In the etiopathogenesis of autistic spectrum disorder (ASD) several hypotheses have been described that include inflammation, metabolic alterations, activation of oxidative stress, changes in the intestinal microbiota and in the elimination capacity of heavy metals. Adjuvant therapies with omega-3 polyunsaturated fatty acids could modify these alterations.

Several hypotheses have been described in the etiopathogenesis and evolution of ASD, among which is that there is greater oxidative stress associated with a proinflammatory state, or even metabolic alterations after exposure to heavy metals, as well as differences in intestinal microbiota. This situation could negatively influence the correct establishment of neuronal synapses and their functioning, which have still been poorly investigated, especially in children. In this way, an early intervention with nutritional supplements with DHA, which could be deficient in autism, could decrease the proinflammatory and oxidative stress state, favoring the formation of neuronal synapses as well as their activity. This intervention could positively influence to prevent the clinical deterioration associated with ASD and it would be of special interest in early childhood since at this stage of neurodevelopment there is maximum neuronal plasticity.

Inclusion Criteria:

• Children and girls aged between 2 and 5 years diagnosed with Autism Spectrum Disorder according to the DSM-V criteria and the Observation Scale for the Diagnosis of Autism (ADOS).
• Informed consent signed by one of the parents or legal representative.

Exclusion Criteria:

• Children under 2 years old.
• Children diagnosed with ASD over 4 years old.
• Coexistence of another diagnosis associated with autism.
• Patients who are receiving some type of supplement or concomitant medication that does not allow a period of washing.
• Patients diagnosed with other pathologies or with mediation that may affect the study variables (oxidative stress, inflammation, cell adhesion molecules, lipid profile or microbiota).

The nutritional supplement used will be a product marketed according to the European Union regulation. This supplement (EUPOLY-3® DHA Infant) will be provided by Biosearch SA (Granada, Spain), as well as the placebo, in identical containers labeled with a numeric code. Product code: EUP007. The composition of both will differ only in that the formula with DHA will be fish oil refined and stabilized by the addition of soy lecithin, tocopherols of natural origin and ascorbic palmitate. In addition, its level of toxic in the raw material is controlled. This product, and the placebo, will keep the rest of the fatty acid profile similar (eg content of linoleic and linolenic fatty acids). It will be designed in a formulation suitable for preschool children with ASD; in liquid form and in a concentrated dose to ingest orally in the least amount possible (approximately 1.5cc in each dose).