Adult MTM1-related myopathy carriers: Classification based on deep phenotyping.

OBJECTIVE: To better characterize adult myotubularin 1 (MTM1)-related myopathy carriers and recommend a phenotypic classification. METHODS: This cohort study was performed at the NIH Clinical Center. Participants were required to carry a confirmed MTM1 mutation and were recruited via the Congenital Muscle Disease International Registry (n = 8), a traveling local clinic of the Neuromuscular and Neurogenetic Disorders of Childhood Section, National Institute of Neurological Disorders and Stroke, NIH and Cure CMD (n = 1), and direct physician referral (n = 1). Neuromuscular examinations, muscle MRI, dynamic breathing MRI, cardiac MRI, pulmonary function tests (PFTs), physical therapy assessments including the Motor Function Measure 32 (MFM-32) scale, and X chromosome inactivation (XCI) studies were performed. RESULTS: Phenotypic categories were proposed based on ambulatory status and muscle weakness. Carriers were categorized as severe (nonambulatory; n = 1), moderate (minimal independent ambulation/assisted ambulation; n = 3), mild (independent ambulation but with evidence of muscle weakness; n = 4), and nonmanifesting (no evidence of muscle weakness; n = 2). Carriers with more severe muscle weakness exhibited greater degrees of respiratory insufficiency and abnormal signal on muscle imaging. Skeletal asymmetries were evident in both manifesting and nonmanifesting carriers. Skewed XCI did not explain phenotypic severity. CONCLUSION: This work illustrates the phenotypic range of MTM1-related myopathy carriers in adulthood and recommends a phenotypic classification. This classification, defined by ambulatory status and muscle weakness, is supported by muscle MRI, PFT, and MFM-32 scale composite score findings, which may serve as markers of disease progression and outcome measures in future gene therapy or other clinical trials.

A multicenter, retrospective medical record review of X-linked myotubular myopathy: The recensus study.

INTRODUCTION: X-linked myotubular myopathy (XLMTM), characterized by severe hypotonia, weakness, respiratory distress, and early mortality, is rare and natural history studies are few. METHODS: RECENSUS is a multicenter chart review of male XLMTM patients characterizing disease burden and unmet medical needs. Data were collected between September 2014 and June 2016. RESULTS: Analysis included 112 patients at six clinical sites. Most recent patient age recorded was ≤18 months for 40 patients and >18 months for 72 patients. Mean (SD) age at diagnosis was 3.7 (3.7) months and 54.3 (77.1) months, respectively. Mortality was 44% (64% ≤18 months; 32% >18 months). Premature delivery occurred in 34/110 (31%) births. Nearly all patients (90%) required respiratory support at birth. In the first year of life, patients underwent an average of 3.7 surgeries and spent 35% of the year in the hospital. DISCUSSION: XLMTM is associated with high mortality, disease burden, and healthcare utilization. Muscle Nerve 57: 550-560, 2018.

A natural history study of X-linked myotubular myopathy.

OBJECTIVE: To define the natural history of X-linked myotubular myopathy (MTM). METHODS: We performed a cross-sectional study that included an online survey (n = 35) and a prospective, 1-year longitudinal investigation using a phone survey (n = 33). RESULTS: We ascertained data from 50 male patients with MTM and performed longitudinal assessments on 33 affected individuals. Consistent with existing knowledge, we found that MTM is a disorder associated with extensive morbidities, including wheelchair (86.7% nonambulant) and ventilator (75% requiring >16 hours of support) dependence. However, unlike previous reports and despite the high burden of disease, mortality was lower than anticipated (approximate rate 10%/y). Seventy-six percent of patients with MTM enrolled (mean age 10 years 11 months) were alive at the end of the study. Nearly all deaths in the study were associated with respiratory failure. In addition, the disease course was more stable than expected, with few adverse events reported during the prospective survey. Few non-muscle-related morbidities were identified, although an unexpectedly high incidence of learning disability (43%) was noted. Conversely, MTM was associated with substantial burdens on patient and caregiver daily living, reflected by missed days of school and lost workdays. CONCLUSIONS: MTM is one of the most severe neuromuscular disorders, with affected individuals requiring extensive mechanical interventions for survival. However, among study participants, the disease course was more stable than predicted, with more individuals surviving infancy and early childhood. These data reflect the disease burden of MTM but offer hope in terms of future therapeutic intervention.