After the age of 3 years drawings are very useful, indicating a defect in visual motor integration. The cerebellum, hypothalamus, visual system, and hippocampus are relatively spared. Studies of human cretin brains by modern techniques are badly needed. The frequency of goiter and thyroid dysfunction in these defectives is similar to the ones observed in the general population. Cortical and striatal neuron proliferation, migration, and early formation of neuropil occur between 12 and 18 weeks.
Cochlear development occurs at the same time.
These data correlate well with the data from the Papua New Guinea trial which indicated that iodine repletion must occur by three months of pregnancy to prevent cretinism 44 . Studies already cited above on the effect of iodine deficiency on brain cell development in the newborn rat, sheep and marmoset suggest that iodine deficiency has an early effect on neuroblast multiplication. Brain weight is reduced with a reduced number of cells as indicated by lowered DNA, a greater density of cells in the cerebral cortex and reduced cell acquisition in the cerebellum 136 . Recently it was found that an autosomal recessive predisposition, besides maternal iodine deficiency, may play an etiological role in neurological cretinism 137 . Administration of PTU to pregnant mice also causes abnormalities in their pups in the tectorial membrane of the organ of Corti and results in deafness 138 .