“Genetic Screening for Deafness in Pregnant Women and Newborns”, “Genetic Diagnosis of Patients with Hearing Impairment” …… These prevention or treatment activities related to hereditary deafness are becoming more and more popular among families More and more families are familiar with these prevention or treatment activities related to hereditary deafness! The most common questions are: How can my child’s deafness be hereditary when neither of our families has had a deaf patient for generations? Can deaf people marry each other and have offspring with normal hearing? What should I do if I detect a deafness mutation? What should I do if I detect a deafness mutation?
In layman’s terms, there are 22 pairs of autosomes and 1 pair of sex chromosomes in the nucleus of each cell in the human body. Each pair of chromosomes has numerous gene fragments in its DNA. Each gene fragment consists of two alleles. Genes are divided into dominant and recessive genes. When a pair of genes are both dominant or one of the pair is dominant and one is recessive, then a dominant trait is expressed; while a pair of genes are both recessive, a recessive trait is expressed. Genetic deafness is predominantly recessive.
Figure 1 Classification and proportion of hereditary deafness
The most common autosomal recessive inherited deafness (autosomal recessive deafness) has the causative gene on the autosome, and the genetic trait is recessive, i.e., the disease trait is only displayed when purely congenic. The following is an example of the most common type of autosomal recessive deafness, which varies according to the hearing of the parents and the genes responsible for the deafness.
A Parents with normal hearing
(i) Both parents are carriers of the deafness-causing mutation with normal hearing (heterozygous), and the patient is a pure heterozygote (or compound heterozygote) for the disease causing gene.
(ii) Each parent has a ¼ chance of having a child with deafness with each pregnancy, and both sexes have an equal chance of developing the disease.
(iii) There are no consecutive generations of inheritance in the family, and both parents, distant grandparents and collateral relatives of the patient usually do not have the same patient.
(iv) The incidence of the disease in the offspring is significantly higher when close relatives marry.
B Both parents are at 100% risk of having a deaf child due to the same mutated gene, which is shown to be inherited from generation to generation.
Figure 3: Deafness is caused by the same mutation in both parents, with the deafness-causing mutation in red.
C Both parents are deaf due to different mutations and their children have normal hearing but are carriers of the deaf mutation.
Figure 4 Parental deafness due to different mutations, with deafness-causing mutations in red.
D If one parent is deaf and the other parent is a carrier of the same mutation with normal hearing, there is a 50% chance of having a deaf child and a 50% chance of having a carrier of the deaf mutation with normal hearing for each pregnancy.
E If one parent is deaf and the other parent has normal hearing and is not a carrier, the child will have normal hearing but be a carrier of the deaf-causing gene.
Figure 5 Combinations of autosomal recessive inheritance, with a representing the disease-causing mutation
You can substitute, combine and analyze the risk of having a deaf child in various cases based on the knowledge related to what has been said above!
Indeed, it’s a wonderful world, but autosomal recessive deafness, which is caused by a single gene, generally follows the above-mentioned pattern! The various combinations of parents will not be listed here, nor will the various scenarios of autosomal dominant inheritance be analyzed. I think by now you understand at least two things.
1, that hereditary deafness is not always passed from generation to generation, and that there are many different forms of expression.
2. Once you have received your deafness genetic screening or diagnosis report, you need to receive interpretation and guidance from a medical professional: help in analyzing the inheritance pattern, the risk of having another child, and how to prevent it.