Section 15 — Human Genetics 



15.56. Genetic Variation and Leprosy. S. G. Spickett 

 (Cambridge, Great Britain). 



The causative organism of leprosy is Mycobac- 

 terium leprae. There is evidence that some human 

 individuals are resistant to parasitism by this 

 pathogen. Susceptibility to leprosy would 

 appear to be determined by a single irregularly 

 dominant gene. The frequency and penetrance of 

 this gene varies between populations. 



Leprosy may be manifest in several forms, the 

 relative frequency of these forms shows striking 

 variation between populations. There is more- 

 over a significantly higher concordance between 

 monozygotic than between dizygotic twins in 

 the form of leprosy suffered. This and other 

 evidence suggests that the genotype of the human 

 host is of importance in determining the course 

 of the disease. Evidence of higher concordance 

 between unrelated contacts than random expec- 

 tation and the failure to find any environmental 

 factor to account for this, is suggestive of an 

 effect of the genotype of the pathogen on the 

 course of the disease. 



The history of epidemic leprosy is consistent 

 with there being genetic control of incidence 

 and form of leprosy by both host and pathogen. 



Current studies indicate that drug resistance is 

 increasing in pathogen populations with the 

 risk that the control of leprosy may become more 

 difficult in the future. Moreover, leprosy is 

 increasing in some populations that have been 

 free of it for many generations. It is probable 

 that this is associated with a rise in the gene 

 frequency for susceptibility (in the absence of 

 selection pressure against it) coupled with the 

 greater chance of contact with the disease that 

 is associated with the greater mobility of indi- 

 viduals between populations. 



15.57. The Role of Genetics in Diabetics. Nancy 



E. Simpson (Toronto, Canada). 



Analysis of the genetics of diabetics will be 

 presented from data obtained from a voluntary 

 register of diabetics in Canada sponsored by the 

 Canadian Diabetic Association. For the past 

 two years diabetics have been asked to complete 

 questionnaires which contain detailed infor- 

 mation regarding their immediate relatives 

 (parents, sibs and offspring). 



The register will be a continuing one in 

 which respondents will be asked to keep the 

 information regarding their families up to date. 

 Ultimately a history for three generations of 

 families in which there is at least one diabetic 

 will be available for genetic analysis. These sort 



of data have long been needed to establish 

 the genetic role in the etiology of this condition 

 with variable age at onset. 



From the register, the proportions of diabetics 

 among offspring of two diabetic parents and one 

 diabetic parent (selected through the matings) 

 are compared with each other and a suitable 

 population control. The ages at onset and 

 treatment of the diabetics are taken into con- 

 sideration. The data suggest that diabetes is not 

 genetically homogeneous. The results lead to 

 interesting speculations on the role of genetics 

 in diabetes and to discussion of future advantages 

 of the register when complete histories for the 

 generations become available. 



15.58. The Natural History of Hyperuricemia and 

 Gout. M. T. Rakic, H. A. Valkenburg, 

 R. T. Davidson, J. P. Engels, W. M. Mikkel- 

 sen, J. V. Neel and I. F. Duff (Ann Arbor, 

 U.S.A.). 



To determine with more precision the natural 

 history of hyperuricemia and gout, the families 

 of 19 proposity (a total of 99 relatives) studied 

 in 1938-42 or 1946 were reinvestigated in 1961-62. 

 Nine of the propositi (all still with signs and 

 symptoms of their disease) and 262 relatives 

 (69 from the first study, the remainder seen for 

 the first time) could be examined. In the period 

 of follow-up gout was present in 14 male 

 relatives and 6 female relatives. The mean age of 

 onset gout was in males 39 years and in females 

 54 years (P < 0.005). 



Thirty-five male relatives and 34 female rela- 

 tives were seen in both studies. Eleven of the 26 

 male relatives with normal serum uric acid levels 

 in the previous study developed hyperuricemia 

 as determined by the colorimetric method and 

 defined as a level in males of 6.0 mg per cent or 

 greater and in females of 5.0 mg per cent or 

 greater. Of these 11 two had developed gout. Of 

 the 9 hyperuricemic male relatives in the first 

 study 1 had developed gout. Five of the 9 adult 

 males with a normal serum uric acid level in the 

 previous study apparently developed hyperuri- 

 cemia in the interim. Eight of the 27 female 

 relatives with normal serum uric acid levels in the 

 previous study now had hyperuricemia and two 

 of these had gout. Hence gout developed in equal 

 numbers in these 35 male and 34 female relatives. 

 No significant differences existed between the two 

 sexes regarding the incidence and development 

 of hyperuricemia in the previous and the present 

 study. These apparent similar findings could be 

 explained by a significant difference in mean age 

 at the time of the first study, the male relatives 



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