Autism Spectrum Disorder (ASD)

Autistic spectrum disorder (ASD) is characterised by persistent deficits in the ability to initiate and to sustain reciprocal social interaction and social communication, and by a range of restricted, repetitive and inflexible patterns of behaviour, interests or activities that are clearly atypical or excessive for the individual's age and sociocultural context

Aetiology

  • No clear unifying pathological mechanism - combination of environmental, biological, and genetic factors
  • M:F ratio about 4:1
    • Suggested link to sex hormones
    • Some have suggested the difference is due to misdiagnosis of girls
  • Comorbidities frequent e.g. depression, anxiety, EDs, Tourettes, OCD, ADHD, learning disabilities

Risk factors

  • Rubella in the pregnant mother
  • Tuberous sclerosis
  • Fragile X syndrome
  • Encephalitis
  • Untreated PKU
  • ASD and gender identity:
    • 8-10% of children and adolescents seen at GID clinics meet the clinical diagnostic critera for autism (3-4 x more common than in general population)
    • Studies in girls with congenital adrenal hyperplasia showed more traits of ASD than controls and higher levels of gender dysphoria

Pathophysiology

Neuroanatomy of autism

  • Frontal lobes, amygdala, and cerebellum appear pathological in autism

Neurochemistry of autism

  • Glutamine receptors, GABA and serotonin seem implicated
  • GABA has a key role in the regulation of early developmental stages of cell migration, neuronal differentiation and stages of maturation
  • Glutamate is an essential exctitatory neurotransmitter which dysregulation can lead to neuronal damage
  • Serotonin neurotransmitter system has a critical role in the regulation of crucial steps of neuronal development
  • The role of catecholamines and ACh is still poorly understood

Clinical presentation

Social communication

  • Generally good language skills but find it hard to grasp the underlying meaning of conversation
  • Difficulties understanding jokes, idioms, metaphors and sarcasm
  • Voices often sound monotonous
  • Language can be pedantic and idiosyncratic
  • Often have narrow interests which dominate their converations (lack of reciprocity)

Social interaction

  • Difficulties picking up non-verbal cues
  • Appear self-focused and lacking in empathy, when in fact they are simply trying to figure out social situations
  • Continually struggle to make and sustain personal and social relationships

Social imagination

  • Difficulties thinking flexibly and in abstract ways
  • Inability to understand other people's points of view, taking things literally
  • Difficulties applying knowledge and skills across settings with different people
  • Difficulties projecting themselves into the future or planning goals sensibly

Repetitive impairment

  • Stereotyped or repetitive motor movements, use of objects or speech
  • Insistance on sameness, inflexible adherence to routines, or ritualised patterns of behaviour or nonverbal behaviour
  • Highly restricted, fixated interests that are abnormal in intensity of focus
  • Hyper- or hypo- reactivity to sensory input or unsual interest in sensory aspects of the environment

Investigations

Diagnostic tools

  • Good quality developmental history and collateral history from parents, other relatives, schools, employers, partners etc.
  • Screening questionnaires and semi-structured interviews
  • Standardised assessment tools - ADOS
  • No biological markers
  • Ultimately a subjective clinical judgement

Essential critera

  • Symptoms must be present in the early developmental period
  • Symptoms cause clinically significant impairment in social, occupational, or other important areas of current functioning (regardless of age)
  • Disturbances are not better explained by other mental health problems, intellectual disability, or global developmental delay

Management

  • Treatment is mainly through education and social interventions
  • Medication rarely required other than to treat main comorbidities
    • Risperidone is licensed for management of severe aggression and significant self-injury