GSTM1 and Schnyder corneal dystrophy: A study of 9 identical twins and 350 age-gender-matched sibling pairs in Jamaica found no significant differences among identical twins with SCD regarding attained height for age, weight for height, HbF levels, total Hb, mean cell volume, mean cell hemoglobin and total bilirubin levels, occurrence and grade of splenomegaly, susceptibility to priapism, and age at menarche.