43 | I 14 [ 414 Lei a2 10 [- 71.0 Oo a 8]ee wm “oO 4.8 }_ —_ —— L 7 4b 44 ae 0 a : 1 10 | 5 1 20 4.2 | 2.5 oO mg BAIB LOG mg GREATININE Figure 47. Urinary BAIB excretion (mg-f-amino-ise-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 BAIB in man **:*4 and excreted in urine, since no rik people 83% were high excretors, whichis not significantly different from the Rongelap group appreciable tubular reabsorption of BAIB occurs.** It is unlikely that the high incidence of high BAIB excretors found in Rongelapis due to radiation. The identical average BAIB valuesin the exposed and unexposed groups preclude the possibility that the elevation is due to the fallout exposure 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®* body burdens cluded in the Rongelap sample (i.e., father, retained internal radiation. The nearly identical Cs**’ levels and BAIB levels shows nocorrelation (Figure 47), and neither does a similar plot between Zn* levels and BAIB tevels. The mean BAIB excretion level for 18 Micronesians, who were on Utirik at the time of the atomic explosion andtherefore not exposed to significant radiation, was 2.21 +0.13, which is extremely close to the mean value for the Rongelapese. Amongthe Uti- percentage. A number of complete families are in- mother and at least one child); of these the high- excretor 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 other re- mains as an unexplained exception to genetic hypothesis. Rubiniet al.** have recently demonstrated that BAIB excretion can be a sensitive indicator of radiation exposure. The mechanism involvedis > ro oc o Cit probably the same as that underlyingtheeffect of nitrogen mustard on BAIB excretion.** Such agents markedly increase DNA breakdown; the thymine thusreleased is effectively converted to rules against the elevation being due to the present values in the Utirik group who received a very small dose of radiation, and who have muchlower _ body burdensof radionuclides, is also consistent with the thesis that a high incidence of the gene underlying 6-amino-iso-butyric aciduria is responsible for the observed BAIB excretion rate. The expression of the normal genetic difference is 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