Browsing by Author "Sequeiros, Jorge"
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- Novel MAG Variant Causes Cerebellar Ataxia with Oculomotor Apraxia: Molecular Basis and Expanded Clinical PhenotypePublication . Santos, Mariana; Damásio, Joana; Kun-Rodrigues, Celia; Barbot, Clara; Sequeiros, Jorge; Brás, José; Alonso, Isabel; Guerreiro, RitaHomozygous variants in MAG, encoding myelin-associated glycoprotein (MAG), have been associated with complicated forms of hereditary spastic paraplegia (HSP). MAG is a glycoprotein member of the immunoglobulin superfamily, expressed by myelination cells. In this study, we identified a novel homozygous missense variant in MAG (c.124T>C; p.Cys42Arg) in a Portuguese family with early-onset autosomal recessive cerebellar ataxia with neuropathy and oculomotor apraxia. We used homozygosity mapping and exome sequencing to identify the MAG variant, and cellular studies to confirm its detrimental effect. Our results showed that this variant reduces protein stability and impairs the post-translational processing (N-linked glycosylation) and subcellular localization of MAG, thereby associating a loss of protein function with the phenotype. Therefore, MAG variants should be considered in the diagnosis of hereditary cerebellar ataxia with oculomotor apraxia, in addition to spastic paraplegia.
- Rare occurrence of severe blindness and deafness in Friedreich ataxia: a case reportPublication . Damásio, Joana; Sardoeira, Ana; Araújo, Maria; Carvalho, Isabel; Sequeiros, Jorge; Barros, JoséBackground: Friedreich ataxia is the most frequent hereditary ataxia worldwide. Subclinical visual and auditory involvement has been recognized in these patients, with co-occurrence of severe blindness and deafness being rare. Case report: We describe a patient, homozygous for a 873 GAA expansion in the FXN gene, whose first symptoms appeared by the age of 8. At 22 years-old he developed sensorineural deafness, and at 26 visual impairment. Deafness had a progressive course over 11 years, until a stage of extreme severity which hindered communication. Visual acuity had a catastrophic deterioration, with blindness 3 years after visual impairment was first noticed. Audiograms documented progressive sensorineural deafness, most striking for low frequencies. Visual evoked potentials disclosed bilaterally increased P100 latency. He passed away at the age of 41 years old, at a stage of extreme disability, blind and deaf, in addition to the complete phenotype of a patient with Friedreich ataxia of more than 30 years duration. Discussion: Severe vision loss and extreme deafness has been described in very few patients with Friedreich ataxia. Long duration, severe disease and large expanded alleles may account for such an extreme phenotype; nonetheless, the role of factors as modifying genes warrants further investigation in this subset of patients.