Rigid spine with muscular dystrophy type 1. Deficiency of selenoprotein N.
Incidence
Autosomal recessive. This is a relatively common form of congenital muscular dystrophy.
Clinical Characteristics
The most common presentation of rigid spine muscular dystrophy 1 is that of axial hypotonia and weakness in the first year of life, but usually in a child with otherwise normal motor milestones. Motor difficulties secondary to mild-to-moderate proximal muscle weakness, mild Achilles tendon tightness, and rigidity of the spine are also common. Ambulation is usually maintained into adulthood. The overall muscle bulk is reduced, especially the medial aspects of the thighs. The most prominent clinical features are spinal rigidity and scoliosis, which may develop between 3 and 12 years of age. Contractures usually are mild and affect the ankles. Nasal speech secondary to palatal weakness is common. Vital capacity due to stiffness of the rib cage is low and decreases over time, and this is almost invariably aggravated by diaphragmatic weakness leading to respiratory failure. Muscle weakness is slowly progressive, and ambulation may be maintained for many years. The cardiac system is usually normal. Intelligence and brain MRIs are normal. It is due to defect of endoplasmic reticulum proteins of unknown function.
Precipitants
None
Provocation Tests
None
Diagnostic Procedures
Serum CK levels are usually normal or mildly elevated. The muscle biopsy typically shows significant intramyofibrillar disruption, at times featuring minicores. Mutation analysis of the selenoprotein N is necessary to confirm the diagnosis.