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PMID 20301739

Abstract

X-linked infantile spinal muscular atrophy (XL-SMA) is characterized by congenital hypotonia and areflexia and evidence of degeneration and loss of anterior horn cells (i.e., lower motor neurons) in the spinal cord and brain stem. Often congenital contractures and/or fractures are present. Intellect is normal. Life span is shortened because of progressive ventilatory insufficiency resulting from chest muscle involvement. The diagnosis of XL-SMA is based on clinical findings; evidence of degeneration and loss of anterior horn cells in the spinal cord and brain stem; normal XL-SMA is inherited in an X-linked manner. Carrier females have a 50% chance of transmitting the pathogenic variant with each pregnancy. Males who inherit the pathogenic variant will be affected; females who inherit the pathogenic variant will be carriers and will usually not be affected. Affected males do not reproduce. Carrier testing for family members at risk and prenatal testing for at-risk pregnancies are available if the