Methylene cyclopropyl-glycine (MCPG) or hypoglycin G was detected in both semi-ripe and ripe lychee fruit by a team of virologists led by T. Jacob John at the Christian Medical College (CMC), Vellore, in Tamil Nadu. The findings were published in Current Science last month (December 2015).
The chemical is akin to another toxin methylene cyclopropylalanine (MCPA), which is found in ackee (Blighia sapida), a West Indian fruit. Both lychee and ackee come from the Sapindaceae (soapberry) family of plants.
MCPG is known to cause hypoglycaemic encephalopathy, a metabolic illness that affects the brain when body sugar levels are low due to fasting or undernourishment. Earlier, viral encephalitis was suspected to be causing the deaths. “When no virus was detected, researchers suspected a toxin from pesticides or from the fruit itself,” says John.
In 2013, at the request of India’s ministry of health and family welfare, John camped in Muzaffarpur, Bihar, where many of the deaths had occurred. “Children there were found having low blood sugar levels which aided metabolic diseases,” John tells SciDev.Net.
Only undernourished children living near lychee orchards appeared to suffer and during May and June, when the fruit is harvested. “The victims had signs of brain cell damage and seizures, indicating that a toxin and not just undernourishment was causing the disease,’’ says John.
MCPG forms compounds with carnitine and coenzyme A and makes them less available for important metabolic reactions in the body. Both carnitine and coenzyme A are essential for fatty acid metabolism.
When a person is fasting, stored glycogen is released initially for energy production. Later, body fat is mobilised and this requires breakdown of fatty acids aided by carnitine and coenzyme. “When this metabolism is impaired, hypoglycaemia develops,” Maya Thomas, a paediatric neurologist at CMC Vellore, tells SciDev.Net.
The toxin is seen in high concentrations in the seed and semi-ripe pulp. “Children who are malnourished are most vulnerable as they have low glycogen stores,” says Thomas.
While MCPG was known to be present in lychee seeds, the study established its presence in the flesh of the fruits as well, says John.
Immediate treatment for victims includes administration of glucose, says John. “Villagers have been told to let children eat the fruit only after a meal,” John says.
This piece was produced by SciDev.Net’s South Asia desk.