Patient's question:
If siblings engage in those kinds of acts, will the children they have be mentally retarded?Doctor's answer:
Here is the English translation of the provided text, with line breaks preserved as instructed:Hello, marriage between individuals with close kinship. A couple is considered close relatives if they share common ancestors in generations below the great-grandparents. Marriage between cousins is a relatively common form of consanguineous marriage. Most countries discourage consanguineous marriage, even prohibiting it. Consanguineous marriage leads to high mortality rates in offspring and often results in cases of mental retardation, (deformed children), and genetic diseases. This is because couples in consanguineous marriage inherit more identical genes from their common ancestors, making it easier for harmful recessive genes detrimental to survival to meet (i.e., become homozygous) in the offspring, thus increasing the likelihood of producing children with poor quality. According to the World Health Organization, each person in the population carries approximately 5–6 disease-causing alleles for recessive genetic disorders. In random mating (non-consanguineous mating), since the couple has no blood relationship, identical genes are rare, and the recessive disease-causing alleles they carry are different, making it less likely to form homozygotes (patients) for recessive disease-causing alleles. In consanguineous marriage, however, the couple is highly likely to carry the same recessive disease-causing alleles, which can easily meet in the offspring, increasing the incidence of genetic diseases. The following table lists several recessive genetic diseases, showing that the incidence rate in offspring of consanguineous marriage is several times higher than that in offspring of non-consanguineous marriage. Additionally, polygenic genetic diseases such as hypertension, schizophrenia, congenital heart disease, anencephaly, and epilepsy also have significantly higher incidence rates in children born from consanguineous marriage compared to those born from non-consanguineous marriage. For this reason, many countries have laws prohibiting consanguineous marriage. The sixth article of China's Marriage Law states: "Direct blood relatives and collateral blood relatives within three generations are prohibited from marrying." Direct blood relatives refer to relationships between parents and children, grandparents and grandchildren, and paternal/maternal grandparents and grandchildren. Collateral blood relatives within three generations include siblings, uncles/aunts and nieces/nephews, cousins, and（） (paternal/maternal cousins). Surveys show that the consanguineous marriage rate is approximately 0.7% in urban areas, 1.2% in rural areas, and as high as 2.8% in some mountainous rural areas and islands, where transportation is underdeveloped, leading to higher rates of consanguineous marriage and thus more genetic diseases. Therefore, prohibiting consanguineous marriage is an effective measure to reduce or eliminate the incidence of recessive genetic diseases, improve population quality, and is one of the main components of eugenics.