Autism Pathophysiology and USMLE tie Ins 

In the USMLE we have 7 lines on the Autism Spectrum Disorder 

1. First of all, why is it called autism spectrum disorder ? What is the spectrum about ? 

   1. Spectrum because it is a range of symptoms, severity and ability

   2. Range of symptoms --> Some may struggle a lot with language and daily living skills, others may be highly verbal and independent.

   3. Range of severity --> From very mild difficulties that only show up in complex social settings

   4. Range of abilities --> Some autistic people have intellectual disability, Some have average abilities,Some have exceptional or savant-like talents.

2. Why does Autism occur in early childhood ? 

   1. Many of the genes linked to autism affect how the brain grows and connects during fetal life and the first years after birth.Brain development is rapid in infancy and toddlerhood. The first 2–3 years of life are a period of explosive brain growth—new neurons, synapses, and neural networks form at very high rates.

3. Why does autism have social/communication deficits, repetitive/ritualised behaviours/ restricted interest ?

   1. (1) Social & Communication Deficits

      1. Brain circuits for social cognition (like the “social brain network” involving the amygdala, superior temporal sulcus, medial prefrontal cortex, and fusiform gyrus) develop differently in autism.

      2. Differences in:

      3. Face and eye processing → less automatic recognition of facial expressions and social cues.

   2. (2) Repetitive & Ritualized Behaviors = Neurological imbalance between excitatory and inhibitory signals in the brain → repetitive motor patterns emerge.

   3. (3) Restricted & Intense Interests = Enhanced perceptual and memory systems → easier to notice fine details and patterns.

4. Why do we have intellectual disability and/or above average ability in specific skills ?

   1. Autism involves atypical neural development, affecting how brain regions connect and communicate.

   2. Some pathways may be under-connected (leading to difficulties in complex reasoning, social understanding, or flexible thinking), while others may be over-connected or highly specialized, producing exceptional skills in narrow domains (e.g., memory, math, music, art).

5. Males more common 

   1. Certain autism risk genes are carried on the X chromosome. Since males have only one X chromosome, a mutation there may have stronger effects than in females, who have two X chromosomes (and a "backup" copy).

6. Why increase head and/or brain size ? 

   1. Possible Mechanisms could be excess neuron proliferation/ reduce pruning (decrease cutting off of the neurons) In autism, there may be too many neurons or connections retained, leading to increased size.

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