Electrophysiological Correlates of Familial Dyslexia in Two Siblings: A Case Report

Background and Clinical Significance: Developmental dyslexia is diagnosed through behavioral neuropsychological and language assessment, which depends on the child's attention, motivation, and cooperation during testing. Auditory-evoked potentials provide objective, non-behavioral indices of neural encoding along the auditory pathway, but they are usually examined in group-level designs and in separate cohorts, so that intra-familial variability, and the level of the pathway at which atypical encoding emerges, remain poorly described. Characterizing siblings who share genetic background, family environment and schooling, using a single protocol that spans the brainstem, subcortical and cortical levels, is therefore clinically informative. Case Presentation: Two non-twin brothers (aged 13 and 11) with a clinical diagnosis of familial dyslexia and normal peripheral hearing underwent independent neuropsychological, speech-language and electrophysiological evaluations, comprising the click auditory brainstem response (ABR), the frequency-following response (FFR) to /da/ (80 dB SPL) in quiet and in ipsilateral and contralateral noise (masker 70 dB SPL; SNR ≈ +10 dB), and the P300 cognitive potential (auditory oddball). Click-ABR latencies and interpeak intervals were normal in both siblings, with an isolated, age-inappropriate V/I amplitude-ratio reduction in one. The FFR showed a condition-dependent, sibling-specific pattern of degradation, ipsilateral in one brother and contralateral in the other, with selective F0 collapse. The P300 was altered in both, with prolonged or absent components and low target-detection accuracy. All comparisons are descriptive. Conclusions: Preserved brainstem transmission contrasted with vulnerable subcortical speech encoding and altered cortical processing, revealing a central and biologically heterogeneous profile even within a family, and supporting the combined use of ABR, FFR and P300 as a complementary objective characterization of auditory processing in dyslexia.