MedGen

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]

The kneecap normally is located within the groove termed trochlea on the distal femur and can slide up and down in it. Patellar dislocation occurs if the patella fully dislocates out of the groove. [from HPO]

Downbeat nystagmus is a type of fixation nystagmus with the fast phase beating in a downward direction. It generally increases when looking to the side and down and when lying prone. [from HPO]

Lack of the foveal reflex, which normally occurs as a result of the reflection of light from the ophthalmoscope in the foveal pit upon examination. The foveal reflex is a bright pinpoint of light that is observed to move sideways or up and down in response to movement of the opthalmoscope. [from HPO]

Congenital chylothorax is a rare, potentially life-threatening neonatal condition characterized by the accumulation of chyle within the pleural space leading to respiratory distress, malnutrition and immunological compromise, either immediately after birth or within the first few weeks of life. Congenital chylothorax is the most common cause of pleural effusion in neonates; it can occur primarily due to developmental anomalies of the lymphatic duct or can be associated with chromosomal anomalies (e.g. Noonan syndrome, Turner syndrome and Down syndrome), hydrops fetalis, mediastinal neuroblastoma and other congenital malformations. [from ORDO]

The kneecap normally is located within the groove termed trochlea on the distal femur and can slide up and down in it. Patellar subluxation refers to an unstable kneecap that does not slide centrally within its groove, i.e., a partial dislocation of the patella. [from HPO]

Acute myeloid leukemia or myelodysplastic syndrome occurring in children with Down syndrome. The acute myeloid leukemia is usually an acute megakaryoblastic leukemia, and is associated with GATA1 gene mutation. [from NCI]