Genetics and transcriptomicsSaturday, October 13, 2007, 15:30 - 17:00
Genetic analysis of AQP4 in neuromyelitis optica patientsM. Matiello, D. Hebrink, A. Jacob, J. Schaefer-Klein, B. Weinshenker for the NMO Genetics Consortium
Objective: To search for genomic mutations in AQP4 that may explain neuromyelitis optica (NMO) susceptibility.
Background: The etiology of NMO is unknown. Occasional occurrence of NMO in relatives and excess of non-Caucasian ancestry in patients with NMO suggest a genetic component of NMO susceptibility. Antibodies to AQP4 are highly specific for NMO and the pathogenicity is suggested by the concordance between brain lesions and both macroscopic and microscopic sites of high AQP4 immunoreactivity(Pittock et al., Arch Neurol. 2006) by the immunopathological location of immunoglobulin and complement in NMO lesions(Lucchinetti et al. Brain 2002) and by the specific abolition of NMO reactivity in early NMO lesions(Roemer, et al. Brain 2007). Autoimmune responses to other mutant proteins have apparently resulted in a late appearing autoimmune disease. We hypothesized that structural mutations of AQP4 might account for susceptibility to NMO.
Design/Methods: Patients with NMO or a NMO spectrum disorder were ascertained at 3 sites (Mayo Clinic-Rochester, the Walton Centre,UK and the Univ.of Vienna, Austria). Sera were tested for NMO-IgG by indirect immunofluorescence assay; in this report, all but two patients were seropositive for NMO-IgG. The promoter region (1000 bp), exons 1-5, 5’ and 3’untranslated regions and the splice consensus sequences flanking the exons were amplified by PCR and subsequently sequenced at Mayo Clinic in both forward and reverse directions by the dye-terminator sequencing method. The patients’ sequences and the AQP4 Genbank reference file (NC_000018) was compared using Mutation Surveyor v2.61(Softgenetics, S.College, PA).
Results: Thirty-six sporadic patients and one familial case were studied, 33(89.2%) women, 4 (10.8%) men. 26(70.2%) were Caucasian, 5(13.5%) Hispanic, 2(5.4%) Asian, 1(2.7%) African, 1 Arabic and 2 unknown. Twelve of 17 known SNPs in the general population (NCBI SNP database) were polymorphic in the NMO patients evaluated thus far. We identified three novel exonic SNPs in one patient, one in the coding region of exon 2 (synonymous) and two in the 3’untranslated region in exon 5.
Conclusions/Relevance: Structural mutations were not found in the AQP4 gene of 36 sporadic and 1 familial NMO patients. The ascertainment and analysis of patients with different ethnic background and of familial cases is ongoing.
The NMO Genetics consortium also includes: M.Boggild (Walton Centre, UK) and W.Kristoferitsch (Vienna, Austria).