These DNA tests can show us your child's susceptibility for a disease from a metabolic perspective. If your child has problems detoxifying, s/he is more likely to accumulate toxins, which at a certain point can lead to regression into autism.
The same holds true if your child has a genetic mutation that leads to an exaggerated inflammatory response to toxins. Neuro-inflammation leads to damage of neurons and the pathways that connect them and therefore there is a higher chance of regression into autism.