ORTHODACTYLY 



1-'ki:dekick X. Uixcax 

 Professor oj Biology, Sovthcrn Methodist University, Dallas, Tex. 



IX 19C1 G. Walker described a family 

 marked by inherited stiffness of 

 finj^er joints, and in 1915 Harvey 

 Gushing comjjiled the j^cnealoj^y . throujj;h 

 seven j^enerations, of another such family 

 comprisin<,' 452 individuals. ' These were 

 all descendants of one William B., who 

 had come U) \'ir<.^inia from Scotland 

 about 1700. 



I have recently found a family which 

 shows the same peculiarity. It is not 

 included in Cushing's chart, but prob- 

 ably derives the trait from the same 

 source, since family tradition traces it to 

 ancestors in Scotland. 



It is not the purpose of this i:>aper to 

 give the anatomy of the stiff joints, but 

 only to jjoint out their inheritance. 

 The joints affected are the second ones 

 of the fingers and frequently the corre- 

 sponding ones of the toes. The joints 

 are absolutely rigid. That the bones 

 are not always fused is evidenced by the 

 fact that one case is known where the 

 joint was accidentally disjointed. The 

 abnormality may occur in two, three or 

 four of the fingers. 



This trait behaves as a Mendelian 

 dominant. Whenever the trait does 

 not occur in an individual that person 

 is unable to transmit it, that is, the 

 normal hand is recessive to this trait 

 and cannot transmit it. 



Inspection of the chart shows the 

 f(jllowing facts. If we discard the D 

 generation where the size of the famil\' 

 is small and consider only the B and C 

 generations, we find that the number of 

 affected individuals is eleven and the 

 numVjer of normal is four. 



As only ])art of generation B shows the 

 trait, it evidently was not homozygous 

 in generation A. Further, as it a])]jears 

 to be a dominant trait, it could not 

 ha\'e been carried by the mother in 

 generation A, since she would have 

 shown it if she had it. This leaves only 

 one possible type of mating to fit the 

 fact — a mating of heterozygous domi- 

 nant with homozygous recessive. From 

 such a mating it would be exjjectcd 

 that affected and normal offsjjring 

 would be produced in equal numbers, 

 or 7.5 :7.5, whereas the figures actually 

 found are 11 : 4. This is very poor 

 agreement, although not impossible 

 when the nim:ibers in\'olved are so small. 



Gushing charts 150 children from 

 such matings, of whom 78, or 52%, 

 were affected. This is so near the 

 expected 50% as to make it practically 

 certain that the abnormality is due to a 

 single Mendelian factor. 



Recent work of Gushing, Marie and 

 others makes it seem probable that the 

 trait here studied is related to some 

 l^renatal interference with the normal 

 function of the jjituitary body. Its 

 a]Ji>arent relation with brachydactyly, 

 a well-established Mendelian character, 

 is evident. 



Gushing has called this trait s\-m- 

 l^halangism, a good descriptive term. 

 Before I knew of his work I called the 

 trait orthodactyly, or straight linger. 

 As this trait is so similar in character 

 and inheritance to other digital abnor-' 

 malities it seems that it would be better 

 to give it a similar name; however, the 

 name is of little con^eriuence. 



' CushiriK, Harvey. Heredity anchylo.sis of the jmiximal jjliahmgeal jnints (.symi)halanRisni'l. 

 Genetics, i, pp. ^0-106, January, 1916, 



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