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Seeing double: the village in deepest Kerala where twins have taken over

Indian doctor trying to unravel mystery thinks the answer may be in the water. Jeremy Laurance reports

It is the village of the doppelganger. Turn a corner in Kodinhi in rural Kerala, one of India's greenest and richest states, and if you have seen one child you will probably run into its double soon after. In this community of 2,000 families there are 250 sets of twins. In 2008 alone, of the 300 families who had children, 15 pairs were born, a rate at least six times higher than the average for the country. India has one of the lowest twinning rates in the world, but Kodinhi is close to the top of the global twinning league.

Krishnan Sribiju, a doctor at the Tirurangadi Taluk hospital, just outside the village, said the number of twins born was increasing year by year. In the past five years, up to 60 pairs had been born, and the 250 pairs who had been registered understated the true total. The high number of children with indistinguishable features makes life difficult for teachers. Abhi, 16, standing beside his brother, said: "I comb my hair to the right and he combs his hair to the left. I also have a mark on my neck. Apart from these differences there is nothing else."

Dr Sribiju, a dermatologist and public health specialist who has been studying the high twinning rate for nine years, said the cause remained a mystery. In a telephone interview yesterday, he said: "We are working on a hypothesis that it is something in nature, or in the water or the sand. We do not think it is something in the food because they don't have something particular that they eat. There are thousands of heavy metals that could be in the water and affecting the people but it takes a long time to work out. It is very difficult."

He dismissed suggestions that the cause could be the high rate of intermarriage among the predominantly Muslim population. "It is not limited to Muslim families. It is also seen in Hindus and Christians and it does not affect Muslim communities elsewhere. Families that move to the area are also affected after living there for a few years. This is a very small geographical area measuring three to four kilometres. It is likely to be something external not genetic."

Dr Sribiju said he believed most of the twins were non-identical. That meant, he said, that something was affecting the mothers causing them to produce extra eggs. Identical twins develop from a single embryo that splits soon after fertilisation while non-identical twins are the product of separate eggs that have been fertilised at the same time.

"There must be something that is stimulating the ovaries to produce eggs," he said. "In Western countries such as the UK, Spain and France the use of fertility drugs which stimulate the ovaries has led to a rise in the twinning rate. The use of IVF has also contributed [as more than one embryo was placed in the womb] but these techniques are not available in this part of India so they cannot be responsible."

Kodinhi is not the only place with a high number of twins. The global average twinning rate is about six per 1,000 live births but in Kodinhi it is 35-40 per 1,000, according to Dr Sribiju. The village of Mohammad Pur Umri, near Allahabad, also has a high rate identified five years ago, as does Candido Godoi, a village in Brazil promoted as the twins capital of the world. The highest rate in the world is believed to be among the Nigerian Yoruba tribe which has a twinning rate of 45 per 1,000 births.

"I see understanding the high twinning rate in Kodinhi as a public health challenge," said Dr Sribiju. "We are meeting with doctors from Nigeria and Brazil to try to solve this problem. We hope to find the answer."

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