Genetic analysis of aquaporin-4 in neuromyelitis optica.

OBJECTIVE: Autoantibodies to aquaporin-4 (AQP4) are specific and pathogenic for neuromyelitis optica (NMO). Therefore, we evaluated whether AQP4 single-nucleotide polymorphisms (SNPs) are associated with susceptibility to NMO or whether mutations that potentially alter AQP4 structure or expression are present in some patients. METHODS: We genotyped 8 AQP4 SNPs chosen based on their minor allele frequency, location, and novelty in 177 NMO sporadic cases, 14 NMO familial cases, and 1,363 matched controls by TaqMan-based assay. We performed bidirectional sequencing of the promoter (1 kb), exons 0-4, and flanking splice consensus sequences, and the 5' and 3' untranslated regions of 177 sporadic and 14 familial NMO cases. RESULTS: One of 8 SNPs (minor allele frequency = 0.01) was associated with NMO (NC 18.8; chrom pos. 22695167: T>A): odds ratio (95% confidence interval) = 13.1 (1.4-126.7); p = 0.026. In 3 patients with NMO (2 related), we detected 2 different missense allelic mutations at Arg19 (R19I and R19T). None of the 1,363 control subjects had Arg19 mutations (p = 0.001). CONCLUSIONS: Except for one uncommon SNP, no tested SNP was associated with NMO, nor were 3 SNP haplotypes, providing no support for the hypothesis that genetic variation in AQP4 accounts for overall susceptibility to NMO. Two different allelic Arg19 missense mutations are specific to NMO and segregated with the disease in one pedigree. Although the pathobiology underlying this is not yet established, their effects on the structure of the M1 isoform N terminus or the regulatory sequence of the M23 isoform by virtue of their location support a role of AQP4 orthogonal array formation on molecular susceptibility to NMO.

IFNG polymorphisms are associated with gender differences in susceptibility to multiple sclerosis.

Interferon-gamma (IFNgamma) treatment is deleterious in multiple sclerosis (MS). MS occurs twice as frequently in women as in men. IFNgamma expression varies by gender. We studied a population-based sample of US MS patients and ethnicity-matched controls and independent Northern Irish and Belgian hospital-based patients and controls for association with MS, stratified by gender, of an intron 1 microsatellite [I1(761)*CAn], a single nucleotide polymorphism 3' of IFNG [3'(325)*G --> A] and three flanking microsatellite markers spanning a 118 kb region around IFNG. Men carriers of the 3'(325)*A allele have increased susceptibility to MS compared to noncarriers in the USA (P=0.044; OR: 2.58, 95% CI: 0.97-8.08) and Northern Ireland (P=0.019; OR: 2.37, 95% CI: 1.10-5.13). There is a nonsignificant trend in the same direction in Belgian men (P=0.299; OR: 1.50, 95% CI: 0.71-3.26). Men carriers of I1(761)*CA13, which is in strong linkage disequilibrium with the 3'(325)*A, have increased susceptibility (P=0.050; OR: 2.22, 95% CI: 0.98-5.40), while men carriers of I1(761)*CA12 have decreased susceptibility (P=0.022; OR: 0.46, 95% CI: 0.23-0.90) to MS in the USA. Similar associations were reported in Sardinia between the I1(761)*CA12 allele and reduced risk of MS in men. Flanking markers were not associated with MS susceptibility. Polymorphisms of IFNG may contribute to differences in susceptibility to MS between men and women.

Association of APOE polymorphisms with disease severity in MS is limited to women.

The authors studied the association of an exon 4 (E4*epsilon2/3/4) and three promoter polymorphisms of APOE with disease course and severity stratified by gender in 221 patients with multiple sclerosis from two overlapping population-based prevalence cohorts. Women carriers of the E4*epsilon2 allele took longer to attain an Expanded Disability Status Scale score of 6 (p = 0.015) and had more favorable ranked severity scores than noncarriers (p = 0.009). There was no association in men. Alleles epsilon3 or epsilon4 and promoter polymorphisms were not associated with disease course or severity.

Association of two variants in IL-1beta and IL-1 receptor antagonist genes with multiple sclerosis.

We studied the putative association of a C-->T polymorphism in exon-5 of IL-1beta and an 85 bp tandem repeat in intron-4 of IL-1 receptor antagonist (IL-1ra) genes with susceptibility to or outcome of MS. DNA from 122 cases from a population-based cohort in Olmsted County, MN who were previously categorized for disease severity and temporal course and 244 ethnically-matched controls were analyzed. There was no association between either polymorphism and disease susceptibility. Allele-2 of IL-1beta and allele-3 of the IL-1ra polymorphisms were associated with a favorable outcome (P=0.023 and P=0.030).

Association of a myeloperoxidase promoter polymorphism with multiple sclerosis.

Myeloperoxidase (MPO) generates hypochlorous acid and other reactive oxygen intermediates leading to tissue damage. MPO is expressed in macrophages-microglia in multiple sclerosis (MS) lesions. A G-->A substitution that abolishes an SP1 transcription factor consensus sequence in the promoter reduces gene expression. We studied the association of the genetic variant with MS. We did not find an association with gender, age at onset, susceptibility to, or the course and severity of MS in a population-based sample of 122 patients from Olmsted County.

Genetic variation in the B7-1 gene in patients with multiple sclerosis.

Co-stimulation of T cells by B7-1, a protein that is expressed on antigen presenting cells, favors a T helper type1 (Th1) cellular response. Th1/Th2 bias may influence disease susceptibility or course of MS. We screened the entire coding sequence as well as the 5'- and 3'-untranslated regions of the B7-1 gene using a mutation scanning technique, dideoxyfingerprinting, in DNA from 111 patients with MS from Olmsted County, Minnesota. We identified five genetic variants. None alter protein structure nor have apparent functional significance. Selected variants of sufficient frequency were tested for an association with course and severity of MS and one was tested for an association with susceptibility; none of the association tests were positive.

DNA compression caused by an upstream point mutation.

We observed an apparent series of insertions and deletions beginning 5 bp downstream of an A-->G silent transition in exon 1 of the tumor necrosis factor receptor 1 gene. The apparent sequence anomaly was observed only in individuals carrying the transition. Formamide gel electrophoresis revealed that the apparent sequence anomaly was due to compression. The compression is plausibly explained by a hairpin in the reaction products in a region of trinucleotide CAG repeats. One should suspect the presence of DNA compression when a series of deletions and insertions follows a single base pair mutation that leads to a series of trinucleotide repeats.

Screening the monoamine oxidase B gene in 100 male patients with schizophrenia: a cluster of polymorphisms in African-Americans but lack of functionally significant sequence changes.

The monoamine oxidase B (MAO-B) gene was examined in 100 alleles derived from 80 Caucasian, 10 African-American, 5 Asian, and 5 Native American male patients with schizophrenia to identify sequence changes that might be associated with the disease. Approximately 235 kb of genomic sequence, primarily in coding regions, were screened by dideoxy fingerprinting, a modification of single-strand conformational polymorphism (SSCP) analysis that detects virtually 100% of sequence changes [Sarkar et al. (1992): Genomics 13:441-443; Liu and Sommer (1994): PCR Methods Appl 4:97-108]. No sequence changes of likely functional significance were identified, suggesting that mutations affecting the structure of the MAO-B protein are uncommon in the general population and are unlikely to contribute significantly to the genetic predisposition to schizophrenia. Eight polymorphisms were identified in African-Americans and Native Americans, but none were identified among Caucasians. Of the eight observed polymorphisms, a set of five transitions and one microdeletion was identified within approximately 17 kb of genomic sequence in the same 3 African-American individuals, while the remaining 7 African-Americans had a sequence identical to that in Caucasians. The presence of two such haplotypes, without intermediates, is compatible with the hypothesis that germline mutations can occur in clusters, as also suggested by other recent findings.