Partial deletion of AFG3L2 causing spinocerebellar ataxia type 28

Objective: To identify the genetic cause of autosomal dominant spinocerebellar ataxia type 28 (SCA28) with ptosis in 2 Belgian families without AFG3L2 point mutations and further extend the clinical spectrum of SCA28 through the study of a brain autopsy, advanced MRI, and cell-based functional assays exploring the underlying disease mechanism. Methods: Two large families were clinically examined in detail. Linkage analysis and multiplex amplicon quantification were performed. A brain autopsy was obtained. Brain MRI with voxel-based morphometry and diffusion tensor imaging was performed. RNA and Western blot analysis and blue native-polyacrylamide gel electrophoresis experiments were performed. Results: MRI analysis demonstrated a significant cerebellar atrophy, as well as white matter degeneration in the cerebellar peduncles, corticospinal tracts, corpus callosum, and cingulum. A brain autopsy showed severe atrophy of the upper part of the cerebellar hemisphere. Ubiquitin and p62 immunoreactive intranuclear inclusions were found in cerebral and cerebellar cortical neurons, in neurons of the hippocampus, and in pontine and medullary nuclei. An identical heterozygous partial deletion of exons 14 to 16 of the AFG3L2 gene was found in both families. Additional functional assays in patient-derived cell lines revealed haploinsufficiency as the underlying disease mechanism. Conclusions: Our study expands the phenotypic characterization of SCA28 by means of brain pathology and diffusion tensor imaging/voxel-based morphometry MRIs. The identification of a partial AFG3L2 deletion and the subsequent functional studies reveal loss of function as the most likely disease mechanism. Specific testing for deletions in AFG3L2 is warranted because these escape standard sequencing

PRRT2 mutations: exploring the phenotypical boundaries

Mutations in the proline-rich transmembrane protein 2 (PRRT2) gene have been identified in patients with benign (familial) infantile convulsions (B(F)IC), infantile convulsions with choreoathetosis (ICCA) and paroxysmal dyskinesias (PDs). However it remains unknown whether PRRT2 mutations are causal in other epilepsy syndromes. After we discovered a PRRT2 mutation in a large family with ICCA containing one individual with febrile seizures (FS) and one individual with West syndrome, we analysed PRRT2 in a heterogeneous cohort of patients with different types of infantile epilepsy.status: publishe