Hangul dysgraphia in patients with Alzheimer's disease

Abstract

Background: Dysgraphia is the collective term used for various acquired disorders of spelling and writing caused by diverse neurological diseases or brain damages. Dysgraphia may take various forms depending on the specific graphemic system of a given language. The Korean alphabet, Hangul (or Hangeul), is unique in its written application. Linguistically, each of the 24 Hangul characters corresponds to one phoneme. Unlike the alphabetic written language system (e.g., English and Italian), Hangul has nonlinguistic characteristics, such as physical forms of graphemes and visuospatial/constructional arrangement of graphemes within a syllable. Especially, Hangul syllables differ from those in alphabetical systems which are written horizontally. Due to these visuospatial/constructional features, the configuration of Hangul syllables invokes visuospatial/constructional functions that other writing systems use less extensively. Traditionally, the left hemisphere might control a linguistic component in writing, while the right hemisphere might control a nonlinguistic component. Hangul has both linguistic and nonlinguistic value. Therefore, interactivity between the left and right hemispheres may be essential to ensure Hangul writing processing. Alzheimer’s disease (AD) is characterized by the deposition of beta-amyloid plaques and neurofibrillary tangles in the brain. Due to the bilateral involvement of the tempoparietal-frontal areas, the disease can result in both visuoconstructional and language dysfunction in some stage of their disease process. Because of the specialized characteristics of Hangul, the nonlinguistic errors, as well as the linguistic ones may be easily observed in the Korean patients with AD. Objectives: The purpose of this study is to delineate 1) the characteristics of writing in Korean patients with AD, 2) the feature of visuospatial representation of Hangul syllable, 3) the relationship between Hangul task and other related cognitive functions, and 4) associated neural correlates of Hangul writing. Methods: A study sample of 75 patients with AD and 20 healthy controls (HC) performed a Hangul writing task. We analyzed the erroneous responses of the subjects according to linguistic and nonlinguistic characteristics. A Hangul representation task was used to assess the knowledge of the general shape of a Hangul syllable. In addition, we evaluated the relationship between Hangul writing and the neuropsychological variables. [F]fluoro-2-deoxy-D-glucose(18FDG)-positron emission tomography (PET) was utilized to measure the resting state regional brain glucose metabolism. Results: The number of total erroneous responses significantly differed according to disease severity. In addition, the patients demonstrated nonlinguistic errors even in the early stages of the disease. The performance of Hangul representation might be relatively preserved in the later stage of AD patients even though these patients showed low performance in the writing to dictation task. Multiple cognitive domains such as attention, language, immediate memory, visuospatial and frontal executive functions significantly correlated with the performance of Hangul writing. Glucose metabolism correlated with the number of correct responses was located in the right occipitotemporal lobe and the left temporoparietal lobe. Conclusions: Language-specific features our patients showed may represent the unique arrangement of graphemes within the square form of a Hangul syllable. The PET findings objectively support the notions that Hangul has both linguistic and nonlinguistic (visuoconstructional) characteristics, and the impairment of Hangul writing performance in Korean AD patients might be closely related to a functional decline in both the right and left hemispheres. The results provide clinical implications in that the writing impairment would be one of the possible clues of diffuse brain changes, and thus, writing ability should be monitored from an early stage of the disease.