A child’s DNA determines how the brain is constructed, such as the sizes of the different parts and the nerve connections it will have. However, there are external factors that can create changes to that brain construction. These factors include: poor nutrition, exposure to harmful things (eg. toxins, viruses, bacterial infections, drugs) and most interestingly, the child’s experiences with other people and the world also affect brain construction. Poor nutrition and exposure to toxins and infections can affect the brain specially during the time the baby is still in the uterus, when the brain is just being formed. For more information, please check out this article:

https://www.cdc.gov/ncbddd/childdevelopment/early-brain-development.html