Some genes are selectively important in specific neuronal populations, as exemplified by leukoencephalopathy with brainstem and spinal cord involvement (LBSL) due to mutations in the mitochondrial aspartyl-tRNA synthetase 2 (DARS2), or pontocerebellar hypoplasia caused by argynyl tRNA synthetase 2 (RARS2) defect (Scheper et al., 2007; Edvardson et al., 2007). The gene discussed is DARS2; the disease is Leukoencephalopathy.