How is lathyrism caused? Understanding the neurotoxic legume and risk factors

December 25, 2025 •

3 min read

Hippocrates first described a neurological disorder caused by Lathyrus seed consumption in 400 BC, making lathyrism one of the oldest known neurotoxic diseases. It is primarily caused by the overconsumption of legumes from the Lathyrus genus, particularly the grass pea (Lathyrus sativus), which contain harmful neurotoxins. This debilitating, irreversible condition is a major public health issue in regions facing drought and famine, where the resilient grass pea becomes a primary food source.

Quick Summary

Lathyrism results from ingesting specific Lathyrus legumes, which contain neurotoxins like ODAP. This leads to the degeneration of motor neurons and can cause spastic paralysis and other irreversible neurological damage. The condition is most common during periods of food scarcity when people rely heavily on uncooked or improperly prepared grass peas.

Key Points

Toxin Exposure: Lathyrism is caused by neurotoxins, primarily β-ODAP, found in legumes of the Lathyrus genus, such as the grass pea (Lathyrus sativus).
Excitotoxic Mechanism: The neurotoxin β-ODAP acts as an excitotoxin, overstimulating glutamate receptors in motor neurons, leading to cellular damage and death.
Environmental Triggers: The disease is often triggered by environmental stress, like drought and famine, which forces heavy reliance on the toxin-containing legume as a food source.
Inadequate Preparation: Insufficient soaking and cooking of the seeds fail to reduce the neurotoxin concentration, increasing the risk of toxicity.
Irreversible Damage: Prolonged consumption causes irreversible neurological damage, most commonly manifesting as spastic paralysis in the legs.
Two Distinct Forms: Neurolathyrism affects the nervous system via β-ODAP, while osteolathyrism and angiolathyrism impact connective tissues and blood vessels via BAPN.
Prevention is Key: The most effective way to prevent lathyrism is through food security measures, proper food preparation, and agricultural diversification.

The Core Cause: Neurotoxins in Lathyrus Legumes

The fundamental cause of lathyrism lies in the presence of naturally occurring neurotoxins within certain legumes of the Lathyrus genus, such as Lathyrus sativus (chickling pea or grass pea) and Lathyrus cicera. There are primarily two types of toxins responsible for different forms of lathyrism:

β-N-oxalyl-L-α,β-diaminopropionic acid (β-ODAP): This is the neurotoxin linked to neurolathyrism, the most common form affecting humans and animals. It's a glutamate analogue that overstimulates glutamate receptors, causing excitotoxicity that damages and ultimately kills motor neurons. This damage leads to progressive and irreversible paralysis, particularly in the lower limbs.
Beta-aminopropionitrile (BAPN): Found in other Lathyrus species like the sweet pea (Lathyrus odoratus), BAPN is responsible for osteolathyrism and angiolathyrism. Instead of the nervous system, it affects connective tissues and blood vessels by inhibiting the enzyme lysyl oxidase, which is crucial for collagen and elastin cross-linking. This can result in skeletal deformities and aortic aneurysms.

The Pathophysiology of Neurolathyrism

The process by which the neurotoxin β-ODAP causes neurological damage is complex and involves several cascading cellular events.

Excitotoxicity: β-ODAP mimics the neurotransmitter glutamate, leading to overstimulation of AMPA/kainate-type glutamate receptors on motor neurons.
Calcium Overload: This overstimulation causes an excessive influx of calcium ions ($Ca^{2+}$) into the neurons, overwhelming their ability to regulate intracellular calcium levels.
Oxidative Stress: The prolonged and elevated intracellular calcium levels induce oxidative stress, which generates reactive oxygen species (ROS) and damages mitochondria, the energy factories of the cell.
Neuronal Apoptosis: The cumulative damage from excitotoxicity and oxidative stress eventually triggers programmed cell death (apoptosis) in motor neurons, especially those in the spinal cord's pyramidal tracts. This leads to the characteristic spastic paralysis of neurolathyrism.

Environmental and Socioeconomic Risk Factors

While the neurotoxin is the direct cause, environmental and socioeconomic conditions are key catalysts for lathyrism outbreaks. The grass pea's resilience is a double-edged sword, as it becomes a staple in regions where other crops fail.

Drought and Famine: During periods of drought and famine, the grass pea is often the only crop that survives and yields a harvest. This forces impoverished populations to rely heavily on it for sustenance, increasing their consumption of the legume and thus their exposure to the toxin.
Lack of Food Diversity: A diet that is not varied and consists of more than one-third of grass pea seeds for an extended period significantly increases the risk of ODAP accumulation. Access to alternative, less-toxic food sources is crucial for prevention.
Ineffective Preparation: The level of toxicity can be reduced by proper preparation, such as soaking the seeds in water overnight, boiling, or parching. However, during times of crisis, these detoxification methods may be overlooked or improperly performed due to lack of resources or knowledge, leading to a higher risk.
Consumption of Immature Seeds: Immature seeds of the grass pea contain higher concentrations of the neurotoxin. Consuming these seeds, sometimes without processing, is a modifiable risk factor associated with an increased odds of neurolathyrism.

Comparison of Lathyrism Types


Feature	Neurolathyrism	Osteolathyrism	Angiolathyrism
Associated Toxin	β-N-oxalyl-L-α,β-diaminopropionic acid (β-ODAP)	Beta-aminopropionitrile (BAPN)	Beta-aminopropionitrile (BAPN)
Primary Target	Motor neurons in the central nervous system	Connective tissues, including bones and cartilage	Blood vessels, particularly the aorta
Caused by Which Legume?	Primarily Lathyrus sativus (chickling pea)	Lathyrus odoratus (sweet pea)	Lathyrus odoratus (sweet pea)
Main Symptoms	Irreversible spastic paralysis, muscle weakness, and leg muscle atrophy	Skeletal deformities, bone pain, and abnormal cartilage growth	Aortic aneurysms and potential sudden death from rupture

Prevention is Key

The irreversibility of lathyrism makes prevention the only effective strategy. This includes public health initiatives focused on diversifying food sources, especially in drought-prone regions. The development and promotion of low-toxin strains of the grass pea, alongside educational campaigns on proper cooking and food preparation techniques, are critical steps. Ensuring food aid during crises can also prevent overreliance on the potentially toxic legume.

Conclusion: A Preventable Tragedy

In conclusion, the root cause of lathyrism is the excessive, chronic consumption of certain legumes from the Lathyrus genus, particularly the grass pea, which contain potent neurotoxins like β-ODAP. This toxic exposure, exacerbated by famine and poor food preparation, leads to devastating and irreversible neurological damage, notably spastic paralysis. By addressing the underlying factors of food insecurity and promoting safe agricultural practices and dietary diversity, the incidence of lathyrism can be significantly reduced and, ideally, prevented altogether. Learn more from this comprehensive review: BMC Neurology.

Frequently Asked Questions

The primary cause of lathyrism is the consumption of certain legumes from the Lathyrus genus, particularly the grass pea (Lathyrus sativus), which contain toxic compounds known as β-ODAP and BAPN.

Neurolathyrism is caused by the neurotoxin β-ODAP (β-N-oxalyl-L-α,β-diaminopropionic acid), which affects the motor neurons in the central nervous system.

Lathyrism outbreaks are common during droughts and famines because the grass pea is a highly resilient crop. In such conditions, desperate populations heavily rely on it as a primary food source, increasing their exposure to the toxin.

Yes, proper preparation methods like prolonged soaking and boiling can significantly reduce the concentration of the toxins in the seeds, thereby decreasing the risk of developing lathyrism.

No, while neurolathyrism is the most recognized form, osteolathyrism and angiolathyrism are also caused by other toxins from the Lathyrus genus and affect connective tissues and blood vessels, respectively.

Early symptoms often include walking difficulties, muscle weakness, and severe leg cramps. The condition can progress to spastic paralysis of the legs.

Lathyrism is generally considered an irreversible condition. While discontinuing consumption of the toxic legume can prevent further progression, the damage already done, particularly neurological, cannot be reversed.

Studies have shown a higher prevalence in males in some regions, possibly due to higher dietary intake of grass pea or differing nutritional needs and metabolic factors, although further research is needed.