Family history of cognitive disabilities in first-degree relatives of autistic and mentally retarded children.
Families of kids with autism and mental retardation show equal rates of cognitive disability, but within autism, girls and lower-IQ children carry the heavier family load.
01Research in Context
What this study did
The team looked at first-degree relatives of kids with autism and kids with mental retardation.
They wanted to know if one group had more family members with cognitive disabilities.
The study used a simple case series design to count relatives with learning or IQ problems.
What they found
Both groups had the same rate of cognitive disability in parents and siblings.
Inside the autism group, girls and kids with lower IQ had more affected relatives.
Family risk looks equal across the two diagnoses, but clusters in certain autism sub-groups.
How this fits with other research
Schaal et al. (1990) compared the same two diagnoses years earlier. They tracked daily-living skills instead of family history, giving an earlier benchmark for autism-vs-MR contrasts.
Burack et al. (2004) extended the picture by showing that autism plus severe ID brings five times more psychiatric disorders than ID alone. Together the papers sketch a line: family risk is equal, but added autism can multiply behavior problems.
Chiang et al. (2014) pooled 52 studies and found unique IQ profiles in high-functioning autism. Their meta-analysis includes work like the target paper, showing why cognitive heterogeneity in autism matters for diagnosis.
Why it matters
You can stop assuming autism families carry more genetic cognitive load than ID families.
Do watch girls and lower-IQ learners on your caseload; their relatives may need extra screening.
When you see both autism and severe ID, plan for more co-occurring behavior issues, not less.
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02At a glance
03Original abstract
We compared with a family history method the rate of cognitive disabilities (CD) in 156 first-degree relatives of 49 autistic (AU) probands to that found in 55 first-degree relatives of 18 mentally retarded (MR) probands. Broadly defined CD were found in, respectively, 17 and 16% of the relatives of the AU and MR probands. However, the characteristics of the probands associated with a family history of CD are different in AU and MR: Female and low IQ AU probands have more first-degree relatives with CD. Our findings suggest that a positive family history of CD is not specific to autism when compared to mental retardation. The observation that female and low IQ probands have higher family history of CD may suggest heterogeneity within autistic children and provides leads for future family studies.
Journal of autism and developmental disorders, 1997 · doi:10.1023/a:1025891824269