Lathyrism

Lathyrism is a neurological and musculoskeletal disorder caused by the prolonged consumption of certain species of Lathyrus (grass pea) seeds that contain a neurotoxic amino acid. The condition primarily affects populations dependent on Lathyrus sativus (commonly known as kesari dal, grass pea, or chickling pea) as a staple food during famine or drought. Lathyrism leads to irreversible paralysis of the lower limbs, commonly referred to as spastic paraparesis.
It is considered one of the oldest known neurotoxic diseases associated with diet and remains a public health concern in parts of South Asia and Africa.

Causative Agent and Pathogenesis

Lathyrism results from the ingestion of the toxic amino acid β-N-oxalyl-L-α,β-diaminopropionic acid (β-ODAP), found in the seeds of Lathyrus sativus.
Mechanism of toxicity:

• β-ODAP acts as an excitatory neurotransmitter analogue, overstimulating the neurons in the spinal cord.
• Prolonged exposure leads to degeneration of motor neurons in the corticospinal tract, which control voluntary movement in the lower limbs.
• This neuronal damage results in spastic paralysis, particularly affecting leg muscles.

The toxin’s impact depends on the duration and quantity of consumption, nutritional status, and other dietary factors. Diets low in protective amino acids such as methionine and cysteine (common in protein-poor diets) exacerbate toxicity.

Types of Lathyrism

Lathyrism can be classified into three major types based on the systems affected:

1. Neurolathyrism:
   • The most common and severe form.
   • Caused by β-ODAP in Lathyrus sativus.
   • Affects the central nervous system, leading to spastic paralysis of lower limbs.
2. Osteolathyrism:
   • Results from the ingestion of Lathyrus odoratus (sweet pea), containing the toxin β-aminopropionitrile (BAPN).
   • Interferes with collagen cross-linking, causing skeletal deformities, bone fragility, and connective tissue defects.
3. Angiolathyrism:
   • Also linked to BAPN exposure.
   • Affects the vascular system, weakening the walls of blood vessels and predisposing them to aneurysms.

Among these, neurolathyrism is of primary epidemiological importance in human populations.

Epidemiology and Geographic Distribution

Lathyrism has been reported historically in parts of India, Bangladesh, Nepal, Ethiopia, China, and Afghanistan, where Lathyrus sativus is cultivated as a drought-resistant crop.
In India, it has been most prevalent in the states of Madhya Pradesh, Uttar Pradesh, Bihar, Chhattisgarh, and Odisha. The disease tends to occur in regions experiencing famine or crop failure, where grass pea becomes a dietary staple due to its resilience and availability.

Clinical Features

Symptoms of neurolathyrism typically appear after three to six months of continuous consumption of grass pea as the main dietary protein source.
Key clinical manifestations include:

• Gradual onset of stiffness and weakness in the legs.
• Spastic gait (legs crossing during walking, “scissor-like” movement).
• Difficulty in walking, running, or climbing.
• In severe cases, complete paralysis of the lower limbs.
• Reflexes in the legs become exaggerated, while sensory functions remain intact.
• The upper limbs and cognitive abilities are usually unaffected.

The disease often affects young adult males (15–45 years) more than women and children, possibly due to higher consumption and physical activity.

Diagnosis

Diagnosis of lathyrism is based on:

• Clinical presentation: Spastic paraparesis with intact sensory functions in individuals consuming Lathyrus sativus.
• Epidemiological history: Evidence of dependence on grass pea as a major food source.
• Exclusion of other causes: Ruling out infectious or traumatic causes of paralysis (e.g., poliomyelitis or spinal injury).

In research settings, neurophysiological studies and biochemical tests can confirm exposure to β-ODAP, but clinical and dietary history remain the main diagnostic tools.

Prevention and Control

Controlling lathyrism requires a combination of agricultural, dietary, and public health interventions:

1. Dietary Diversification:
   • Encourage inclusion of alternative legumes and protein sources such as lentils, chickpeas, and soybeans.
   • Promote balanced nutrition with adequate vitamins and amino acids (especially methionine).
2. Processing of Grass Pea:
   • Detoxification methods can significantly reduce β-ODAP levels:
     • Soaking seeds in water and discarding the soaking water.
     • Boiling or parboiling and draining the cooking water.
     • Fermentation or germination processes.
3. Agricultural Strategies:
   • Development and distribution of low-ODAP varieties of Lathyrus sativus.
   • Crop rotation and awareness campaigns discouraging over-reliance on grass pea.
4. Legislative Measures:
   • Several countries, including India, have regulated or banned the sale and cultivation of Lathyrus sativus for human consumption under the Prevention of Food Adulteration Act (1954).
   • The ban is gradually being reconsidered due to the availability of low-toxin strains and the crop’s importance in food security.
5. Public Health Education:
   • Awareness campaigns emphasising the risks of excessive consumption.
   • Community-based nutritional education in drought-prone and impoverished regions.

Treatment and Management

There is no specific cure for neurolathyrism once neurological damage has occurred, as it is largely irreversible. Treatment focuses on symptom management and rehabilitation:

• Physiotherapy: To improve muscle strength and mobility.
• Assistive devices: Braces, crutches, or wheelchairs for mobility support.
• Nutritional rehabilitation: Balanced diet with vitamins, minerals, and amino acids.
• Community rehabilitation programmes: Aimed at social and occupational inclusion of affected individuals.

Experimental therapies involving antioxidants, neuroprotective agents, and amino acid supplementation have shown limited success.

Socioeconomic and Cultural Aspects

Grass pea (Lathyrus sativus) plays a complex role in rural economies. Despite its toxicity, it remains a vital subsistence crop due to its resilience to drought, flooding, and poor soils. It requires minimal inputs, fixes nitrogen in the soil, and serves as both food and fodder.
Thus, eradication of the crop is not feasible; instead, sustainable approaches focus on safe utilisation through improved varieties and awareness.

Research and Developments

Ongoing research aims to:

• Identify genetic and environmental factors influencing ODAP levels.
• Develop biofortified or genetically modified low-toxin cultivars.
• Understand the molecular mechanism of β-ODAP-induced neurotoxicity.
• Explore protective nutrients and compounds that can mitigate its effects.

International organisations such as the International Centre for Agricultural Research in the Dry Areas (ICARDA) and the Indian Council of Agricultural Research (ICAR) are actively engaged in developing safe Lathyrus varieties.

Public Health Significance

Lathyrism exemplifies the intersection of nutrition, poverty, and food security. It remains a concern in regions where climatic adversity compels populations to rely on limited food sources. Effective prevention requires coordinated efforts across health, agriculture, and education sectors to ensure that populations do not have to choose between hunger and paralysis.