In 1959, five days after
Jérôme Lejeune described the
trisomy-21 in Down syndrome, basing himself off
Marthe Gautier's work, Jacobs and
John Strong described an additional X chromosome in male patients (the 47,XXY karyotype) also known as
Klinefelter syndrome, as
Harry Klinefelter had already diagnosed the symptoms in 1942. Despite her work being on XXY syndrome, the
XYY syndrome is instead sometimes called Jacobs syndrome: After it had been incidentally discovered by
Avery Sandberg in 1961, the syndrome was also found in a chromosome survey of 315 men at a hospital for
developmentally disabled, made by Jacobs and hence considered the first little research on it. However, the experimental design had many flaws, including small sample sizes, biased sampling, and poor definition of the phenotype "aggression", resulted in the mischaracterization of XYY individuals as aggressive and violent criminals, which led the path for many biased studies on height-selected, institutionalised XYY individuals in the following decades. ==Personal life and death==