Guidelines for pre-clinical animal and cellular models of MuSK-myasthenia gravis.

Muscle-specific tyrosine kinase (MuSK) autoantibodies are the hallmark of a form of myasthenia gravis (MG) that can challenge the neurologist and the experimentalist. The clinical disease can be difficult to treat effectively. MuSK autoantibodies affect the neuromuscular junction in several ways. When added to muscle cells in culture, MuSK antibodies disperse acetylcholine receptor clusters. Experimental animals actively immunized with MuSK develop MuSK autoantibodies and muscle weakness. Weakness is associated with reduced postsynaptic acetylcholine receptor numbers, reduced amplitudes of miniature endplate potentials and endplate potentials, and failure of neuromuscular transmission. Similar impairments have been found in mice injected with IgG from MG patients positive for MuSK autoantibody (MuSK-MG). The active and passive models have begun to reveal the mechanisms by which MuSK antibodies disrupt synaptic function at the neuromuscular junction, and should be valuable in developing therapies for MuSK-MG. However, translation into new and improved treatments for patients requires procedures that are not too cumbersome but suitable for examining different aspects of MuSK function and the effects of potential therapies. Study design, conduct and analysis should be carefully considered and transparently reported. Here we review what has been learnt from animal and culture models of MuSK-MG, and offer guidelines for experimental design and conduct of studies, including sample size determination, randomization, outcome parameters and precautions for objective data analysis. These principles may also be relevant to the increasing number of other antibody-mediated diseases that are now recognized.

ß-glucans reduce LDL cholesterol in patients with myasthenia gravis.

We aimed at evaluating whether ß-glucans could improve low-density lipoprotein (LDL) cholesterol levels and/or glycemic control in patients with myasthenia gravis (MG), in whom statins usually have muscle-related side effects. Fifty-nine MG patients participated in the study and received a daily dietary supplement of 3 g of ß-glucans during 8 weeks. Body mass index (BMI) and blood sample analysis of lipid and glucose status were performed before and after 8 weeks intake of ß-glucans. In the 52 patients who completed the study, there was a significant reduction in total cholesterol, LDL, ApoA1 and ApoB (all P<0.003). However, glycemic control and BMI were unaltered. The present study indicates that 8 weeks daily intake of 3 g of ß-glucans significantly reduces total cholesterol, LDL, ApoA1 and ApoB in MG patients. ß-glucans may therefore be of value in improving lipid status in MG patients, without the muscle-related side effects accompanied by statins.

Vitamin D deficiency in patients with myasthenia gravis and improvement of fatigue after supplementation of vitamin D3: a pilot study.

BACKGROUND: Myasthenia gravis (MG) is a chronic autoimmune neuromuscular disorder. Vitamin D has important roles both in the autoimmune response and in skeletal muscles. We determined the levels of 25-hydroxy vitamin D [25(OH)D] in patients with MG and in healthy subjects to determine whether vitamin D deficiency is present in MG and whether vitamin D supplementation has beneficial effects on fatigue. METHODS: Plasma levels of 25(OH)D were analyzed in 33 patients with MG (22 males; mean age, 58 years) and in 50 healthy age- and sex-matched blood donors, without vitamin D3 medication. MG composite (MGC) score assessed fatigue. Thirteen patients with MG without previous vitamin D3 supplementation were started on vitamin D3 supplementation (cholecalciferol) 800 IU/day, with a follow-up examination after 2.5-10 months (mean, 6 months). RESULTS: Patients with MG without pre-existing vitamin D3 supplementation (N = 16) had a mean MGC of 4.5 and lower plasma 25(OH)D levels (mean, 51 ± 19 nM) than healthy controls (69 ± 21 nM) (P = 0.017). Seventeen patients had pre-existing vitamin D3 supplementation, because of corticosteroid treatment, and their mean 25(OH)D was 79 ± 22 nM and mean MGC was 5.5. In the 13 patients who received cholecalciferol, 25(OH)D was overall increased at follow-up with 22% (P = 0.033) and MGC score improved by 38% (P = 0.05). CONCLUSIONS: Plasma 25(OH)D levels are significantly lower in patients with MG compared with healthy controls. As vitamin D has beneficial effects on the autoimmune response and on fatigue score in patients with MG, we suggest monitoring this parameter in patients with MG and supplementation with vitamin D3 when 25(OH)D levels are low.

Monozygous twins with neuromuscular transmission defects at opposite sides of the motor endplate.

Disorders affecting the postsynaptic side of the neuromuscular junction include autoimmune myasthenia gravis (MG) as well as some of the congenital myasthenic syndromes (CMS). Lambert-Eaton myasthenic syndrome (LEMS) is an acquired autoimmune neuromuscular disorder in which autoantibodies are directed against the presynaptic calcium channels. Here we describe two monozygous twin brothers: case 1 was diagnosed with an indeterminate form of acquired postsynaptic neuromuscular junction defect at age 32 and case 2 with LEMS at age 47. Case 1 presented clinically with mild generalized myasthenic weakness, neurophysiological examination revealed disturbed neuromuscular transmission along with probable myositis and serum analysis regarding antibodies against the acetylcholine receptor and muscle-specific tyrosine kinase was negative. Case 2 presented with proximal muscle fatigue accompanied by areflexia at rest and antibodies against the P/Q-type voltage-gated calcium channels were present. Neurophysiologically, case 2 had reduced baseline compound motor action potential amplitudes on neurography, decrement on low-frequency repetitive nerve stimulation (RNS) and pathological increment on high frequency RNS. To our knowledge this is the first case report of its kind and adds an intriguing contrast to the more common diagnosis of CMS in monozygous twins.