How to determine the FF (Fetal Fraction Fractionation Rate) from STRs of paternity tests

Summary of this article

親子鑑定における胎児分画率（FF：Fetal Fraction）は、特に非侵襲的出生前親子鑑定（NIPT：Non-invasive Prenatal Paternity Test）において重要です。この値は、母親の血液に含まれる胎児のDNA（cfDNA：cell-free DNA）が全体のDNAの中で占める割合を示しています。胎児分画率が低すぎると、鑑定の精度が下がり、正確な結果が得られない可能性があるため、胎児分画率を正確に測定することが重要です。

How to obtain FF (Fetal Fraction Fractionation Rate) from STR analysis

STR (Short Tandem Repeat) is a method for analyzing the repeat pattern of a specific region of DNA in paternity testing.

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Procedure:

Separation of maternal and fetal cfDNA:

cfDNA is collected from the mother’s blood to distinguish between DNA of maternal and fetal origin. Fetal-derived DNA is less abundant than maternal-derived DNA because it flows mainly from the placenta into the mother’s blood.

特定のSTRマーカーの解析：

STR markers are short repeating sequences in specific gene regions that have different patterns in different individuals. DNA from the mother and presumptive father are compared and the STR profile of the fetus is matched to that of the mother.

Calculation of Fetal Fractionation Rate (FF):

The peak ratios of common and different STR markers of the mother and fetus are used to calculate the fraction of DNA of fetal origin. Specifically, the peak intensities of maternal cfDNA and fetal cfDNA are compared, and the fetal fractionation rate is derived from the ratios. Usually, a highly reliable result is obtained when the fractionation rate of DNA of fetal origin is 4% or higher.

結果の確認：

After the fetal fractionation rate is calculated, the reliability of the results of the paternity test is confirmed. If the fractionation rate is low, retesting may be necessary.

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Fetal fractionation rate criteria:

It is usually recommended that the fetal fractionation rate be at least 4% for non-invasive paternity testing performed after the sixth week of pregnancy.This ensures that the fetal DNA is sufficiently contained to provide a reliable test result.

Fetal fractionation rate is an important indicator to ensure the reliability of the paternity test, and this value must be adequate to obtain accurate test results.

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