Proximal myotonic myopathy

Proximal myotonic myopathy (PROMM), also known as myotonic dystrophy type 2 (DM2) or Ricker syndrome, is a genetic multisystem disorder caused by a CCTG tetranucleotide repeat expansion in the CNBP gene (formerly ZNF9) on chromosome 3q21. It belongs to the family of myotonic dystrophies but is distinguished from myotonic dystrophy type 1 (DM1) by its predominantly proximal pattern of muscle weakness rather than distal involvement. The disease affects multiple body systems. Skeletal muscle involvement includes myotonia (difficulty relaxing muscles after contraction), proximal muscle weakness and pain particularly in the thighs and hip flexors, and muscle stiffness. Beyond the musculoskeletal system, patients may develop cataracts (often posterior subcapsular), cardiac conduction abnormalities and arrhythmias, insulin resistance or diabetes mellitus, thyroid dysfunction, hypogonadism, and elevated liver enzymes (gamma-GT). Some patients experience tremor, and cognitive or neuropsychological changes may occur, though typically less severe than in DM1. Muscle pain is a particularly prominent and sometimes debilitating feature that may precede other symptoms. There is currently no cure or disease-modifying treatment for PROMM/DM2. Management is symptomatic and multidisciplinary, involving regular cardiac monitoring with ECG and echocardiography, ophthalmologic surveillance for cataracts, screening for endocrine abnormalities, and physical therapy to maintain muscle function. Myotonia, when symptomatic, may be treated with medications such as mexiletine. Pain management is often a significant component of care. Certain anesthetic agents should be used with caution due to the risk of malignant hyperthermia-like reactions. Genetic counseling is recommended for affected individuals and their families due to the autosomal dominant inheritance pattern.

Data sourced from FDA regulatory filings and ClinicalTrials.gov. Updated periodically.

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