TUBB1 and Impaired glucose tolerance: Ab had impaired glucose tolerance and low expression of several blood glucose transporters; failed to express three genes in the homocystinuria type Cb1C pathway, which may explain her abnormally low glutathione and cysteine-glutathione levels; and showed up-regulation of TUBB1, consistent with high platelet counts because loss of function of the gene is reported to lead to thrombocytopenia.