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Abstract
Objective To characterize clinically and molecularly an early-onset, variably progressive neurodegenerative disorder characterized by a cerebellar syndrome with severe ataxia, gaze palsy, dyskinesia, dystonia, and cognitive decline affecting 11 individuals from 3 consanguineous families.
Methods We used whole-exome sequencing (WES) (families 1 and 2) and a combined approach based on homozygosity mapping and WES (family 3). We performed in vitro studies to explore the effect of the nontruncating SQSTM1 mutation on protein function and the effect of impaired SQSTM1 function on autophagy. We analyzed the consequences of sqstm1 down-modulation on the structural integrity of the cerebellum in vivo using zebrafish as a model.
Results We identified 3 homozygous inactivating variants, including a splice site substitution (c.301+2T>A) causing aberrant transcript processing and accelerated degradation of a resulting protein lacking exon 2, as well as 2 truncating changes (c.875_876insT and c.934_936delinsTGA). We show that loss of SQSTM1 causes impaired production of ubiquitin-positive protein aggregates in response to misfolded protein stress and decelerated autophagic flux. The consequences of sqstm1 down-modulation on the structural integrity of the cerebellum in zebrafish documented a variable but reproducible phenotype characterized by cerebellum anomalies ranging from depletion of axonal connections to complete atrophy. We provide a detailed clinical characterization of the disorder; the natural history is reported for 2 siblings who have been followed up for >20 years.
Conclusions This study offers an accurate clinical characterization of this recently recognized neurodegenerative disorder caused by biallelic inactivating mutations in SQSTM1 and links this phenotype to defective selective autophagy.
Glossary
- BSA=
- bovine serum albumin;
- CCCP=
- protonophore carbonyl cyanide m-chlorophenyl hydrazone;
- DQ=
- dye-conjugated;
- EBSS=
- Earle balanced salt solution;
- Ig=
- immunoglobulin;
- LC3=
- microtubule-associated protein 1A/1B-light chain 3;
- MO=
- morpholino oligonucleotide;
- OXPHOS=
- oxidative phosphorylation;
- PDB=
- Paget disease of bone;
- SNP=
- single nucleotide polymorphism;
- WES=
- whole-exome sequencing
Footnotes
↵* These authors equally contributed to this work.
↵† These authors jointly coordinated this work.
Go to Neurology.org/N for full disclosures. Funding information and disclosures deemed relevant by the authors, if any, are provided at the end of the article.
- Received January 25, 2018.
- Accepted in final form April 18, 2018.
- © 2018 American Academy of Neurology
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