The same genetic lightning bolt: Rare DNA defects among some autistic and developmentally delayed children

The girls had never met, but they looked like sisters. There was no missing the similarities: the flat bridge of their noses, the thin lips, the fold near the corner of their eyes. And to the families of 14-year-old Samantha Napier and 4-year-old Taygen Lane, there was something else, too. In the likeness was lurking an explanation for the learning difficulties, the digestion problems, the head-banging that had troubled each of them for so long.

Several of the adults wiped tears from their eyes. "It's like meeting family," said Samantha's older sister, who accompanied her and their mother to a Kentucky amusement park last July to meet Taygen.

But the two families are not related, and would never have met except for their unusual bond: a few months earlier, a newly available DNA test revealed that Samantha and Taygen share an identical nick in the short arm of their 16th chromosomes.

Doctors are now learning that the symptoms of many children who are diagnosed as "autistic”"or "developmentally delayed" can be traced to the deletion or duplication of particular parts of the children's DNA. Some mutations are so rare that they are known only by their chromosomal address. For example, Samantha and Taygen are two of only six children in the world who are known to have defects in the 16p11.2 section of their DNA. (The most common mutation, on the other hand, is Down syndrome, which occurs in people with an extra 21st chromosome in addition to the usual pair.)

The affected children are typically the only ones in their families to have the disorder. So, many parents are searching out strangers who've been struck by the same genetic lightning bolt. They want solace, advice and answers to what the future might bring. From other families of children with the same chromosomal anomaly, they are seeking insight into their own. Sometimes what they find is unsettling; more often, in the emerging communities of the genetically rare, what they find is sustaining.

The genetic counselor at the University of Louisville Hospital put the girls' mothers in touch. The first time the mothers spoke, they talked on the phone for hours. When they met face to face, the questions continued.

Was Samantha sensitive to small noises? Even a cough or a sneeze can make Taygen shudder.

Samantha makes her mother unplug the clock every night because she can't stand its ticking.

Taygen is often sweet and then nasty in bewildering succession.

Samantha slaps you and then hugs you. You never know what is coming next.

It got easier, Samantha's mother told Taygen's mother. She has fewer tantrums now, and has learned her letters.

Advice to parents of autistic and developmentally delayed children: Consider getting help from an organization in Britain called Unique. They seek to link families with rare chromosomal disorders.

Browse for related stories in the index at the very bottom of this page, or read another story on the misdiagnosis of a rare genetic condition.

Thanks to Amy Harmon for the source story in the December 28 issue of the NY Times.