Autism seems to play a genetically inspired hide-and-seek game in some families. Undiagnosed siblings in families that include two or more children with autism often grapple with language delays, social difficulties and other mild symptoms of the disorder, a new study suggests.

Genes prompt autism symptoms of varying intensity among members of these families, including in some kids who don’t qualify as having an autism spectrum disorder, say psychiatrist John Constantino of Washington University School of Medicine in St. Louis and his colleagues. Researchers have generally limited their search for DNA peculiarities to children diagnosed with autism or related disorders (SN: 7/3/10, p.12), a strategy that overlooks those with mild autism signs, Constantino’s group asserts in a paper published online October 1 in the American Journal of Psychiatry.

“Subtle aspects of the autistic syndrome have not been accounted for in most studies of its intergenerational transmission,” Constantino says.

“Given Constantino’s data, it is clearly wrong to label all nonautistic individuals as unaffected by an underlying genetic liability for the condition,” Piven says.

Approximately one in five siblings of children with autism who don’t meet criteria for the disorder display mild or “subclinical” autism traits, Constantino’s team estimates. these traits consist of language delays, the use of odd or repeated phrases and other unusual speech qualities and difficulties interacting with others. Most such children come from families with at least two other youngsters who have an autism spectrum disorder.

Four times as many boys as girls meet psychiatric criteria for autism. But the inclusion of mild autism traits narrows that ratio to three boys for every two girls.

Males and females inherit the same autism-related genes, but in females those genes frequently interact with other genetic factors or with environmental influences to reduce the severity of symptoms, Constantino theorizes.

Subclinical autistic traits deserve close scrutiny for possible detrimental effects on children, Constantino adds. Kids with undiagnosed autism-related social deficits may find it hard to make friends and could experience a worsening of other conditions such as learning disabilities and attention-deficit hyperactivity disorder.

Subclinical traits may have benefits as well, he adds. Disinterest in social activities and a focus on details might boost math, science and computer skills.

Constantino’s team assessed signs of autism in 2,920 children from 1,235 families participating in a national online research registry. each family in the registry includes at least one child with an autism spectrum disorder and at least one biological sibling. Data came from questionnaires completed by parents.

Their responses indicated that 134 families, or 11 percent, had more than one child diagnosed with autism. About one in four families, including nearly all of those with multiple autism cases, also contained siblings with mild symptoms.

Among unaffected boys and girls, 20 percent had received a diagnosis of language delay or speech problems early in life, double the prevalence in the general population.

Constantino emphasizes that, for three in four families, one child had an autism spectrum disorder and the rest showed no signs of autism. he suspects that autism-related genes work in an all-or-nothing fashion in these families.

Clinicians should measure the intensity of autism symptoms over time in individual children and determine points at which interventions become necessary, much as they use growth charts to ascertain childhood obesity, he recommends.

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