Both parents are normal, why would the child suffer from hereditary deafness?

Author: Wang Qiuju, Chief Physician of the General Hospital of the Chinese People's Liberation Army

Reviewer: Wang Quangui, Chief Physician, Peking University First Hospital

Hereditary deafness is a very specific concept. It refers to the deafness caused by the genetic material of parents being passed on to their offspring.

In clinical practice, parents of children with hearing loss often have such questions: Both my husband and I are normal, but we gave birth to a deaf child, and tests found that it was caused by genetic abnormalities. What is going on?

There are six ways of inheritance of hereditary deafness, namely autosomal dominant inheritance, autosomal recessive inheritance, X-linked dominant inheritance, X-linked recessive inheritance, Y-linked inheritance, and maternal inheritance of mitochondrial mutation.

Among them, autosomal dominant inheritance accounts for about 20%; autosomal recessive inheritance is the most common, accounting for about 80%; X-linked, Y-linked plus mitochondrial inheritance accounts for 1%-3%.

① Autosomal dominant inheritance: one of the parents is deaf and passes the disease-causing gene to the offspring. This inheritance pattern will cause 50% of the offspring to become deaf.

② Autosomal recessive inheritance: This is the most common phenomenon, that is, both parents are normal, and there is no clear deafness patient in the family, but the offspring have deafness. This is because both parents carry the pathogenic gene for deafness, and there is a 25% probability that the offspring will have hereditary deafness. This kind of inheritance may not be passed down from generation to generation in the family, but a model of passing down from generation to generation.

③X-linked recessive inheritance: We often see that the mother is normal, but her children, especially sons, will have this problem, which we call skipped generations. There is also a situation where the mother is normal and the father is deaf, and their sons are all normal, while the daughters are all carriers of the disease-causing gene but do not develop the disease.

Figure 1 Original copyright image, no permission to reprint

④X-linked dominant inheritance: If the mother is sick, the child has a 50% chance of being sick, and there is no gender difference; if the father is sick, all daughters they give birth to will be sick, and none of the sons will be sick.

Figure 2 Original copyright image, no permission to reprint

⑤Y-linked inheritance: This mode of inheritance will cause the disease to be passed down from male to generation, because its pathogenic gene is on the Y chromosome, so as long as a boy is born, the pathogenic gene will be passed on, causing the boy to become ill. This is called Y-linked inheritance, which is a relatively rare mode of inheritance.

⑥ Maternal inheritance of mitochondrial mutation: Because the mitochondria of all offspring come from the mother during the embryonic period, after the mother carries the disease-causing gene, it will be passed on to her offspring, whether it is a boy or a girl. This is called maternal inheritance of mitochondrial mutation.

However, mitochondrial mutations are maternally inherited and are a form of gene mutation mainly caused by drug sensitivity. Therefore, when using ototoxic drugs, such as aminoglycosides, like gentamicin, metronidazole, kanamycin, imipenem, etc., the pathogenic mitochondria are very sensitive to these drugs. We call it one shot of deafness. Deafness may occur after one shot. Therefore, these ototoxic drugs should be used with great caution during pregnancy.

From the perspective of classification, hereditary deafness can be mainly divided into two types, one is called syndromic hereditary deafness, and the other is called non-syndromic hereditary deafness.

Among patients with hereditary deafness, 70% suffer from non-syndromic hereditary deafness, which mainly manifests as hearing problems, that is, deafness problems, while other organ systems are normal.

Syndromic hereditary deafness, in addition to hearing problems, also has vision problems, hair color problems, eye color problems, skin color problems, liver and kidney function damage, developmental malformations, etc. There are about 400 related syndromes that occur simultaneously with other organs. In order to determine what kind of syndrome it is, in addition to observing the patient's appearance and examining the general condition, genetic testing is also required to finally determine the type of syndrome.

From the perspective of prognosis, hereditary deafness cannot be completely cured at present. What we can do is to detect and intervene early. The most important thing is to ensure that the children with hereditary deafness are not affected in language, so early intervention is necessary.

In fact, the fetus's auditory system has been established at 6 months of pregnancy. Between birth and 2 years old, it is a period of time when a large amount of information is input. 2-6 years old is also a very important stage in the child's language development. Therefore, during these time periods, he needs to be able to hear sounds to help him learn language and communicate.

Therefore, all early detection and early intervention are to enable him to develop and mature language so that he can communicate normally in society in the future.