A treatable metabolic cause of encephalopathy: cobalamin C deficiency in an 8-year-old male

Clinical, phenotypic and genetic landscape of case reports with genetically proven inherited disorders of vitamin B12 metabolism: A meta-analysis

Inherited disorders of B₁₂ metabolism produce a broad spectrum of manifestations, with limited knowledge of the influence of age and the function of related genes. We report a meta-analysis on 824 patients with a genetically proven diagnosis of an inherited disorder of vitamin B₁₂ metabolism. Gene clusters and age categories are associated with patients' manifestations. The "cytoplasmic transport" cluster is associated with neurological and ophthalmological manifestations, the "mitochondrion" cluster with hypotonia, acute metabolic decompensation, and death, and the "B₁₂ availability" and "remethylation" clusters with anemia and cytopenia. Hypotonia, EEG abnormalities, nystagmus, and strabismus are predominant in the younger patients, while neurological manifestations, such as walking difficulties, peripheral neuropathy, pyramidal syndrome, cerebral atrophy, psychiatric disorders, and thromboembolic manifestations, are predominant in the older patients. These results should prompt systematic checking of markers of vitamin B₁₂ status, including homocysteine and methylmalonic acid, when usual causes of these manifestations are discarded in adult patients.

Diagnosis of cobalamin C deficiency with renal abnormality from onset in a Chinese child by next generation sequencing: A case report

The aim of the present study was to present the diagnosis and treatment course of a patient with cobalamin C deficiency (cblC) hospitalized with renal function abnormality from the onset. A female, 7-year-old patient who presented with a cough and progressive dyspnea for 1 day was admitted to the Children's Hospital of Nanjing Medical University (Nanjing, China). A routine clinical examination was performed, including physical examination, routine blood and urine tests, blood gas analysis, computed tomography scans of the head, chest and abdomen, electrocardiogram, echocardiography and abdominal ultrasonography. In addition, laboratory tests were performed, including tests for viral infection and markers of autoimmunity, humoral immunity, myocardial enzymes and tumors. Tandem mass analysis and renal biopsy were conducted. Next generation sequencing (NGS) was performed to identify mutated genes, and structural investigation was conducted to identify the key residue mutations in the patient. Routine clinical examination revealed that the patient had multiple organ failure, indicating the presence of metabolic disease. Tandem mass analysis and renal biopsy also indicated that the patient had methylmalonic acidemia (MMA) and thrombotic microangiopathy combined with focal renal cortical necrosis. Furthermore, next-generation sequencing identified the presence of two heterozygous mutations in the MMA cblC type with homocystinuria (MMACHC) gene. Structural analysis demonstrated that the two mutations were in key components of the MMACHC protein. The patient was finally diagnosed with cblC according to the results obtained. In conclusion, NGS may aid in the diagnosis and therapeutic management of cblC with renal abnormality from the onset in children.

Ocular disease in the cobalamin C defect: a review of the literature and a suggested framework for clinical surveillance

The association between combined methylmalonic acidemia and homocystinuria of cblC type (cobalamin C defect, cblC) and ocular disease is now well recognized, and is a significant component of morbidity and disability associated with the condition. In this review, through collation of historically reported cases of early- and late-onset cblC and previously unreported cases, we have attempted to characterize the epidemiology, clinical features, and pathomechanisms of individual ocular features of cblC. These data suggest that maculopathy and nystagmus with abnormal vision are extremely common and affect the majority of children with early-onset cblC, usually before school age; strabismus and optic atrophy are also seen at relatively high frequency. The timing of progression of macular disease may coincide with a critical period of postnatal foveal development. Maculopathy and retinal disease may be subclinical and show only partial correlation with the extent of visual deficits, and visual deterioration may be relentlessly progressive in spite of aggressive treatment of biochemical abnormalities. In later-onset forms of the disease, visual loss and ocular complications appear to be infrequent. Finally, we discuss investigational strategies in diagnosing and characterizing eye disease in individuals with cblC, explore possible therapeutic avenues that may attenuate progression and severity of eye disease, and propose a clinical surveillance guideline for monitoring progression of ocular disease in children and adults with cblC.