest that the notion that HLA-DRB1*15 is the sole major-histocompatibility-complex determinant of susceptibility in northern-European populations with MS may be incorrect. It remains possible that the association of MS with HLA-DRB1*15 is due to linkage disequilibrium with a nearby locus and/or to the presence of disease-influencing allele(s) in DRB1*15-negative haplotypes.

Alleles↗
PubMed2001

Evidence for linkage disequilibrium between the dopamine transporter and bipolar disorder.

A role for the dopamine transporter (DAT) in bipolar disorder is implicated by several lines of pharmacological evidence, as well as suggestive evidence of linkage at this locus, which we have reported previously. In an attempt to identify functional mutations within DAT contributing a susceptibility to bipolar disorder, we have screened the entire coding region, as well as significant portions of the adjacent non-coding sequence. Though we have not found a definitive functional mutation, we have identified a number of single nucleotide polymorphisms (SNPs) that span the gene from the distal promoter through exon 15. Of the 39 SNPs that are suitable for linkage disequilibrium (LD) studies, 14 have been analyzed by allele-specific PCR in a sample of 50 parent-proband triads with bipolar disorder. A haplotyped marker comprised of five SNPs, spanning the region between exon 9 and exon 15, was constructed for each individual, and transmission/disequilibrium test (TDT) analysis revealed this haplotype to be in linkage disequilibrium with bipolar disorder (allele-wise TDT p = 0.001, genotype-wise TDT p = 0.0004). These data replicate our previous finding of linkage to markers within and near DAT in a largely different family set, and provide further evidence for a role of DAT in bipolar disorder. Published 2001 Wiley-Liss. Inc.

Alleles↗
PubMed2001

A genome survey indicates a possible susceptibility locus for bipolar disorder on chromosome 22.

Bipolar disorder or manic depressive illness is a major psychiatric disorder that is characterized by fluctuation between two abnormal mood states. Mania is accompanied by symptoms of euphoria, irritability, or excitation, whereas depression is associated with low mood and decreased motivation and energy. The etiology is currently unknown; however, numerous family, twin, and adoption studies have argued for a substantial genetic contribution. We have conducted a genome survey of bipolar disorder using 443 microsatellite markers in a set of 20 families from the general North American population to identify possible susceptibility loci. A maximum logarithm of odds score of 3.8 was obtained at D22S278 on 22q. Positive scores were found spanning a region of nearly 32 centimorgans (cM) on 22q, with a possible secondary peak at D22S419. Six other chromosomal regions yielded suggestive evidence for linkage: 3p21, 3q27, 5p15, 10q, 13q31-q34, and 21q22. The regions on 22q, 13q, and 10q have been implicated in studies of schizophrenia, suggesting the possible presence of susceptibility genes common to both disorders.

Bipolar Disorder↗
PubMed2001

Genetic susceptibility to MS: a second stage analysis in Canadian MS families.

Four published genome screens have identified a number of markers with increased sharing in multiple sclerosis (MS) families, although none has reached statistical significance. One hundred and five markers previously identified as showing increased sharing in Canadian, British, Finnish, and American genome screens were genotyped in 219 sibling pairs ascertained from the database of the Canadian Collaborative Project on Genetic Susceptibility to MS (CCPGSMS). No markers examined met criteria for significant linkage. Markers located at 5p14 and 17q22 were analyzed in a total of 333 sibling pairs and attained mlod scores of 2.27 and 1.14, respectively. The known HLA Class II DRB1 association with MS was confirmed (P<0.0001). Significant transmission disequilibrium was also observed for D17S789 at 17q22 (P=0.0015). This study highlights the difficulty of searching for genes with only mild-to-moderate effects on susceptibility, although large effects of specific loci may still be present in individual families. Future progress in the genetics of this complex trait may be helped by (1) focussing on more ethnically homogeneous samples, (2) using an increased number of MS families, and (3) using transmission disequilibrium analysis in candidate regions rather than the affected relative pair linkage analysis.

Canada↗
PubMed2001

To treat or not to treat the person with clinical multiple sclerosis--a dilemma.

Disease-modifying therapies for MS are believed to reduce the exacerbation frequency and thus perhaps improve a patient's "quality of life". Increasingly, such therapies are being offered to young persons with relatively mild or very early disease. Concerns about whom to treat, based on knowledge about the role of genetics on "MS risk" and the possible teratogenic effects of disease-modifying treatments on a developing fetus, are discussed.

Adolescent↗
PubMed2001

Genetic counselling and genetic screening for Alzheimer's disease and other dementias.

Genetic and nongenetic factors have been identified to have roles in the etiology of dementia. Etiologic heterogeneity and genetic heterogeneity are recognized, especially for Alzheimer's disease which is the most common form of dementia. Asymptomatic individuals are increasingly requesting genetic services such as genetic counselling, predictive testing and screening for genetic risk factors. This paper provides an overview of the current knowledge about genetic counselling and genetic screening for dementia as well as guidelines for the physician.

Aged↗
PubMed2000

Head injury and the risk of AD in the MIRAGE study.

OBJECTIVES: It has been suggested in some studies that head injury is a risk factor for AD, and that this risk is heightened among carriers of the APOE-epsilon4 allele. We examined the effects of head injury and APOE genotype on AD risk in a large family study. SUBJECTS: A total of 2,233 probands who met criteria for probable or definite AD and their 14,668 first-degree family members (4,465 parents, 7,694 siblings, and 2,509 spouses) were ascertained at 13 centers in the United States, Canada, and Germany participating in the MIRAGE (Multi-Institutional Research in Alzheimer Genetic Epidemiology) project. Information on head injury was collected by interview of multiple informants and review of medical records. Nondemented relatives and spouses served as control subjects for this study. METHODS: Odds of AD for head trauma with or without loss of consciousness were computed by comparing probands with unaffected spouses using conditional logistic regression analysis. To account for the unique biologic relationship between probands and their parents and siblings, odds of AD were computed using a generalized estimating equation (GEE) Poisson regression approach. GEE logistic regression was used to examine the joint effects of APOE genotype and head injury on the odds of AD in probands and a control group comprised of unaffected siblings and spouses. RESULTS: Comparison of probands with their unaffected spouses yielded odds ratios for AD of 9.9 (95% CI, 6.5 to 15.1) for head injury with loss of consciousness and 3.1 (2.3 to 4.0) for head injury without loss of consciousness. The corresponding odds derived from the comparison of probands with their parents and sibs were 4.0 (2.9 to 5.5) for head injury with loss of consciousness and 2.0 (1.5 to 2.7) for head injury without loss of consciousness. Head injury without loss of consciousness did not significantly increase the risk of AD in spouses (OR = 1.3; 95% CI, 0.4 to 4.1). The joint effects of head injury and APOE genotype were evaluated in a subsample of 942 probands and 327 controls (spouses and siblings). Head injury increased the odds of AD to a greater extent among those lacking epsilon4 (OR = 3.3) than among epsilon4 heterozygotes (OR = 1.8) or homozygotes (OR = 1.3). CONCLUSION: Head injury is a risk factor for AD. The magnitude of the risk is proportional to severity and heightened among first-degree relatives of AD patients. The influence of head injury on the risk of AD appears to be greater among persons lacking APOE-epsilon4 compared with those having one or two epsilon4 alleles, suggesting that these risk factors may have a common biologic underpinning.

Aged↗
PubMed2000

Genetic analysis of vitamin D related genes in Canadian multiple sclerosis patients. Canadian Collaborative Study Group.

The objective of this study was to investigate genes involved in the metabolism and function of vitamin D as candidate genes for genetic susceptibility to MS. Restriction fragment length polymorphisms and highly polymorphic microsatellite markers within or very close to the 1,25(OH)2D3 receptor (VDR) [12q14], the vitamin D binding protein (DBP) [4q12], and the 25(OH)D2 1alpha-hydroxylase [12q13] loci were analyzed for linkage or association with MS. We found no evidence for linkage or association of these candidate genes with MS in the Canadian population.

Alleles↗
PubMed2000

Evaluating the parent-of-origin effect in bipolar affective disorder. Is a more penetrant subtype transmitted paternally?

BACKGROUND: Numerous genetic mechanisms and modes of transmission underlying bipolar affective disorder (BPAD) have been postulated. Recently, the discovery of genomic imprinting and mitochondrial transmission of illness in humans has stimulated study of parent-of-origin effects in the transmission of BPAD. METHODS: We examined a large sample of families from an associated linkage study to search for a possible parent-of-origin effect. Selecting for unilineal families with at least one offspring and/or parent diagnosed with BPAD after structured interview, we conducted three analyses: (1) the rates of illness among mothers and fathers of offspring affected with BPAD; (2) the observed frequency of transmission and rates of illness among maternal and paternal lineages; and (3) the rates of affective illness among offspring of parents affected with BPAD. RESULTS: Our results indicate no significant differences in the rates of illness among mothers and fathers of offspring affected with BPAD. Also, the frequency of transmission and rates of illness among maternal and paternal lineages did not differ significantly. However, the rate of BPAD among the offspring of fathers affected with BPAD was significantly higher than for mothers with the illness. LIMITATIONS: Substantially more women than men, and maternal than paternal relatives were studied - introducing possible gender biases. CONCLUSIONS: These results suggest a possible paternal parent-of-origin effect.

Bipolar Disorder↗
PubMed2000

Factors influencing sib risks for multiple sclerosis.

Multiple sclerosis (MS) is now thought to be a complex trait determined by genetic and non-genetic (environmental) factors. The study group, identified from the Canadian Collaborative Project on Genetic Susceptibility to MS, consisted of 1,083 MS index cases, 2,166 of their parents and 3,112 of their sibs. The results, together with those of a previous study on an independent data set, suggest that gender, age of MS onset and having one parent with MS may individually and interactively alter sib risks for MS. These data are important for genetic counselling and for molecular genetic (genome screens, candidate gene analyses) studies.

Adolescent↗
PubMed2000

The natural history of multiple sclerosis: a geographically based study: 8: familial multiple sclerosis.

We have examined the demographics and long-term outcome of 1044 patients with sporadic and familial multiple sclerosis in a population-based cohort from London, Ontario. The mean follow-up was 25 years in duration, and by this time most patients had reached the unambiguous endpoint scores of the Kurtzke disability status scale (DSS), DSS 6, 8 or 10. An affected family member was identified in 19.8% of the total population, and this subgroup was further divided arbitrarily into the following three groups by the type and number of relatives affected: (i) first degree only; (ii) first degree plus others; (iii) second or third degree. The outcome in these groups was compared with that for those patients who, at a mean 25 year follow-up, had no relatives known to be affected. Familial cases closely resembled those remaining sporadic in both demographics and outcome, although onset in the most heavily loaded families was earlier and male/female ratio was greater. The times to DSS 6, 8 and 10 did not differ significantly when sporadic, familial and familial subgroups were compared. These results provide no clinical support for viewing familial multiple sclerosis as distinct from the sporadic form. The observed recurrence rate for siblings in a strictly defined epidemiological sample was 3.5%, much as projected. These results validate the recurrence risks which have previously been derived from age-corrected data for these first-degree relatives.

Adult↗
PubMed2000

Conjugal multiple sclerosis: population-based prevalence and recurrence risks in offspring. Canadian Collaborative Study Group.

From a population-based sample of 15,504 patients attending Canadian multiple sclerosis (MS) clinics, we have determined the frequency of conjugal MS and have estimated the recurrence risk in offspring of such matings. Twenty-three MS cases were found among 13,550 spouses of study probands for a crude conjugal rate of 0.17% (95% CI of 0.10%-0.24%). Despite ascertainment bias that expectedly inflates this number, this is a frequency intermediate between the point prevalence (0.1%) and lifetime risk (0.2%) for the general population and close to an order of magnitude less than reported for half siblings reared apart (1.06%) from the same population. Six of the 49 offspring of conjugal pairs also had MS, and age conversion gives a rate similar to the concordance rate for Canadian monozygotic twins. However, this correction may not be appropriate in this special case. Despite an ascertainment bias in favor of recognizing affected spouses and a large population sample, the common environment in adulthood shared by spousal pairs could not be shown to increase the risk of conjugal MS. Although the high recurrence rate in offspring is similarly subject to an upward bias, the low risk for MS spouses and the high risk for offspring support other data indicating that familial risk is genetically determined. Furthermore, these results imply that susceptibility alleles are shared by unrelated individuals with the disease.

Adult↗
PubMed1999

Genetic counselling in multiple sclerosis: risks to sibs and children of affected individuals.

Genetic factors are recognized as having important roles in both the overall etiology and the familial aggregation of multiple sclerosis (MS), leading to increased requests for genetic counselling. This paper is designed to provide familial risk data in a practical format for use during genetic counselling for MS. Depending on the amount of genetic sharing among family members, the relative risk of MS compared with that for the general population can range from 1 (adopted sibs and children of the MS proband, with whom they share no genetic material) to 190 (monozygotic co-twins of MS patients, with whom they share 100% of their genetic material). When counselling full sibs of MS patients, risks can be better calculated if information is available on the age of MS onset in the patient and whether or not one parent has MS.

Age Factors↗
PubMed1998

Canadian collaborative project on genetic susceptibility to MS, phase 2: rationale and method. Canadian Collaborative Study Group.

BACKGROUND: Results from the Canadian Collaborative Project on Genetic Susceptibility to Multiple Sclerosis (MS)-Phase 1 (CCPGSMS-Phase 1) together with other family data published since 1982 have led to the following conclusions about the etiology of MS: (i) genetic and non-genetic (environmental) factors are involved in the etiology of MS on a population basis; (ii) the familial aggregation of MS is genetic; (iii) maternal factors do not influence the risk for siblings to develop MS; and (iv) MS appears to be oligogenic. The present paper describes the rationale and methodology for the CCPGSMS-Phase 2. METHOD: The CCPGSMS-Phase 2 is a nation-wide collaborative effort involving all the 15 Canadian MS clinics. A series of structured questionnaires is administered to MS index cases, spouse controls and mothers of index cases and spouse controls (if available) by trained interviewers. Blood samples are taken for molecular genetic studies. This national effort is coordinated by the MS Clinics in Vancouver and London. RESULTS: The CCPGSMS-Phase 2 is in progress so specific results are not available. The study is designed to (i) increase the database for genetic epidemiological/molecular genetic research and (ii) gather population-based data to further our understanding of the non-genetic factors in the etiology of MS. CONCLUSIONS: It is anticipated that the results from this study will impact on the eventual prevention, cure and treatment of MS.

Canada↗