Complex kinship tests

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When we talk about complex kinship tests involving grandparents, grandchildren, aunts, uncles, nephews, nieces, nephews or cousins, we are talking about the set of tests that are carried out in family relationship tests and that determine the probability that two people belong to the same family. How are they carried out? Discover it in this article.

The so-called complex parentage tests, which are carried out with non-direct relatives such as grandparents, grandchildren, aunts, uncles, nephews, nieces, nephews or cousins, are usually carried out with the idea of proving a blood relationship in the absence of the biological parent. For various reasons it may happen that a person needs to prove his or her relationship as a child and the biological parent is not present because, for example, his or her death has been followed by a cremation and this makes it impossible to carry out a DNA test. In these cases, what can be done is a study between the child and persons who are directly related to the biological father or mother. From this test it follows that, if the family relationship is verified, it will consequently also be established with the parent. This study is particularly sensitive and requires experienced professionals to carry it out. Pay attention to the details of this complex parentage test.

Evidence of biological kinship

Biological kinship testing is a scientific analysis carried out within the genetics laboratory to determine if there is a kinship relationship, i.e. if those persons who are participating in the study are related to each other.

This test is performed by taking a small sample of DNA. This genetic material will provide the markers that will then be studied and compared to confirm or disconfirm the relationship between the people tested. The most common way to acquire this DNA sample is through saliva, using a buccal swab. In the simplest cases it is usually possible to obtain conclusive results by analysing a small number of STRs (Short Tandem Repeats) or genetic markers, with a reliability of more than 99.9%. But there are other less simple cases (cadaveric remains, or more distant kinship relationships) in which STRs are not sufficient and complementary markers are required. These cases may comprise up to 15% of the total number of cases analysed.

Analyzing the various genetic markers is what will allow us to establish the relationship we are looking for, or to determine whether the biological ancestry is shared in order to look for other types of relationships or to exclude them. As the genetic markers are received randomly from the biological parents, finding patterns that differ from the presumed biological parents, it leads us to the conclusion that they are not the parents. And, the more markers shared between samples without exclusions, the greater the probability that we are dealing with the biological father of the person tested. By analyzing large numbers of markers, we can use statistical procedures to confirm or rule out the relationship.

Processes in biological kinship analysis

To determine the kinship of the two subjects under analysis, two consecutive processes take place: first, the genetic profile of each of them is determined and then they are compared to each other in order to calculate the probability of a biological relationship between them. This second process requires computer intelligence to perform statistical calculations. It is very important to clarify that these processes should always be carried out by qualified and experienced professionals to avoid confusion or misinterpretation.

Complex kinship tests: how are they carried out?

As mentioned above, complex kinship tests are tests in which we do not use samples from the people involved (in this case the parents) because they are not available, and so what it’s done is to indirectly infer the link. To do this, we do not use the most common markers (STRs), as they do not provide sufficient determination, but we add complementary markers such as SNPs. SNPs are single nucleotide variations found throughout the genome, which do not change the total length of the DNA sequence in the region. They are very abundant in the human genome: at a rate of one SNP per 1000 base pairs. Most SNPs are located in the non-coding regions, and have no direct impact on an individual’s phenotype and have the potential to detect functional genetic variation.

This type of analysis is performed in the same way as simple paternity tests, taking into account that as the distance between individuals increases, so does the genetic distance. What does this mean? That the test may require higher statistical power to be considered conclusive. What is done in these cases is to add a greater number of genetic markers to increase the resolution of the test. In this way, the results are powerful enough to be mathematically accurate.

When is this test required?

Their applications are many, but broadly speaking, these are the most frequent examples:

1. Identification of human remains.
2. Proof of paternity or maternity of a deceased relative
3. Identification of persons who are presumed to be related and whose samples are not available.
4. Descendants of emigrants who have already died and want to prove their status and only other relatives are available.

In all of the above procedures, those involved will be required to have read and signed a consent form and, in the case of minors, a legal guardian will be required to give consent and be present. In cases where this procedure is court-mandated, this step will not be necessary.

Is the process reliable?

The reliability of the biological kinship test will be ensured by the number and type of markers used in the test. The greater number of markers will make the test more reliable by statistical probability. When the cases are simple, it is sufficient to analyze a small number of markers, but in cases of complex kinship, complementary markers must be used and only the most advanced centers can perform this test with a high probability of confirming or rejecting the biological relationship between the two individuals.

When it comes to distant or indirect relationships, it is more difficult to obtain reliable results. So this is where it is important to seek expertise to find the different markers we need to be able to interpret the results.

Are you looking for such a test? At Ambar Lab we are specialists in this type of tests and we carry out several genetic identity studies in order to verify kinship relationships. As this is a very specific issue, we have a counselling service available. Together we can decide which study is the most appropriate in each of the situations our patients bring to us and guide them according to the samples available to them. We offer an interpretation of these analyses so that there is no doubt about the results. Contact us so that we can help you and clear all your doubts throughout the process.

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