GSTM1 and alpha thalassemia spectrum: Examples of further clinical testing include (1) purines and pyrimidines for beta-ureidopropionase deficiency (U023), (2) X-inactivation studies and transferrin electrophoresis for X-linked congenital disorder of glycosylation type II (U033), and (3) Hb H inclusion bodies for alpha-thalassemia/mental retardation syndrome (U003).