The following lines are in Naunyn's1 textbook on diabetes:
Very interesting and instructive in its bearing on our conception of the hereditary transmission of the anlage is the fact that diabetes (in father and sons) can appear earlier in the sons than in the father. I have seen that once.... Quite similar cases are reported by Bence Jones,2 Grube,3 Niessen4 (1865-1897). Niessen saw a child of 13 years after scarlatina that followed a typhus develop... diabetes and die of it a year later. The father, a chemist, often examined his own urine but found it always sugar free until five years later, when suddenly the disease also appeared in him.... The second case of Niessen's is entirely similar.
Extending these earlier observations, Woodyatt5 has noted further that when diabetes occurs in three generations of a single family it may appear earlier in the second than
WOODYATT RT, SPETZ M. ANTICIPATION IN THE INHERITANCE OF DIABETES. JAMA. 1942;120(8):602–605. doi:10.1001/jama.1942.02830430024007