CXVI1I BOWMAN LECTURE. 



25 years between 14 and 39 in 26 cases, in the critical 

 years between 40 and 50 in only 10 cases. 



We commonly notice that the age of onset is almost 

 the same for all cases in the same genealogy all very 

 early in one, all unusually late in another. But marked 

 exceptions are seen, as in a case (Fig 103) where one of 

 two brothers lost his sight at 21, the other not until 60. 

 The latter was diabetic at about the same period, and one 

 cannot help suspecting that had he not been so he might 

 have escaped the disease of his optic nerves. 



Consanguinity of parents is seldom met with ; I find 

 at present only 6 or possibly 8 cases. In Arnold Knapp's 

 case, given fully below, a woman with Leber's disease 

 (Fig. 50 ; III, 3), whose father was also affected, married 

 her normal first cousin, the son of a normal brother 

 of the affected father. In Gunn's case*" a woman with 

 the optic nerve disease from childhood married her healthy 

 first cousin and has so far two children, female and male, 

 both affected at 3 or 4 years of age. 



1904. (Fig. 50.) Knapp (Arnold), A. of 0., xxxiii, 

 p. 383 (1904, and further information, March, 1909). 



I, 1 and 2 normal. If, 1 failed at 24, recovered 

 slowly enough to read, is now 67 (1904) j had 2 brothers 

 and 3 sisters, 1 of whom died at 17, 1 at 30, 1 at 67 

 and 2 still living ; none affected. Ill, 1 to 4 all failed 

 during their early school years. I, 1 has 2 sons, normal 

 (1909). Ill, 2 lately married (1909). Ill, 4 married, no 

 issue (1909). Ill, 3 married son of her father's brother; 

 6 children, of whom IV, 2, 4 and 5 all failed at early 

 school age. IV, 3 and 6 remain normal, ages 15 and 9 in 

 1909. IV, 7 died at 4, with good sight. 



This scarcity of consanguineous parentage in the history 

 of Leber's disease is what we expect in a sex-limited affec- 

 tion. In such a disease, as already shown (Figs. 1 to 5), 

 when two unaffected cousins marry only one, the wife, can 

 possibly carry the disease, since the husband will so far as 

 we know always show it at the proper age if he contains 

 * Fig. 46, Appendix VI, a. 



