Weakness of the limb-girdle muscles (also known as the pelvic and shoulder girdles), that is, lack of strength of the muscles around the shoulders and the pelvis.

Presence of an increased amount of fat tissue within a cardiac ventricle with corresponding reduction of muscle tissue.

A type of motor delay characterized by a delay in acquiring the ability to control the large muscles of the body for walking, running, sitting, and crawling.

Breakdown of muscle fibers that leads to the release of muscle fiber contents (myoglobin) into the bloodstream.

The presence of an abnormal lateral curvature of the spine.

A lack of strength of the proximal muscles.

A phenomenon whereby patients are not able to stand up without the use of the hands owing to weakness of the proximal muscles of the lower limbs.

Reduced ability to climb stairs.

A chronic loss of wrist joint motion due to structural changes in muscle, tendons, ligaments, or skin that prevent normal movement of the joints of the wrist.

Lack of full passive range of motion (restrictions in flexion, extension, or other movements) of the hip joint resulting from structural changes of non-bony tissues, such as muscles, tendons, ligaments, joint capsules and/or skin.

An abnormal curvature of the spine in both a coronal (lateral) and sagittal (back-to-front) plane.

A limitation in the passive range of motion of the elbow resulting from loss of elasticity in the periarticular tissues owing to structural changes of non-bony tissues, such as muscles, tendons, ligaments, joint capsules or skin.

Weakness of the muscles involved in neck flexion (sternocleidomastoid, longus capitus, longus colli, and scalenus anterior).

An abnormally high degree of muscle fiber size variation. This phenotypic feature can be observed upon muscle biopsy.

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).

Reduced ability to move the vertebral column with a resulting limitation of neck and trunk flexion.

Nemaline rods are abnormal bodies that can occur in skeletal muscle fibers. The rods can be observed on histological analysis of muscle biopsy tissue or upon electron microscopy, where they appear either as extensions of sarcomeric Z-lines, in random array without obvious attachment to Z-lines (often in areas devoid of sarcomeres) or in large clusters localized at the sarcolemma or intermyofibrillar spaces.

An abnormal reduction in the amount of air a person can expel following maximal inspiration.

An elevation of the level of the enzyme creatine kinase (also known as creatine phosphokinase (CK; EC 2.7.3.2) in the blood. CK levels can be elevated in a number of clinical disorders such as myocardial infarction, rhabdomyolysis, and muscular dystrophy.