37 children born to an exposed parent or parents have shown, on the basis of incidence of gross anomalies. no evidence of inherited radiationinduced mutations. The principal aberrations noted in Marshallese adults and children have been bilateral shortening of the fifth finger, prominent head ofulna, dislocated wrist, enlarged cornea, tortuosity of retinal vessels, asymmetryof face, congenital nystagmus, and pigmentationof the cornea. Studies of familia! patterns of such defects have not been done; they are not related to exposure. The possible increase in miscarriages andstillbirths among the exposed women duringthe first 5 years maylead to speculations that radiation in- duced lethal mutations in germ cells of the ovary or, less likely, in sperm cells.* The presence of chromosomeaberrations in peripheral blood lymphocytes in the Marshallese 10 years post exposure, and the possible somatic mutation in the hemoglobin, described above, support speculations that mutations in the germ plasm occurred and might be detected in the offspring by moresensitive tests. However, in view of the relatively small dose of radiation and the small size of the popula- uon, on a priort grounds a clear-cut demonstration of a genetic effect of radiation in the children born to exposed parents would seem unlikely. Nevertheless, given the nature of the circumstances, it has been deemed desirable to make every effort to collect such data. Since recessive combinations * About one-half the miscarriages occurred in exposed women married to unexposed men. may take several generationsto affect the pheno- type, recognition of their radiation etiology may be extremelydifficult. Neel et al. are at present carrying out more sophisticated studies in the Jap- anese, concerned with the occurrence of variant forms of 24 serum proteins and erythrocyte enzymes. He and Dr. R.E. Ferrell kindly consented to examine blood samples collected in 1974 from 187 Marshallese children and parents (exposed and unexposed). The results, summarized below, included nosignificant findings indicating radiation-induced mutations. b. The Frequency of “Rare’’ Protein Variants. The blood samples mentioned above were subjected to electrophoretic analyses for polymorphisms andrare variants of proteins and erythrocyte enzymes.®* The findings were summarized by Neelet al.8? as follows. ‘*Blood specimens from a sample of 187 Marshall Islanders were studied with reference to variants of 24 serum proteins and erythrocyte enzymes. Six of the traits studied exhibited genetic polymorphisms (adenosine deaminase, phosphogtucomutase;, acid phosphatase, 6-phosphogluconate dehydrogenase, haptoglobin, group specific component). There was in addition one‘rare’ variant (of albumin) in 4047 determinations. These results on rare variants have been combinedwith those of others on Micronesians, and the frequeney of rare variants in Micronesians comparedwiththefrequencies in West European Caucasians, Japanese, and Amerindians. There are manydifficulties in such comparisons, and, although the observed val- ues for the four ethnic groups differ by a factor of iw a . . ~ Table 22 Gene Frequenciesfor Six Genetic Polymorphisms in the Marshall Islands®” oe System Adenosine deaminase Groupspecific component Haptoglobin* Phosphoglucomutase, ** . | aaa : Acid phosphatase 6-Phosphogluconate dehydrogenase - 1 167 * 116 56 156 AL 101 164 Phenotype “ws 2-1 2 50 93 26 2 32 1 AB B 18 73 21 0 1H 0 Total “185 168 177 184. = Lom, ta 185 _ Genefrequency ADA! = 0951 Ge! = 0.839 Hp! = 0.579 PGM;! = 0.912 | APA = 0.743 6-PGDA = 0.943 *The Hp® tvpe was observedin 4 individuals. **Two examples of the PGM phenotype 2-7 and a single phenotype 1-7 were observed (PGM,7 =0.008).