A neurological disorder caused by prolonged, heavy consumption of grass pea, Lathyrus sativus, a hardy pulse grown in parts of Asia and northern and eastern Africa. The seeds contain the neurotoxin ODAP, which damages motor neurons and produces irreversible spastic paralysis of the legs. Lathyrism strikes during famines and droughts when grass pea, one of the few crops to survive, becomes the dietary staple. It predominantly affects young men performing physical labour. Prevention depends on dietary diversity, limiting grass pea intake, and developing low-toxin varieties through plant breeding. The disease illustrates the dangers of over-reliance on a single wild or semi-domesticated food.