The short version
- Autism is strongly heritable. A large five-country register study estimated a median heritability of about 81% (range 73-86%) [1].
- ADHD and autism often occur together and share some genetic liability (Tier B; exact overlap figures not yet verified).
- In a Swedish register study, autistic people died at higher rates than matched controls across almost every diagnostic category, from a wide range of medical causes [2].
- Both facts point the same way for care: these are lifelong neurodevelopmental conditions with medical consequences. They are not conditions that belong only under mental health services.
The usual mix-up
"Autism and ADHD are separate, so their genetics are separate." They are separate diagnoses with overlapping biology. A person can have both, and current diagnostic manuals allow both to be recorded together (not yet verified).
The plain-English layer
Heritability
The Bai et al. study pooled data on 2,001,631 individuals, including 22,156 with autism, across five countries. The median heritability was 80.8% (range 73.2-85.5%), and the maternal effect was small (0.4-1.6%) [1]. As with ADHD (GEN-01), heritability describes why people differ in a population. It does not describe a share of any one person's autism.
Genetic architecture
As with ADHD, autism involves many common variants of small effect and rarer variants of larger effect, including new (de novo) variants (Tier B, general; not yet verified for gene counts). GEN-04 explains the difference.
What genes say about needs
Genes do not tell you a person's support needs. Autistic people vary enormously in communication, independence and health needs, and no gene result predicts those for an individual.
The medical-care evidence
The Swedish study followed 27,122 people diagnosed with autism between 1987 and 2009 against 2,672,185 matched controls. During follow-up, 706 autistic people (2.60%) had died compared with 0.91% of the general population (odds ratio 2.56; 95% CI 2.38-2.76). Mortality was raised for almost all diagnostic categories, with sex and general intellectual ability moderating the pattern [2]. The authors concluded that premature mortality was markedly increased owing to a multitude of medical conditions.
Why this belongs in a genetics series. If a neurodevelopmental condition is associated with raised risk across many medical causes, then care cannot be organised as if the condition were only a mental-health matter. Whole-person medical care, with clear ownership, is the evidence-consistent model. The policy argument is developed in the policy section of this site.
Limits
- Register studies show association, not cause. The mortality study is Swedish and covers diagnoses made between 1987 and 2009; care systems and diagnostic practice have changed since.
- The 81% figure is a pooled estimate across countries and designs; individual studies differ.
- The overlap between ADHD and autism genetics is stated here only in general terms until the source figures are verified.
- Nothing here is advice about any individual's diagnosis or needs.
Sources
Bibliographic details checked against PubMed.