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B. P. Brooks, P. Tanpaiboon, J. Sloan, D. Blain, C. Venditti; Correlation of Clinical, Biochemical and Genotypic Findings in Patients With Cobalamin C Deficiency. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1304.
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Cobalamin C deficiency (cblC) is an autosomal recessive inborn error of vitamin B12 metabolism characterized by neurologic, ophthalmologic, and hematologic pathology as well as elevated plasma methylmalonic acid and homocysteine. We have correlated the clinical, biochemical and genotypic findings in a series of twelve patients with cblC deficiency.
Twelve patients (ages 1 to 17, 7 males, 5 females) underwent systemic, ophthalmic, and biochemical evaluations. Sequencing of the cblC gene, MMACHC, was performed to identify mutations.
Best-corrected visual acuity was reduced in all 11 patients where formal testing was possible. Strabismus was present in five and nystagmus in eight patients. Four had refractive errors necessitating correction. Nine patients had macular changes_most characteristically a "bulls-eye maculopathy" and six had non-macular retinal changes (e.g., peripheral pigmentary changes). Five patients had optic nerve pallor. The most commonly observed mutation in MMACHC was c.271dupA. Correlation of systemic clinical, biochemical, and genotype findings suggest the following: 1. CblC deficiency may be a developmental disorder, as well as a degenerative disease. 2. Prenatal treatment with vitamin B12 may reduce systemic and ophthalmic pathology. 3. Macular changes, considered the most characteristic eye finding, are not invariably present. 4. There is no strict correlation between genotype and phenotype or biochemical control and phenotype. 5. Elevation of MMA does not itself cause retinal degeneration. 6. Elevation of homocysteine itself does not lead to lens dislocation.
Patients with cblC have a broad range of phenotypes. Correlation with genotypic and biochemical parameters has increased our understanding of the pathogenesis of this disease.
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