What are the signs of Klinefelter syndrome, and how is it diagnosed?

[Anonymous]

What are the signs of Klinefelter syndrome, and how is it diagnosed?

[Genetic Counselor]

Klinefelter syndrome looks different from person to person, and its features often go unrecognized: current estimates suggest that only about a quarter to a third of affected individuals are ever correctly identified, and those who are diagnosed are, on average, around 30 years old at the time. Recognizing the pattern at any stage of life starts the process of getting the right support in place.

• In infancy. Most infants with Klinefelter syndrome look typical at birth, though some have a smaller-than-average penis, undescended testicles, or reduced muscle tone. Fewer than 1 in 10 individuals are identified before puberty begins.
• In childhood. Speech and language delay is common, and roughly two-thirds of affected children eventually need speech therapy. Some children are identified during evaluation for a learning difference, attention difficulty, or autism spectrum features, which occur in about 1 in 10 individuals with Klinefelter syndrome.
• At and after puberty. This is when the pattern most often becomes clear. Typical features include taller-than-average height, small and firm testicles, breast tissue enlargement (called gynecomastia), reduced facial and body hair, and, for many, lower muscle strength than peers. Some adolescents and young men develop a fine trembling of the hands, seen in roughly 20 to 50 percent of individuals.
• In adulthood. Many men are only diagnosed when they or their partner seek help for difficulty conceiving, since Klinefelter syndrome is found in about 3 in 100 men evaluated for infertility, or when low testosterone symptoms prompt hormone testing.
• Before birth. An increasing number of cases are picked up through Non-Invasive Prenatal Testing or through chromosome analysis performed for another reason, such as advanced maternal age; because Non-Invasive Prenatal Testing is a screening test, a positive result for an extra X chromosome is confirmed with a diagnostic test such as amniocentesis or chorionic villus sampling before any conclusions are drawn.

Diagnosis at any age is confirmed with a chromosome analysis, called a karyotype, performed on a blood sample, or with chromosomal microarray testing. Blood testing of reproductive hormones is often used alongside this: individuals with Klinefelter syndrome typically show elevated follicle-stimulating hormone and luteinizing hormone alongside low or low-normal testosterone, a combination called hypergonadotropic hypogonadism, reflecting that the testicles themselves are not responding fully to the body’s hormonal signals.

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