Genetic Birth Defects, Down syndrome, Phenylketonuria or PKU, Fragile X syndrome

Genetic Birth Defects

The known genetic birth defects are:

Down syndrome
Phenylketonuria or PKU
Fragile X syndrome

Down syndrome

The Down syndrome is due to the existence of a superfluous chromosome, referred to as chromosome 21. Down syndrome leads to mental retardation and certain external physical features.

Phenylketonuria or PKU

PKU is due to a particular recessive gene from both parents. It leads to the abnormal metabolism of protein which may lead to mental retardation.

Fragile X syndrome

Fragile X syndrome also leads to mental retardation, as well as autism and attention deficit disorders. The father with this defective gene can pass on the illness to all his daughters but not to the sons. However, the mother who has the faulty gene can affect half of her children, both daughters and sons.