Zika twin mystery explored by Brazilian scientists

Jaqueline Jessica Silva de Oliveira hoped doctors were wrong when a routine ultrasound showed that one of her unborn twins would be born with the condition, marked by stunted head size and developmental issues.

Her son Lucas, who she holds in her arms, was born healthy in November. His twin sister Laura, whose head is visibly much smaller, requires regular treatment by a team of neurologists and physiotherapists in nearby Sao Paulo.

"I thank God for giving her to me ... I would never abandon her," Oliveira said, adding she had never questioned why only one child was born with microcephaly. "The doctors want to study them so they can see what protected Lucas in case it can help other children."

Clues to predisposition

Cases of only one twin developing a disease, such as rheumatoid arthritis or diabetes, have been widely documented. Medical research has focused on the interaction between the environment and genetic issues.

Similar cases of newborn twins one with and one without microcephaly caught the attention of doctors last year in northeastern Brazil, where the mosquito-borne Zika was detected for the first time in the Americas. The divergence in twins was one reason why researchers began to suspect the presence of a new disease.

The Zika outbreak is affecting large parts of Latin America and the Caribbean, with Brazil the hardest hit so far. It is likely to spread to all countries in the Americas except for Canada and Chile, the World Health Organization has said.

Last month, the U.S. Center for Disease Control and Prevention officially confirmed that infection with Zika in pregnant women is a cause of microcephaly and other severe brain abnormalities in babies.

"The importance of these twins is that they could give us some very important answers," said Mayana Zatz, director of the Human Genome Research Center at the university.

Recent studies have shown evidence of Zika in amniotic fluid, placenta and fetal brain tissue. Zatz said the placenta of one twin may be permeable to Zika, while the other may not, barring the virus from attacking the fetus.

"The third possibility that we want to investigate is that certain genes predispose the child to microcephaly, and they are altered by the presence of the Zika virus," Zatz said, noting that around 15 genes are believed to govern microcephaly.