Genetic factors for susceptibility to and manifestations of neuromyelitis optica

Abstract

Objective: To identify genetic factors associated with susceptibility to and clinical features of neuromyelitis optica spectrum disorders (NMOSD).

Methods: Genome-wide single nucleotide polymorphism (SNP) genotyping was conducted in 211 Japanese patients with NMOSD fulfilling the 2006 criteria with or without anti-aquaporin-4 (AQP4) antibody and 1,919 Japanese healthy controls (HCs). HLA-DRB1 and HLA-DPB1 alleles were genotyped in 184 NMOSD cases and 317 HCs. Multiple sclerosis (MS) risk alleles outside the major histocompatibility complex (MHC) region were tested in NMOSD and MS genetic burden (MSGB) scores were compared between HCs and NMOSD.

Results: A SNP (rs1964995) in the MHC region was associated with NMOSD susceptibility (odds ratio (OR) = 2.33, P = 4.07 × 10^-11 ). HLA-DRB1*08:02 (OR = 2.86, P = 3.03 × 10^-4 ) and HLA-DRB1*16:02 (OR = 8.39, P = 1.92 × 10^-3 ) were risk alleles for NMOSD susceptibility whereas HLA-DRB1*09:01 was protective (OR = 0.27, P = 1.06 × 10^-5 ). Three MS risk variants were associated with susceptibility and MSGB scores were significantly higher in NMOSD than in HCs (P = 0.0095). A SNP in the KCNMA1 (potassium calcium-activated channel subfamily M alpha 1) gene was associated with disability score with genome-wide significance (rs1516512, P = 2.33 × 10^-8 ) and transverse myelitis (OR = 1.77, P = 0.011). KCNMA1 was immunohistochemically detected in the perivascular endfeet of astrocytes and its immunoreactivity was markedly diminished in active spinal cord lesions in NMOSD.

Interpretation: Specific HLA-DRB1 alleles confer NMOSD susceptibility and KCNMA1 is associated with disability and transverse myelitis in NMOSD.

Figure 1

Flowchart of sample quality control. Following quality control procedures for samples, 203 cases and 1782 controls were available for the genome‐wide association study for NMOSD.

Figure 2

P‐values from the genome‐wide association study and multiple sclerosis genetic burden scores of NMOSD. (A) Manhattan plot of association signals with NMOSD susceptibility. The P‐value (‐log₁₀ P) of the association (ordinate) adjusted by sex is plotted against the base pair position for each chromosome variant (abscissa). A peak association (rs1964995) was observed in the MHC region between HLA‐DRA and HLA‐DR5. (B) MS genetic burden score of individuals is plotted and compared between NMOSD and HCs.

Figure 3

Associations of a variant in KCNMA1 with disability and spinal cord damage of NMOSD. (A) Manhattan plot of association signals with rank‐normalized EDSS scores adjusted for age of onset and disease duration. A peak association (rs1516512) was located in KCNMA1 of chromosome 10. (B) Box‐whisker plot of raw EDSS scores in each rs1516512 allele carrier. (C) Frequency of transverse myelitis in each rs1516512 allele carrier. TM, transverse myelitis.

Figure 4

Expression pattern of KCNMA1 in spinal cords of a control (A–C) and NMOSD patients (D–U). (A) KCNMA1 is diffusely expressed in the gray matter showing neuropil staining (insert). (B) KCNMA1 has a mesh‐like appearance in the white matter, (B, C) and is densely expressed in the glia limitans (B) and perivascular foot processes (C, arrows). (D–F) Active lesions in NMOSD cases. Immunostaining for CD68 (brown color) shows massive infiltration of macrophages in extensive spinal cord lesions in NMOSD‐1 (D), NMOSD‐2 (E), and NMOSD‐3 (F) cases. (G–U) Immunoreactivity for KCNMA1 in active lesions is diminished similar to the loss of AQP4 and MOG in the spinal cord at the 12th thoracic spinal segment from an NMOSD‐1 case (G–I), at the 3rd thoracic spinal cord segment from an NMOSD‐2 case (J–L) and at the 8th thoracic spinal segment from an NMOSD‐3 case (M–U). Immunoreactivity for KCNMA1 is diminished in astrocytes of active lesions (I, L, O, R). (P–R) Higher magnification view of arrowhead in M–O. Expressions of AQP4 and KCNMA1 are markedly diminished in the white matter perivascular region (P and R, arrowheads). Minimal vacuolation of the spinal cord tissue without obvious demyelination around the affected vessel (Q, arrowhead). (S–U) Higher magnification of the rectangle in M–O. Immunoreactivity for AQP4 is diminished more extensively than for KCNMA1 (S and U, arrowheads). Immunostaining for MOG reveals no demyelination and/or vacuolation of spinal cord tissue in the KCNMA1‐preserved area (T, U, arrowheads). Scale bars = 2 mm (A, D–O), 200 µm (B, P–U) and 20 µm (C).