The COL5A3 and MMP9 genes interact in eczema susceptibility.

BACKGROUND: Genetic studies of eczema have identified many genes, which explain only 14% of the heritability. Missing heritability may be partly due to ignored gene-gene (G-G) interactions. OBJECTIVE: Our aim was to detect new interacting genes involved in eczema. METHODS: The search for G-G interaction in eczema was conducted using a two-step approach, which included as a first step, a biological selection of genes, which are involved either in the skin or epidermis development or in the collagen metabolism, and as a second step, an interaction analysis of the selected genes. Analyses were carried out at both SNP and gene levels in three asthma-ascertained family samples: the discovery dataset of 388 EGEA (Epidemiological study on the Genetics and Environment of Asthma) families and the two replication datasets of 253 SLSJ (Saguenay-Lac-Saint-Jean) families and 207 MRCA (Medical Research Council) families. RESULTS: One pair of SNPs, rs2287807 in COL5A3 and rs17576 in MMP9, that were detected in EGEA at P ≤ 10-5 showed significant interaction by meta-analysis of EGEA, SLSJ and MRCA samples (P = 1.1 × 10-8 under the significant threshold of 10-7 ). Gene-based analysis confirmed strong interaction between COL5A3 and MMP9 (P = 4 × 10-8 under the significant threshold of 4 × 10-6 ) by meta-analysis of the three datasets. When stratifying the data on asthma, this interaction remained in both groups of asthmatic and non-asthmatic subjects. CONCLUSION: This study identified significant interaction between two new genes, COL5A3 and MMP9, which may be accounted for by a degradation of COL5A3 by MMP9 influencing eczema susceptibility. Further confirmation of this interaction as well as functional studies is needed to better understand the role of these genes in eczema.

A second locus for Marfan syndrome maps to chromosome 3p24.2-p25.

Marfan syndrome (MFS) is an autosomal dominant connective-tissue disorder characterized by skeletal, ocular and cardiovascular defects of highly variable expressivity. The diagnosis relies solely on clinical criteria requiring anomalies in at least two systems. By excluding the chromosome 15 disease locus, fibrillin 1 (FBN1), in a large French family with typical cardiovascular and skeletal anomalies, we raised the issue of genetic heterogeneity in MFS and the implication of a second locus (MFS2). Linkage analyses, performed in this family, have localized MFS2 to a region of 9 centiMorgans between D3S1293 and D3S1283, at 3p24.2-p25. In this region, the highest lod score was found with D3S2336, of 4.89 (theta = 0.05). By LINKMAP analyses, the most probable position for the second locus in MFS was at D3S2335.

Season of birth and not vitamin D receptor promoter polymorphisms is a risk factor for multiple sclerosis.

Both genetic and environmental factors contribute to multiple sclerosis, the most common neurodegenerative disorder with onset in young adults. The objective of the current study is, based on the hypothesis that environmentally predisposed individuals are at risk for multiple sclerosis, to investigate whether they also carry genetic variants within the vitamin D machinery. Using medical files and DNA samples from 583 trios (a patient and both parents) of the French Multiple Sclerosis Genetics Group as well as data from the French Statistics Bureau, we aimed to assess whether: (1) a seasonality of birth was observed in French multiple sclerosis patients; (2) three single nucleotide polymorphisms within the promoter region of the vitamin D receptor were associated with multiple sclerosis susceptibility; and (3) the combination of a high risk month of birth and vitamin D receptor polymorphisms were correlated to multiple sclerosis incidence. We observed a significantly reduced number of individuals born in November who were later diagnosed as multiple sclerosis patients. However, we found no association between the three studied vitamin D receptor polymorphisms and multiple sclerosis. In conclusion, our data suggest that high levels of vitamin D during the third trimester of pregnancy could be a protective factor for multiple sclerosis.

HLA-DRB1*15 allele influences the later course of relapsing remitting multiple sclerosis.

Most of the published works so far have aimed at finding genes associated with multiple sclerosis (MS) susceptibility. Very few studies have attempted to correlate disease features with DNA variants. In a well-characterized sample (651 patients) representative of multiple sclerosis natural history, we engaged a comprehensive study of the role of human leukocyte antigen (HLA) in the course of the disease. We investigated the role of HLA-DRB1*15 allele in samples stratified according to severity evaluated by the Multiple Sclerosis Severity Score (MSSS), time to reach EDSS 6.0 and disease type. We found that HLA-DRB1*15 genotype does not influence MS severity even among patients presenting with a given type of the disease. However, we show for the first time that HLA-DRB1*15 allele modulates the course of MS for relapsing-remitting (RR) onset patients likely by precipitating the secondary progressive (SP) phase.

IL2RA and IL7RA genes confer susceptibility for multiple sclerosis in two independent European populations.

Multiple sclerosis (MS) is the most common chronic inflammatory neurologic disorder diagnosed in young adults and, due to its chronic course, is responsible for a substantial economic burden. MS is considered to be a multifactorial disease in which both genetic and environmental factors intervene. The well-established human leukocyte antigen (HLA) association does not completely explain the genetic impact on disease susceptibility. However, identification and validation of non-HLA-genes conferring susceptibility to MS has proven to be difficult probably because of the small individual contribution of each of these genes. Recently, associations with two single nucleotide polymorphisms (SNPs) in the IL2RA gene (rs12722489, rs2104286) and one SNP in the IL7RA gene (rs6897932) have been reported by several groups. These three SNPs were genotyped in a French and a German population of MS patients using the hME assay by the matrix-assisted laser desorption/ionization time of flight technology (Sequenom, San Diego, CA, USA). We show that these SNPs do contribute to the risk of MS in these two unrelated European MS patient populations with odds ratios varying from 1.1 to 1.5. The discovery and validation of new genetic risk factors in independent populations may help toward the understanding of MS pathogenesis by providing valuable information on biological pathways to be investigated.

A systematic study of oligodendrocyte growth factors as candidates for genetic susceptibility to MS. French Multiple Sclerosis Genetics Group.

OBJECTIVE: To test 23 genes coding for growth factors and their receptors as candidates for MS genetic susceptibility in 84 multiplex families of French origin by linkage analysis. BACKGROUND: Epidemiologic studies have indicated that genetic susceptibility in MS exists. To identify MS susceptibility genes, association and linkage studies were performed with candidate genes suggested by the pathology of MS. The most consistent result was genetic association and linkage of MS to human leukocyte antigen (HLA) DR15. Recent advances in the knowledge of MS pathology have suggested that the oligodendrocyte, the myelin-forming cell in the CNS, and its growth factors might play a crucial role in MS. METHODS: Fifty-two polymorphic markers within or flanking 23 candidate genes were used. Data were analyzed with the maximum likelihood score (MLS) approach. We also searched for a genetic interaction with HLA. RESULTS: Negative results were obtained for all candidate genes. The lower limits of the relative risk (Xs) possibly excluded for any candidate gene ranged from 1.3 to 2.8. Positive MLS values (up to 0.93) were observed for transforming growth factor beta 3 (TGFbeta3) in HLA DR15-associated families, suggesting a possible role for this growth factor in interaction with HLA. CONCLUSIONS: Oligodendrocyte growth factors do not play a significant role in MS genetic susceptibility, at least in the tested sample. TGFbeta3, the only gene highlighted by this study, deserves further analysis.

Cytokines in genetic susceptibility to multiple sclerosis: a candidate gene approach. French Multiple Sclerosis Genetics Group.

The immune system is involved in the pathophysiology of multiple sclerosis (MS) but the initiating antigen(s) is not yet identified. Since cytokines control both the intensity and the quality of the immune response they may be relevant candidates for the genetic susceptibility to MS. To analyze the contribution of type 1 and type 2 cytokine and cytokine receptor genes in the genetic susceptibility to MS, we have examined, in 116 French MS sibpairs, whether there is significant linkage between MS and 15 cytokine or cytokine receptor genes using 31 highly polymorphic genetic markers. The data were analyzed using the maximum likelihood score and the transmission disequilibrium approaches. None of the candidate genes tested was significantly linked to MS on the whole population. However, after stratification of the analysis on the basis of sharing (or not) of the HLA-DRB1*1501 allele, indication of linkage was found for the IL2-RB gene. These findings suggest that the IL2-RB locus contributes to the genetic susceptibility in a subgroup of MS patients.

Childhood-onset systemic lupus erythematosus: antiphospholipid antibodies in 37 patients and their first-degree relatives.

OBJECTIVE: Antiphospholipid antibodies (aPL) are noted with increased frequency in patients with systemic lupus erythematosus (SLE). The main manifestations found to be associated with aPL are arterial and venous thrombotic events, thrombocytopenia, and recurrent pregnancy loss. This study is an attempt to define the incidence of aPL in patients with childhood-onset SLE and in their relatives and to correlate their presence with clinical manifestations, and especially, to evaluate the risk of thrombosis in aPL-positive subjects. METHODOLOGY: We studied 37 unrelated patients and 107 of their first-degree relatives. VDRL, IgG and IgM anticardiolipin, and IgG antiphosphatidylethanolamine antibodies were studied in all probands during periods of clinical remission and in first-degree relatives at the time of interview. Lupus anticoagulant had only been studied in probands during an SLE flare-up. RESULTS: Thirty-eight percent of probands and 19% of relatives were positive for at least one aPL, with little overlap between the different aPL studied. -No aPL-negative proband developed thrombosis. Two of the aPL-positive probands had thrombotic events before testing, and a third one showed thrombosis after testing. Only two probands had high levels of IgG aCL and showed thrombosis. The occurrence of aPL positivity in relatives was not always related to its presence in probands. None of the aPL-positive relatives had had thrombosis, but recurrent fetal loss was noted in one aPL-positive mother with SLE. Although there was a high frequency of SLE, SLE-like disease, auto-immune disorders or positive serological findings for lupus in first-degree relatives, many of these relatives did not test positive for aPL. CONCLUSION: The high levels of IgG aCL may be considered a risk factor for thrombosis. Findings in relatives suggest a multifactorial origin for autoimmune disease and antibody production.

Characteristics of familial aggregation in early-onset Alzheimer's disease: evidence of subgroups.

Characteristics of familial aggregation of Alzheimer's Disease were studied in 92 families ascertained through a clinically diagnosed proband with an onset below age 60 years. In each family data were systematically collected on the sibships of the proband, of his father, and of his mother. A total of 926 relatives were included and 81% of the living relatives (i.e., 251 individuals) were directly examined. The estimated cumulative risk among first degree relatives was equal to 35% by age 89 years (95% confidence interval 22 to 47%). This result does not support the hypothesis that an autosomal dominant gene, fully penetrant by age 90 years, is segregating within all these pedigrees. Despite the fact that all probands were selected for an onset before age 60 years it was shown that two types of families could be delineated with respect to age at onset among affected relatives: all secondary cases with an onset below age 60 years were contributed by a particular group of families (type 1 families), whereas all secondary cases with an onset after age 60 years were contributed by another group of families (type 2 families). Although genetic interpretation of these findings is not straightforward, they support the hypothesis of etiologic heterogeneity in the determination of early-onset Alzheimer's disease.

Segregation analysis of Alzheimer pedigrees: rare Mendelian dominant mutation(s) explain a minority of early-onset cases. French Alzheimer Collaborative Group.

Segregation analysis of Alzheimer disease (AD) in 92 families ascertained through early-onset ( < or = age 60 years) AD (EOAD) probands has been carried out, allowing for a mixture in AD inheritance among probands. The goal was to quantify the proportion of probands that could be explained by autosomal inheritance of a rare disease allele "a" at a Mendelian dominant gene (MDG). Our data provide strong evidence for a mixture of two distributions; AD transmission is fully explained by MDG inheritance in < 20% of probands. Male and female age-of-onset distributions are significantly different for "AA" but not for "aA" subjects. For "aA" subjects the estimated penetrance value was close to 1 by age 60. For "AA" subjects, it reaches, by age 90, 10% (males) and 30% (females). We show a clear cutoff in the posterior probability of being an MDG case.

Association of apolipoprotein E allele epsilon 4 with late-onset sporadic Alzheimer's disease.

Apolipoprotein E, type epsilon 4 allele (ApoE epsilon 4), is associated with late-onset sporadic Alzheimer's disease (AD) in French patients. The association is highly significant (0.45 AD versus 0.12 controls for epsilon 4 allele frequencies). These data support the involvement of ApoE epsilon 4 allele as a very important risk factor for the clinical expression of AD.

Power and robustness of the linkage homogeneity test in genetic analysis of common disorders.

The power and robustness of the admixture test are studied. The power of the test depends on the genetic parameters at the disease locus. In particular, the power decreases drastically with the level of penetrance. The test is robust to errors in genetic parameters provided that the recombination fraction is not fixed a priori. However, misspecifying genetic parameters leads to a bias in the estimates of both the recombination fraction and the proportion of linked families.

Failure to replicate linkage between chromosome 5q11-q13 markers and schizophrenia in 28 families.

Sherrington et al. (1988) reported linkage between markers located on the 5q11-q13 region of chromosome 5 and schizophrenia in five Icelandic and two British families. To date, however, all attempts to replicate the initial finding have failed. Using three markers of chromosome 5, we have studied 28 additional French pedigrees. When our data were analyzed both with parametric (i.e., lod scores) and nonparametric methods, we found no evidence of linkage. Thus, we were unable to replicate the earlier report by Sherrington et al.

Testing genetic models for IDDM by the MASC method.

The MASC method has been applied to the GAW5 data. The method uses the simultaneous information on association and segregation of the HLA marker with the disease and the segregation of the HLA marker in affected families. It also takes into account the differential risk for parents of a patient, as well as the different HLA haplotype sharing, according to the HLA genotype of the patient. The goodness of fit of several genetic models has been tested. The observed data are not compatible with a two-allele, one-locus model, but they fit a three-allele, one-locus model and a complementation two-locus model if additional familial correlation is allowed.

Polymorphism and genetic evolution in an isolate in the Antilles: Saint-Barthélémy.

St Barthélémy, a small island near Guadaloupe, has been isolated since the eighteenth century. The population is made up of two geographical isolates, genetically separated. In each, the inbreeding level is increasing on account of random genetic drift, which is reinforced by village endogamy, equivalent to a kind of spouse selection. Consanguinity between spouses has been analysed to give an estimate of the contributions of random genetic drift and spouse choice to total inbreeding. A second estimate to inbreeding can be obtained from the variation in observed gene frequencies. The two estimates obtained are of the same order, 0.6-1.0%, and are comparable with those still observed in isolated villages of the French Pyrenees.

Triangle test statistic in discordant sib pairs: test of genetic heterogeneity of asthma and atopy in CSGA families.

The purpose of our study was to detect genetic heterogeneity (i.e., different genotype relative risks of genetic factor) between atopic and non-atopic asthma and between atopy associated or independent of asthma. Genetic heterogeneity was tested in the Caucasian Collaborative Study on the Genetics of Asthma families using the TTS (triangle test statistic) and the predivided sample test. The TTS was proposed to detect both linkage and intra-sib-pair genetic heterogeneity; such heterogeneity may exist if the sibs differ for a factor on which the penetrances of the putative linked gene depend. The TTS has been applied to asthmatic pairs discordant for atopy and atopic sib pairs discordant for asthma. To confirm genetic heterogeneity detected by the TTS, the predivided sample test was also applied among concordant and discordant sib pairs. The analyses detected a genetic factor on chromosome 8p that could be involved in atopy with different genotype relative risks according to whether asthma is present. This would suggest a pleiotropic effect of this genetic factor in asthma and atopy. Two other regions located on chromosomes 8q and 20p were detected for genetic heterogeneity with asthma and atopy, respectively, but the factor of heterogeneity could be independent from the presence of atopy or asthma, respectively. It could be a characteristic of the disease such as the severity or the presence of an environmental factor.

Genetics of celiac disease.

Celiac disease (CD) is a chronic inflammatory disease of the gut resulting from ingestion of gluten, occurring in genetically susceptible individuals. The strong genetic association of CD with the DQ2 and DQ8 HLA heterodimers has been known for long, but others non-HLA genes are involved. In order to identify susceptibility genes to CD, several studies have been performed, based on either linkage analyses or candidate gene approaches. This review describes these different studies and their results. The hypothesis of the implication of the DR53 heterodimer in the HLA region has been proposed. The existence of a susceptibility locus on chromosome 5q has been evidenced through linkage analysis and candidate gene strategies have revealed the role of CTLA-4 and of the immunoglobulin gamma genes in the disease.

HLA-associated diseases: a new method for performing linkage analysis with other markers than HLA.

It has been shown that genetic factors within the HLA region are involved in the etiology of several diseases. For some of these, the existence of another genetic factor has been suggested, although not proven. A possible way to give evidence for another locus (G) is to show that the disease and an unlinked HLA-marker locus (M) do not segregate independently. The usual lod-score method, which assumes monogenic inheritance, is inappropriate for this test. We propose a correction of this method for performing a linkage analysis between the G and M loci, taking into account the role of HLA. A very simple way of using the HLA information is by modifying, for each individual of a pedigree, the penetrance values at the G locus according to the number of HLA haplotypes shared with the index case. These penetrance values are inferred from the observed IBD (identity-by-descent) distribution of HLA haplotypes in a sample of affected sib-pairs. The advantage of using this empirical distribution is that it is not based on any assumptions concerning the mode of inheritance at the HLA-linked locus. This correction method was established using a two-locus model with restrictive assumptions. Its value is discussed for various sets of parameters in more general and realistic two-locus models using simulations.

Sampling strategy in linkage studies of affective disorders.

Evidence of linkage in families of bipolar patients has so far been identified with genetic markers on chromosome X and 11. However, replications of these data have not consistently been reported in either case, which favours the hypothesis of genetic heterogeneity. Therefore, we have tried to outline a sampling strategy for linkage replication in affective disorders. We estimated the average number of nuclear families required to replicate X or 11 linkage as a function of the degree of heterogeneity as well as the number to prove heterogeneity given that linkage exists. The results are presented and discussed.