Nonketotic hyperglycinemia treated with strychnine, a glycine receptor antagonist.

A 6 1/2-month-old boy suffering from nonketotic hyperglycinemia has been treated for at least 12 months with oral strychnine. The drug caused improvement of muscle tone, motoricity, vigilance and social behavior. Glycine is one of the putative neurotransmitters of postsynaptic inhibition, particularly at the spinal and reticular levels, strychnine its antagonist at the postsynaptic membrane. Strychnine improved the patient's motoricity presumably by blocking the excessive glycine-mediated inhibition of motoneurons. The beneficial effect of strychnine on vigilance and social behavior is more difficult to explain but may have been related to its antagonism of glycine inhibition of brainstem reticular neurons.