The first human chromosome abnormalities
We are here to celebrate Tjio & Levan’s epic discovery in 1956 of the correct number of human chromosomes. This was followed three years later by one of the most momentous years in human genetics. In 1959 the first chromosome abnormalities were described in our species: the additional X chromosome in Klinefelter syndrome which showed, contrary to established dogma, that the mammalian Y chromosome was male determining, and the first autosome abnormality, namely the additional chromosome 21 in mongolism, as Down syndrome was then called. In the same year the 45,X constitution associated with Turner syndrome, the first case of mosaicism, an XXY/XX male with Klinefelter syndrome, and sex chromosome reversal in a female with Testicular Feminisation were all described. In addition the first structural abnormality, a D/D Robertsonian translocation, and the first condition actually defined by a chromosome abnormality, the Trisomy X female, were published. But 1959 was only a beginning. 1960 saw the description of the other two major autosomal trisomies found in the newborn, trisomies 13 and 18, the first syndrome, “cri-du-chat”, caused by a demonstrable deletion of chromosome material and the first specific chromosome abnormality, the Philadelphia chromosome, associated with a malignant disease. In the same year the blood culture technique was described which enabled high quality preparations to be made from an easily obtained tissue thereby revolutionising human cytogenetics. Thus by the end of 1960 all was in place for the burgeoning of cytogenetics as both a research and a diagnostic discipline.
It was a great privilege to be a young scientist at that time and to have the opportunity of contributing to some of these momentous discoveries. I hope to share some of the excitement with you.