Loss of the sphingolipid desaturase DEGS1 causes hypomyelinating leukodystrophy

Sphingolipid imbalance is the culprit in a variety of neurological diseases, some affecting the myelin sheath. We have used whole-exome sequencing in patients with undetermined leukoencephalopathies to uncover the endoplasmic reticulum lipid desaturase DEGS1 as the causative gene in 19 patients from 13 unrelated families. Shared features among the cases include severe motor arrest, early nystagmus, dystonia, spasticity, and profound failure to thrive. MRI showed hypomyelination, thinning of the corpus callosum, and progressive thalamic and cerebellar atrophy, suggesting a critical role of DEGS1 in myelin development and maintenance. This enzyme converts dihydroceramide (DhCer) into ceramide (Cer) in the final step of the de novo biosynthesis pathway. We detected a marked increase of the substrate DhCer and DhCer/Cer ratios in patients' fibroblasts and muscle. Further, we used a knockdown approach for disease modeling in Danio rerio, followed by a preclinical test with the first-line treatment for multiple sclerosis, fingolimod (FTY720, Gilenya). The enzymatic inhibition of Cer synthase by fingolimod, 1 step prior to DEGS1 in the pathway, reduced the critical DhCer/Cer imbalance and the severe locomotor disability, increasing the number of myelinating oligodendrocytes in a zebrafish model. These proof-of-concept results pave the way to clinical translation. This study was supported by the ISCIII (FIS PI14/00581) (cofunded by the European Regional Development Fund); ‘La Marató de TV3’ Foundation 345/C/2014 (to AP, C. Casasnovas, and CP); the Hesperia Foundation and CIBER on Rare Diseases (CIBERER) (ACCI14-759) and the Secretariat for Universities and Research of the Ministry of Business and Knowledge of the Government of Catalonia (2017SGR1206) to AP; the Spanish Ministry of Economy and Competitiveness (MINECO-FEDER) (BFU2015-67400-P) to CP; the Spanish Institute for Health Carlos III (Miguel Servet program CPII16/00016) to SF; CIBERER to NL and MR; and a predoctoral fellowship awarded to DP from the Government of Catalonia through L′Agència de Gestió d’Ajuts Universitaris i de Recerca (AGAUR; FI-DGR 2014). XJ acknowledges a Sara Borrell postdoctoral fellowship from Instituto de Salud Carlos III.