Discordant Growth Pattern and Ovarian Function in Monozygotic Twins with 45,X/46,XX Mosaicism

BACKGROUND: We report on phenotypically discordant female monozygotic twins with 45X/46,XX mosaicism in both lymphocytes and fibroblasts. RESULTS: At 11.5 years, twin A was prepubertal, her height was 126.8 cm (-3.15 SD), bone age (BA) 9.7 years (TW2), FSH 47 IU/l and IGF-I 280 ng/ml (-0.89 SD), but twin B was pubertal (P2, B3), her height was 143.4 cm (-0.92 SD), BA 13.6 years (TW2), FSH 3.4 IU/l and IGF-I 380 ng/ml (-0.21 SD). One year later, twin A had grown 11.1 cm due to growth hormone therapy and had IGF-I 1,400 ng/ml (+5.91 SD), whereas the growth velocity of twin B (no therapy) was 5.9 cm, IGF-I 540 ng/ml (+0.57 SD) and she started regular menstruation at 12.1 years. CONCLUSION: To our knowledge, this is the first report on monozygotic twins with Turner mosaicism in both lymphocytes and fibroblasts who developed a discordant phenotype probably due to an unequal distribution of the two cell lines in distinct tissues.