Males with 47 XXY. Klinefelter's syndrome is a genetic disorder in which there is at least one extra x chromosome to a normal human male karyotype, for a total of 47 chromosomes. The principal effects are hypogonadism and reduced fertility. By adulthood, XXY males look similar to males without the condition, although they are often taller. Gynecomastia (enlarged breats) is present in about a third of individuals.