Overview and Prospects for Whole Chromosome Testing

Introduction

All-chromosome testing, which tests all autosomes, including sex chromosomes, rather than the conventional testing of only three autosomes in prenatal diagnosis.

In this article, I would like to explain the details regarding such all-chromosome testing.

We will provide basic information on all-chromosome testing and a deep dive into prenatal diagnosis that incorporates all-chromosome testing into the examination, which is being performed by several unlicensed facilities, as an example.

We will also mention other clinics in Japan where you can take a full chromosome test and the costs involved. We hope this will help those who are wondering whether or not to undergo prenatal diagnosis.

What is Comprehensive Chromosomal Testing?

Comprehensive chromosomal testing is a diagnostic method conducted in prenatal diagnosis to examine abnormalities in the number of all autosomes, including chromosomes 1 to 22 (known as autosomes) and sex chromosomes. This approach has gained prominence in recent years.

Traditionally, prenatal testing primarily focused on screening for trisomies 13, 18, and 21, which involve abnormalities in sex chromosomes.

The rationale behind this was that these specific autosomes, even in cases of complete trisomy, typically have relatively fewer adverse effects on survival and often result in a reasonable birth rate. In contrast, abnormalities in other autosomes generally lead to lower survival rates, sometimes even implying non-viability, hence not routinely tested unless clinically indicated.

However, cases have been reported where individuals who were deemed low-risk based on the absence of abnormalities in the initial screening for chromosomes 13, 18, and 21 were found to have abnormalities in sex chromosomes upon further testing.

Therefore, the necessity for comprehensive chromosomal testing for all autosomes became increasingly advocated. Users' preferences for having a broader range of options further supported this shift, prompting an increase in clinics offering comprehensive chromosomal testing.

Characteristics of Prenatal Diagnosis with Comprehensive Chromosomal Testing

Currently, comprehensive chromosomal testing is not permitted in accredited facilities.

In Japan, apart from the testing provided by Verinata, options include Serenity24 from CooperGenomics. Since June 19, 2020, Human Investor has been conducting these tests through clinics across Japan.

Comprehensive chromosomal testing examines all autosomes (chromosomes 1 to 22) for abnormalities and can also detect sex chromosome abnormalities like Monosomy X (Turner syndrome).

As such, it represents one of the most advanced prenatal tests available in Japan.

With comprehensive chromosomal testing, blood samples are collected in a single visit, and results are typically available within approximately 10 days, minimizing time and physical strain.

It's important to note that comprehensive chromosomal testing is applicable only for singleton pregnancies. In cases of multiple pregnancies (twins or more), testing typically focuses on the traditional 13, 18, 21 autosomes and Y chromosome analysis.

Unapproved Facilities Allow a Broader Range of People to Receive Testing

A new type of prenatal diagnosis that only tests for trisomies 21, 18, and 13 at accredited facilities has faced challenges due to separate consultation and testing costs, as well as mandatory genetic counseling, which collectively increase the overall expenses.

Furthermore, another issue with this new prenatal diagnosis at accredited facilities is the strict eligibility criteria, such as only allowing pregnant women between 10 to 18 weeks gestation and aged 35 or older to undergo testing.

Currently, there is a trend among accredited facilities to significantly relax age-related criteria, allowing anyone over 10 weeks pregnant to undergo testing.

The cost for testing all chromosomes varies depending on the plan, but in Japan, it generally ranges around 200,000 yen.

Below is an example, as of July 2020, of clinics in Japan offering whole chromosome testing along with their respective costs. Please note that the locations listed are representative and there are clinics nationwide offering this service, so please inquire to see if there are clinics in your area.

＜Example of Facilities Offering Comprehensive Chromosomal Testing＞

Should Comprehensive Chromosomal Testing Implementation Continue?

Here, we would like to delve into the significance and considerations regarding whole chromosome testing.

In fact, opinions on whole chromosome testing have sparked debate both in Western countries and in Japan.

As mentioned earlier, traditionally, testing focused solely on abnormalities related to trisomies 21, 18, and 13, which are among the most common chromosomal abnormalities leading to miscarriages and high incidence after birth.

However, it could be argued that mothers have the right to know everything possible about their baby's condition, hence testing for all chromosomes seems a natural step (although this discussion does not touch on the ethics of abortion).

Regarding the ethical aspects of abortion issues, please refer to the following article for more information.

In reality, various testing companies in Western countries conduct whole chromosome testing, addressing a definite need to know fetal information early on.

While abnormalities in chromosomes 21, 18, and 13 are more frequently identified, the positive detection rate from other chromosomes tends to be lower.

According to specific statistical surveys, the positive rate for whole chromosome detection in chorionic villus sampling is 0.56%, meaning a positive result is found in approximately one out of every 2,000 individuals.

Considering this data, wouldn't it be necessary to conduct testing on all chromosomes in order to promptly "know" the fetus's condition?

Conclusion

Even if abnormalities are found in autosomal chromosomes other than 21, 18, and 13, it does not necessarily mean that the fetus will inevitably face mortality, as cases exist where pregnancies proceed to term despite such conditions.

Considering this perspective, wouldn't the widespread adoption of whole chromosome testing, which allows for more comprehensive examination of autosomal chromosomes, be desirable for all mothers and children?

As of July 2020, Tokyo Metropolitan Institute of Public Health in Japan has taken over the testing previously conducted by the American company Verinata, eliminating constraints, risks, and reducing costs associated with transportation, time, and finances.

In this way, issues related to the cost and age restrictions associated with whole chromosome testing are gradually being eased.

Ultimately, the author hopes for the proliferation of prenatal diagnostics that are safer, more accurate, and cost-effective.