The clinical manifestations of glycogen storage disease type IV (GSD IV) discussed in this entry span a continuum of different subtypes with variable ages of onset, severity, and clinical features. Clinical findings vary extensively both within and between families. The fatal perinatal neuromuscular subtype presents in utero with fetal akinesia deformation sequence, including decreased fetal movements, polyhydramnios, and fetal hydrops. Death usually occurs in the neonatal period. The congenital neuromuscular subtype presents in the newborn period with profound hypotonia, respiratory distress, and dilated cardiomyopathy. Death usually occurs in early infancy. Infants with the classic (progressive) hepatic subtype may appear normal at birth, but rapidly develop failure to thrive; hepatomegaly, liver dysfunction, and progressive liver cirrhosis; hypotonia; and cardiomyopathy. Without liver transplantation, death from liver failure usually occurs by age five years. Children with the non-progressive hepatic subtype tend to present with hepatomegaly, liver dysfunction, myopathy, and hypotonia; however, they are likely to survive without progression of the liver disease and may not show cardiac, skeletal muscle, or neurologic involvement. The childhood neuromuscular subtype is rare and the course is variable, ranging from onset in the second decade with a mild disease course to a more severe, progressive course resulting in death in the third decade.

Congenital myopathy-1B (CMYO1B) is an autosomal recessive disorder of skeletal muscle characterized by severe hypotonia and generalized muscle weakness apparent soon after birth or in early childhood with delayed motor development, generalized muscle weakness and atrophy, and difficulty walking or running. Affected individuals show proximal muscle weakness with axial and shoulder girdle involvement, external ophthalmoplegia, and bulbar weakness, often resulting in feeding difficulties and respiratory insufficiency. Orthopedic complications such as joint laxity, distal contractures, hip dislocation, cleft palate, and scoliosis are commonly observed. Serum creatine kinase is normal. The phenotype is variable in severity (Jungbluth et al., 2005; Bharucha-Goebel et al., 2013). Some patients show symptoms in utero, including reduced fetal movements, polyhydramnios, and intrauterine growth restriction. The most severely affected patients present in utero with fetal akinesia, arthrogryposis, and lung hypoplasia resulting in fetal or perinatal death (McKie et al., 2014). Skeletal muscle biopsy of patients with recessive RYR1 mutations can show variable features, including multiminicores (Ferreiro and Fardeau, 2002), central cores (Jungbluth et al., 2002), congenital fiber-type disproportion (CFTD) (Monnier et al., 2009), and centronuclear myopathy (Wilmshurst et al., 2010). For a discussion of genetic heterogeneity of congenital myopathy, see CMYO1A (117000).

Congenital myopathy-12 (CMYO12) is an autosomal recessive disorder characterized by severe neonatal hypotonia resulting in feeding difficulties and respiratory failure within the first months of life. There is evidence of the disorder in utero, with decreased fetal movements and polyhydramnios. Additional features may include high-arched palate and contractures. Skeletal muscle biopsy shows myopathic changes with disrupted sarcomeres and minicore-like structures (Compton et al., 2008). For a discussion of genetic heterogeneity of congenital myopathy, see CMYO1A (117000).

Congenital myopathy-11 (CMYO11) is an autosomal recessive skeletal muscle disorder characterized clinically by severe hypotonia apparent at birth, resulting in early feeding problems, motor delay, and walking difficulties. However, the course of the disease is nonprogressive: most affected individuals achieve independent ambulation and tend to show improvement of muscle weakness throughout childhood and early adulthood. There is no respiratory or cardiac involvement; cognitive development is normal. Muscle biopsy may show rare centralized nuclei, type 1 fiber hypotrophy, and type 1 fiber predominance, suggestive of a pathologic diagnosis of congenital fiber-type disproportion (CFTD). However, the findings on skeletal muscle biopsy may be nonspecific (Muhammad et al., 2013). For a discussion of genetic heterogeneity of congenital myopathy, see CMYO1A (117000).

Congenital myopathy-10B (CMYO10B) is an autosomal recessive skeletal muscle disorder characterized by infantile- or childhood-onset myopathy, areflexia, dysphagia, and respiratory distress that usually requires nocturnal ventilation. Other common features include facial and neck muscle weakness, feeding difficulties, contractures, scoliosis, high-arched palate, hyporeflexia, and difficulties walking. The disorder is slowly progressive and most patients follow a chronic course. Muscle biopsy shows variable findings, including type 1 fiber predominance, minicore lesions, and myofibrillar disorganization (Boyden et al., 2012; Harris et al., 2018). Patients with missense mutations affecting conserved cysteine residues in the EGF-like domain show the mild variant phenotype (CMYO10B) with later onset of respiratory failure and minicores on muscle biopsy, whereas patients with more damaging mutations, including nonsense or frameshift null mutations, show the severe variant phenotype (CMYO10A) (Croci et al., 2022). For a discussion of genetic heterogeneity of congenital myopathy, see CMYO1A (117000).

Mitochondrial complex III deficiency, nuclear type 8, is an autosomal recessive disorder characterized by progressive neurodegeneration with onset in childhood. Affected individuals may have normal or delayed early development, and often have episodic acute neurologic decompensation and regression associated with febrile illnesses. The developmental regression results in variable intellectual disability and motor deficits, such as hypotonia, axial hypertonia, and spasticity; some patients may lose the ability to walk independently. Laboratory studies show increased serum lactate and isolated deficiency of mitochondrial complex III in skeletal muscle and fibroblasts. Brain imaging shows a characteristic pattern of multifocal small cystic lesions in the periventricular and deep cerebral white matter (summary by Dallabona et al., 2016). For a discussion of genetic heterogeneity of mitochondrial complex III deficiency, see MC3DN1 (124000).

Centronuclear myopathy-5 (CNM5) is an autosomal recessive congenital myopathy characterized by severe neonatal hypotonia with respiratory insufficiency and difficulty feeding. Some patients die in infancy, and some develop dilated cardiomyopathy. Children show severely delayed motor development (summary by Agrawal et al., 2014). For a discussion of genetic heterogeneity of centronuclear myopathy, see CNM1 (160150).

Congenital myopathy-24 (CMYO24) is an autosomal recessive congenital myopathy characterized by onset of slowly progressive muscle weakness in the first decade. Affected individuals present with gait difficulties due to proximal muscle weakness and atrophy mainly affecting the lower limbs and neck. Muscle biopsy shows nemaline bodies. Some patients may have mild cardiac or respiratory involvement, but they do not have respiratory failure (summary by Miyatake et al., 2017). For a discussion of genetic heterogeneity of congenital myopathy, see 117000. For a discussion of genetic heterogeneity of nemaline myopathy, see 256030.

SPTBN4 disorder is typically characterized by severe-to-profound developmental delay and/or intellectual disability, although two individuals in one family had a milder phenotype, including one individual with normal cognitive development. Speech and language skills are often severely limited. Affected individuals rarely achieve head control. Most are unable to sit, stand, or walk. Affected individuals typically have congenital hypotonia that may transition to hypertonia. Axonal motor neuropathy leads to hyporeflexia/areflexia and weakness, which can result in respiratory difficulties requiring ventilatory support. Most affected individuals require tube feeding for nutrition. Half of affected individuals develop seizures. Cortical visual impairment and auditory neuropathy have also been reported.

Centronuclear myopathy is a condition characterized by muscle weakness (myopathy) and wasting (atrophy) in the skeletal muscles, which are the muscles used for movement. The severity of centronuclear myopathy varies among affected individuals, even among members of the same family.\n\nPeople with centronuclear myopathy begin experiencing muscle weakness at any time from birth to early adulthood. The muscle weakness slowly worsens over time and can lead to delayed development of motor skills, such as crawling or walking; muscle pain during exercise; and difficulty walking. Some affected individuals may need wheelchair assistance as the muscles atrophy and weakness becomes more severe. In rare instances, the muscle weakness improves over time.\n\nA key feature of centronuclear myopathy is the displacement of the nucleus in muscle cells, which can be viewed under a microscope. Normally the nucleus is found at the edges of the rod-shaped muscle cells, but in people with centronuclear myopathy the nucleus is located in the center of these cells. How the change in location of the nucleus affects muscle cell function is unknown.\n\nSome people with centronuclear myopathy experience mild to severe breathing problems related to the weakness of muscles needed for breathing. People with centronuclear myopathy may have droopy eyelids (ptosis) and weakness in other facial muscles, including the muscles that control eye movement. People with this condition may also have foot abnormalities, a high arch in the roof of the mouth (high-arched palate), and abnormal side-to-side curvature of the spine (scoliosis). Rarely, individuals with centronuclear myopathy have a weakened heart muscle (cardiomyopathy), disturbances in nerve function (neuropathy), or intellectual disability.

Congenital myopathy-14 (CMYO14) is an autosomal recessive skeletal muscle disorder characterized by onset of severe muscle weakness apparent at birth and sometimes in utero. Affected infants have difficulty breathing independently and usually require mechanical ventilation for variable lengths of time. Other features include delayed motor development with delayed walking, hypo- or areflexia, and high-arched palate. Skeletal muscle biopsy shows variation in fiber size with specific atrophy of the fast-twitch type II fibers. Cardiac muscle is not affected (summary by Ravenscroft et al., 2018). For a discussion of genetic heterogeneity of congenital myopathy, see CMYO1A (117000).

Myogenic-type arthrogryposis multiplex congenita-3 (AMC3) is an autosomal recessive disorder characterized by decreased fetal movements, hypotonia, variable skeletal defects, including clubfoot and scoliosis, and delayed motor milestones with difficulty walking (summary by Baumann et al., 2017).

Axonal Charcot-Marie-Tooth disease type 2II (CMT2II) is an autosomal dominant neurologic disorder characterized by a slowly progressive sensorimotor peripheral neuropathy affecting mainly the lower limbs, resulting in distal muscle weakness and atrophy and subsequent walking difficulties. Some patients may have upper limb involvement with atrophy of the intrinsic hand muscles. The age at onset is highly variable, ranging from infancy to adulthood. Electrophysiologic studies are usually consistent with an axonal process, although some may show intermediate or even demyelinating values (Park et al., 2020; Ando et al., 2022). One family with possible autosomal recessive inheritance has been reported (Bogdanova-Mihaylova et al., 2021). For a discussion of genetic heterogeneity of axonal CMT, see CMT2A1 (118210).

Autosomal recessive limb-girdle muscular dystrophy-28 (LGMDR28) is characterized by progressive muscle weakness affecting the proximal and axial muscles of the upper and lower limbs. The age at onset is highly variable, usually in the first decade, although onset in the fourth decade has also been reported. The disorder can be rapidly progressive or show a slower course. Most patients have limited ambulation or become wheelchair-bound within a few decades, and respiratory insufficiency commonly occurs. Laboratory studies show increased serum creatine kinase and elevated fasting blood glucose levels, although cholesterol is normal. EMG shows a myopathic pattern; muscle biopsy is generally unremarkable, but can show nonspecific myopathic or dystrophic features (Yogev et al., 2023; Morales-Rosado et al., 2023). For a discussion of genetic heterogeneity of autosomal recessive limb-girdle muscular dystrophy, see LGMDR1 (253600).

Immunodeficiency-115 with autoinflammation (IMD115) is an autosomal recessive disorder characterized by the onset of symptoms of immune dysregulation in early infancy. Affected individuals have immunodeficiency with recurrent bacterial, viral, and fungal infections, as well as autoinflammatory features, including arthritis and dermatitis. Some patients may have more systemic involvement, such as myopathy, gastrointestinal abnormalities, and anemia. Laboratory studies show variable B-cell and T-cell defects, sometimes with defective antibody responses and hypogammaglobulinemia (Boisson et al., 2015; Oda et al., 2019).