Obsessive-compulsive disorder as a first manifestation of Ataxia with Oculomotor Apraxia type 2 due to a novel mutation of SETX gene.

Background: Ataxia with oculomotor apraxia type 2 (AOA2) is an autosomal recessive disorder presenting with cerebellar ataxia, sensory-motor axonal neuropathy, oculomotor apraxia, cerebellar atrophy and high alpha-fetoprotein (AFP) serum level. AOA2 is due to coding mutations of the SETX gene, mapped to chromosome 9q34. Seldom noncoding mutations affecting RNA processing have been reported too. To date psychiatric symptoms have never been reported in AOA2.

Case Presentation: A 19 years-old man came to our attention for progressive gait ataxia debuted five years earlier. His past medical history was unremarkable, while his parents were consanguineous. On neurological examination, he had bilateral horizontal gaze-evoked nystagmus with hypometric saccades and saccadic horizontal smooth pursuit, appendicular ataxia, limbs and trunk myoclonic involuntary movements with hands' dystonic postures and dance of the tendons. Psychological evaluation described intrusive and obsessive thoughts experienced by the patient, then diagnosed as obsessive-compulsive disorder. Blood tests detected an elevated AFP level. Brain MRI showed cerebellar atrophy, while electroneuromyography revealed an axonal sensory-motor polyneuropathy. In the suspicion of a pathology belonging to the autosomal recessive cerebellar ataxias (ARCA) spectrum disorder, a direct search of point mutations by whole-exome sequencing was performed revealing a novel biallelic variant in SETX gene (c.6208+2dupT), which was classified as likely pathogenic.

Conclusion: The present case expands the genotypic and phenotypic spectrum of AOA2, reporting a novel likely pathogenic SETX mutation (c.6208+2dupT) and highlighting an early psychiatric involvement in AOA2, suggesting the need for psychiatric assessment in these neurologic patients.