Infantile-onset X-linked spinal muscular atrophy

Infantile-onset X-linked spinal muscular atrophy (also known as X-linked spinal muscular atrophy type 2, SMAX2, or arthrogryposis multiplex congenita – X-linked type 1) is a rare and severe neuromuscular disorder caused by mutations in the UBA1 gene located on the X chromosome. Because it follows X-linked recessive inheritance, it predominantly affects males. The disease is characterized by degeneration of motor neurons in the spinal cord, leading to progressive muscle weakness and atrophy beginning in infancy. Key clinical features include severe hypotonia (low muscle tone) at birth or in early infancy, areflexia (absence of reflexes), joint contractures (arthrogryposis), and progressive respiratory failure. Affected infants often present with difficulty feeding, weak cry, and limited spontaneous movement. Fasciculations of the tongue and fingers may also be observed. Chest deformities and fractures can occur due to profound weakness. The condition is typically very severe, and many affected infants experience life-threatening respiratory insufficiency within the first months or years of life. There is currently no curative treatment for infantile-onset X-linked spinal muscular atrophy. Management is supportive and focuses on respiratory care (including ventilatory support), nutritional support, physical therapy to manage contractures, and orthopedic interventions as needed. Genetic counseling is important for affected families. The prognosis is generally poor, with significant morbidity and early mortality in most cases. Research into potential targeted therapies is ongoing but no disease-modifying treatments have been approved to date.

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