Behavioral phenotypic variation in autism multiplex families: evidence for a continuous severity gradient

Area of Science:

• Neuroscience
• Genetics
• Developmental Psychology

Background:

• Autism multiplex families, with multiple affected siblings, are crucial for genetic studies.
• Limited understanding exists regarding the behavioral phenotypes of siblings with autism within these families.

Purpose of the Study:

• To investigate behavioral phenotypic variability and similarity among siblings with autism in multiplex families.
• To determine if distinct behavioral subgroups exist or if autism severity represents a continuum.

Main Methods:

• Utilized cluster analysis and correlations on data from 351 siblings with autism in 171 multiplex families.
• Employed Autism Diagnostic Interview-Revised (ADI-R) scores, verbal-nonverbal status, and nonverbal IQ scores for analysis.
• Assessed heritability of the observed severity gradient.

Main Results:

• Cluster analyses revealed autism severity as a continuum, not discrete subgroups.
• This severity gradient was evident across ADI-R scores, verbal-nonverbal status, and nonverbal IQ.
• The severity continuum demonstrated heritability, with a sib correlation of 30% (heritability of 60%).

Conclusions:

• No evidence of discrete behavioral subgroups in affected individuals or families was found.
• Autism phenotypes in multiplex families are best characterized by a single, heritable, continuous severity dimension.
• Findings suggest a shared genetic influence on autism severity across siblings.