Teratogenesis 



705 



a riboflavin deficiency caused micromelia. 

 Essentially similar abnormalities were pro- 

 duced by biotin deficiencies by Couch et al. 

 ('48). These were eliminated by injections of 

 biotin into the deficient eggs. Essentially the 

 same syndrome has been produced by sulfa- 

 nilamide and eserine sulfate (Ancel, '45a), 

 by insulin (Landauer, '47a), thallium (Kar- 

 nofsky, Ridgeway and Patterson, '50), boric 

 acid (Landauer, '52) and pilocarpine (Lan- 

 dauer, '53). With all of these substances, in- 

 jected at the proper time, both the extremi- 

 ties and the head are affected and the limbs 

 of both sides are involved symmetrically 

 (there are frequently other associated anoma- 

 lies but these will not be discussed here) . Usu- 

 ally the most severe cases of micromelia are 

 found in embryos which are quite dwarfed. 



Even though a similar syndrome is pro- 

 dviced by all of these treatments a number 

 of significant facts are revealed by a close 

 inspection of the data. The critical period is 

 different for different substances. Insulin 

 must be injected at 120 hours (Landauer, 

 '47a), sulfanilamide at 48 hours (Zwilling 

 and DeBell, '50) and boric acid at 96 hours 

 (Landauer, '52) for maximum incidence and 

 severity of micromelia. This does not neces- 

 sarily mean that sulfanilamide and boric 

 acid are inactive until a later stage. Rather 

 the evidence points to their continued activ- 

 ity over a period of time which, for maxi- 

 mum effect, mvist inckide the earlier stages. 



While the micromelias produced by the 

 various substances are superficially similar, 

 a detailed analysis reveals that there are 

 differences in detail. With insulin (Land- 

 auer, '54) and sulfanilamide (Zwilling and 

 DeBell, '50) all of the long bones of the leg 

 are shortened and the tibiotarsus shows the 

 greatest relative reduction. With boric acid 

 (Landauer, '52) and pilocarpine (Landauer, 

 "54) the femur and tibia are rf>lativelv nor- 

 mal but the tarsometatarsvis is greatly re- 

 duced. There are, in addition, differences in 

 digital involvement; insulin and sulfanil- 

 amide cause little or no toe reduction while 

 boric acid does result in shortening or ab- 

 sence of the toes. Although differences in 

 incidence may result from injecting these 

 substances at times other than the optimum, 

 the morphological details remain constant for 

 a given chemical. 



The various dietary deficiencies which re- 

 sidt in micromelia involve substances (bi- 

 otin, riboflavin) which are generally accepted 

 as components of co-enzymes involved in car- 

 bohydrate cycles. It is thus of extreme im- 

 portance that carbohydrates are involved in 



some way in the action of most of the mi- 

 cromelia-inducing chemicals (thallium is ex- 

 ceptional). The teratogenic effects of insulin 

 may be almost completely eliminated by 

 simviltaneous injections of nicotinamide 

 (Landauer, '48a). In addition, insulin pro- 

 duces hypoglycemia (Zwilling, '48, '51) and 

 other pronounced carbohydrate disturbances. 

 Both severity and incidence of hypoglycemia 

 correlate well with the degree and incidence 

 of micromelia. In like manner the teratogenic 

 effects of sidfanilamide (Zwilling and De- 

 Bell, '50), of eserine sulfate (Landauer, '49) 

 and of pilocarpine (Landauer, '53) may be 

 more or less completely mitigated by injec- 

 tions of nicotinamide (which is a component 

 of co-enzyme I). The effects of boric acid 

 (Landauer, '52) are most convincingly re- 

 lated to its capacity to complex with ribo- 

 flavin and render the latter metabolically 

 inactive. Nicotinamide is not effective in 

 alleviating boric acid defects. This last point 

 is of great significance, since it might be con- 

 sidered that nicotinamide merely provides an 

 alternate source of energy which may be 

 used to overcome general depressing effects 

 of the chemicals. That it does not do so with 

 boric acid points to a more specific action of 

 the chemicals on one or another link in the 

 carbohydrate chain. It is of great importance 

 that these diverse chemicals have been shown 

 to have some relation to carbohydrate metab- 

 olism. This provides the first basis for the 

 elimination of some of the vagueness in pre- 

 vious discussions of etiology of anomalies. 

 The fact that different substances differ in 

 the details of their effects points to rather 

 subtle and specific metabolic requirements of 

 the components of the limb rudiments. 



This material also allows us to evaluate 

 the importance of lowered developmental 

 rate as a prime factor in teratogenesis. At 

 least two substances [adrenal cortical ex- 

 tracts (Landauer, '47b; Karnofsky, Ridgeway 

 and Patterson, '51) and para-aminobenzoic 

 acid (Zwilling and DeBell, '50)] cause 

 dwarfing of chick embryos after injection at 

 5 days. The size reduction is perfectly pro- 

 portionate, with no special effects on th^ 

 limbs; it is of the same order of magnitude 

 as that produced by sulfanilamide and in- 

 sulin and occurs over the same period of 

 time. Moreover, there is no mitigation of the 

 dwarfing when the micromelia produced by 

 sidfanilamide and insidin is eliminated by 

 nicotinamide therapy. These facts indicate 

 that a substance may produce quite general 

 effects (i.e., retardation) as well as specific 

 effects but that the latter need not be causally 



