39 These data also mavbe useful as a baseline, should genetic changes appear in later generations, possibly related to radiation exposure. IV. Thyroid Findings A. EARLY FINDINGS Examinationsfor possible thyroid abnormalities were an importantpart of the program from the be- ginning. At the time of the accident it was not considered likely that the thyroid had received a sufficient dose of radioiodine to result in abnormalities. In retrospect this proved to be quite wrong, since thyroid injury and its sequelae have been the mostserious late result of the fallout ex- posure in the Marshallese people. A chronological review of events leading to the development of thyroid abnormalities follows. Beginning several vears after exposure it was noted that 5 of 19 children exposed at <10 years of age showedretardation of growth.8.16 This was particularly notable in the boys exposed at <5 years of age (Figure 26). The cause ofthis retardation was not immediately apparent. It was recog- nized that thyroid hormonedeficiency from thyroid injury could result in such growth retardation. However, examinations duringthis early period did Figure 27. Growth-retarded boys exposed at age | year (No. 3, left, and No. 5), 6 months after start of treatment at age 11 (1966). not reveal any thyroid abnormalities, and the PBI levels in these children as well asin all Marshallese were in the normalto high rapge. The growthretardation gradually became bre apparent, and at 180-— TT 8— OS Tey o wa T Height (cm) 165 bh Figure 26. Starural growth in Rongelap boys exposed at <5 years of age, 1958-1967. Figure 28. Bone dysgenesis of heads of humeri in subject No. 5, typical of hypothyroid disease (1965).