From OMIM
Leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation (LBSL) is defined on the basis of a highly characteristic constellation of abnormalities observed by magnetic resonance imaging and spectroscopy (Scheper et al., 2007). Affected individuals develop slowly progressive cerebellar ataxia, spasticity, and dorsal column dysfunction, sometimes with a mild cognitive deficit or decline.  http://www.omim.org/entry/611105

From MedlinePlus Genetics
Leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation (commonly referred to as LBSL) is a progressive disorder that affects the brain and spinal cord. Leukoencephalopathy refers to abnormalities in the white matter of the brain, which is tissue containing nerve cell fibers (axons) that transmit nerve impulses.

Most affected individuals begin to develop movement problems during childhood or adolescence. However, in some individuals, these problems do not develop until adulthood. People with LBSL have abnormal muscle stiffness (spasticity) and difficulty with coordinating movements (ataxia). In addition, affected individuals lose the ability to sense the position of their limbs or vibrations with their limbs. These movement and sensation problems affect the legs more than the arms, making walking difficult. Most affected individuals eventually require wheelchair assistance, sometimes as early as their teens, although the age varies.

People with LBSL can have other signs and symptoms of the condition. Some affected individuals develop recurrent seizures (epilepsy), speech difficulties (dysarthria), learning problems, or mild deterioration of mental functioning. Some people with this disorder are particularly vulnerable to severe complications following minor head trauma, which may trigger a loss of consciousness, other reversible neurological problems, or fever.

Distinct changes in the brains of people with LBSL can be seen using magnetic resonance imaging (MRI). These characteristic abnormalities typically involve particular parts of the white matter of the brain and specific regions (called tracts) within the brainstem and spinal cord, especially the pyramidal tract and the dorsal column. In addition, most affected individuals have a high level of a substance called lactate in the white matter of the brain, which is identified using another test called magnetic resonance spectroscopy (MRS).  https://medlineplus.gov/genetics/condition/leukoencephalopathy-with-brainstem-and-spinal-cord-involvement-and-lactate-elevation