Is Superman Syndrome A Real Thing?

Superman syndrome, also called Jacobs syndrome or 47,XYY syndrome, is a chromosomal disorder in which a male is born with an extra Y chromosome. It occurs in roughly 1 in 1,000 male newborns and is usually mild: most affected men are slightly taller than average, may have learning or speech delays, but have normal life expectancy and are typically fertile.

The DNA that has been passed on to us by our long line of ancestors makes us who we are. They decide how we look, how our bodies function, and they even affect our personality. When all the pieces of our genes fall together in line, we get a perfectly “normal” human being. However, there are times when even nature makes small mistakes that can have catastrophic outcomes.

Nature’s imperfections can manifest as differences in the human body. You have likely heard of chromosomal disorders like Down syndrome. Such disorders are caused by some glitch that occurs during the process of cell division.

One such rarely heard about chromosomal disorder is Superman Syndrome. A chromosomal abnormality causes Superman syndrome, which is also known as Jacobs syndrome (named after the British cytogeneticist Patricia Jacobs). About 1 in 1,000 male newborns has the 47,XYY karyotype, making it one of the more common sex chromosome aneuploidies.

So, what exactly is the “Superman syndrome”? What causes it and how does it affect a person?

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Sex Chromosomes

Before we dive into the complexities of this chromosomal disorder, let’s revisit the basics of genetics. In humans (and most mammals), individuals fall into two main karyotypes based on their sex chromosomes (other species use very different systems, such as ZW in birds or temperature-dependent sex determination in many reptiles, but mammals stick with XY). Humans have 46 chromosomes in each cell. Of these 46, two chromosomes—X and Y—determine the sex of the individual. A large chunk of the human population has two sex chromosomes. Females have two X chromosomes, while males have one X and one Y chromosome.

In rare events, the zygote may end up with 3 sex chromosomes instead of two (XX or XY). One such abnormality is male sex chromosome aneuploidy disorder: Superman Syndrome.

What Is Superman Syndrome?

The sex-determining cells in our body, sperm and eggs, demonstrate meiotic division (Click here to learn more about meiosis). If all things go normally during the cell division of the gametes, we end up with a normal individual with either XX or XY chromosomes.

47,XYY arises when the two sister chromatids of the Y chromosome fail to separate during meiosis II of sperm formation (a "nondisjunction" event), producing a sperm that carries two Y chromosomes instead of one. Thus, such individuals (typically males) have an extra Y chromosome attached to their two sex chromosomes: XY. Meaning, they have 47 chromosomes in each cell and have the sex chromosome XYY. Thus, the Superman Syndrome in the world of medical science is formally known as 47,XYY syndrome.

47,XYY syndrome has been observed in about 1 in 1,000 male newborns. Despite being a common disorder, only around 20% of the cases are reported. This is because symptoms like having a tall stature and developmental delays are not specific to this disorder. This makes it difficult to differentiate such individuals from the normal population.

Although it is caused by a genetic defect, the condition is not hereditary. This is because the syndrome results from an error that occurs during sperm cell formation.

How Does It Affect An Individual?

Any abnormality in the body that is as significant as an extra Y chromosome is bound to display itself in some way. Chromosomes have crucial genes that regulate various parts of the body. If you add or subtract the number of chromosomes, it affects the way the body develops and regulates itself.

One of the most consistent effects is accelerated growth from early childhood. As adults, XYY men are on average about 7 cm (roughly 2.75 in) taller than their expected family height, with cohort averages around 188 cm (6 ft 2 in).

Some XYY men show low muscle tone (hypotonia), poor fine-motor and handwriting skills, larger-than-average teeth (macrodontia, sometimes with taurodontism), and an increased risk of genitourinary issues such as cryptorchidism. Cardiovascular and renal malformations have been reported in case studies, but are not core features.

As if affecting the physiology of the body was not enough, the 47,XYY syndrome also undermines the mental capability of the person. Boys with XYY suffer from verbal learning deficiencies due to delayed speech development. Some find it difficult to recall words, understand figurative and metaphorical language, and tend to show ADHD-like attention-related problems.

It is believed that men with XYY syndrome are infertile. However, science says otherwise. Many men with 47,XYY are fertile because the extra Y chromosome is typically eliminated before the spermatocyte stage, so their sons and daughters are usually karyotypically normal. Recent cohort studies (Bardsley 2013, Tartaglia 2018) also report an autism spectrum disorder rate of roughly 14% in XYY boys, which is well above the general population, and noninvasive prenatal testing (NIPT) is increasingly picking up the karyotype before birth, raising new questions about counselling and follow-up.

Why Is It Called “Superman” Syndrome?

If you’re hoping that there is some deep scientific meaning behind naming a disorder after a popular fictional superhero, I’m sorry, but you’re in for some disappointment.

Due to the presence of an extra Y chromosome, a chromosome that is characteristic of males, people with XYY are considered “super”-male. Contrary to your expectations brought on by the name, a super-male doesn’t possess great powers that can save us from villains like Lex Luthor.

Though they’re not superheroes, they’re not villains either. It is worth mentioning that it is an unproven notion that XYY men tend to be aggressive or have criminal inclinations. This is because some notorious murderers like Sean Farley and Daniel Hugon were reported to have XYY chromosomes, but correlation does not equal causation. It’s not always in the genes. Men and women with a perfectly normal set of sex chromosomes also have the ability to commit the most heinous of crimes.

Conclusion

Sex chromosome abnormalities such as 47,XYY are the result of a small yet profound screw-up by nature. Apart from this, a similar kind of goof-up can be seen in Klinefelter syndrome. In that condition, a male receives an extra X chromosome and ends up with 47,XXY syndrome. However, this syndrome doesn’t have a name as cool as the Superman syndrome. Despite all the side effects, individuals with Superman syndrome are projected to have a normal life expectancy.