It has been discovered recently that these "dumb" genes turn the letter genes on and off. They determine whether a cell becomes a brain or kidney cell, for example. There are 3 billion base gene structures, so there is a long way to go in understanding basic functions. At any one time 80 per cent of genes are active. Some are triggered by proteins. Others change into RNA that regulate letter genes.
In regard to understanding human health, many bases just keep chromosomes quiet. A complicating factor is that genes overlap and have many end points - not singular. Over 4 million gene triggers have be found and they are not all located near their target letter gene. The next step is to find out which base changes affect susceptibility to arthritis, diabetes and so on.