106 J. LEJEUNE 



only get the leukaemia in a few of the cases. In the trisomies, do the three 2rs look the 

 same always? 



LEJEUNE: Yes they are. There is no detectable change in the karyotype of bone-marrow or 

 blood. 



lamerton: You don't get any variation, and yet you still only get an increase in the 

 leukaemia by a factor of 10. Many people who have those tliree apparently identical 

 chromosomes don't get leukaemia. 



LEJEUNE: That is not so simple, because we don't know at all whether they get it or not. 

 When we are deaUng with the mongols, we have to say that we are dealing with a new 

 population — because they are now allowed to live their lives with antibiotics but 

 previously they were dying much earlier. We have a small proportion of leukaemia 

 which was 20 times higher than in the normal population, but they have been at risk for 

 a relatively short period. It is not known, but likely that mongols wiU possibly get a lot 

 more leukaemia, when they reach 20 or 30 years old, which is quite unobserved at the 

 moment. 



LAMERTON: Is uot this figure of twenty times very misleading? 



LEJEUNE: It is very misleading. Roughly it compares 6-year-old children — mongols — 

 with the normal 6-year-old population— that does not give an estimate of the general 

 risk during the whole Ufe-time. 



UPTON: I've been very much interested in discussing this problem with P. R. J. Burch 

 who is spending a year at Oak Ridge. I tliink it's his belief that the Philadelphia chromo- 

 some acts merely as the equivalent to mutations in two loci. He visuaUzes that one must 

 have homologous loci on both cliromosomes, in other words a four-liit situation for 

 chronic myelogenous leukaemia. With the Philadelphia cliromosome you have two to 

 four hits. 



ALEXANDER: Dr. Lejeune, you had 2 cases of these acute leukaemias. Does this mean that 

 only 2 cases have ever been looked at? 



LEJEUNE: So far as I know, for acute myeloblastic leukaemia; yes, just last week a third 

 one was pubhshed; in that case there was quite a big deletion of the 21, not a complete 

 disappearance. 



KEPES: What is the frequency of this cliromosome anomaly? 



LEJEUNE: In both cases there are 2 populations of cells m these individuals. One is 

 entirely normal, and the other shows the abnormality. In the cases we have checked 

 there was one boy and one gul — the girl died too early, but we could also do the skin of 

 the boy — to show that he has quite normal cells of the skin. As to the frequency of the 

 abnormal cells it is of the order of one-half or more — but the actual numbers are possibly 

 greatly disturbed by differential survival in vitro. 

 BiNGELLi: Have you done any electron microscopy on this problem? 

 LEJEUNE: Electron microscopy of human chromosomes is technically very difficult. They 

 are too big and too thick. 



BINGELLI: I thought you might have done serial sections. 



LEJEUNE: Yes, but when you do that you are on a very diff"erent scale so you do not 

 know what you are seeing. The only pubhshed attempt has given an enlargement which 

 is not greater than that obtamed with the optical microscope; so the electron microscope 

 for the moment is of no use at all. The only way m our opinion is for the cy togeneticists 

 to become as inteUigent as Drosophila and to become able to produce polytene chromo- 

 somes in vitro. 



