Not long ago, a pregnant woman in Sichuan, who was 15 weeks pregnant, found out about the chromosomal abnormality in the fetus, suffering from XYY syndrome, during prenatal genetic testing. The medical results posted online sparked discussions. What is XYY syndrome all about?
Destigmatizing “47XYY”
Currently, XYY syndrome testing is not a routine prenatal checkup item, and this detection was an accidental finding. Huang Hui, a genetic counseling expert from BGI Genomics, provided detailed scientific explanations about this genetic phenomenon during an interview with journalists.
The normal chromosome for a male is 46XY, which means 23 pairs or 46 chromosomes in total. Meanwhile, 47XYY results from having an extra Y chromosome.
The mechanism behind this is that in 84% of cases, during the sperm formation process, the sperm precursor cell fails to separate the Y chromosome during the second meiotic division, resulting in the combination of YY sperm with a normal egg; the remaining 16% occurs during early embryo development, where an error during mitosis leads to the possibility of a mosaic form. The genetic test report in the article showed a male with a mosaic of 46XY and 47XYY.
In 2012, a large-scale study in Denmark involving over 160 47XYY males and more than 15,000 individuals from the general population for criminal behavior revealed slight increases in all types of crimes and incidence rates among 47XYY males, with an HR risk value of 1.42.
However, after adjusting for sociodemographic factors such as education background and living environment, the overall risk of criminal behavior reduced to a similar level as the control group. Currently, based on research results, there is insufficient scientific evidence proving a violent tendency within the 47XYY population.
In previous years, individuals in this population were primarily diagnosed with developmental delays or behavioral issues after seeking medical care. This research contributes to raising awareness of the “severe” end of the symptom spectrum.
In recent years, with the advancement of large-scale genomic projects, many 47XYY symptoms have been found to be mild or even asymptomatic. A recent study from the UK Biobank discovered that out of 143 males detected with 47XYY, only one person was previously aware of their chromosomal abnormality, highlighting the potential significant variations in symptoms within this population.
Differences exist in intellectual and emotional cognitive performances among 47XYY individuals. In terms of intelligence, studies conducting IQ tests showed that the intelligence of 47XYY individuals generally falls within the normal range or has a slight decrease. Other research results indicated that the median IQ of XYY syndrome individuals is 10-15 points lower than the lower limit of the normal reference range.
However, there are reports suggesting that 47XYY individuals may also have advantages in other aspects, such as curiosity, sense of humor, and team spirit, or in fields like science, technology, engineering, and mathematics.
In conclusion, Huang Hui mentioned that within the mystery of human chromosomes, XYY syndrome exists relatively mildly among us. While the extra Y chromosome may pose some additional challenges for a small portion of this population, the majority of 47XYY males are similar to us, without significant differences.
