Case 1
The abnormality was discovered when a foreign man came to Eurofins Gentis to undergo an administrative father–child DNA test for birth registration and citizenship procedures. Based on the documents provided by the customer, the father was 36 years old, the child was a 5-month-old male, and the mother was a 20-year-old Vietnamese woman.
The testing was conducted according to standard procedures, and the results confirmed that the tested man and the child had a biological father–son relationship. The unusual point lay in the child’s sex. When analyzed using the 24-marker PowerPlex Fusion Kit, including Amelogenin and DYS391 for sex differentiation, the child’s genotype showed only XX at Amelogenin and no allele at DYS391, indicating a female genotype (see Peak image).
To establish a basis for concluding a sex abnormality, the company coordinated with the family to carry out a clinical examination, which confirmed that the child’s phenotype was male with clearly developed external genitalia.
Additionally, another test was performed to ensure accuracy: an analysis of the Y chromosome using the PowerPlex Y23 Kit. The results showed no Y-haplotype alleles at all (see Peak image).
Based on these findings, the company’s scientific council concluded that the child had 46, XX male syndrome (also known as XX Male Syndrome).
The cause of this phenomenon is unequal crossing-over between the Y chromosome and the X chromosome during the father’s meiosis. As a result, the X chromosome carries the SRY gene (the sex-determining gene). This occurs at the terminal region of the short arms of the X and Y chromosomes, where the SRY gene is normally located on the Y chromosome. When an X chromosome containing SRY combines with a normal maternal X chromosome at fertilization, it produces a 46, XX male genotype.
46, XX male syndrome occurs in approximately 1 in 20,000 newborn males, and individuals with this syndrome are infertile.
Case 2
A 42-year-old man visited the company with his 4-year-old son to request an administrative DNA test for father–son relationship verification. When asked why he wanted the test, he said he had a feeling the boy was not his because the child did not resemble him or his paternal relatives. His suspicion was emotional rather than factual—for accuracy, only DNA testing could provide an answer. Every customer has their own reasons for testing, often impossible to fully express.
Two days later, the results were completed. When he returned and learned that he and the boy were not biologically related, he fell silent for a moment, thanked the staff, and left.
About a week later, he returned again—this time with a prepared sample, stating it belonged to his 7-year-old daughter, and requested a comparison with his earlier sample. The results were astonishing: the daughter also had no biological relationship with him. Thus, both children he had tested were not his biological offspring.
Given the complicated circumstances, the scientific council analyzed the case carefully, especially because the Peak data at sex-related markers showed abnormalities. They decided to conduct an additional analysis using an X-test kit. The results revealed that the man had an XXY genotype, also known as Klinefelter syndrome (see Peak image).
The Peak chart clearly showed a male genotype (XY) at Amelogenin. However, most X-STR markers displayed two alleles (heterozygous), indicating two X chromosomes, while some X-STR markers showed a single peak (homozygous).
Klinefelter syndrome (XXY) occurs in males due to an extra X chromosome—typical males have XY. The syndrome arises randomly during gamete formation due to nondisjunction of sex chromosomes during meiosis. It occurs in approximately 1 in 500–1000 newborn males.
Males with XXY syndrome are typically infertile. Therefore, the fact that neither child was biologically related to him is understandable, and only the children’s mother would know who their biological father truly is.
Colonel Hà Quốc Khanh
