X-linked infantile spinal muscular atrophy – Genetics Home Reference
X-linked infantile spinal muscular atrophy is a condition that affects only boys and is characterized by severe muscle weakness and absent reflexes (areflexia). Affected children often have multiple joint deformities (contractures) from birth that cause joint stiffness (arthrogryposis) and impair movement. In severe cases, affected infants are born with broken bones. The muscle weakness worsens over time; affected children reach some early motor developmental milestones, such as sitting unassisted, but these skills are often lost (developmental regression).
Additional features of X-linked infantile spinal muscular atrophy include an unusually small chin (
There is shortening and narrowing of the mandible and chin.
Use of illustrations and other content
” data-alt=”Photograph of the face of a person with micrognathia.” title=”Image” data-source-href=”https://elementsofmorphology.nih.gov/index.cgi?tid=8bbf61b4ad7ca2ef” class=”img-popup img-popup-2″ target=”_blank” href=”http://ghr.nlm.nih.gov/art/large/micrognathia.jpeg” data-toggle=”lightbox”>micrognathia), abnormal curvature of the spine (kyphosis), and undescended testes (cryptorchidism).
Weakness of the chest muscles used for breathing often leads to life-threatening breathing problems. Children with X-linked infantile spinal muscular atrophy usually do not survive past early childhood due to respiratory failure, although, in rare cases, affected individuals can survive into adolescence.