HPRT1 and hyperinsulinemic hypoglycemia, familial, 4: Therefore in an attempt to define some of the molecular and cellular basis of striatal defects in HPRT-deficiency, we have examined the expression of several striatally-enriched genes in HPRT-deficient mouse striatal STHdh cells, principally the transcription factor B-cell leukemia 11b (Bcl11b) (also known as Citp2).