Does Consanguineous Marriage Cause Genetic Diseases? Examining the Evidence [News SeolCham]

⑧Marriage, How Close Is Too Close?
Cousin Couples' Children, Genetic Disease Incidence Up to 7.35%
"Refusing Marriage or Childbirth Due to Genetic Diseases? Human Discrimination"
Legal Restrictions on Marriage Partners Violate the Principle of Proportionality

Editor's Note'Seolcham' is a newly coined term meaning to refer to explanations for more detailed understanding. In [News Seolcham], we aim to pinpoint and explain in more detail the parts of the news that require fact-checking or further explanation.

There is a saying that offspring from close relatives have a high risk of genetic diseases. This is often used as a reason to oppose narrowing the scope of consanguineous marriage. When genetic diseases caused by consanguineous marriage are mentioned, people often think of the Habsburg jaw of the European Habsburg family, but recent studies say that marriages beyond the fifth cousin do not significantly increase the risk of genetic diseases. Consanguinity (近親) refers to close kinship. How close can marriage be allowed?

There are two main reasons for opposing the narrowing of the taboo (禁忌) scope of consanguineous marriage in society. The first is the destruction of the traditional family concept. If marriage between close relatives is allowed without limits, sexual competition or conflicts may arise within the family, breaking the stability of the family community. It is also seen as reflecting human natural and psychological nature. In fact, the prohibition of incest is commonly observed worldwide. Rule-of-law countries have created prohibitive marriage clauses to maintain family order and protect the functions of the family system.

The second reason is the increased risk of genetic diseases. Close relatives have similar genetic information, so there is a high risk that recessive genes causing genetic diseases will overlap. The European Habsburg royal family, which enjoyed powerful authority for several centuries from the 13th century to the early 20th century, is a representative example. To protect their noble bloodline, they chose spouses within the family, passing down genetic defects through generations. It is said that members of the Habsburg family developed mandibular prognathism (Habsburg jaw) around puberty, making it difficult to chew food or close their mouths.

The consanguineous marriage of the American Whitaker family is also famous. The Whitaker family in West Virginia, USA, known through a 2020 documentary, has continued their family line through consanguineous marriages for 100 years. Although the United States prohibits marriage within the fourth cousin, this family married not only within the fourth cousin but also between identical twins or siblings, and had children. Most family members suffered from various genetic diseases and disabilities.

What is the scientific evidence for the increased risk of genetic diseases due to consanguineous marriage? The most frequently cited study is the "Genetic Counseling and Testing for Consanguineous Couples and Their Offspring" (2001) by the National Society of Genetic Counselors (NSGC) in the United States, a group of experts in genetics. The recent research report commissioned by the Ministry of Justice for narrowing the scope of consanguineous marriage, "Study on the Prohibition Scope and Effectiveness of Marriage Between Relatives" (Hyun So-hye, 2023), also cites this study. In 2021, NSGC explained in related guidelines that the average probability of a child being born with congenital malformations or genetic diseases is 3.45?4.55%, but for children of cousins without genetic diseases, the probability is about 1.7?2.8% higher than average. This means the risk of genetic disease can reach up to 7.35%. However, there is no direct causal relationship between increased genetic disease incidence and offspring of couples married beyond the fifth cousin.

However, the argument that marriage should be prevented due to the risk of genetic diseases faces ethical criticism. It is similar to the logic of eugenics that prevents reproduction of populations with poor genes. The Ministry of Justice's discussion on narrowing the scope of consanguineous marriage began in October 2022 when the Constitutional Court ruled the Civil Code provision that invalidated marriages between blood relatives within the eighth cousin as "unconstitutional." Justices Yoon Nam-sung, Lee Seok-tae, Kim Ki-young, and Moon Hyung-bae pointed out in their opinion that "prohibiting marriage itself solely based on concerns about the high possibility of recessive gene expression is based on unclear hypotheses and cannot be a reasonable reason to restrict the freedom to choose a marriage partner."

These justices also stated, "The genetic perspective is linked to the notion that only those with dominant genes can have children and maintain families, which discriminates and instrumentalizes humans, violating the constitutional requirement that marriage and family systems be regulated based on the fundamental idea of respecting human dignity." They further noted that restricting the right to freely choose a marriage partner violates the principle of proportionality.

[Image source=Pixabay]

Perspectives on consanguineous marriage have changed over time. In the past, marriage between relatives of the same social status was an effective means to maintain class purity and strengthen family ties, thereby preserving wealth and power. Today's regulations on consanguineous marriage are based on the Civil Code enacted on January 1, 1960, which invalidated marriages between direct blood relatives, collateral blood relatives within the eighth cousin, and relatives of the same surname and clan. The 1991 amended Civil Code maintained the prohibition of marriage between relatives of the same surname and clan, but this lost effect following the 1999 Constitutional Court's ruling of unconstitutionality.

Currently, regulations on consanguineous marriage are again facing revision following the Constitutional Court's decision. Professor Hyun So-hye of Sungkyunkwan University Law School, who conducted the Ministry of Justice's commissioned research, proposed narrowing the prohibited marriage scope to within the fourth cousin, but there is strong opposition from Sungkyunkwan University and others. The Ministry of Justice plans to listen to and reflect various opinions to draft the amendment. The deadline for the Civil Code amendment related to consanguineous marriage is by the end of this year.