Klinefelter syndrome in children and adolescents

Klinefelter syndrome is a chromosomal pathology, which is the most common anomaly of sex chromosomes and the most common form of primary male hypogonadism. The presence of an extra X-chromosome in the karyotype causes infertility, azoospermia, small size of testicles, high level of gonadotropins and low level of testosterone, tallness and disproportionate physique, learning difficulties, and developmental speech disorders. Despite the high incidence of the syndrome in the population, only 25% of patients are aware of their disease during their lifetime. Late diagnosis and delayed treatment are often due to pronounced clinical polymorphism of the disease, different symptom onset time, as well as high incidence of associated conditions, so that these patients are followed by various specialists, but they are not aware of the main diagnosis. This review presents data on the history, etiology of the syndrome, clinical and laboratory features characteristic of children, adolescents, and adults. The most common associated diseases are listed and current data on their prevalence and the effect of testosterone replacement therapy on these conditions are provided.