Looking to study genetic disabilities? Here is one for you!
A complete go-through of Klinefelter Syndrome and all its aspects highlighted together in a single video!
So, let’s start taking notes!
▬ 📌 What do you understand by the term Klinefelter Syndrome?
Klinefelter syndrome is a disorder found in males associated with a 47, XXY karyotype.
The major clinical features of Klinefelter syndrome are attributable to hypogonadism characterized by low production of androgens.
Because of this primary testicular failure, these individuals often present with gynecomastia (enlargement and swelling of breasts in males), infertility (unable to reproduce), and a “eunuchoid habitus” (a body habitus that is tall, slime, and underweight, with long legs and long arms i.e., arm span exceeds height by 5cm or more).
▬ 📌 Which clinical features and variants should I look for?
Hypo-mentation (decreased IQ) is relatively common in this condition; however, many individuals with this condition have normal intellect.
The overall mean IQ with Klinefelter syndrome is around 90 which falls into a normal IQ window.
It is important to note that 40%-50% of males with Klinefelter syndrome have no discernable physical features so that is why in most of the cases it remains unnoticed.
They only present as male infertility due to azoospermia (no production of sperm).
Variants of Klinefelter syndrome include 48, XXXY, and 49, XXXXY. In general, these individuals have a Klinefelter-like phenotype.
The primary differences are that with an increasing number of X’s, there is an increase in growth restriction and a decrease in IQ.
Many individuals with these variants may have some mild craniofacial and skeletal changes not otherwise seen in 47, XXY Klinefelter syndrome.
▬ 📌 What happens in Klinefelter syndrome?
You should keep in mind that this syndrome can be transferred from either parent to offspring that has meiotic non-disjunction at the M1 phase.
In males, when we look at normal meiosis I, we see that XY chromosomes get equally separated into two cells. One of them is X and the other one will be Y. Then, at meiosis II, they will form two kinds of sperms that will carry either X or Y chromosomes.
Now in normal fertilization, either one of them succeeds in fertilizing an egg and forming XX and XY chromosomes for the offspring. Now, in Klinefelter due to this meiotic non-disjunction, both the XY chromosomes will be transferred into a single germ cell while the other one remains empty.
In this way, when fertilization occurs of XY chromosomes containing cells, it will fertilize more than 2 chromosomes i.e., one from the mother and 2 defective pairs from the father, and will have 3 chromosomes in total.
A similar mechanism is followed in females as the cell will transfer both of its XX chromosomes to a single cell and the other cell will remain empty.
When we look at the normal mechanism, they will produce two normal cells (meiosis I) that will be fertilized and then they would perform meiosis II but, in the syndrome, we can see that the cell is transferring both of its XX chromosomes to one cell and the other cell will remain as a polar body.
Thus, the result of such abnormalities would cause the production of 3 chromosomes in total i.e., 2 defective pairs from the mother and one normal pair from the father.
▬ 📌 How do you distinguish the genotypes?
There are 3 genotypes observed commonly, related to Klinefelter Syndrome:
🔵 Karyotype 47, XXY
🔵 Karyotype 48, XXXY
🔵 Karyotype 49, XXXXY
▬ 📌 What about its life expectancy?
The frequency of this syndrome is an average of 1/600 males.
Life expectancy for a diseased individual is almost Normal, but 50% die before birth.
▬ 📌 How is it expressed in affected individuals?
👉 The phenotype is basically male, tall with elongated lower legs and forearms, but with a feminine body shape and low muscle mass.
👉 There is gynecomastia in one-third of the population and a risk of osteoporosis and breast cancer.
👉 They might have small, soft testes (less than 10mL, 2 cm); most are sterile or produce few sperm, because of atrophy of the seminiferous tubules.
👉 Testicles and penis remain small; there is low libido and impotence.
👉 Blood tests show high gonadotrophins i.e., LH and FSH, and low testosterone levels.
👉 Pubic, axillary, and chest hair are sparse, and daily facial shaving is rarely necessary.
Other features include:
✦ Scoliosis (Sideway curvature of spine)
✦ Emphysema (alveolar damage)
✦ Varicose veins
✦ Leg ulcers
✦ Diabetes mellitus in 8%
✦ Thyroid problems
✦ Childhood with clumsiness, learning difficulties, and poor verbal skills.
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