From OMIM
Biotin-thiamine-responsive basal ganglia disease (BTBGD), also known metabolism dysfunction syndrome-2 (THMD2) or thiamine-responsive encephalopathy, is an autosomal recessive metabolic disorder characterized by episodic encephalopathy, often triggered by febrile illness, presenting as confusion, seizures, external ophthalmoplegia, dysphagia, and sometimes coma and death. Administration of high doses of biotin, and sometimes thiamine, during these crises results in partial or complete improvement within days. If untreated, encephalopathies can result in permanent dystonia. Brain imaging may show characteristic bilateral lesions of the basal ganglia. It is not known why biotin administration results in clinical improvement, as the molecular basis of the disorder is mutation in a gene encoding a thiamine transporter. However, biotin may increase the gene expression of SLC19A3 (summary by Debs et al., 2010). For a discussion of genetic heterogeneity of disorders due to thiamine metabolism dysfunction, see THMD1 (249270).  http://www.omim.org/entry/607483

From MedlinePlus Genetics
Biotin-thiamine-responsive basal ganglia disease is a disorder that affects the nervous system, including a group of structures in the brain called the basal ganglia, which help control movement. As its name suggests, the condition may improve if the vitamins biotin and thiamine are given as treatment. Without early and lifelong vitamin treatment, people with biotin-thiamine-responsive basal ganglia disease experience a variety of neurological problems that gradually get worse. The occurrence of specific neurological problems and their severity vary even among affected individuals within the same family.

The signs and symptoms of biotin-thiamine-responsive basal ganglia disease usually begin between the ages of 3 and 10, but the disorder can appear at any age. Many of the neurological problems that can occur in biotin-thiamine-responsive basal ganglia disease affect movement, and can include involuntary tensing of various muscles (dystonia), muscle rigidity, muscle weakness on one or both sides of the body (hemiparesis or quadriparesis), problems coordinating movements (ataxia), and exaggerated reflexes (hyperreflexia). Movement problems can also affect the face, and may include the inability to move facial muscles due to facial nerve paralysis (supranuclear facial palsy), paralysis of the eye muscles (external ophthalmoplegia), difficulty chewing or swallowing (dysphagia), and slurred speech. Affected individuals may also experience confusion, loss of previously learned skills, intellectual disability, and seizures. Severe cases may result in coma and become life-threatening.

Typically, the neurological symptoms occur as increasingly severe episodes, which may be triggered by fever, injury, or other stresses on the body. Less commonly, the signs and symptoms persist at the same level or slowly increase in severity over time rather than occurring as episodes that come and go. In these individuals, the neurological problems are usually limited to dystonia, seizure disorders, and delay in the development of mental and motor skills (psychomotor delay).  https://medlineplus.gov/genetics/condition/biotin-thiamine-responsive-basal-ganglia-disease