Twin Data on the Genetics of Ageing 135 



Virtually nothing is known about the gene-specific metabolic 

 disturbances that may be at the root of these two types of 

 early brain atrophy. Conjecturally it may be stated that the 

 given disturbances are likely to differ as much in character as 

 do the structural changes produced by them. It is regrettable 

 that our search for verified twin cases of either type has not 

 been successful, but it may be useful here to describe some of 

 the histopathological differences observed between the two 

 conditions. 



In Alzheimer's disease (Fig. 1), the atrophy of the brain, 

 although most pronounced in the temporal and frontal lobes, 

 is rather generalized. On the whole, the narrowing of the 

 gyri and the widening of the sulci are more severe than the 

 common atrophic changes associated with the senium. 

 Microscopically, there are early and marked degenerative 

 changes, and the cytoarchitecture is so disorganized that some 

 areas are entirely lacking in nerve cells. 



Application of the silver impregnation method discloses an 

 abundance of senile plaques, and typical neurofibrillary 

 degeneration is seen in the greatly magnified cell inserted 

 (Fig. 2). Parenthetically it may be noted that these degenera- 

 tive changes are not argentophilic. 



Compared with the atrophic changes observed in Alz- 

 heimer's disease, the atrophy of the brain in Pick's disease 

 (Fig. 3) is more circumscribed and usually most severe in the 

 frontal lobes. The postcentral and parietal regions tend to be 

 better preserved. Microscopically, the cytoarchitecture of the 

 frontal lobe may show complete disorganization (Fig. 4). In 

 this instance, there are scarcely any nerve cells left, and 

 certainly fewer than in Alzheimer's disease. 



Using Holzer's method for glia fibres (Fig. 5), one finds a 

 marked cortical gliosis, a symptom which distinguishes 

 Pick's from Alzheimer's disease. Greatly magnified, a typical 

 cell described by Pick (Fig. 6) is characterized by an eccentric 

 nucleus and a ballooned appearance of the cellular body. 



Within the cell body (Fig. 7), one sees a massive accumula- 

 tion of lipid material which is highly argentophil in character. 



