High rate of hypomorphic variants as the cause of inherited ataxia and related diseases: study of a cohort of 366 families.

PURPOSE: Diagnosis of inherited ataxia and related diseases represents a real challenge given the tremendous heterogeneity and clinical overlap of the various causes. We evaluated the efficacy of molecular diagnosis of these diseases by sequencing a large cohort of undiagnosed families. METHODS: We analyzed 366 unrelated consecutive patients with undiagnosed ataxia or related disorders by clinical exome-capture sequencing. In silico analysis was performed with an in-house pipeline that combines variant ranking and copy-number variant (CNV) searches. Variants were interpreted according to American College of Medical Genetics and Genomics/Association for Molecular Pathology (ACMG/AMP) guidelines. RESULTS: We established the molecular diagnosis in 46% of the cases. We identified 35 mildly affected patients with causative variants in genes that are classically associated with severe presentations. These cases were explained by the occurrence of hypomorphic variants, but also rarely suspected mechanisms such as C-terminal truncations and translation reinitiation. CONCLUSION: A significant fraction of the clinical heterogeneity and phenotypic overlap is explained by hypomorphic variants that are difficult to identify and not readily predicted. The hypomorphic C-terminal truncation and translation reinitiation mechanisms that we identified may only apply to few genes, as it relies on specific domain organization and alterations. We identified PEX10 and FASTKD2 as candidates for translation reinitiation accounting for mild disease presentation.

Leucine-Rich Glioma-Inactivated 1 Encephalitis: Broadening the Sphere.

Background: Leucine-rich glioma-inactivated 1 (LGI1) encephalitis is a rare entity. Its typical features are seizures, faciobrachial dystonic seizures (FBDS), cognitive impairment, and personality changes. Case report: We report the case of a 66-year-old man with an unusual presentation, consisting of two types of FBDS, one starting in the foot and the other consisting of asynchronous myoclonic and dystonic jerks of the face triggered by noise and chin stimulation. The patient displayed no personality changes or cognitive impairment. Discussion: LGI1 encephalitis is a heterogeneous disease. Many different forms of FBDS may be observed, and these seizures can be the only symptom. This type of encephalitis should be suspected in presenting very frequent episodic events with dystonic features, regardless of the part of the body affected.