Adhd, is there a link between attention deficit disorder and the microbiome?

Can the microbial composition of the gut cause attention deficit disorder in a child? The gut is said to be the second brain. And there is mounting evidence that the microbiome-brain axis does indeed play a role in the development of psychiatric disorders. Several scientific studies have already found links between an inefficient bacterial flora and a greater susceptibility to ADHD, autism spectrum disorders, depression and schizophrenia.