Background Consanguineous kindred presented with an autosomal recessive syndrome of intrauterine growth retardation, marked developmental delay, spastic quadriplegia with profound contractures, pseudobulbar palsy with recurrent aspirations, epilepsy, dysmorphism, neurosensory deafness and optic nerve atrophy with no eye fixation. Affected individuals died by the age of 4. Brain MRI demonstrated microcephaly, semilobar holoprosencephaly and agenesis of corpus callosum. We aimed at elucidating the molecular basis of this disease.
Methods Genome-wide linkage analysis combined with whole exome sequencing were performed to identify disease-causing variants. Functional consequences were investigated in fruit flies null mutant for the Drosophila SEC31A orthologue. SEC31A knockout SH-SY5Y and HEK293T cell-lines were generated using CRISPR/Cas9 and studied through qRT-PCR, immunoblotting and viability assays.
Results Through genetic studies, we identified a disease-associated homozygous nonsense mutation in SEC31A. We demonstrate that SEC31A is ubiquitously expressed, and that the mutation triggers nonsense-mediated decay of its transcript, comprising a practical null mutation. Similar to the human disease phenotype, knockdown SEC31A flies had defective brains and early lethality. Moreover, in line with SEC31A encoding one of the two coating layers comprising the Coat protein complex II (COP-II) complex, trafficking newly synthesised proteins from the endoplasmic reticulum (ER) to the Golgi, CRISPR/Cas9-mediated SEC31A null mutant cells demonstrated reduced viability through upregulation of ER-stress pathways.
Conclusion We demonstrate through human and Drosophila genetic and in vitro molecular studies, that a severe neurological syndrome is caused by a null mutation in SEC31A, reducing cell viability through enhanced ER-stress response, in line with SEC31A’s role in the COP-II complex.
- COP-II complex
- neurological syndrome
- genetic mutation
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HF and OSB contributed equally.
Contributors DH, RK, YP, BR, UA, RB, HF and OSB contributed to the conception and design of the study. DH, ZS, LG, IS, MD, YY, OW, EE and EB contributed to the acquisition and analysis of data. DH, RK, YP and BR contributed to preparing the figures. DH and OSB drafted the text.
Funding Funding for this research was provided by the Legacy Heritage Bio-Medical Program of the Israel Science Foundation (grants no. 1814/13 and 1798/16) awarded to Professor Ohad Birk and the National Knowledge Center for Rare/Orphan Diseases sponsored by the Israel Ministry of Science, Technology and Space.
Competing interests None declared.
Patient consent Obtained.
Ethics approval Soroka Medical Center IRB.
Provenance and peer review Not commissioned; externally peer reviewed.