Hypotonia

Abnormally decreased skeletal muscle tone, characterized by diminished resistance to passive movement, often associated with neuromuscular or central nervous system disorders. Common causes are genetic disorders (Down syndrome, Prader-Willi syndrome, Marfan syndrome), anoxic brain damage during birth, neuromuscular disorders (spinal muscular atrophy, muscular dystrophy, myasthenia gravis), vitamin B12 deficiency, hypothyroidism, and exposure to toxins.