918 form is soluble and cytoplasmic in mice6 and man H. 2 loci, Got-1 and Got-2 are postulated to be the structural deter- minants of the soluble and mitochondrial forms of GOT respectively. The 2 GOT isozymes are found with high activity in most tissues. In red blood cells, however, they are not expressed in mouse 6 and only the soluble form is observed in man 11. We observed relatively high GOT activity in liver, kidney, brain and heart and lower activity in spleen and lung in adults. In general, the enzyme activity per g of tissue was higher in adults as compared to new- borns and prenatals which follows earlier findings 6. Figure 2 also shows that the relative histochemical staining activity of the 2 isozymes is comparable throughout the develop- mental stages in +/+ individuals. Also, there are no genotype differences observed in the new-borns and adults. In 2- and 3-week-old mice, however, the isozyme patterns are indeed different in the 3 genotypes. In 2-week-old animals the mitochondrial form is absent in dyZJ/dy 2J and reduced (about 20% of the soluble form) in +/dy2Jgeno - type. Furthermore, in 3:week-old mice, the relative activity of the mitochondrial form is about 30% and nearly equal to the soluble form in dy25/dy25 and +/dy 2J genotypes respec- tively. The genotype differences observed in 2- and 3-week-old animals are of interest because the expression of ds;strophy is associated with age. The dy2J/dyRjgenotypes show the first sign of dystrophy around day 21. The absence of mitochondrial GOT in dystrophic genotype in 2-week-old mice only suggests that the Got-2 locus itself is not the primary defect of dystrophy. However, the temporal ex- pression of this locus is affected by the dy2J mutation, which could be involved in the expression of dystrophy. The expression of Got-2 locus follows cis rather than trans action of the involved regulatory mechanism. Here the mitochondrial GOT is affected in +/dy 2J and dy2J/dy2J genotypes during a critical period of development, just Experientia 38 (1982), Birkh~userVerlag, CH-4010 Basel/Switzerland prior to the expression of dystrophy in dy2J/dy2J animals. A number of genetic mechanisms are known to be involved in the processing of structural genes 12. One such mechanism involves temporal genes, that regulate the developmental programing and are responsible for the appearance and relative tissue distribution of an enzyme during develop- ment. These regulatory mechanisms themselves may depend on internal and/or external 'cue(s)' and are not expected to function in isolation. The observed GOT developmental pattern in dystrophy in this report suggests an association between genotype at the dy 2J lOCUSand the temporal regulator for the Got-2 locus. The dy 2J mutation may provide internal 'cue(s)' for the regulation of GOT and other enzymes that have been implicated to be involved in muscular dystrophy. 1 This research was supported by a Natural Science and En- gineering Research Council Canada grant to S.M.S. 2 C.M. Pearson, New Engl. J. Med. 256, 1065 (1957). 3 R.F. Shaw, C.M. Pearson, S.R. Chowdhury and F.E. Drei- fuss, Archs Neurol. 16, 115 (1967). 4 I. Matsuda, S. Miyoshino, T. Mijke, N. Nagata, H. Tamari, N. Taniguchi, H. Ohno and H. Watanabe, Clinica chim. Acta 83, 231 (1978). 5 H. Gutfreund, K.E. Ebner and L. Mendiola, Nature, Lond. 192, 820 (1961). 6 R.J. DeLorenzo and F.H. Ruddle, Biochem. Genet. 4, 259 (1970). 7 K.B. Augustinsson and K. Erne, Experientia 17, 396 (1961). 8 Y. Morino, H. Kagamiyama and H. Wada, J. biol. Chem. 239, 943 (1964). 9 R.L. Sidman, J.S. Cowan and E.M. Eieher, Ann. N.Y. Acad. Sci. 317, 497 (1979). 10 H. Harris and D.A. Hopkinson, The handbook of enzyme electrophoresis in human genetics. North-Holland, Amster- dam 1976. 11 H. Wada and Y. Morino, Vitams Horm. 22, 411 (1964). 12 K. Paigen, A. Rev. Genet. 13, 417 (1979). Mendelian recessive ratios in acute poststreptococcal glomerulonephritis 1 B. Rodriguez-Iturbe, H. Moreno-Fuenmayor, L. Rubio, R. Garcia and Z. Layrisse Hospital Universitario de Maracaibo and Instituto Venezolano de Investigaciones Cientlficas, Apartado Postal 1430, Maracaibo-Zulia 4001-A (Venezuela), 9 November 1981 Summary. A prospective study of 15 families (61 siblings) of index cases of acute poststreptococcal glomerulonephritis detected a proportion of 0.260 +_ 0.016 SEM. This is an excellent fit for a single autosomal recessive trait. Acute poststreptococcal glomerulonephritis (APSGN) is an immune complex disease that develops after streptococcal infection 2. It appears sporadically in most communities, but in some geographical areas it has an endemic incidence with epidemic outbreaks3-5. Familial aggregation of cases has been reported 6, but since there are no recognized markers for a disease that is transient in nature, the dif- ficulty of determining genetic patterns derives from at least 2 considerations; first, the occurrence of asymptomatic cases which are missed in any survey that does not con- template serial testing of the individuals during the period in which they are at risk, and second that, although some bacterial types have been associated with nephritis, the nephritogenicity (potential to cause nephritis) of a given streptococcus can only be established unquestionably a posteriori, because there is disagreement as to the nature of the relevant bacterial componentv-9. We have recently reported a prospective family study l~ that took into ac- count the considerations noted above and the present work concerns findings that suggest that susceptibility to develop nephritis may be a mendelian recessive trait. Patients and methods. In Maracaibo, APSGN presents endemo-epidemic characteristics 11. Since 1977 we have studied in a prospective manner 25 families of patients with clinical APSGN after the appearance of the 1st case (index case) in each family. The study protocol included serial weekly testing of all family members for a period of 4-6 weeks after the detection of the index case (period of close observation) and at least every 6 months after- wards (period of delayed observation). The only condition for selection of these families was the willingness to par- ticipate and compliance with the conditions of the study. Details of this work have appeared in a previous com- munication 10. On the assumption that only those individuals with a recent infection would be at risk of developing APSGN,