A compound found in litchi seeds might be responsible for a mysterious brain disease that strikes many young children in Muzaffarpur district of Bihar each summer, according to two independent groups of researchers.
“Eating litchis is absolutely not dangerous for adults or well-nourished children,” said T. Jacob John, who is a paediatrician but is better known as a leading virologist. He was with the Christian Medical College at Vellore in Tamil Nadu.
Along with colleagues, Dr. Jacob John had published two papers last year in Current Science suggesting that ‘methylenecyclopropylglycine’ (MCPG), a substance that exists in litchi seeds, could be behind the yearly outbreaks in Muzaffarpur, a major cultivation centre for this fruit.
The symptoms In these annual outbreaks, which peak in June, young children would be healthy in the evening but early next morning have convulsions and even become unconscious.
A large proportion of those affected died and many of those who survived continued to suffer from mental retardation, muscle paralysis or movement disorders.
It was under-nourished children who were affected by the disease, Dr. Jacob John told this correspondent. Children in poor rural families, typically of labourers working in litchi orchards, were the ones at risk.
In work just published in the Morbidity and Mortality Weekly Report (MMWR) , a large team of Indian and U.S. researchers, including from the National Centre for Disease Control in New Delhi and the Centers for Disease Control and Prevention in the U.S., ruled out bacterial and viral infections as causative factors.
“One specific hypothesis” to explain the disease was that exposure to MCPG might cause very low blood sugar levels and brain problems in some children, noted Aakash Shrivastava and others in the MMWR paper.
In tests carried out in animals, MCPG has been shown to lower blood sugar levels and produce brain problems. It was found to interfere with a biochemical pathway in cells that turns fatty acids into glucose, which also resulted in the accumulation of toxic molecules.
In under-nourished children, who had little glucose reserves in their body, MCPG could be blocking their cells' ability to utilise fatty acids when blood sugar levels dropped early in the morning, remarked Dr. Jacob John.
As a result, the brain could then be deprived of the glucose it needed. The toxic substances that MCPG produced could also be taking their toll on brain cells.
MCPG’s mechanism of action is thought to be similar to the one produced by a toxin found in unripe ackee, a fruit found in West Indies and West Africa.
The clinical symptoms of ackee poisoning are similar to those displayed by affected Muzaffarpur children.
However, it has still to be conclusively established that MCPG in litchi is indeed the cause of the disease seen in children.
During the forthcoming litchi season, the MCPG levels in unripe and ripe litchi fruit as well as seeds would be examined, said Mukul Das of the CSIR-Indian Institute of Toxicology Research at Lucknow, a co-author of one of the Current Science papers published last year.
The published literature indicated that the compound was present in litchi seeds. The unripe fruit might be having more of it than the ripe fruit. “These things need to be tested,” he remarked.
In the MMWR paper, Dr. Shrivastava and colleagues said that laboratory investigations to assess the possibility of MCPG in litchis being the cause and to understand why only some children were affected are ongoing.