Affected Pedigree Member Research Articles

Linkage of angiotensinogen gene polymorphisms with hypertension in a sibling study of Hong Kong Chinese

The angiotensinogen gene has been linked with human essential hypertension in whites but the relationship in Asian populations has been less consistent. This study aimed to examine genetic associations between hypertension and the M235T, T174M, and G-217A polymorphisms of the angiotensinogen gene in Chinese siblings. We studied members of 126 families with a hypertensive proband, including 434 siblings, of which 178 were hypertensive. Parental history of hypertension was recorded. The M235T, T174M, and G-217A polymorphisms were examined using a microarray method, validated by sequencing. The transmission disequilibrium test was applied to identify whether the genetic polymorphism loci were related to hypertension. Haplotype analysis of the combined polymorphisms was applied using the TRANSMIT program. Linkage study was conducted by applying the affected pedigree member method. A significant overtransmission was observed for the T235 allele at the M235T polymorphism and hypertension (chi2 = 4.41, P = 0.036) but not for the T174M and G-217A polymorphisms. The haplotype analysis showed a significant association with the haplotypes of paired markers (T174 and T235) with chi2 value of 8.131 (P = 0.004; global test chi2 = 9.131, P = 0.028). Linkage between M235T and hypertension was detected (T = -2.25, P = 0.019), and a tendency for linkage with central obesity-related hypertension was found for the M235T and T174M polymorphisms (P = 0.0087 and P = 0.01). The M235T and T174M variants, especially the T235 allele, contribute to an increased risk of hypertension in these Chinese patients.

Maladies multifactorielles : un cauchemar pour le généticien

Common diseases are often familial, but they do not show in most families, a simple pattern of inheritance. In a few families these diseases may be caused by a mutation in a single gene. In most families these diseases are multifactorial, they result from a complex interaction between a genetic component which is often polygenic and many environmental factors. Two major, model free, methods are used to locate and identify susceptibility genes that predispose to multifactorial diseases. The first is a non parametric linkage analysis that relies on affected sib pairs, or an affected pedigree member, the second method is association studies which looks for increase frequency of particular alleles or genotypes in affected compared with unaffected individuals in the population. Most of the results have not been replicated, identifying susceptibility genes is proving much more difficult than most geneticists imagined 20 years ago. The main reason for this irreproducibility is genetic heterogeneity.

An affected pedigree member analysis of linkage between the dopamine D2 receptor gene TaqI polymorphism and obesity and hypertension

Background Dopamine modulates a variety of physiological functions including natriuresis and satiety. We have previously reported that the TaqI polymorphism of the dopamine D2 receptor (DD2R) gene is associated with both blood pressure and obesity indices in a normoglycaemic Hong Kong Chinese population. In this study, we present evidence confirming the linkage between this gene polymorphism, obesity and hypertension. Methods Two hundred and seventy-four siblings from 96 normoglycaemic hypertensive families were recruited, including 133 who were hypertensive. Central obesity was defined as a waist-to-hip ratio of ≥0.9 and ≥0.85 in males and females, respectively, and was identified in 99 of the siblings. The DD2R gene TaqI polymorphism was identified with a polymerase chain reaction based restriction fragment length polymorphism protocol. The affected pedigree member (APM) linkage analysis (sib-pair program, version 0.99.9, by D.L. Duffy) was used to assess for linkage between this gene polymorphism, obesity and hypertension in 73 families with siblings discordant for hypertension. Results The A1 allele frequencies were similar in the 133 hypertensive, and 141 normotensive siblings, including the 99 centrally obese siblings at 0.431, 0.421 and 0.418, respectively. APM linkage analysis suggested that the DD2R gene TaqI polymorphism had evidence of linkage with blood pressure ( T=−1.86, P=0.013), as well as with obesity ( T=−1.58, P=0.007). Conclusion Our data in normoglycaemic Hong Kong Chinese supports that the DD2R gene TaqI polymorphism is a marker associated with the pathogenesis of obesity and hypertension.

An affected pedigree member analysis of the linkage between the Taql polymorphism of the dopamine D2 receptor gene and obesity-related hypertension in Hong Kong Chinese

An affected pedigree member analysis of the linkage between the Taql polymorphism of the dopamine D2 receptor gene and obesity-related hypertension in Hong Kong Chinese

Molecular genetics of age-related macular degeneration.

The numerous conditions that clinicians group under the term 'age-related macular degeneration' (AMD) are collectively the most common cause of severe visual loss in the developed world. Moreover, the number of people affected by these diseases is expected to nearly double in the next 25 years. A growing body of data suggests that a large fraction of AMD is caused by genetic factors. As a result, numerous investigators have sought genes that contribute to this disorder. At least six genes have now been identified that cause heritable macular disease, but none of these seem to cause even a moderate fraction of AMD. Affected pedigree member studies suggest that some regions of the genome do harbor AMD predisposing genes, but none have yet been identified by this approach. Studies of human donor tissue have yielded important new insights into pathways associated with AMD. These studies, when combined with the power of genetic approaches, are likely to ultimately reveal a set of genes responsible for a sizeable fraction of AMD.

Possible association but no linkage of the HSD11B2 gene encoding the kidney isozyme of 11beta-hydroxysteroid dehydrogenase to hypertension in Black people.

The HSD11B2 (HSD11K) gene encoding the kidney isozyme of 11beta-hydroxysteroid dehydrogenase is mutated in the syndrome of apparent mineralocorticoid excess, an autosomal recessive form of salt-sensitive hypertension. This gene is thus a logical candidate locus for risk of essential hypertension. Because hypertension in Black people tends to be of the low-renin, salt sensitive type, we genotyped independent sets of hypertensives of Afro-American (59 kindreds) and Afro-Caribbean (66 kindreds) origin using a highly polymorphic (heterozygosity index 0.84) CA repeat polymorphism in the first intron of HSD11B2. Linkage was assessed by the affected pedigree member method. No linkage of hypertension to this locus could be demonstrated, but statistically significant allelic associations were noted. HSD11B2 does not have a strong influence on the development of essential hypertension in Black people, but weaker effects on blood pressure cannot be ruled out.

Linkage of familial moyamoya disease (spontaneous occlusion of the circle of Willis) to chromosome 17q25.

Moyamoya disease is a cerebrovascular disease of unknown cause that mainly affects Japanese children. The incidence of familial occurrence accounts for 9% of cases. The characteristic lesions of moyamoya disease are occasionally seen in neurofibromatosis type 1, of which the causative gene (NF1) has been assigned to chromosome 17q11.2. To determine whether a gene related to moyamoya disease is located on chromosome 17, we conducted microsatellite linkage analyses on 24 families containing 56 patients with moyamoya disease. Leukocyte DNA extracted from the family members was subjected to polymerase chain reaction for a total of 22 microsatellite markers on chromosome 17. The amplified polymerase chain reaction fragments were analyzed with GeneScan on an automated sequencer. Two-point linkage analysis gave a maximum log(10) odds (LOD) score of 3.11 at the recombination fraction of 0.00 for the marker at locus D17S939. The affected pedigree member method also showed a significantly low P value (<1. 0x10(-5)) for the 5 adjacent markers at 17q25. Multipoint linkage analysis also indicated that the disease gene is contained within the 9-cM region of D17S785 to D17S836, with a maximum LOD score of 4. 58. A gene for familial moyamoya disease is located on chromosome 17q25.

The CTLA-4 gene is associated with multiple sclerosis

We have investigated whether three intragenic polymorphisms of the CTLA-4 gene, a C/T base exchange in the promoter (p.−318), an A/G substitution in exon 1 (p.49) and a dinucleotide repeat polymorphism in exon 4 (p. 642), were associated with genetic susceptibility to multiple sclerosis (MS). We observed a significant association ( p<0.05) for homozygosity for the G 49 allele in a case-control analysis of 378 MS patients and 237 controls, and a transmission disequilibrium ( p<0.02) for the G 49 allele in 31 MS families. This was further corroborated by evidence for linkage by the affected pedigree member (APM) analysis ( p<0.0002) and a transmission distortion ( p<0.05) of the exon 4 642 polymorphism. Sequencing of the promoter, the first and second exons and the parts of the first intron revealed no further polymorphisms. Our results suggest that a dysregulation of CTLA-4-driven downregulation of T-cell activation could be involved in the pathogenesis of MS.

Linkage analysis of candidate genes and gene-gene interactions in chinese hypertensive sib pairs.

Previous studies of hypertension in humans and experimental animal models have identified a number of candidate genes that have since been implicated as possibly contributing to essential hypertension. Among them are the genes encoding angiotensinogen, renin, the beta- and gamma-subunits of the epithelial sodium channel (beta/gamma-ENaC), alpha-adducin, and kallikrein (KLK). To examine the role of possible contribution of these genes in ethnic Chinese, as well as the epistatic interaction among them, we studied a large cohort of hypertensive sib pairs from China. DNA samples from 310 concordant affected sibling pairs with hypertension were tested for linkage with the use of excess allele-sharing algorithms based on genotyping with highly informative GT-repeat microsatellite markers localized in the immediate vicinity of the genes encoding angiotensinogen, renin, beta- and gamma-ENaC, alpha-adducin, and KLK. Affected sib pair analysis conducted according to 3 different methods (Statistical Analysis for Genetic Epidemiology [S.A.G.E. ]/SIBPAL, MAPMAKER/SIBS, and affected pedigree member [APM] methods) revealed no evidence for linkage of any of these genes to primary hypertension in the population studied. Moreover, 2-locus sib pair linkage analyses to test for gene-gene interactions among each possible pair of candidate genes failed to yield any statistically significant results. Our findings provide no support for a significant contribution of the angiotensinogen, renin, beta/gamma-ENaC, alpha-adducin, or KLK genes, alone or in concert, to the pathogenesis of essential hypertension among Chinese. Our results emphasize the possible role of ethnic differences for complex disease genetics, as well as the need for large, well-characterized investigations.

Association and linkage analysis of candidate chromosomal regions in multiple sclerosis: indication of disease genes in 12q23 and 7ptr-15.

Four recent genome-wide screen studies in multiple sclerosis (MS) identified a number of candidate regions for susceptibility genes in addition to the HLA complex in 6p21. However, none of these regions provided formally significant evidence for genome-wide linkage. We have investigated such regions in 46 Swedish multiplex MS families, 28 singleton families, 190 sporadic MS patients and 148 normal controls by parametric and nonparametric linkage and association analysis. One microsatellite marker, in 12q23, provided evidence for association in addition to suggestive transmission distortion and slightly positive linkage. In addition, a marker in 7ptr-15 showed a significant transmission distortion as well as a highly significant score in affected pedigree member analysis, but not quite significant deviations in association analysis. One of three markers in 5p, a region implicated in all four previous studies, showed a weakly positive lod score, but no other evidence of importance. Markers in 2p23, 5q11-13, 6q25, 7q21-22, 11q21-23, 13q33-34, 16p13.2, 18p11.32-23, Xp21.3 provided little or no evidence of importance for MS. In summary, these data support the importance of genome-wide screens in the identification of new candidate loci in polygenic disorders.

The eNos Gene: A Candidate for the Preeclampsia Susceptibility Locus?

Objective: To investigate the endothelial cell nitric oxide synthase (eNOS) gene as a candidate for susceptibility to preeclampsia.Methods: Twenty-six Australian families containing 11 eclamptics, 59 severe preeclamptics, and 27 mild preeclamptics were used to test for linkage between the eNOS gene region and preeclampsia. Two microsatellite markers (D7S483 and D7S505) in the proximity of the eNOS gene were used.Main Outcome Measures: Logarithm of odds (LOD) scores were used to examine the cosegregation of alleles with the disease under a variety of inheritance models. Model-independent analysis, affected pedigree member method (AFFPED), and pairwise haplotype sharing between affected sibs were also used.Results: Two-point LOD score analysis gave no evidence of linkage between preeclampsia and two markers in close proximity to the eNOS gene (LOD scores <1) for any of the inheritance models investigated, with no evidence of heterogeneity between pedigrees. The AFFPED and the pairwise haplotype sharing test on affected sibs also gave no evidence of linkage (β-values ± 0.05).Conclusion: This study provides no evidence for linkage between two markers in close proximity to the eNOS gene and preeclampsia in these families. These results do not support the recent suggestion that eNOS could be a familial pregnancy-induced hypertension gene (Arngrimsson R, et al., Am J Hum Genet 1997;61:354-62). Distinguishing preeclampsia from other hypertensive disorders in pregnancy is difficult. Hypertension appears to be a consequence, rather than a primary cause of preeclampsia. Given the vasodilatory role of the eNOS gene product, it is possible that the linkage recently reported for eNOS reflects its relationship with hypertension rather than preeclampsia.

Absence of Linkage of Phonological Coding Dyslexia to Chromosome 6p23-p21.3 in a Large Family Data Set

Previous studies have suggested that a locus predisposing to specific reading disability (dyslexia) resides on chromosome 6p23-p21.3. We investigated 79 families having at least two siblings affected with phonological coding dyslexia, the most common form of reading disability (617 people genotyped, 294 affected), and we tested for linkage with the genetic markers reported to be linked to dyslexia in those studies. No evidence for linkage was found by LOD score analysis or affected-sib-pair methods. However, using the affected-pedigree-member (APM) method, we detected significant evidence for linkage and/or association with some markers when we used published allele frequencies with weighting of rarer alleles. APM results were not significant when we used marker allele frequencies estimated from parents. Furthermore, results were not significant with the more robust SIMIBD method using either published or parental marker frequencies. Finally, family-based association analysis using the AFBAC program showed no evidence for association with any marker. We conclude that the APM method should be used only with extreme caution, because it appears to have generated false-positive results. In summary, using a large data set with high power to detect linkage, we were unable to find evidence for linkage or association between phonological coding dyslexia and chromosome 6p markers.

Linkage and association analysis of chromosomal regions containing genes related to neuroendocrine or serotonin function in families with early‐onset, recurrent major depression

Recurrent unipolar depression with an early age of onset is a severe form of unipolar depression that has both genetic and environmental components. We genotyped the members of 16 families identified by probands with early onset (⩽25 years), recurrent unipolar, major depression for 38 simple sequence tandem repeat polymorphisms (SSTRPs) from chromosomal regions containing 12 genes involved in neuroendocrine or serotonergic functioning. Pairwise linkage analysis was performed with the software package FASTLINK. The affected phenotype was defined four ways, and both dominant and recessive models of depression were analyzed. Seven SSTRPs showed lod scores >1.00 at θ values between 0.10–0.20. The members of an additional 18 families were genotyped for these seven SSTRPs, and the complete sample of 34 families was evaluated using lod score analysis, affected pedigree member linkage analysis, and within-family association analysis. Evidence for linkage between D11S929 and affective illness remained positive, necessitating the analysis of four additional SSTRPs within 3 cM of D11S929. After all confirmatory analyses were completed, no evidence suggestive of linkage remained between any of the 38 SSTRPs and the affected phenotypes. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 81:443–449, 1998. © 1998 Wiley-Liss, Inc.

Linkage and association analysis of chromosomal regions containing genes related to neuroendocrine or serotonin function in families with early-onset, recurrent major depression

Recurrent unipolar depression with an early age of onset is a severe form of unipolar depression that has both genetic and environmental components. We genotyped the members of 16 families identified by probands with early onset (< or = 25 years), recurrent unipolar, major depression for 38 simple sequence tandem repeat polymorphisms (SSTRPs) from chromosomal regions containing 12 genes involved in neuroendocrine or serotonergic functioning. Pairwise linkage analysis was performed with the software package FASTLINK. The affected phenotype was defined four ways, and both dominant and recessive models of depression were analyzed. Seven SSTRPs showed lod scores > 1.00 at theta values between 0.10-0.20. The members of an additional 18 families were genotyped for these seven SSTRPs, and the complete sample of 34 families was evaluated using lod score analysis, affected pedigree member linkage analysis, and within-family association analysis. Evidence for linkage between D11S929 and affective illness remained positive, necessitating the analysis of four additional SSTRPs within 3 cM of D11S929. After all confirmatory analyses were completed, no evidence suggestive of linkage remained between any of the 38 SSTRPs and the affected phenotypes.

Absence of linkage with the neuronal nitric oxide synthase (NOS1) gene in 41 multiplex Swedish MS families

Several genetic factors are likely to play a role in the aetiology of multiple sclerosis (MS), although so far only the HLA gene complex has been clearly identified as important. In addition, several studies support the importance of nitric oxide synthase (NOS) as a component in the pathogenesis of MS. We have investigated the role of the neuronal nitric oxide synthase (NOS1) gene in 41 Swedish multiplex MS families by parametric and nonparametric linkage analysis with two polymorphic intragenic markers. Two‐point lod scores were clearly negative, effectively excluding a role of the NOS1 gene in most models tested. Non‐parametric linkage analysis (NPL), affected pedigree member (APM) analysis and extended transmission disequilibrium test (ETDT) also failed to provide evidence for a susceptibility locus in this gene. Thus, a contribution of the NOS1 gene to the genetic background of MS is unlikely in this population.

Suggestive Linkage between Markers on Chromosome 19q13.2 and Nonsyndromic Orofacial Cleft Malformation

Nonsyndromic cleft lip with or without cleft palate (OFC) is a common birth defect that has genetic bases. The nature of the genetic contribution is still to be clarified; however, some chromosome regions and candidate genes have been proposed for this malformation. We examined linkage between BCL3, a proto-oncogene located in 19q13.2, and OFC in a sample composed of 40 multiplex pedigrees using both nonparametric and parametric methods. The affected pedigree member statistics and the transmission disequilibrium test supported a role for BCL3 in causing OFC, while no evidence of linkage or genetic heterogeneity was found with the lod score method.

Linkage and association analysis of genes encoding cytokines and myelin proteins in multiple sclerosis

Several genetic factors are likely to play a role in the etiology of multiple sclerosis (MS). We used a candidate gene strategy in a study of polymorphic markers within or close to genes encoding cytokines (interferon- γ (IFN- γ), interleukin-2 (IL-2), IL-4, IL-4 receptor (IL-4R), IL-10, transforming growth factor- β1 and - β2) and myelin proteins (2′,3′-cyclic-nucleotide 3′-phosphohydrolase (CNP:ase), myelin associated glycoprotein, oligodendrocyte myelin glycoprotein, proteolipid protein) in 34 Swedish multiplex MS families and in 147 sporadic MS patients and 95 healthy controls. No evidence for linkage was observed in two-point linkage analysis. However, a slightly positive LOD score of 0.88 ( θ=0.01) for IFN- γ was found. Affected pedigree member (APM) analysis indicated a possible linkage with TGF- β2 ( p=0.008) and IL-4R ( p=0.043). None of the cytokine markers were associated with MS in case-control analysis. Our results suggest a possible importance of the TGF- β2, IL-4R and IFN- γ genes in MS.

A Susceptibility Locus for Bipolar Affective Disorder on Chromosome 4q35

Bipolar affective disorder (BAD) affects approximately 1% of the population and shows strong heritability. To identify potential BAD susceptibility loci, we undertook a 15-cM genome screen, using 214 microsatellite markers on the 35 most informative individuals of a large, statistically powerful pedigree. Data were analyzed by parametric two-point linkage methods under several diagnostic models. LOD scores >1.00 were obtained for 21 markers, with four of these >2.00 for at least one model. The remaining 52 individuals in the family were genotyped with these four markers, and LOD scores remained positive for three markers. A more intensive screen was undertaken in these regions, with the most positive results being obtained for chromosome 4q35. Using a dominant model of inheritance with 90% maximum age-specific penetrance and including bipolar I, II, schizoaffective/mania, and unipolar individuals as affected, we obtained a maximum two-point LOD score of 2.20 (theta = .15) at D4S1652 and a maximum three-point LOD score of 3.19 between D4S408 and D4S2924. Nonparametric analyses further supported the presence of a locus on chromosome 4q35. A maximum score of 2.62 (P=.01) was obtained between D4S1652 and D4S171 by use of the GENEHUNTER program, and a maximum score of 3.57 (P=.0002) was obtained at D4S2924 using the affected pedigree member method. Analysis of a further 10 pedigrees suggests the presence of this locus in at least one additional family, indicating a possible predisposing locus and not a pedigree-specific mutation. Our results suggest the presence of a novel BAD susceptibility locus on chromosome 4q35.

Linkage analysis of familial melanoma and chromosome 6 in 14 Australian kindreds.

CDKN2A (9p21) and CDK4 (12q13) have been identified as melanoma susceptibility genes in certain familial melanoma (FM) kindreds. There remain other FM families, however, for which there is little or no evidence for linkage of melanoma to these loci. Other loci may be involved in susceptibility to this malignancy. Chromosome 6 is deleted or rearranged in 66% of melanomas and has been targeted by several studies in an attempt to identify chromosomal regions associated with initiation or progression of melanoma. Previous studies of familial melanoma and chromosome arm 6p reported evidence suggestive of linkage for markers flanking the HLA complex. We have carried out genetic linkage analysis in 14 Australian familial melanoma kindreds using 16 short tandem repeat polymorphism (STRP) markers spanning 6p23-6q27. Analysis by maximum likelihood and non-parametric (affected pedigree member) techniques showed no evidence of linkage of melanoma in this family set to chromosome 6 (two-point Zmax = 0.5 at theta = 0.2 for D6S285). Lod scores > 1.0 were obtained for the loci D6S285, D6S105, D6S265, D6S292, and D6S311 in three individual kindreds but these were insufficiently strong for formal heterogeneity testing to confirm that a chromosome 6-linked subset of families exists. These data imply little or no role for a major chromosome 6 melanoma susceptibility locus; however the possibility of such a locus remains open and warrants further investigation.

Migraine association and linkage studies of an endothelial nitric oxide synthase (NOS3) gene polymorphism.

Migraine shows strong familial aggregation. However, the number of genes involved in the disorder is unknown and not identified. Nitric oxide is involved in the central processing of pain stimuli and plays an important role in the regulation of basal or stimulated vasodilation. Nitric oxide synthase, which controls the synthesis of nitric oxide, could possibly be a cause, or candidate gene, in migraine etiology. In this study, we detected a polymorphism for endothelial nitric oxide synthase by polymerase chain reaction and tested this for association and linkage to migraine. Results from the study did not show an association of the nitric oxide synthase microsatellite when tested in 91 affected and 85 unaffected individuals. Using the FASTLINK program for parametric linkage analysis, the polymorphism did not show significant linkage to migraine when tested in four migraine pedigrees composed of 116 individuals, 52 affected. Total LOD scores excluded linkage up to 8.5 cM between the nitric oxide synthase polymorphism and migraine. Results using the nonparametric affected pedigree member form of analysis also did not support a role for this gene in migraine etiology.