Clinical Manifestations

The diverse typology of languages often precipitates distinct language-specific symptomatologies. While dyslexia and dysgrahia are included in the diagnostic criteria of Primary Progressive Aphasia (PPA), the descriptions predominantly pertain to alphabetic scripts, with a lack of insight into their manifestations in logographic systems. This study examines the dyslexia phenotypes of Chinese-speaking PPA patients.

The Chinese Language Assessment for PPA (CLAP) study recruited Mandarin and Cantonese-speaking participants [cognitively normal (CN, n = 68) and individuals with PPA (16 semantic variant (sv)PPA, 16 nonfluent/aggramatic variant (nfv)PPA ), 21 logopenic variant (lv)PPA] using a neurolinguistic tailored battery for Chinese languages. In the CLAP character reading test, participants are required to read 250 Chinese characters, encompassing a range of lexical types (pictographic, regular compound, and irregular compound characters), frequencies, and levels of concreteness. Participants are also tasked to read aloud pairs of compound words that include heteronyms (i.e., words with same spelling but pronounced differently; e.g., 'bow tie' versus 'bow down'). Additionally, voxel-based morphometry was utilized to investigate the neural basis of reading performance.

In the character reading test, svPPA participants demonstrated significantly lower performance than other study groups, even after adjusting for age, education, and testing language (pictographic: p <0.001; regular compound: p <0.001; irregular compound characters: p <0.001). While over-regularization errors (i.e., surface dyslexia) were prevalent across control and PPA groups, they were not specific to svPPA (p = 0.495). In contrast, on the heteronym word reading test, both svPPA and lvPPA showed significantly lower accuracy (both p <0.001), with over-regularization errors occurring more frequently in the svPPA group (p <0.001). Across all lexical categories, character reading scores were significantly correlated with volumetric changes in the left middle and inferior temporal regions while heteronym reading accuracy were positively correlated with left temporal pole and inferior temporal areas.

Contrary to English svPPA patients who primarily struggled with irregular word reading and frequently exhibit surface dyslexia, Chinese PPA patients showed no variant-specific differences across lexicality, and svPPA-specific over-regularization phenomenon were found at the lexical (i.e., heteronym-reading) and not sub-lexical reading. These findings underscore that diagnostic criteria for PPA syndromes should be linguistically tailored to accommodate language topology effect.