Brody disease (BROD) is an autosomal recessive skeletal muscle disorder characterized by exercise-induced muscle stiffness and cramps primarily affecting the arms, legs, and eyelids, although more generalized muscle involvement may also occur. Symptom onset is most often in the first decade, but many patients present and are diagnosed later in life. Skeletal muscle biopsy typically shows variation in fiber size, increased internal nuclei, and atrophy of type II muscle fibers. Rare patients have been reported to develop malignant hyperthermia after administration of anesthesia, suggesting that patients with the disorder should be tested. The disorder results from defective relaxation of fast-twitch (type II) skeletal muscle fibers due to defects in calcium homeostasis and reuptake in the muscle fiber (summary by Odermatt et al., 2000 and Molenaar et al., 2020).

Schwartz-Jampel syndrome type 1 (SJS1) is a rare autosomal recessive disorder characterized by muscle stiffness (myotonia) and chondrodysplasia. Affected individuals usually present in childhood with permanent muscle stiffness or bone deformities. Common clinical features include mask-like facies (narrow palpebral fissures, blepharospasm, and pursed lips); permanent muscle stiffness with continuous skeletal muscle activity recorded on electromyography; dwarfism; pectus carinatum; kyphoscoliosis; bowing of long bones; and epiphyseal, metaphyseal, and hip dysplasia. The disorder is slowly progressive but does not appear to alter life span (summary by Stum et al., 2006).

Centronuclear myopathy-1 (CNM1) is an autosomal dominant congenital myopathy characterized by slowly progressive muscular weakness and wasting. The disorder involves mainly limb girdle, trunk, and neck muscles but may also affect distal muscles. Weakness may be present during childhood or adolescence or may not become evident until the third decade of life, and some affected individuals become wheelchair-bound in their fifties. Ptosis and limitation of eye movements occur frequently. The most prominent histopathologic features include high frequency of centrally located nuclei in a large number of extrafusal muscle fibers (which is the basis of the name of the disorder), radial arrangement of sarcoplasmic strands around the central nuclei, and predominance and hypotrophy of type 1 fibers (summary by Bitoun et al., 2005). Genetic Heterogeneity of Centronuclear Myopathy Centronuclear myopathy is a genetically heterogeneous disorder. See also X-linked CNM (CNMX; 310400), caused by mutation in the MTM1 gene (300415) on chromosome Xq28; CNM2 (255200), caused by mutation in the BIN1 gene (601248) on chromosome 2q14; CNM4 (614807), caused by mutation in the CCDC78 gene (614666) on chromosome 16p13; CNM5 (615959), caused by mutation in the SPEG gene (615950) on chromosome 2q35; and CNM6 (617760), caused by mutation in the ZAK gene (609479) on chromosome 2q31. The mutation in the MYF6 gene that was reported to cause a form of CNM, formerly designated CNM3, has been reclassified as a variant of unknown significance; see 159991.0001. Some patients with mutation in the RYR1 gene (180901) have findings of centronuclear myopathy on skeletal muscle biopsy (see 255320).

Oculopharyngodistal myopathy-1 (OPDM1) is an autosomal dominant disorder characterized by adult-onset ptosis, external ophthalmoplegia, facial muscle weakness, distal limb muscle weakness and atrophy, and pharyngeal involvement, resulting in dysphagia and dysarthria. Skeletal muscle biopsy shows myopathic changes with rimmed vacuoles. There are variable manifestations of the disorder regarding muscle involvement and severity (summary by Ishiura et al., 2019). Genetic Heterogeneity of Oculopharyngodistal Myopathy See also OPDM2 (618940), caused by trinucleotide repeat expansion in the GIPC1 gene (605072) on chromosome 19p13; OPDM3 (619473), caused by trinucleotide repeat expansion in the NOTCH2NLC gene (618025) on chromosome 1q21; and OPDM4 (619790), caused by trinucleotide repeat expansion in the RILPL1 gene (614092) on chromosome 12q24. Oculopharyngeal muscular dystrophy (OPMD; 164300) is a similar disorder with overlapping features. It is caused by a similar heterozygous trinucleotide repeat expansion in the PABPN1 gene (602279) (summary by Durmus et al., 2011).