GSTM1 and glycogen storage disease VI: In patients aged 24-26 years old, the prevalence of Proliferative Sickle Retinopathy (PSR) was 43% in persons with Haemoglobin (Hb)SC disease and 14% in persons with homozygous sickle cell (Hb SS) disease in the Jamaica Sickle Cell Cohort Study [4].