Text Box: COMPARISON OF FINAL HEGHT BETWEEN A PAIR OF MONOZYGOTIC TWINS: ONE WITH SEVERE GROWTH HORMONE (GH) DEFICIENCY TREATED WITH LOW DOSE OF GH Sato H1, Miyamoto S1, Sasaki N2 1Division of Endocrinology, Chiba Children¡¯s Hospital, Chiba, Japan 2Department of Pediatrics, Saitama Medical School, Saitama, Japan Objective: The impact of growth hormone (GH) dose on the achievement of genetic height potential in patients with idiopathic GH deficiency remains unclear. We report final heights of a pair of monozygotic twins, in which one is a patient with isolated and severe GH deficiency (twin A) treated with low dose of GH, whereas the other (twin B) is healthy. Methods: Twin A with short stature (-3.3 SD) was diagnosed as severe GH deficiency at 4.9 years of age. At the same time, twin B was normal in height (+0 SD). Twin A¡¯s GH treatment was started at the age 5 years and the average dose of GH was 0.35 U (0.112 mg) /kg/week during the treatment period. Results: Twin A achieved his final height of 165.1 cm (-0.9 SD) compared to that of 166.5 cm in twin B (-0.7 SD) at 17.3 years of age. Conclusions: Correlation coefficient for adult height was reported to be markedly high in monozygote twins. Our result indicates that a relatively low dose of GH treatment started at early age may preserve near genetic height potential in severe GH deficiency. 2499