TUBB4A and Leukoencephalopathy: This approach has described several new diseases, including “hypomyelination with brain stem and spinal cord involvement and leg spasticity”, due to autosomal recessive mutations in the aspartyl-tRNA synthetase gene DARS [51], and “leukoencephalopathy hypomyelination with atrophy of the basal ganglia and cerebellum” due to de novo mutation in the gene TUBB4A [50].