While no official diagnosis of the cause of de la Rosa's short stature is known, it has been speculated that he was born with the genetic syndrome MOPD II (microcephalic osteodysplastic primordial dwarfism type II). The primary symptoms of the syndrome include extreme proportional short stature, as well as distinct facial features similar to those exhibited by Nelson de la Rosa. There are approximately 100 known cases of MOPD II in the world at this time, spread throughout various ethnic backgrounds.