MedGen

Congenital myopathy-3 with rigid spine (CMYP3) is an autosomal recessive disorder of the skeletal muscle characterized by hypotonia and proximal muscle weakness apparent from birth or early childhood. Affected individuals show delayed motor development and develop progressive severe and deforming scoliosis ('rigid spine') in the first or second decades. Respiratory involvement due to diaphragmatic weakness is common, and most patients require ventilatory support due to nocturnal hypoventilation; recurrent respiratory infections are also observed. Additional features may include facial muscle weakness, amyotrophy, joint contractures, distal hyperlaxity, pulmonary hypertension with secondary cardiac dysfunction, and insulin resistance in those with a low BMI. The muscle weakness is not progressive, and most patients remain ambulatory. Skeletal muscle biopsy typically shows multiminicores, although there are often other abnormal nonspecific myopathic findings. This phenotype has been referred to as 'rigid spine syndrome' (Scoto et al., 2011; Fan et al., 2022; Varone et al., 2019). For a discussion of genetic heterogeneity of congenital myopathy, see CMYP1A (117000). [from OMIM]

Rigid spine muscular dystrophy (RSMD) is a form of congenital muscular dystrophy. Disorders in this group cause muscle weakness and wasting (atrophy) beginning very early in life. In particular, RSMD involves weakness of the muscles of the torso and neck (axial muscles). Other characteristic features include spine stiffness and serious breathing problems.

In RSMD, muscle weakness is often apparent at birth or within the first few months of life. Affected infants can have poor head control and weak muscle tone (hypotonia), which may delay the development of motor skills such as crawling or walking. Over time, muscles surrounding the spine atrophy, and the joints of the spine develop deformities called contractures that restrict movement. The neck and back become stiff and rigid, and affected children have limited ability to move their heads up and down or side to side. Affected children eventually develop an abnormal curvature of the spine (scoliosis). In some people with RSMD, muscles in the inner thighs also atrophy, although it does not impair the ability to walk.

A characteristic feature of RSMD is breathing difficulty (respiratory insufficiency) due to restricted movement of the torso and weakness of the diaphragm, which is the muscle that separates the abdomen from the chest cavity. The breathing problems, which tend to occur only at night, can be life-threatening. Many affected individuals require a machine to help them breathe (mechanical ventilation) during sleep.

The combination of features characteristic of RSMD, particularly axial muscle weakness, spine rigidity, and respiratory insufficiency, is sometimes referred to as rigid spine syndrome. While these features occur on their own in RSMD, they can also occur along with additional signs and symptoms in other muscle disorders. The features of rigid spine syndrome typically appear at a younger age in people with RSMD than in those with other muscle disorders. [from MedlinePlus Genetics]