It is believed that people with Down’s syndrome have always existed. However, it was not until 1866 that the English doctor, John Langdon Down published a description of the condition, which subsequently took his name. In 1959 Professor Jérome Lejeune proved that Down’s syndrome is a chromosomal irregularity. Instead of 46 chromosomes usually present in each cell, Lejeune noted 47 in the cells of people with Down’s syndrome. It was later determined that this additional chromosomal material results in the physical characteristics associated with the condition and the different course in development.