43 | 414 2b \ 10l- 410 | a] 4 8/- 18 BL wn « ° BF = a > ae . 2 ze 5 44 : bar 0 i 46 | L LL 20 15 LO ° . \ } Jig 25 mg BAIB LOG TF CREATININE Figure 47. Urinary BAIB excretion (mg-8-amino-iso-butyric acid per mg creatinine) versus body load of Cs'** (uC), Rongelap inhabitants, 1959. 0.06; unexposed, 2.10-0.04). A scatter plot of Cs'** levels and BAIB levels shows no correlation (Figure 47), and neither does a similar plot between Zn" levels and BAIB levels. The mean BAIB excretion level for 18 Micronesians, who were on Utirik at the time of the atomic explosion and therefore not exposed to significant radiation, was 2,21 +0.1£3, which is extremely close to the mean value for the Rongelapese. Amongthe Utirik people 83% were high excretors, which is not significantly different from the Rongelap group percentage. A numberof complete families are included in the Rongelap sample (i.e., father, mother and at least one child); of these the highexcretor by high-excretor matings are the only ones providing significant genetic information. There were 11 such matings with a total of 31 offspring (29 high excretors and 2 low excretors). One of the low excretor offspring wasillegitimate,as determined by blood group data, but the otherremains as an unexplained exception to genetic hypothesis. Rubiniet al.?* have recently demonstrated that BAIB excretion can be sensitive indicator of radiation exposure. The mechanism involvedis probably the sameas that underlying the effect of nitrogen mustard on BAIB excretion.**? Such agents markedly increase DNA breakdown; the thyminethusreleased is effectively converted to BAIB in man **** and excreted in urine, since no appreciable tubular reabsorption of BAIB oc- curs.”* It is unlikely that the high incidence of high BAIB excretors found in Rongelap ts due to radiation. The. identical average BAIB valuesin the exposed and unexposed groups preclude the possibility that the elevation is due to the fallout ex- posure in 1954, and it appears that radiation exposure (at the levels received at Rongelap) has no long-term effect on BAIB excretion. The lack of correlation with the Cs'*’ and Zn* bodv burdens rules against the elevation beingdueto the present retained internal radiation. The nearly identical values in the Utirik group whoreceived a verv small dose of radiation, and who have much lower body burdensof radionuclides, is also consistent with the thesis that a high incidenceof the gene underlying B-amino-zse-butyric aciduria is responsible for the observed BAIB excretion rate. The expression of the normal genetic difference 1s probably dueto differential metabolism of BAIB by high and low excretors.** The level of BAIB excretion among the Marshallese is the highest yet reported for any population. Blood group*® and other anthropological data on these people suggest a Southeast Asiatic origin; if this is true, a high BAIB level can be predicted for the populations of that region. Studies of some Asiatic populations have given