Stroke-like episodes (SLE) occur in phosphomannomutase deficiency (PMM2-CDG), and may complicate the course of channelopathies related to Familial Hemiplegic Migraine (FHM) caused by mutations in CACNA1A (encoding CaV2.1 channel). The underlying pathomechanisms are unknown. We analyze clinical variables to detect risk factors for SLE in a series of 43 PMM2-CDG patients. We explore the hypothesis of abnormal CaV2.1 function due to aberrant N-glycosylation as a potential novel pathomechanism of SLE and ataxia in PMM2-CDG by using whole-cell patch-clamp, N-glycosylation blockade and mutagenesis. Nine SLE were identified. Neuroimages showed no signs of stroke. Comparison of characteristics between SLE positive versus negative patients’ group showed no differences. Acute and chronic phenotypes of patients with PMM2-CDG or CACNA1A channelopathies show similarities. Hypoglycosylation of both CaV2.1 subunits (α1A and α2α) induced gain-of-function effects on channel gating that mirrored those reported for pathogenic CACNA1A mutations linked to FHM and ataxia. Unoccupied N-glycosylation site N283 at α1A contributes to a gain-of-function by lessening CaV2.1 inactivation. Hypoglycosylation of the α2δ subunit also participates in the gain-of-function effect by promoting voltage-dependent opening of the CaV2.1 channel. CaV2.1 hypoglycosylation may cause ataxia and SLEs in PMM2-CDG patients. Aberrant CaV2.1 N-glycosylation as a novel pathomechanism in PMM2-CDG opens new therapeutic possibilities.

Objective: Phosphomannomutase deficiency (PMM2 congenital disorder of glycosylation [PMM2-CDG]) causes cerebellar syndrome and strokelike episodes (SLEs). SLEs are also described in patients with gain-of-function mutations in the CaV2.1 channel, for which acetazolamide therapy is suggested. Impairment in N-glycosylation of CaV2.1 promotes gain-of-function effects and may participate in cerebellar syndrome in PMM2-CDG. AZATAX was designed to establish whether acetazolamide is safe and improves cerebellar syndrome in PMM2-CDG. Methods: A clinical trial included PMM2-CDG patients, with a 6-month first-phase single acetazolamide therapy group, followed by a randomized 5-week withdrawal phase. Safety was assessed. The primary outcome measure was improvement in the International Cooperative Ataxia Rating Scale (ICARS). Other measures were the Nijmegen Pediatric CDG Rating Scale (NPCRS), a syllable repetition test (PATA test), and cognitive scores. Results: Twenty-four patients (mean age = 12.3 AE 4.5 years) were included, showing no serious adverse events. Thirteen patients required dose adjustment due to low bicarbonate or asthenia. There were improvements on ICARS (34.9 AE 23.2 vs 40.7 AE 24.8, effect size = 1.48, 95% confidence interval [CI] = 4.0-7.6, p < 0.001), detected at 6 weeks in 18 patients among the 20 responders, on NPCRS (95% CI = 0.3-1.6, p = 0.013) and on the PATA test (95% CI = 0.5-3.0, p = 0.006). Acetazolamide improved prothrombin time, factor X, and antithrombin. Clinical severity, epilepsy, and lipodystrophy predicted greater response. The randomized withdrawal phase showed ICARS worsening in the withdrawal group (effect size = 1.46, 95% CI = 2.65-7.52, p = 0.001). Interpretation: AZATAX is the first clinical trial of PMM2-CDG. Acetazolamide is well tolerated and effective for motor cerebellar syndrome. Its ability to prevent SLEs and its long-term effects on kidney function should be addressed in future studies. ANN NEUROL 2019;85:740-751 View this article online at wileyonlinelibrary.com.

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BackgroundMucopolysaccharidosis type II (MPS II) is an inherited X-linked disease associated with a deficiency in the enzyme iduronate 2-sulfatase due to iduronate 2-sulfatase gene (IDS) mutations. Recent studies in MPS II carriers did not find clinical involvement, but these were mainly performed by anamnesis and patients’ self-reported description of signs and symptoms. So although it is rare in heterozygous carriers, investigations in other types of inherited X-linked disorders suggest that some clinical manifestations may be a possibility. The aim of this study was to evaluate the clinical pattern in female carriers of MPS II and to determine whether clinical symptoms were associated with the X-chromosome inactivation (XCI) pattern and age.MethodsFemale carriers of MPS II were genetically identified by molecular analysis of IDS. The clinical evaluation protocol included pedigree analysis, a comprehensive anamnesis, complete physical examination, ophthalmological evaluation, brain-evoked auditory response, electrocardiogram, echocardiogram, pulmonary function tests, abdominal sonogram, skeletal survey, neurophysiological studies, blood cell counts and biochemistry, urine glycosaminoglycan (GAGs) quantification, karyotype and pattern of XCI.ResultsTen women were included in the study. The mean age of the participants was 40.2 ± 13.1 years. Six carriers presented a skewed XCI pattern, 3 of whom (aged 38, 42 and 52 years) had increased levels of GAGs in the urine and showed typical MPS II clinical manifestations, such as skeletal anomalies, liver abnormalities, carpal tunnel syndrome, recurrent ear infection, hypoacusia and more frequent severe odontological problems without coarse facial features.ConclusionsThis is the first study performing a comprehensive evaluation of heterozygous MPS II carriers. Our results provide evidence of possible progressive, age-dependent, mild clinical manifestations in MPS II female carriers with a skewed XCI pattern, most likely affecting the normal allele. Further comparative studies with systematized clinical examinations in larger age-stratified populations of MPS II female carriers are required.

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