Autosomal recessive severe infantile nemaline myopathy-5A (NEM5A) is a skeletal muscle disorder characterized by symptom onset soon after birth or in early infancy. Affected infants show axial hypotonia, stiffness, rigid spine with progressive kyphosis, pectus deformities, and contractures or limited movement of the large joints. Some patients show transient tremors. There is muscle atrophy and poor gross motor development. Respiratory insufficiency develops in the first years of life, often leading to death. Muscle biopsy shows nemaline rods (Johnston et al., 2000; Geraud et al., 2021). For a discussion of genetic heterogeneity of nemaline myopathy, see NEM2 (256030).

A rare genetic neuromuscular disease with characteristics of adult-onset muscle weakness and atrophy in a scapuloperoneal distribution, mild involvement of the facial muscles, dysphagia, and gynaecomastia. Elevated serum CK levels and mixed myopathic and neurogenic abnormalities are associated clinical findings. Caused by heterozygous mutation in the DES gene on chromosome 2q35.

Myofibrillar myopathy-7 (MFM7) is an autosomal recessive muscle disorder characterized by early childhood onset of slowly progressive muscle weakness that primarily affects the lower limbs and is associated with joint contractures (summary by Straussberg et al., 2016). For a general phenotypic description and a discussion of genetic heterogeneity of myofibrillar myopathy, see MFM1 (601419).

Autosomal dominant adult-onset distal myopathy-6 (MPD6) is a muscle disorder characterized by slowly progressive distal muscle weakness, primarily affecting the lower limbs and resulting in gait difficulties. Some patients develop involvement of proximal and upper limb muscles (summary by Savarese et al., 2019)

Congenital myopathy-9B (CMYP9B) is an autosomal recessive early-onset skeletal muscle disorder mainly affecting proximal muscles. Affected individuals have neonatal hypotonia followed by mildly delayed walking in childhood. Muscle weakness is slowly progressive, resulting in positive Gowers sign and difficulty running or climbing, but most patients remain ambulatory. Some patients develop respiratory involvement requiring ventilatory support, whereas cardiac function is unaffected. Muscle biopsy shows type 1 fiber predominance with disorganized Z-lines and multiminicore myopathy (Estan et al., 2019). For a discussion of genetic heterogeneity of congenital myopathy, see CMYP1A (117000).

Distal myopathy with rimmed vacuoles (DMRV) is an autosomal dominant myopathic disorder characterized by adult onset of muscle weakness affecting the distal upper and lower limbs, which may result in walking difficulties, as well as proximal weakness of the shoulder girdle muscles. Muscle biopsy shows rimmed vacuoles (summary by Bucelli et al., 2015).

Myofibrillar myopathy-11 (MFM11) is an autosomal recessive skeletal muscle disorder characterized by onset of slowly progressive proximal muscle weakness in the first decade of life. Some patients may present at birth with hypotonia and feeding difficulties, whereas others present later in mid-childhood. Although most patients show delayed walking at 2 to 3 years, all remain ambulatory into adulthood. More variable features may include decreased respiratory forced vital capacity, variable cardiac features, and calf hypertrophy. Skeletal muscle biopsy shows myopathic changes with variation in fiber size, type 1 fiber predominance, centralized nuclei, eccentrically placed core-like lesions, and distortion of the myofibrillary pattern with Z-line streaming and abnormal myofibrillar aggregates or inclusions (summary by Donkervoort et al., 2020). For a phenotypic description and a discussion of genetic heterogeneity of myofibrillar myopathy, see MFM1 (601419).