Presumptive isochromosomes for the long arm of <i>X</i> in man. Analysis of five families

Summary The cytological study of five female individuals is indicative of the existence in man of iso‐chromosomes for the long arm of the X chromosome. Phenotypically these subjects are characterized by primary amenorrhoea, short stature, elevated excretion of gonadotropins and low excretion of oestrogens in urine. Laparotomy revealed in two of them gonadal streaks. Analysis of dermatoglyphics showed patterns similar to those found in XO individuals. The five subjects are sex chromatin positive in buccal mucosa smears and in cultured cells, and drumsticks are found consistently in their neutrophils. The karyotypes of the five patients are consistent in their appearance in all the cells with forty­six chromosomes from different tissues bone marrow, skin and blood there are fifteen chromosomes in the 6­12­X group instead of sixteen, and an extra metacentric chromosome similar to those of pair no· 3. These cells are interpreted as having one normal X chromosome and a presumptive iso­chromosome for the long arm of X. In one or more of the tissues cultured from patients A.S., L.A. and B.J. there is a proportion of cells with forty‐five chromosomes and with an XO constitution. The origin of the iso‐chromosomes is thought to be meiotic and paternal. This hypothesis is discussed on the basis of an apparent deficiency of females in the sibships of the patients and of the genetical information provided by the study of the sex‐linked Xg blood group system in the family of B.J. This family, in which red‐green colour blindness is segregating, provides also evidence that the Xg and the red‐green colour blindness loci are located on the short arm of the X chromosome. Personal, family and laboratory data are provided in Appendices, together with the cytological data and chromosome measurements. The writers wish to express their gratitude to all those who cooperated in this investigation. In particular they would like to thank Sarah B. Holt, I. Kugelberg, L. S. Penrose, R. R. Race, A. Remeck, Ruth Sanger, M. Svenmar, Anita Tillberg. They would specially mention the kindness of C. E. Ford who critically reviewed the manuscript. This research has been aided in part by grants from ‘Solstickans fund för forskning rörande kroniska och invalidiserande sjukdomar hos barn’ and by a personal grant to R. Luft from the Knut and Alice Wallenberg Foundation.