Late Onset Cobalamin C Disease: A Case Report of an Adolescent Presenting with Peripheral Neuropathy (P03.189)

Abstract

Objective: To describe a case of late onset Cobalamin C disease presenting with peripheral neuropathy. Background Cobalamin C disease is a rare autosomal recessive disorder due to defective intracellular cobalamin metabolism. Clinical symptoms can include neurological complaints, psychiatric disturbances, and thromboembolic complications. Late onset forms of Cobalamin C disease are difficult to diagnose because they are usually lacking indicative hematological signs. There are only a few cases reported on the late onset presentation of Cobalamin C disease, and a dearth in cases describing its detailed electrophysiological findings. Design/Methods: We report on the clinical, laboratory, electrophysiological, and radiological findings of a 17 year old male who presented with bilateral lower extremity weakness, and was eventually diagnosed with methylmalonic aciduria and homocystinuria Cobalamin C type. Results: Initial neurological examination was notable for the motor examination revealing distal greater than proximal muscle weakness in patient9s bilateral lower extremities, and reflex examination revealing generalized hyperreflexia except for diminished reflexes at the left ankle, with bilateral extensor plantar responses. Additionally, patient appeared to have impairment in all sensory modalities in his distal lower extremities. Although initial laboratory values revealed a vitamin B-12 level of 908 pg/ml, diagnosis was still made with urine and plasma biomarkers which revealed an MMA level of 1980.1 mmol/mol cr, homocysteine level of 163.1 nanomol/ml, and a methionine level of 4 micromol/lit. Diagnosis was confirmed with genetic analysis showing a homozygous mutation for c.482G>A. Furthermore, nerve conduction studies revealed a sensory motor axonal neuropathy with a proximal to distal gradient. Lastly, MRI brain was notable for increased FLAIR signal within the bilateral frontal white matter. Conclusions: The clinical presentation of neurological complaints, psychiatric disturbances, and/or thromboembolic complications should prompt the evaluation of late onset Cobalamin C disease even in the presence of initially normal hematological values, given the potentially treatable nature of the disease. Disclosure: Dr. Bashir has nothing to disclose. Dr. Sharma has nothing to disclose. Dr. Gualberto has nothing to disclose. Dr. Carrasquillo has nothing to disclose.