The complications of Down syndrome include:
Complications of Down syndrome are: 

Congenital cardiac defects (Most common is ventricular septal defect). 
Increased risk of leukemia particularly ALL (more commonly) and specifically the megakaryoblastic form of AML (M7-AML). 
Hypothyroidism. 
Reduced fertility in females (Males are totally infertile). 
Increased risk of respiratory tract infections.
VSD
ALL
Hypothyroidism
All of the above