The dystrophinopathies cover a spectrum of X-linked muscle disease ranging from mild to severe that includes Duchenne muscular dystrophy, Becker muscular dystrophy, and DMD-associated dilated cardiomyopathy (DCM). The mild end of the spectrum includes the phenotypes of asymptomatic increase in serum concentration of creatine phosphokinase (CK) and muscle cramps with myoglobinuria. The severe end of the spectrum includes progressive muscle diseases that are classified as Duchenne/Becker muscular dystrophy when skeletal muscle is primarily affected and as DMD-associated DCM when the heart is primarily affected. Duchenne muscular dystrophy (DMD) usually presents in early childhood with delayed motor milestones including delays in walking independently and standing up from a supine position. Proximal weakness causes a waddling gait and difficulty climbing stairs, running, jumping, and standing up from a squatting position. DMD is rapidly progressive, with affected children being wheelchair dependent by age 12 years. Cardiomyopathy occurs in almost all individuals with DMD after age 18 years. Few survive beyond the third decade, with respiratory complications and progressive cardiomyopathy being common causes of death. Becker muscular dystrophy (BMD) is characterized by later-onset skeletal muscle weakness. With improved diagnostic techniques, it has been recognized that the mild end of the spectrum includes men with onset of symptoms after age 30 years who remain ambulatory even into their 60s. Despite the milder skeletal muscle involvement, heart failure from DCM is a common cause of morbidity and the most common cause of death in BMD. Mean age of death is in the mid-40s. DMD-associated DCM is characterized by left ventricular dilation and congestive heart failure. Females heterozygous for a DMD pathogenic variant are at increased risk for DCM.

A mild subtype of autosomal recessive limb girdle muscular dystrophy characterized by slowly progressive proximal muscle weakness and wasting of the pelvic and shoulder girdles with onset that usually occurs during the second or third decade of life. Clinical presentation is variable and can include calf psuedohypertrophy, joint contractures, scapular winging, muscle cramping and/or facial and respiratory muscle involvement.

A subtype of autosomal recessive limb-girdle muscular dystrophy characterized by a childhood onset of progressive shoulder and pelvic girdle muscle weakness and atrophy frequently associated with calf hypertrophy, diaphragmatic weakness, and/or variable cardiac abnormalities. Mild to moderate elevated serum creatine kinase levels and positive Gowers sign are reported.

The dystrophinopathies cover a spectrum of X-linked muscle disease ranging from mild to severe that includes Duchenne muscular dystrophy, Becker muscular dystrophy, and DMD-associated dilated cardiomyopathy (DCM). The mild end of the spectrum includes the phenotypes of asymptomatic increase in serum concentration of creatine phosphokinase (CK) and muscle cramps with myoglobinuria. The severe end of the spectrum includes progressive muscle diseases that are classified as Duchenne/Becker muscular dystrophy when skeletal muscle is primarily affected and as DMD-associated DCM when the heart is primarily affected. Duchenne muscular dystrophy (DMD) usually presents in early childhood with delayed motor milestones including delays in walking independently and standing up from a supine position. Proximal weakness causes a waddling gait and difficulty climbing stairs, running, jumping, and standing up from a squatting position. DMD is rapidly progressive, with affected children being wheelchair dependent by age 12 years. Cardiomyopathy occurs in almost all individuals with DMD after age 18 years. Few survive beyond the third decade, with respiratory complications and progressive cardiomyopathy being common causes of death. Becker muscular dystrophy (BMD) is characterized by later-onset skeletal muscle weakness. With improved diagnostic techniques, it has been recognized that the mild end of the spectrum includes men with onset of symptoms after age 30 years who remain ambulatory even into their 60s. Despite the milder skeletal muscle involvement, heart failure from DCM is a common cause of morbidity and the most common cause of death in BMD. Mean age of death is in the mid-40s. DMD-associated DCM is characterized by left ventricular dilation and congestive heart failure. Females heterozygous for a DMD pathogenic variant are at increased risk for DCM.

Autosomal dominant myosin storage congenital myopathy-7A (CMYO7A) is a skeletal muscle disorder with wide phenotypic variability. The age at symptom onset can range from early childhood to late adulthood. Affected individuals have proximal muscle weakness affecting the upper and lower limbs and distal muscle weakness of the lower limbs, resulting in gait difficulties and scapular winging (scapuloperoneal myopathy). Additional features may include thin habitus, high-arched palate, foot drop, pes cavus, calf pseudohypertrophy, and decreased reflexes. The severity is also variable: some patients develop respiratory insufficiency, joint contractures, and scoliosis in the first decades, whereas others are clinically unaffected, but show subtle signs of the disorder on examination. Serum creatine kinase may be normal or elevated. The disease is usually slowly progressive and most patients remain ambulatory. Skeletal muscle biopsy can show different abnormalities, including hyaline bodies, type 1 fiber predominance, congenital fiber-type disproportion (CFTD), and nonspecific myopathic changes with myofibrillar disarray. Intrafamilial variability is common (Dye et al., 2006; Pegoraro et al., 2007; review by Tajsharghi and Oldfors, 2013). For a discussion of genetic heterogeneity of congenital myopathy, see CMYO1A (117000).

Nemaline myopathy-2 (NEM2) is an autosomal recessive skeletal muscle disorder with a wide range of severity. The most common clinical presentation is early-onset (in infancy or childhood) muscle weakness predominantly affecting proximal limb muscles. Muscle biopsy shows accumulation of Z-disc and thin filament proteins into aggregates named 'nemaline bodies' or 'nemaline rods,' usually accompanied by disorganization of the muscle Z discs. The clinical and histologic spectrum of entities caused by variants in the NEB gene is a continuum, ranging in severity. The distribution of weakness can vary from generalized muscle weakness, more pronounced in proximal limb muscles, to distal-only involvement, although neck flexor weakness appears to be rather consistent. Histologic patterns range from a severe usually nondystrophic disturbance of the myofibrillar pattern to an almost normal pattern, with or without nemaline bodies, sometimes combined with cores (summary by Lehtokari et al., 2014). Genetic Heterogeneity of Nemaline Myopathy See also NEM1 (255310), caused by mutation in the tropomyosin-3 gene (TPM3; 191030) on chromosome 1q22; NEM3 (161800), caused by mutation in the alpha-actin-1 gene (ACTA1; 102610) on chromosome 1q42; NEM4 (609285), caused by mutation in the beta-tropomyosin gene (TPM2; 190990) on chromosome 9p13; NEM5A (605355), also known as Amish nemaline myopathy, NEM5B (620386), and NEM5C (620389), all caused by mutation in the troponin T1 gene (TNNT1; 191041) on chromosome 19q13; NEM6 (609273), caused by mutation in the KBTBD13 gene (613727) on chromosome 15q22; NEM7 (610687), caused by mutation in the cofilin-2 gene (CFL2; 601443) on chromosome 14q13; NEM8 (615348), caused by mutation in the KLHL40 gene (615340), on chromosome 3p22; NEM9 (615731), caused by mutation in the KLHL41 gene (607701) on chromosome 2q31; NEM10 (616165), caused by mutation in the LMOD3 gene (616112) on chromosome 3p14; and NEM11 (617336), caused by mutation in the MYPN gene (608517) on chromosome 10q21. Several of the genes encode components of skeletal muscle sarcomeric thin filaments (Sanoudou and Beggs, 2001). Mutations in the NEB gene are the most common cause of nemaline myopathy (Lehtokari et al., 2006).

Limb-girdle muscular dystrophies are characterized clinically by predominantly proximal muscle weakness of variable severity and dystrophic changes on muscle biopsy. LGMDR4 is in general a severe form of the disorder, with some patients developing symptoms before 8 years of age and losing the ability to ambulate in their second decade. Some patients have a milder course, with weakness evident in the teenage years and loss of walking ability in their fourth decade (summary by Lim et al., 1995 and Bonnemann et al., 1996). For a general phenotypic description and a discussion of genetic heterogeneity of autosomal recessive limb-girdle muscular dystrophy, see LGMDR1 (253600).