228 recessive genetic disorders identified by Hiro Clinic

70% of Parents Are Carriers? The Utility of Recessive Gene Testing

70% of people carry some form of genetic anomaly (mutation).
Individuals with such genetic mutations are called “carriers.”
Even if there are no visible or physical abnormalities, that gene can potentially affect their children.
When both parents carry a mutation in the same gene, the probability of their child developing the disease is 25%, the probability of becoming a carrier is 50%, and the probability of inheriting normal genes is 25%.

So, what kind of testing is performed for these individuals? Also, what types of diseases can be identified?

① What is Carrier Screening Test 231 at Hiro Clinic?

Hiro Clinic offers a prenatal screening test that can examine genes associated with up to 231 severe recessive genetic disorders affecting the fetus. This screening is internationally recognized as crucial, with major medical organizations such as the American College of Obstetricians and Gynecologists (ACOG) and the American Society of Human Genetics (ASHG) recommending that information about it be widely provided.
Recessive genetic disorders are conditions that can develop in a child when both the father and mother carry mutations in the same gene. In this test, genetic material is collected from the oral mucosa (inner cheek) of both the father and mother to check whether both parents carry the same mutation.

According to research by Hiro Clinic, approximately 70% of individuals are found to carry one or more recessive gene mutations. This state is known as being a “carrier” (gene carrier)—a condition where, despite having no visible symptoms or physical health issues, there is a possibility of passing the gene on to their children.

When both parents carry the same genetic mutation, the risk of their child developing the disease follows these probabilities:

• 25% chance (1 in 4) of developing the disease
• 50% chance (1 in 2) of becoming an asymptomatic carrier
• 25% chance (1 in 4) of inheriting normal genes

If high risk is identified through this test, amniocentesis may be recommended as a confirmatory test.

② Gene “Mutations” Can Sometimes Cause Disease

Our bodies are built according to genetic information that functions like a blueprint. Humans have approximately 20,000 genes, which are passed down from parents to their children. They contain essential information that determines various characteristics, such as hair color, height, and physical constitution.
However, in rare cases, mutations occur in this blueprint. These mutations can sometimes lead to specific diseases.
For example, diseases caused by a mechanism called “recessive inheritance” develop only when a child receives the same type of gene mutation from both the father and the mother. Even if only one parent carries the mutation, the individual will not develop the recessive genetic disorder.
One example of a recessive genetic disorder involves a mutation in the OCA2 gene located on chromosome 15. If a child inherits two copies of this mutation—one from the father and one from the mother—the body becomes unable to produce the “P protein,” which is essential for synthesizing “melanin,” the pigment that determines the color of skin, hair, and eyes. Consequently, melanin is not produced, resulting in a condition known as “Oculocutaneous Albinism,” where the skin and hair appear white.

In addition, diseases caused by abnormalities in the “X chromosome”—a sex chromosome—are known as X-linked recessive disorders, which characteristically affect males more frequently. Because males have only one X chromosome, if a mutation is present, there is no alternative copy to compensate for it, making disease manifestation more likely. On the other hand, females have two X chromosomes; even if one carries an abnormality, as long as the other functions normally, it can compensate for the defect, making disease development far less common.

③ Inherited Disorders That Can Happen to Anyone

Recessive genetic diseases are often thought to be rare, but in fact, there are more than 3,000 distinct types. Taken together, it is estimated that 1 to 2 out of every 100 couples may have a child born with a genetic disorder. In other words, this is a topic that concerns everyone.
For this reason, undergoing screening prior to or during early pregnancy allows couples to calmly consider their options even if a risk is detected. Options may include selecting healthy embryos through in vitro fertilization (IVF) or confirming the baby’s condition after pregnancy via amniocentesis.

④ Also Helpful for Managing Mother and Child Health

Carrier Screening Test 231 not only provides insight into a child’s disease risks but also aids in managing the mother’s health. For example, if risks such as a tendency to bleed—which requires caution during pregnancy—or cardiac disease risks can be identified in advance, doctors can prepare accordingly ahead of time.

In this way, Carrier Screening Test 231 serves as valuable support for a reassuring pregnancy and childbirth. At Hiro Clinic, this screening can be combined with NIPT (Non-Invasive Prenatal Testing). For patients undergoing NIPT, Carrier Screening Test 231 is offered at an optional discounted rate. Naturally, individuals who do not undergo NIPT can also take this test as a standalone option.

⑤ Japanese-Specific Genetic Risks

In Japan, there was a historical period when marriages between cousins were common, which made it easier for specific gene mutations to persist within the population. Consequently, certain genetic conditions are more prevalent among Japanese people.
For example, it has become clear that among eye-related genetic disorders, conditions such as “retinitis pigmentosa” and “fundus albipunctatus” are particularly frequent in Japan. In particular, the EYS gene has been identified as the most frequent causative gene for retinitis pigmentosa in Japanese individuals. Because these diseases are often caused by specific gene mutations, they are surprisingly relevant and close to home.

Such genetic mutations specific to the Japanese population are sometimes not included in overseas databases. Therefore, Carrier Screening Test 231, which is tailored specifically for Japanese individuals, is extraordinarily important.

⑥ Toward Future Healthcare: A Fair Society Where Everyone Has Choices

Future healthcare will focus on “preventing disease” rather than simply “treating disease after it occurs.” Carrier Screening Test 231 represents a vital first step in this direction.
In countries like Australia and the Netherlands, initiatives are underway to incorporate recessive gene testing into national healthcare systems. In Japan, too, there is a growing need to establish systems that allow insurance coverage so that all couples can access screening fairly.
At Hiro Clinic, we recommend Carrier Screening Test 231 for couples, including as part of a pre-marital bridal checkup before pregnancy. Undergoing testing early provides essential decision-making information for future family planning, pregnancy, and childbirth. It allows couples to share results and calmly prepare for delivery.
Furthermore, performing Carrier Screening Test 231 on newborn infants enables early detection of future health risks, facilitating personalized healthcare management. The test can be performed painlessly simply by collecting a sample with a gentle cheek swab.
This screening represents a choice to “know,” aiming to protect future lives. Making this test—which is recommended by major medical societies in the United States—widely understood and accessible to many in Japan is what modern healthcare strives to achieve.

Testing Process

Carrier Screening Test 231 is completed in 3 simple steps: applying at the clinic, collecting a buccal (inner cheek) swab, and receiving email results approximately 3 weeks later.

Step 1

Apply for the Test at the Clinic

At the time of application, consent forms must be filled out by both the expectant mother and her partner.
The testing kit will be provided during your visit.
※Both the pregnant mother and her partner must visit the clinic together.

Step 2

Rub the shaft of the testing swab against the inner cheek mucosa (inside the mouth) to collect cells.
※Please refrain from smoking, eating, drinking, brushing teeth, or chewing gum within 30 minutes prior to collection.
Hand in the collected sample at the clinic before leaving.

Step 3

Test Results Notification

Results will be delivered via email approximately 3 weeks later.
※This report is separate from the results of the maternal blood test.
※The test results will be ready approximately 3 weeks after the sample arrives at the laboratory.