Hyperandrogenism, also known as XYY chromosome syndrome, is a patient with a chromosome of 47XYY. The normal human chromosomes are 22 pairs of autosomes and one pair of sex chromosomes. The male chromosome is 46XY (46 chromosomes in total, of which the sex chromosome is XY) and the female is 46XX (46 chromosomes in total, of which the sex chromosome is XX). In Fernando’s patient, the sex chromatin is negative for X sex chromosome and double positive for Y sex chromosome, i.e. there are two Y chromosomes. The karyotype is 47XYY and the extra Y chromosome is due to the non-separation of chromosomes during meiosis of the father’s germ cells. Cause: Hyperandrogenesis results from the Y chromosome non-disjunction that occurs during the second meiosis of the patient’s father’s sperm formation. The incidence of XYY syndrome in male infants is 1:900. XYY males have an essentially normal phenotype, are tall, often exceeding 180 cm, and occasionally have cryptorchidism, testicular hypoplasia with disorders of the seminal process and reduced fertility, and hypospadias, but most males are fertile. XYY individuals tend to feel unsatisfied with their desires, are averse to school, have poor self-restraint, and are prone to aggressive behavior.