Bone health in neuromyelitis optica: Bone mineral density and fractures.

BACKGROUND: The bone health in neuromyelitis optica spectrum disorder with aquaporin-4 immunoglobulin G antibodies (NMOSD-AQP4) have not been fully evaluated. To evaluate the prevalence of fractures and bone loss in patients with NMOSD-AQP4 compared to healthy controls and patients with multiple sclerosis (MS) and to identify the risk factors associated with fractures and low bone mineral density (BMD) in patients with NMOSD-AQP4. METHODS: Seventy-one patients with NMOSD-AQP4 were included. The two control groups consisted of 213 age-, sex-, menopause-, and body mass index (BMI)-matched healthy participants from the Korean National Health and Nutrition Examination Survey (healthy controls) and 41 patients with multiple sclerosis (disease controls). We collected demographic and clinical data related to bone health including BMD and FRAX score. RESULTS: Patients with NMOSD-AQP4 had a higher prevalence of fractures than the healthy control group (OR = 5.40, CI = 2.004-14.524, p = 0.001), with falling, but not steroid use, being associated with an increased risk of fractures after diagnosis with NMOSD-AQP4 (OR = 24.902, CI = 3.086-200.947, p = 0.003). They also had significantly lower BMD than controls (femur neck, p = 0.044; total hip, p < 0.001), which was more prominent in young participants. The BMD in the NMOSD-AQP4 group was associated with cumulative dose of oral steroids, age, sex, BMI, and partly with the prophylactic calcium supplements. Though the patients with NMOSD-AQP4 did not differ significantly from patients with MS in terms of fracture rate and BMD, they had higher risk of fractures as measured by the Fracture Risk Assessment Tool (for major osteoporotic fractures, (p = 0.001; for hip fractures, p = 0.018). CONCLUSION: Patients with NMOSD-AQP4 had a significantly higher risk of fractures that could mostly be attributed to falling. Additionally, low BMD was observed in these patients; it was more prominent among young patients, associated with steroid use, and may partially prevented by the use of prophylactic calcium supplements.

Mutational analyses of the recombinant globular regions of human C1q A, B, and C chains suggest an essential role for arginine and histidine residues in the C1q-IgG interaction.

The first step in the activation of the classical complement pathway by immune complexes involves the binding of the globular domain (gC1q) of C1q to the Fc regions of aggregated IgG or IgM. Each gC1q domain is a heterotrimer of the C-terminal halves of one A (ghA), one B (ghB), and one C (ghC) chain. Our recent studies have suggested a modular organization of gC1q, consistent with the view that ghA, ghB, and ghC are functionally autonomous modules and have distinct and differential ligand-binding properties. Although C1q binding sites on IgG have been previously identified, the complementary interacting sites on the gC1q domain have not been precisely defined. The availability of the recombinant constructs expressing ghA, ghB, and ghC has allowed us, for the first time, to engineer single-residue substitution mutations and identify residues on the gC1q domain, which are involved in the interaction between C1q and IgG. Because C1q is a charge pattern recognition molecule, we have sequentially targeted arginine and histidine residues in each chain. Consistent with previous chemical modification studies and the recent crystal structure of gC1q, our results support a central role for arginine and histidine residues, especially Arg(114) and Arg(129) of the ghB module, in the C1q-IgG interaction.