"Progressive myoclonic ataxia and developmental/epileptic encephalopathy associated with a novel homozygous mutation in TCN2 gene"

BACKGROUND

Transcobalamin II (TCN2) defect is a rare metabolic disorder associated with a range of neurological manifestations, including mild developmental delay, severe intellectual disability, ataxia, and, in some cases, seizures. Cobalamin, an essential nutrient, plays a crucial role in central nervous system myelination.

CLINICAL PRESENTATION

We present a family with an index patient who exhibited progressive neurodevelopmental regression starting at 9 months of age, accompanied by myoclonic seizures, ataxia, and tremor. No significant hematological abnormalities were observed. Exome sequencing analysis identified a novel homozygous mutation, c.3G>A - P(Met1I), affecting the acceptor site of intron 4 of the TCN2 gene (chromosome 22: 31003321, NM_000355.4), leading to likely pathogenic variant potentially affecting translation. Following treatment with hydroxocobalamin, the patient demonstrated partial clinical improvement. He has a sibling with overt hematological abnormalities and subtle neurological abnormalities who is homozygous to the same mutation. Both parents are heterozygous for the same mutation.

CONCLUSIONS

In infants presenting with unexplained non-specific neurological symptoms, irrespective of classical signs of vitamin B12 deficiency, evaluation for TCN2 defect should be considered. Early diagnosis and appropriate management can lead to favorable outcomes.