Nate Ryan-Chang has an extremely rare syndrome called Trisomy 9 Mosaic - T9M. On Sunday he beat the odds and celebrated his fourth birthday. "To reach four, you go, well that's pretty good," says ...

Only a few hundred people in the world are alive with Grace Darrah’s specific kind of Trisomy: Trisomy 9 Mosaic. At the time she was born, there were only roughly 100 people who had been diagnosed.

People with Mosaic Down syndrome can share the cognitive and physical challenges as those with Trisomy 21 and Translocation Down syndrome. “There's a wide range of abilities,” says Wong.

Mosaic Down syndrome: ... Trisomy 18: This condition slows growth in the womb. This can contribute to the child being born with a smaller-than-normal head and defects in the heart and other organs.