Lathyrism is a neurological disorder affecting humans and animals, caused by consuming certain legumes, particularly in large quantities over extended periods. Its occurrence is often associated with challenging environmental and socio-economic conditions. The disorder highlights the balance between food availability and potential health risks in vulnerable populations.
The Source of Lathyrism
The primary source of lathyrism in humans is the grass pea (Lathyrus sativus), and to a lesser extent, other related Lathyrus species. This legume is widely cultivated in regions like the Indian subcontinent, Ethiopia, and parts of the Mediterranean, valued for its resilience. The grass pea thrives in harsh conditions, including extreme temperatures, drought, and flooding, often surviving when other food crops fail. This makes it a “famine food” for subsistence farmers, providing an affordable protein source during scarcity.
The neurotoxin responsible for neurolathyrism is β-N-Oxalyl-L-α,β-diaminopropionic acid, known as ODAP or BOAA. This non-protein amino acid is present in grass pea seeds and acts as a glutamate analogue, interfering with the nervous system. ODAP concentration in seeds can vary, with drought conditions potentially leading to higher levels, sometimes reaching 5.5 mg per gram.
Physical Effects on the Body
Consuming large quantities of Lathyrus seeds with high ODAP concentrations primarily affects the human nervous system. This condition, neurolathyrism, begins with muscle cramps and stiffness in the lower limbs. As it progresses, individuals often develop spastic paraparesis, characterized by muscular weakness and spasms in both legs. This can severely impair mobility, leading to walking difficulties, a characteristic “scissoring gait,” and eventually reliance on walking aids or even crawling in severe cases.
The neurotoxin ODAP specifically targets motor neurons in the spinal cord, causing excitotoxicity, which results in overstimulation and subsequent death of these neurons. This neuronal loss directly contributes to the paralysis and muscle atrophy observed in the lower limbs, including gluteal muscle atrophy. Children affected by lathyrism may also experience bone deformities and reduced brain development. Another form, osteolathyrism, caused by a different toxin in sweet peas, affects the skeletal system, mainly in animals.
Diagnosis and Symptom Management
Diagnosing lathyrism relies on clinical observation and a thorough dietary history, as no specific laboratory test confirms the condition. Physicians assess characteristic neurological symptoms, such as spastic paraparesis, and correlate them with a history of consuming Lathyrus legumes. Neuroimaging techniques, like MRI, may evaluate neuronal damage, though they are not the primary diagnostic tool.
Once diagnosed, the neurological damage caused by lathyrism is irreversible, with no cure. Management focuses on alleviating symptoms and maintaining mobility. Physical therapy is an important part of this management, involving exercises to reduce spasticity and strengthen muscles, helping individuals retain their ability to walk. Medications may also be prescribed to reduce muscle spasms and stiffness, contributing to improved comfort and function.
Prevention Strategies and At-Risk Populations
Prevention of lathyrism focuses on reducing exposure to the neurotoxin ODAP, primarily through detoxification methods and dietary diversification. Soaking grass pea seeds in water for 24 hours and discarding the water before cooking can significantly reduce toxin content, sometimes halving the risk of neurolathyrism. Thorough boiling of the peas can also help.
Dietary diversity is another important strategy, preventing over-reliance on the grass pea as a staple food. Mixing grass pea with cereals rich in sulfur amino acids, such as wheat or maize, can be protective and dilute the toxin’s concentration. At-risk populations are found in regions prone to drought and food insecurity, where the grass pea is cultivated due to its hardiness. These include parts of India, Bangladesh, Nepal, Pakistan, and Ethiopia, with young adult males often being more susceptible, possibly due to higher consumption or specific agricultural roles.