Abnormal Glycosylation Profile and High Alpha-Fetoprotein in a Patient with Twinkle Variants

The C10orf2 gene encodes Twinkle, a protein involved in mitochondrial DNA (mtDNA) replication. Twinkle mutations cause mtDNA deletion or depletion and are associated with a large spectrum of clinical symptoms including dominant progressive external ophthalmoplegia (adPEO), infantile-onset spinocerebellar ataxia (IOSCA), and early-onset encephalopathy. The diagnosis remains difficult because of the wide range of symptoms and lack of association with specific metabolic changes. We report herein a child with early-onset encephalopathy, unusual abnormal movements, deafness, and axonal neuropathy. All laboratory investigations were normal with the exceptions of high alpha-fetoprotein levels and an abnormal glycosylation profile. These abnormal parameters resulted in misdiagnosis as a previously unidentified congenital disorder of glycosylation (CDG) type I syndrome. Whole exome sequencing revealed two point mutations in C10orf2 that were confirmed by Sanger sequencing; neither had been previously reported. This report enlarges the clinical phenotype of Twinkle mutations and suggests that an abnormal glycosylation profile suggestive of CDG type I associated with high blood alpha-fetoprotein levels without obvious cause should prompt Twinkle sequencing.