Profiles of reading and cognitive-linguistic weaknesses in developmental dyslexia: Evidence from a large clinical sample in a transparent orthography

BACKGROUND: Despite developmental dyslexia being heterogeneous, large clinical datasets from transparent orthographies are limited. We examined the frequency and co-occurrence of phonological processing deficits, reading difficulties, and cognitive-linguistic weaknesses in Polish, a language with a transparent orthography. METHODS: Archival data from 2515 children with dyslexia (ages 10-18) assessed with a standardized diagnostic battery were analyzed. Low performance was defined using age-normed standardized scores within the low-performance range. Analyses were descriptive, focusing on deficit profiles and overlap across nine standardized subtests. RESULTS: Rapid automatized naming deficits were the most common isolated phonological weakness, while phonological awareness difficulties were less frequently observed in isolation. Generalized reading impairments, including decoding, fluency, and comprehension, were more prevalent than selective issues, with comprehension being the most vulnerable. Verbal short-term memory (VSTM) was the most common cognitive-linguistic weakness; however, a substantial subgroup of children meeting dyslexia criteria exhibited no measurable weaknesses in VSTM, lexical knowledge, or general knowledge. Co-occurrence analyses revealed that the range of reading difficulties was correlated with the range of phonological deficits, and multiple phonological weaknesses were associated with broader cognitive-linguistic impairments. CONCLUSIONS: The findings highlight the heterogeneity of dyslexia in transparent orthographies, supporting the conceptualization of overlapping deficit profiles. The results have implications for cross-linguistic theory, diagnostic practice, and targeted interventions.