Case Report: A Case of Adult Methylmalonic Acidemia With Bilateral Cerebellar Lesions Caused by a New Mutation in MMACHC Gene

A case report of neuronal intranuclear inclusion disease and literature review

Neuronal intranuclear inclusion disease (NIID) is a rare progressive neurodegenerative disease with a characteristic pathological feature of eosinophilic hyaluronan inclusions in the nervous system and internal organs. The identification of GGC-repeat expansions in the Notch 2 N-terminal like C (NOTCH2NLC) gene facilitates the accurate diagnosis of NIID. Due to its rareness and high clinical heterogeneity, the diagnosis of NIID is often delayed or missed. Here, we report a case of NIID mimicking autoimmune encephalitis. A 55-year-old Chinese man presented with fever, headache, recurrent seizures, and weakness in the upper and lower left limbs. Brain MRI revealed diffuse T2/ FLAIR-hyperintense lesions in the bilateral basal ganglia, corpus callosum, and periventricular white matter, with swelling of the right temporal, frontal, and parietal cortices accompanied by meningeal enhancement. Abnormally high signal lesions were observed in the corticomedullary junction in diffusion-weighted imaging (DWI). The infectious or autoimmune disease screening of central nervous system using CSF was normal. The test of GGC-repeat expansion in the NOTCH2NLC gene by capillary electrophoresis indicated GGC repeats (48 and 110 GGC repeats), which supported the diagnosis of NIID. After treatment with glucocorticoid, the clinical symptoms of this patient improved significantly. In the literature, 12 cases of NIID presenting with encephalitis-like attacks were identified, most of which were recurrent, accompanied by progressive symptoms such as dementia, Parkinsonism symptoms, migraine, or dysuria. In this case, there was a single encephalitis-like episode without other progressive symptoms. In patients with encephalitis-like symptoms, NIID should be considered, especially when no other evidence of infection is found, as demonstrated in this case. In addition, long-term monitoring of disease progression is also very important.

Late-onset cobalamin C deficiency type in adult with cognitive and behavioral disturbances and significant cortical atrophy and cerebellar damage in the MRI: a case report

Background

Late-onset cobalamin C (cblC) deficiency is associated with a wide range of neurological and psychiatric symptoms, hematological manifestations, anorexia, renal failure, ocular abnormalities, dermatitis, and pancreatitis. However, the neuroimaging characteristics of late-onset cblC deficiency remain insufficiently documented. Common findings include diffuse white matter swelling, varying degrees of severe leukoaraiosis, hydrocephalus, corpus callosum atrophy, and symmetric bilateral basal ganglia lesions. In this report, we present a case of late-onset cblC deficiency in adults presenting with cerebellar ataxia as the primary symptom. The MRI findings revealed bilateral lateral cerebellar hemispheres exhibiting symmetric hyperintensity, primarily observed in diffusion-weighted imaging (DWI), which is a rarely reported imaging change in this context.

Case presentation

Our patient was a male who experienced symptoms starting at the age of 30 years, including unsteady walking, apparent cerebellar ataxia, and cognitive impairment upon nervous system examination. Brain magnetic resonance imaging (MRI) exhibited symmetric hyperintensity in the bilateral lateral cerebellar hemispheres, predominantly manifested in DWI, without any enhancement. Subsequently, significantly elevated blood total homocysteine and urinary methylmalonic acid levels were observed. Genetic analysis confirmed the presence of MMACHC compound heterozygous mutants c.482G > A and c.609G > A, thus confirming the diagnosis of cblC deficiency. These variants were classified as likely pathogenic following the guidelines of the American College of Medical Genetics and Genomics (ACMG) and were verified using Sanger sequencing. Following treatment, the patient experienced improvements in walking ability and cognition, a significant decrease in blood total homocysteine levels, and reversal of the imaging lesions.

In conclusion

Late-onset cblC deficiency presents with diverse clinical and imaging manifestations. Early diagnosis and treatment are crucial in achieving a favorable prognosis. This case serves as a reminder to clinicians not to overlook genetic metabolic disorders, particularly those causing multisite damage, in adult patients with undiagnosed neurological disorders, especially those affecting the cerebellum. Notably, methylmalonic acidemia should be considered within the spectrum of bilateral cerebellar lesions.