ATXN2 and obesity due to melanocortin 4 receptor deficiency: Consistent with this, abnormal fatty acid synthesis was observed in the liver of Atxn2 knockout mice and SC of ATXN2-CAG100 mice (47,48), cellular fat content was increased in Caenorhabditis elegans null for Atxn2 (49), and Atxn2 knockout mice develop obesity (44,50).