Yes, he had lobar holoprosencephaly. Sadly, the lobar form is the best case scenario when it comes to holoprosencephaly.
The vast majority of males with T21 are sterile.
Tetrasomy 21 is not necessarily incompatible with life, however. It manifests pretty much like turbo Down syndrome, particularly with regard to risk of hematological malignancy. For reasons that are poorly understood, children with T21 are
highly susceptible to developing several subtypes of leukemia. In particular, infants and children with DS have a 500-fold likelihood of developing a form of acute myeloid leukemia called acute megakaryoblastic leukemia (
AMKL), which is relatively rare in normal populations. Also,
up to 30% of neonates with T21 have a condition called transient abnormal myelopoiesis (TAM), which is considered a "preleukemia", but not all babies with it go on to develop acute leukemia. It is known that several
genes on human chromosome 21 play a role in leukemogenesis, but it remains poorly elucidated exactly which genes are involved and why not all individuals with DS are affected. Basically, all of this means that individuals with tetrasomy 21 would be at an even higher risk of hematological malignancy because theoretically, they have a higher "dose" of whatever genes are involved.
