Any clinical syndrome, apart from the basic, nuclear or pathognomonic symptoms mentioned, which constitute the basis of the definition, presents a set of secondary or associated symptoms (which are not necessary to include a particular subject in a given diagnostic category) which could notably vary in every individual.
Regarding autism, a first-order associated symptom is intellectual impairment, which affects approximately 50% of the entire population, since in contrary to the fact that it has manifested many times and without a reason, an important proportion of the population suffering from this syndrome shows an IQ within the limits of intellectual impairment.
Along with intellectual impairment, the most frequent secondary symptoms of autism are:
- Hyperactivity (childhood)
- Hypoactivity (adolescence and adulthood)
- Unstable humour
- Low tolerance to frustration
- Anxiety attack (with or without an apparent cause)
- Aggressiveness towards oneself
- Aggressiveness towards others (less frequent than towards oneself)
- Sleep disorders
- Eating disorders (hyperselectivity, nibbling)
- Epileptic seizures (20-25% of the total population)