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"Doctor, neither of our families has a genetic disease, and we are very healthy ourselves, so why would I give birth to a baby with a genetic disease?"
Xiao Gao (pseudonym) and her husband sat in the genetic counseling room of Run Shaw Hospital affiliated to Zhejiang University School of Medicine and asked the doctor incomprehensibly.
Xiao Gao and her husband had a lovely son after marriage, and as the baby grew up, the couple found that their son often walked unsteadily and fell easily. After going to kindergarten, the situation became even more serious, not only could not climb the stairs, but even it was difficult to run and jump with the children.
XiaoGao took the baby to the children's hospital for treatment, and the doctor determined that the baby was suffering from pseudo-hypertrophic muscular dystrophy (DMD) based on symptoms and a series of tests.
The doctor told Xiaogao that DMD not only affects the baby's movements, but also gradually affects his heart and respiratory muscles. According to statistics, most DMD patients cannot walk around the age of 12, and die around the age of 20 due to respiratory muscle weakness and myocardial damage. Thinking of the baby's future painful days, XiaoGao couldn't help but sob, and her husband also bowed his head and did not speak.
Doctors explain that DMD is an X-linked recessive genetic disease. This kind of "recessive" genetic disease is very cunning and will be "hidden" in a healthy population, and couples often have no symptoms and no genetic history in the family, but there is a high risk of having children with genetic diseases.
These terrible genetic diseases will be "invisible", can we find out in advance? How can a family like Xiaogao have a healthy baby?
What is
Recessive single gene genetic disease?
First of all, single-gene genetic disease refers to a type of hereditary disease caused by a single gene mutation, which is divided into recessive and dominant.
Each of us has 46 chromosomes, in pairs, 23 sperm from the father and 23 eggs from the mother. If you compare chromosomes to a book, genes are like every word in a book. Because chromosomes are all paired, genes also have their own partners, medically known as alleles.
Genetic mutations are like typos in a book.
Dominant genetic disease is the disease in two books, as long as there is a typo in one of them. Recessive genetic disease is the occurrence of a typo in the same position in two books; only when one of the books has a typo, it will not become ill, called a gene mutation carrier.
When the parents are carriers, they can not show any symptoms themselves, but when they both pass on this "typo" to the baby at the same time, the baby's "two books" have "typos", resulting in the baby becoming a child with recessive genetic diseases.
Of the 46 chromosomes, 44 are autosomals that are the same for both men and women, and 2 are sex chromosomes, XY for males and XX for females. When the "typo" is located on the autosomal body, it is necessary for both husband and wife to be the carrier of the "typo", and the offspring, male or female, has a 25% probability of being a patient, which we call autosomal recessive genetic disease.
When the "typo" is located on the X chromosome, carrier women usually do not develop the disease because women have two X chromosomes. But when the woman gave birth to a boy, because the male had only one X chromosome, this X chromosome had a 50% chance of inheriting the mother's "typo" and becoming a child. This is the X-linked recessive genetic disease, which is the case of the little Gao family.
Are single-gene genetic diseases harmful?
There are more than 9,000 types of single-gene genetic diseases, which are often severe and diverse, and most of them can cause teratology, disability or death.
According to statistics, single-gene genetic diseases account for 20% of infant deaths, and more surviving children are also accompanied by intellectual disabilities. Moreover, these diseases are difficult to diagnose and lack targeted treatment, and less than 10% of single-gene genetic diseases have targeted drugs.
According to statistics, single-gene genetic diseases cost more than 1 million yuan per person per year. Giving birth to a child with a severe single genetic disorder is a huge trauma and a heavy burden on both the family and society.
Giving birth to children with recessive genetic disorders
Is the risk high?
The total incidence of birth defects in the mainland is about 5.6%, and 90 to 1 million defective children are born every year. About 22% of these defective children are children with single-gene genetic diseases. The comprehensive incidence of single-gene genetic diseases is as high as 1%, and as many as 200,000 children with single-gene diseases are born every year.
Because couples with recessive genetic disease carriers usually do not know that they carry the "typo" gene, and women rarely have "danger warnings" after pregnancy through routine obstetric examinations, recessive genetic diseases need to be detected and prevented in advance than dominant genetic diseases.
Studies have shown that each of us carries an average of 2.8 recessive disease-causing genes. 24% of the population is a carrier of at least one genetic disease, and 5% of the population is a carrier of multiple genetic diseases. The frequency of recessive genetic diseases commonly found in mainland China is shown in the table below:
How to reduce fertility recessive genetic diseases
What is the risk to children?
Couples with fertility plans, including expectant mothers and fathers who are pregnant in the early stages, are recommended to screen for carriers of recessive genetic diseases.
Through blood testing, both husband and wife can detect hundreds of single-gene genetic disease genes that are highly occurring in the mainland at one time, check whether there are disease-causing gene mutations, and assess fertility risks.
What kind of people need to do
What about screening for carriers of recessive genetic disorders?
● Couples who are concerned about eugenics and fertility of offspring can be tested;
● The test is more recommended for couples who are closely related, quasi-assisted reproductive therapy, and sperm donor eggs;
● For couples who are already pregnant, it is recommended to conduct couples screening at the same time to shorten the test waiting time;
● For couples with a family history of genetic diseases, multiple adverse pregnancies and areas with a high incidence of genetic diseases, it is recommended that targeted genetic testing be carried out after the outpatient evaluation of genetic counseling, rather than direct screening of carriers.
If both husband and wife test positive
How do you procreate?
●If the genes carried by the couple are different genes, and the woman does not carry the pathogenic variant of X-linked recessive genetic disease, no special intervention is required.
●If both parties carry a disease-causing mutation of the same gene, or if the woman carries a pathogenic variant of X-linked recessive genetic disease, it can effectively prevent serious single-gene genetic diseases in the fetus through prenatal diagnosis of natural pregnancy or through preimplantation genetic testing technology (commonly known as third-generation IVF technology).
Where can I do this test?
Zhejiang University Shaw Hospital is mature to carry out screening of carriers of recessive genetic diseases and third-generation IVF with single gene diseases. At present, hundreds of couples have undergone the test in our hospital. Moreover, positive couples have helped have healthy babies through three generations of test tubes for single gene disease.
If you are willing to have this test, you can go to our genetic counseling clinic or reproductive clinic for consultation.
Genetic counseling clinic hours
Tuesday afternoon, Thursday afternoon and all day Friday.
bibliography:
1． Report on the Prevention and Control of Birth Defects in China (2012).
2．http://www.omim.org/statistics/entry.
3．Orphan Drug Report（2015）.
4． Wu Lingqian and Zhang Xue, editors-in-chief, Medical Genetics, People's Medical Publishing House, May 2016.
Source: Department of Obstetrics and Gynaecology, Run Run Shaw Hospital
Author: Jin Jiamin Review: Tong Xiaomei
Original works, reprinted please indicate the source and source
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