Vitamin A

• Vitamin A deficiency: Can cause vision problems, including night blindness and xerophthalmia. 
• Vitamin A toxicity: Can lead to headaches, dizziness, nausea, and increased intracranial pressure.

Vitamin B Complex

Vitamin B1 (Thiamine)

• Wernicke encephalopathy: Often seen in malnourished children or those with prolonged parenteral nutrition without supplementation.
• Beriberi: Neurological symptoms include peripheral neuropathy and developmental regression.

Vitamin B2 (Riboflavin)

• Riboflavin transporter deficiency (RTD): Associated with Brown-Vialetto-Van Laere syndrome, characterized by motor neuronopathy, sensory ataxia, and cranial neuropathy.

Vitamin B3 (Niacin)

• Pellagra: Can present with the "three Ds" — dermatitis, diarrhea, and dementia. Neurological symptoms include irritability, ataxia, and seizures.

Vitamin B5 (Pantothenic Acid)

• Pantothenate kinase-associated neurodegeneration (PKAN): A subset may benefit from pantothenic acid supplementation.

Vitamin B6 (Pyridoxine)

• Pyridoxine-dependent epilepsy (PDE): Presents as intractable neonatal seizures responsive to pyridoxine.
• Pyridoxal phosphate deficiency: Similar to PDE but responds better to pyridoxal phosphate supplementation.

Vitamin B7 (Biotin)

• Biotinidase deficiency: Neurological manifestations include seizures, ataxia, hypotonia, and developmental delay. Treated with biotin supplementation.
• Holocarboxylase synthetase deficiency: Responsive to biotin.

Vitamin B9 (Folate)

• Cerebral folate deficiency (CFD): Neurological symptoms include developmental regression, irritability, ataxia, and seizures. Treated with folinic acid.
• Megaloblastic anemia due to folate deficiency: May include neurodevelopmental delays.

Vitamin B12 (Cobalamin)

• Cobalamin C deficiency (CblC): Causes developmental delay, hypotonia, and seizures. Responsive to hydroxocobalamin.
• Subacute combined degeneration: Neurological symptoms include ataxia, paresthesia, and cognitive decline. Associated with B12 deficiency.

Vitamin C (Ascorbic Acid)

• Scurvy: Neurological symptoms are rare but may include depression, irritability, and pseudoparalysis due to pain.

Vitamin D

• Vitamin D deficiency: Can lead to hypocalcemia, manifesting as seizures, tetany, or irritability.
• Vitamin D-dependent rickets type I and II: Respond to calcitriol or high-dose vitamin D.

Vitamin E

• Vitamin E deficiency: Often due to malabsorption (e.g., cystic fibrosis) or abetalipoproteinemia. Symptoms include ataxia, peripheral neuropathy, and myopathy.
• Ataxia with vitamin E deficiency (AVED): Autosomal recessive disorder treatable with vitamin E supplementation.

Vitamin K

• Vitamin K deficiency bleeding (VKDB): Causes hemorrhagic disease of the newborn, which can lead to intracranial hemorrhage and neurological sequelae.

Vitamin-Responsive Neurological Disorders in Metabolic Diseases

• Glutaric aciduria type I: May benefit from riboflavin (B2) supplementation.
• Methylmalonic acidemia: Some forms respond to B12.
• Propionic acidemia: B12 supplementation may help in certain cases.
• Homocystinuria: Responsive to pyridoxine (B6) or B12, depending on the subtype.
• Ornithine transcarbamylase (OTC) deficiency: Treated with arginine and citrulline, but folate can be used in adjunct.
• Nonketotic hyperglycinemia (NKH): Some patients benefit from folinic acid.