There is an ethnic group called the "asian pygmies" that are intentionally going extinct to prevent the passing of their many birth defects
The Taron people live in the Himalayan foothills of Myanmar. Their population is rapidly declining though. These people are also referred to as "Asian pygmies," and their average height is around 4 feet and 3 inches.
In the 1960s, there were 50 pure-blood Taron people. While they suffered from several physical and mental ailments, such as cretinism, mental retardation and goiter, they were overall fairly healthy. However, by 1997, there were only 8 pure-blood Tarons left. This made them some of the most highly endangered people in the world.
It was all on purpose though. Dr. Alan Rabinowitz asked the Taron people just what had happened, and they explained that Taron babies were being born with increasingly worse birth defects. Rather than risk more of these defects, the Taron people decided to voluntarily go extinct. The final remaining Taron, Dawi, was told by his father that he would not marry and would not produce any children in order to ensure extinction.