Ten years ago, when I was studying DNA testing, I met a young mother who came to me for counseling, and she wanted to determine who the child in her belly really belonged to.
There are often fathers who doubt whether their child is biological, but it is rare for a woman like this woman to determine who the father of the fetus is.
Ms. Ho said she was three months pregnant and had not told her fiancé because she was worried that the child was not her fiancé's.
Confused, she remembered to do a paternity test.
Image source: Stand Cool Helo
According to Mendelian genetics, half of the chromosomal DNA of a fetus comes from the mother and the other half from the father.
By detecting STR loci in the relevant parent-mother-fetus DNA, controversial paternity relationships can be identified based on typing results.
The physical examination materials usually collected by paternity testing in forensic clinics include blood, oral swabs, hair, etc.
In 1981, M S Pollack and others in the United States used amniotic fluid puncture to perform prenatal diagnosis and fetal paternity testing [1].
During the 16th to 32nd weeks of maternal pregnancy, more than 1 ml of amniotic fluid is drawn and the DNA of free fetal cells in the amniotic fluid is tested for paternity testing [1-2].
A month later, when Ms. Ho was 16 weeks pregnant, she and a young man came to collect DNA and do amniocentesis.
At that time, I was still a little puzzled, how could this man be so peaceful, and there was a laugh with Ms. He to conduct a fetal paternity test.
The experimental results were quickly tested, and the male who took the sample with Ms. He was excluded as the biological father of the fetus, and the biological father of the fetus was someone else.
Although it was an exclusionary conclusion, Ms. He was relieved when she received the results, and then soon, she brought another sample of a man.
It was a cigarette butt that "he" had smoked, and the cigarette butt usually had a large number of exfoliated cells from the mouth of the smoker, which was also a commonly used DNA test.
DNA test results showed that the smoking man was also not the biological father of the fetus.
The third time, Ms. He was very determined to send an electric razor, saying that the user should be the father of the fetus.
The test results, as Ms. He had expected, determined that the real father of the fetus was her fiancé.
After Ms. He left satisfied with the test results, I didn't even know whether to be happy for her or sad for her fiancé.
In fact, when it comes to amniocentesis, some mothers will have concerns, worried that they will cause contractions and miscarriages due to amniocentesis, so is there any other way in addition to amniocente puncture?
In 1997, Y M Dennis Lo and others [3] people found free fetal DNA in maternal blood circulation. Free fetal DNA is an ideal noninvasive fetal specimen that is clinically used primarily for prenatal screening for disease [4].
With the rapid development of a new generation of sequencing technology, multiple studies at home and abroad have confirmed that with the help of a new generation of sequencing technology, a large number of SNP loci can be detected at one time, and non-invasive prenatal paternity testing can be carried out using free DNA of maternal plasma fetus [5-6].
Most paternity tests are performed at social identification agencies. Many medical universities have attached forensic laboratory centers, such as many large hospitals with forensic clinics, and many independent forensic laboratory centers.
The first condition for selecting an appraisal body is that these appraisal bodies must be qualified institutions that have been reviewed by the local judicial authorities.
On the relevant websites of the judicial departments of each province, it can be publicly queried whether the specific appraisal institution has carried out the record and whether it has relevant qualifications.
For example, Guangdong's court forensic network and Guangxi's legal service network can query local qualified appraisal institutions.
(The picture shows the judicial appraisal network of the court in Guangdong)
(The picture is Guangxi Legal Service Network)
Only when a qualified appraisal institution is allowed to conduct a judicial paternity test, the appraisal certificate may be recognized by relevant departments such as household administration and courts.
In 2016, the Ministry of Justice issued a rule that appraisal institutions may not accept individual entrustment to conduct prenatal paternity tests on pregnant women.
Of course, the public security organs will also involve paternity testing, but generally they only accept cases related to the appraisal, such as bigamy cases, child abduction cases, and cases that confirm the identity of anonymous or unnamed corpses, etc., often requiring paternity testing.
According to the purpose of use, it can be divided into forensic identification and consulting inspection.
Judicial appraisal requires the appraisal to play a legal role.
Since this kind of appraisal requires the issuance of an appraisal certificate, the appraisal institution often requires the appraisee to carry the certificate and personally go to the appraisal institution to sample and take pictures.
Samples are usually taken as blood samples or oral mucosal swabs.
If there is an institution that says that the identification of this kind of appraisal certificate does not require the person to be present to sample and take pictures, it is basically a violation of the law.
On the other hand, consulting and testing, because as long as the parties understand a result, the inspection unit will only issue an inspection report, and is only responsible for the samples sent for testing, and does not trace the source of the samples.
The materials that can be used for detection are also diverse, such as blood, saliva spots, hair with hair follicles. Some institutions will even receive cigarette butts, razors, paper towels, unwashed underwear, etc., generally determined by the type of sample that the parties can provide, and provide the corresponding inspection materials after communicating with the inspection unit in advance.
Compared with traditional paternity testing of parents and children, kinship testing is a larger category that includes the former.
With the widespread use of DNA genetic markers, in cases where parents or parents are absent, such as the recognition of relatives who have been separated for many years, the identification of the source of the corpse, etc.
Paternity testing has been extended to a wider range of kinship appraisals, including the identification of full siblings, semi-siblings, grandchildren, uncles and nephews, cousins and so on.
For the identification of specific blood relations, in addition to determining whether there is a blood relationship by detecting autostained DNA genetic markers, it is also possible to select DNA genetic markers on mitochondrial DNA, X chromosomes and Y chromosomes according to the actual situation to help determine whether there is a blood relationship.
However, it is worth noting that due to the lack of genetic information about the parent and/or mother, the identification of kinship can sometimes not give a very positive conclusion like traditional paternity testing, but can only give a predisposing opinion.
Review expert: Ou Xueling | Forensic Doctoral Supervisor, Chief Forensic Physician
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[2] Yang Rongzhi,Yang Qingen,Yu Chunying,Mei Kun,Chen Hui. Amniotic fluid paternity test and its social problems: An analysis of paternity testing in 28 cases[J].Medicine and Society, 2005(01):12-13.
[3] Y M Dennis Lo,NoemiCorbetta,Paul F Chamberlain,VikRai,Ian L Sargent,Christopher WG Redman,James S Wainscoat. Presence of fetal DNA in maternal plasma and serum[J]. The Lancet,1997,350(9076).
Li Shuxia,Chai Lifen,Liu Linying,Wu Qirui,Zhang Huiping. Clinical application progress of non-invasive prenatal DNA detection technology[J].Journal of Ningxia Medical University,2020,42(09):962-966.
Jiang Haojun. Application of STR and SNP typing technology in non-invasive prenatal paternity testing[D].Southeast University, 2016.
[6] Shi Meng,Zhang Nuenzi,Cao Lichao,Liu Bo. Application of high-throughput sequencing SNP typing technique in non-invasive prenatal paternity testing[J].Journal of Tropical Medicine,2018,18(07):865-868.
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