Observations of Fetal Posture and Causal Mechanisms of Congenital Deformity of Palate, Mandible, and Limbs

¹ 137 Cambridge Terrace, Christchurch 1, New Zealand

Animal experiments that were developed to produce 100 per cent cleft palate by puncture of the amniotic sac prior to palate closure produced fetal phenocopies of the human Piérre Robin syndrome. The causal mechanism involved in the production of cleft palate appeared to be a mechanical change in fetal posture resulting in craniocaudal compression of the fetal body. Limitation of movement of the embryo by the contracted amnion reduced extension of the cephalic flexure. Severe chin-sternum compression maintained the tongue between tha palatal shelves and upset the delicately integrated mechanism of palate closure. Micrognathia resulted from postural molding, and there was subsequent delay in ossification of the body of the mandible. Growth of the mandibular condyle was not affected. The mechanism was capable of spontaneous reversal, with restoration of movement to the fetus. The timing of the return to normal amniotic dynamics decided the variations in the degree of cleft palate, micrognathia, and glossoptosis found at full term.

Deformities of the limbs, ranging from talipes and ring constrictions to intrauterine amputations and phocomelia, were found associated with the Piérre Robin syndrome phenocopies. Ring constrictions were produced by amniotic bands, talipes resulted from postural molding, and intrauterine amputations arose as a result of focal fetal pressure necrosis followed by re-epithelization of the integument. Developmental arrest as a result of defective germ plasm was discounted as a cause of the limb malformations, because the limb buds had reached the stage of complete differentiation into segments and digits prior to the onset of the causal mechanism. Clinical reviews of the Piérre Robin syndrome in human beings report the strong association between this condition and limb malformations similar to those described in these animal experiments.

Acceptance of fetal postural molding (resulting from a change in the amnion-embryo relationship) as a causal mechanism of malformation of the palate, mandible, tongue, and limbs in human beings does not involve abnegation of the role of genetic disturbances in the etiology of these deformities. The amnion-embryo relationship is determined genetically at conception, and both faulty genes and an unfavorable fetal environment may interact to produce the environmental mechanical factors that are involved in the establishment of deformity by this particular causal mechanism.