Do the clinical features in infantile-onset saccade initiation delay (congenital ocular motor apraxia) correlate with brain magnetic resonance imaging findings?

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.

Nosological delineation of congenital ocular motor apraxia type Cogan: an observational study

Background

The nosological assignment of congenital ocular motor apraxia type Cogan (COMA) is still controversial. While regarded as a distinct entity by some authorities including the Online Mendelian Inheritance in Man catalog of genetic disorders, others consider COMA merely a clinical symptom.

Methods

We performed a retrospective multicenter data collection study with re-evaluation of clinical and neuroimaging data of 21 previously unreported patients (8 female, 13 male, ages ranging from 2 to 24 years) diagnosed as having COMA.

Results

Ocular motor apraxia (OMA) was recognized during the first year of life and confined to horizontal pursuit in all patients. OMA attenuated over the years in most cases, regressed completely in two siblings, and persisted unimproved in one individual. Accompanying clinical features included early onset ataxia in most patients and cognitive impairment with learning disability (n = 6) or intellectual disability (n = 4). Re-evaluation of MRI data sets revealed a hitherto unrecognized molar tooth sign diagnostic for Joubert syndrome in 11 patients, neuroimaging features of Poretti-Boltshauser syndrome in one case and cerebral malformation suspicious of a tubulinopathy in another subject. In the remainder, MRI showed vermian hypo-/dysplasia in 4 and no abnormalities in another 4 patients. There was a strong trend to more severe cognitive impairment in patients with Joubert syndrome compared to those with inconclusive MRI, but otherwise no significant difference in clinical phenotypes between these two groups.

Conclusions

Systematical renewed analysis of neuroimaging data resulted in a diagnostic reappraisal in the majority of patients with early-onset OMA in the cohort reported here. This finding poses a further challenge to the notion of COMA constituting a separate entity and underlines the need for an expert assessment of neuroimaging in children with COMA, especially if they show cognitive impairment.

Electronic supplementary material

The online version of this article (doi:10.1186/s13023-016-0486-z) contains supplementary material, which is available to authorized users.

Infantile-onset saccade initiation delay (congenital ocular motor apraxia)

Infantile-onset saccade initiation delay, also known as congenital ocular motor apraxia, typically presents in early infancy with horizontal head thrusts once head control is achieved. Defective initiation of horizontal saccades and saccade hypometria with normal saccadic velocity are characteristic findings. Isolated impairment of vertical saccades is rare. Impaired smooth ocular pursuit may be seen. Other relatively common features include developmental delay, hypotonia, ataxia, or clumsiness. Brain MRI may be normal or show a diverse range of abnormalities, most commonly involving the cerebellum. Defective slow phases of the optokinetic response are commonly associated with brain MRI abnormalities. Isolated defect of vertical saccade initiation may indicate supratentorial brain abnormalities on MRI. Joubert syndrome, a developmental midbrain-hindbrain malformation, and ataxia telangiectasia are both commonly associated with defective volitional and reflexive saccade initiation, saccade hypometria, and head thrusts. Both horizontal and vertical saccades are impaired in these two disorders.