According to the Genetics Home Reference, a website of the U. S. government that seeks to promote education about genetic disorders, small teeth are caused by many different conditions, such as amelogenesis imperfecta, Down syndrome, Larsen syndrome, polydactyly and Coffin-Lowry syndrome. There are approximately 35 conditions that can cause an individual to have small or deformed teeth.
Many of the conditions that cause small teeth are genetic disorders that occur due to gene mutations, chromosomal errors or the presence of an inherited genetic illness.
For example, a melogenesis imperfecta occurs due to a mutation of the genes that determine tooth development. Teeth are small, discolored, malformed and prone to breaking.