MedGen

Childhood-onset biotin-responsive peripheral motor neuropathy (COMNB) is an autosomal recessive disorder characterized predominantly by the onset of distal muscle weakness and atrophy late in the first decade of life. The disorder predominantly affects the upper limbs and hands, resulting in difficulties with fine motor skills. Some patients may have lower limb involvement, resulting in gait difficulties. Electrophysiologic studies and muscle biopsy are consistent with chronic denervation with axonal and demyelinating features. Rare patients may have additional neurologic signs, including spasticity, ataxia, and cerebellar signs. Sensation is intact, and patients have normal cognitive development. Treatment with biotin, pantothenic acid, and lipoic acid may result in clinical improvement (Holling et al., 2022). [from OMIM]

Sodium-dependent multivitamin transporter deficiency (SMVTD) is an autosomal recessive multisystemic metabolic disorder with highly variable manifestations. Affected individuals usually present at birth or in infancy with severe feeding problems, gastrointestinal reflux, cyclic vomiting, and diarrhea associated with failure to thrive. Gastrointestinal hemorrhage may occur; tube-feeding is often required for a short time. The course and severity of the disease varies: some patients have episodes of acute metabolic decompensation during infection that respond well to treatment, whereas others show more permanent neurologic regression with loss of early motor and cognitive milestones in the first year or so of life. Less severely affected patients have normal development or mild growth and motor delays, whereas more severely affected individuals may have seizures, ataxia, spasticity, peripheral neuropathy, immune defects, and osteopenia. In severely affected patients, brain imaging shows cerebral, cerebellar, and brainstem atrophy and thin corpus callosum. Treatment with biotin, pantothenic acid, and alpha-lipoic acid has been shown to result in significant clinical improvement (Byrne et al., 2019; Hauth et al., 2022). [from OMIM]