Transitions are more common. Can insert into any gene, usually destroying the gene. Microsatellites have 2 base repeats, can change number during cell division. Copy number cahnges in male meiosis but not female. One copy of the gene doesn't make enough product.
Precursors build up in blood and cause dementia.
Too much enzyme activity. Normally a minor side pathway from adenosine to inosine. Most adenosine normally goes to ATP, only a small amount to inosine. Mutant that makes 50 x too much ADA shunts most adenosine to inosine, leading to ATP deficiency, which gives fragile red blood cells and anemia. Sometimes one allele make a defective product that meshes with the defective product of the other allele to produce an active product.