Aetiological and risk factors

• genetic component - risk in the siblings of autistic children is 3 or 4 times higher than in the general population; more common in boys than girls (approximately 3:1).
• gene defects and chromosomal anomalies have been found in up to 20% of individuals with ASD and siblings born in families with ASD have a 50 times greater risk of autism. The concordance rate reaches up to 82-92% in monozygotic twins, compared with 1-10% in dizygotic twins (1)
• organic cause is suggested by the development of seizures in some 40% of these children when they reach adolescence.

Kanner in his original description of the condition in 1943 suggested that the behaviour of the autistic child was a response to abnormalities in the parents, characterised as cold, detached and 'obsessive'. These ideas have not been substantiated by research.

Autism is associated with:

• the fragile X syndrome
• Rett's syndrome

NICE note factors associated with an increased prevalence of autism (2)

• a sibling with autism
  
  
• birth defects associated with central nervous system malformation and/or dysfunction, including cerebral palsy
  
  
• gestational age less than 35 weeks
  
  
• parental schizophrenia-like psychosis or affective disorder
  
  
• maternal use of sodium valproate in pregnancy
  
  
• a learning (intellectual) disability
  
  
• attention deficit hyperactivity disorder
  
  
• neonatal encephalopathy or epileptic encephalopathy, including infantile spasms
  
  
• chromosomal disorders such as Down's syndrome
  
  
• genetic disorders such as fragile X
  
  
• muscular dystrophy
  
  
• neurofibromatosis
  
  
• tuberous sclerosis

Reference

1. Park HR, Lee JM, Moon HE, et al; A Short Review on the Current Understanding of Autism Spectrum Disorders. Exp Neurobiol. 2016 Feb;25(1):1-13.
2. NICE. Autism spectrum disorder in under 19s: recognition, referral and diagnosis. Clinical guideline CG128. Published September 2011, last updated December 2017