A Familial Spinal Cord Disorder

Three brothers with hyperglycinemia have a spinal cord disorder with upper and lower motor neuron signs in both legs but sparing sensation and sphincters. Cranial nerves and arms are normal. Five other family members were clinically normal with normal plasma glycine. The two patients studied had an abnormal plasma-serine response to oral glycine load and metabolized glycine-1-14C abnormally. These findings suggest a defect in glycine-serine interconversion in our three patients. Cases of hyperglycinemia have been associated with mental retardation, seizures, and early death, but have not been previously described with normal mentation or a specific spinal cord syndrome. Glycine acts as a post-synaptic inhibitory transmitter and is prevalent in the ventral lumbar spinal cord. Therefore, the cause of the spinal cord syndrome in these patients may be related to abnormal glycine metabolism.