Familial congenital oculomotor apraxia: clinical and electro-oculographic features

Modalities of reading acquisition in three siblings with infantile-onset saccade initiation delay (Cogan congenital ocular motor apraxia): A longitudinal study

This study aims to ascertain the impact of congenital ocular motor apraxia (COMA), alternatively called infantile-onset saccade initiation delay (ISID), on reading acquisition. More specifically, the consequence of defective initiation of horizontal saccades during reading acquisition was investigated. Three siblings (A: male, 11y3m at the first time-point of testing (i.e. T1 hereafter); B: female, 7y3m at T1 and C: male, 5y9m at T1) suffering from ISID were assessed longitudinally over 3 years in various reading tests and their eye movements simultaneously registered. At each time-point, they were compared to control participants matched on reading level. Eye movements during reading tasks were markedly abnormal in children with ISID at the beginning of reading acquisition and their reading scores were poor. With time, the number of fixations, small amplitude saccades and their reading abilities became comparable to those of control children. Despite the abnormal eye movements and difficulties in specifically directing the eyes to the appropriate position, children with ISID do not seem to encounter major difficulties during reading acquisition, although mild delays might be observed during the early stages.

Disconnections in Infantile-Onset Saccade Initiation Delay: A Hypothesis

Infantile-onset saccade initiation delay (ISID), commonly known as congenital ocular motor apraxia, is characterized by difficulty in triggering horizontal volitional saccades. It typically presents with head thrusts in infancy and is often associated with developmental delay. Patients with ISID are reported to have abnormalities in various brain regions including the corpus callosum, brainstem, and cerebellum. We propose that ISID is caused by the disruption or disconnection of axons linking analogous brain regions involved in processing saccades across the two sides of the brain or bilateral damage to these regions.

MRI with fibre tracking in Cogan congenital oculomotor apraxia

BACKGROUND

Congenital ocular motor apraxia (COMA) occasionally shares with Joubert syndrome (JS) and related disorders (JSRDs) a peculiar malformation, the 'molar tooth sign' (MTS). In JSRDs, the absence of superior cerebellar peduncles (SCP) decussation is reported.

OBJECTIVE

To investigate whether COMA demonstrates similar abnormal axonal pathways.

MATERIALS AND METHODS

Eight healthy age-matched controls, three children with clinical COMA and one child with clinical JSRD underwent examination with a 1.5-T MRI scanner. Diffusion-weighted imaging (DWI), colour-coded fractional anisotropy maps and three-dimensional diffusion tensor imaging (DTI) tractography of the cerebellorubral network were analyzed.

RESULTS

On DTI cartography, the 'red dot' originally supposed to represent the SCP decussation in the midbrain was present in controls as well in those with COMA but absent in the single case with JS. In none of the subjects including controls was 3-D FT able to depict the SCP decussation. When seeded, the red dot resulted in the ventral tegmental decussation (VTD). It was normal in controls and in patients with COMA but was absent in our single patient with JSRD. MTS was identified in alla patients with COMA and in the patient with JSRD.

CONCLUSION

MTS can be present in both COMA and JSRD but the underlying anatomy depicted by fibre tracking is distinct. The main difference is the integrity of the VTD in COMA.