HEREDITARY DEFORMING CHONDRODYSPLASIA 297 



All the long bones are not equally affected by this retardation, the ulna 

 is shortened relatively more than the radius, and the fibula more than the 

 tibia. In the forearm this has peculiar results. As long as the upper and 

 lower radio-ulnar ligaments hold, the radius equalizes its increasing length 

 by bowing outward. If the upper ligaments of the radius break loose under 

 the growing strain, a dislocation of the upper end of the radius results. If 

 the lower end gives way, the hand is deflected to the ulnar side. 



The relative shortening of the fibula may cause a valgus of the foot, which 

 gives rise to disability in walking. If the legs retard unequally, there is a 

 secondary scoliosis. Asymetrical growth distortion at the knees may give 

 rise to genu valgus or knock-knee. The phalanges of the fingers and toes 

 may be short, deformed or deflected. 



The bony overgrowth and irregularity is much more frequent at those 

 ends of the long bones where growth in length chiefly occurs, thus at upper 

 end of humerus and lower end of radius and ulna, and at the knee end of 

 femur and tibia. At these points the centre of ossification appears earlier 

 in the epiphysis and the epiphysis unites later. 



Sharp bony excrescences, — exostoses, — appear so frequently as to be 

 characteristic of the disease. Sometimes these give trouble by pressure on 

 nerves or blood vessels; by fracture; by developing bursae, which inflame; 

 by obstructing the birth canal; or rarely, through proliferation of their 

 cartilaginous elements, they develop a fatal malignancy. 



Of immediate interest is the consideration of the transmission of this 

 disease by heredity. And here I will make free use of the statistical study 

 of Stocks. 



In 1,172 cases (excluding all cases with associated enchondroma) Stocks 

 found 765 (or 65.3 per cent) that gave definite evidence of the same dis- 

 order in relatives or antecedents. In 32 per cent the family history was 

 found indefinitely positive, or was not mentioned. In 3 per cent the family 

 history was reported negative. 



In considering these figures, it must be borne in mind that many of the 

 case-reports date back to the days before the diagnostic use of the x-ray, 

 and before heredity was considered seriously as a factor in the disease. Also 

 it must be reckoned that many patients have limited knowledge of their 

 relatives and forebears, and some have a disinclination to give data which 

 they may possess. And the 3 per cent of cases that give a negative family 

 history might yield pertinent data on more persistent inquiry. 



Of 758 cases giving their nearest relative affected, 60.3 per cent inherited 

 directly from a parent, — 43.5 per cent from the father and 16 per cent from 

 the mother. It is interesting to note that 73.7 per cent of the males in this 



