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Blood and Urine Newborn Screening

Home > Topics > Public health > Newborn Screening > Blood and Urine > Diseases detected by screening > Recessive hereditary diseases
Blood and Urine Newborn Screening

Recessive hereditary diseases

A hereditary disease is transmitted to children through their parent’s genes. There are several types of hereditary diseases. A disease is said to be “recessive” when, to become afflicted, a child needs to receive 2 copies of the gene that is associated with the disease, one from its mother and the other from its father.

Transmission of the recessive hereditary disease gene

Individuals have 2 copies of each gene in their genetic make-up: one from the mother and the other from the father. At the time of conception, the genes of the 2 parents randomly combine to create those of the child. This means that for a recessive hereditary disease to be passed on to a child, both parents must be carriers of the gene for the disease, and both must transmit the gene to their child. If only one parent transmits the gene associated with the disease, the child becomes a carrier of the disease and, while not afflicted, can transmit the gene to his or her offspring.

Probability of having a child that is either a carrier of the disease or that is afflicted by it

If both parents are carriers of the gene associated with the disease

For each pregnancy, the probabilities are as follows:  

  • 1 in 4 of having a child that is neither afflicted by the disease nor a carrier of the gene associated with the disease
  • 1 in 2 of having a child that is a carrier of the gene associated with the disease
  • 1 in 4 of having a child that becomes afflicted by the disease

Transmission of a gene associated with a recessive hereditary disease when both parents are carriers

Transmission of a gene associated with a recessive hereditary disease when both parents are carriers

If only 1 parent is a carrier of a gene associated with the disease

For diseases targeted by screening tests, whether the carrier is the mother or the father, there is no risk of the child becoming afflicted. For each pregnancy, the probabilities are as follows:

  • 1 in 2 of having a child who is neither afflicted with the disease nor a carrier of the gene associated with the disease
  • 1 in 2 of having a child who is a carrier of the gene associated with the disease

Transmission of a gene associated with a recessive disease when only one parent is a carrier

Transmission of a gene associated with a recessive disease when only one parent is a carrier

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