Effects:
Thyroid problems
Hearing problems
Congenital heart disease
Eye problems
Seizure disorders
Bone, muscle, nerve, or joint problems
Leukemia and other cancers
Immune system problems
Developmental delay
Mental retardation
Alzheimer's disease.

Symptoms:
Children who have Down syndrome tend to have certain features, such as a flat face and a short neck. They also have some degree of intellectual disability. This varies from person to person. But in most cases it is mild to moderate.

Effects of Down Syndrome