Lalani, S. | Search bioRxiv

bioRxiv2026

A DNM1L GTPase Effector Domain Deletion Causes Intermediate Defects in Peroxisomal and Mitochondrial Dynamics and Reveals a Targetable Metabolic Vulnerability

DNM1L encodes dynamin-related protein 1 (DRP1), a key GTPase regulating mitochondrial and peroxisomal dynamics. Pathogenic DNM1L variants are associated with a broad spectrum of neurodevelopmental and neurodegenerative disorders, with phenotypic severity varying by affected protein domain. While variants in the GTPase domain are typically associated with milder phenotypes and middle-domain variants with severe developmental and epileptic encephalopathy, the functional impact of GTPase effector domain (GED) variants remains less defined. Here, we describe four individuals harboring a recurrent heterozygous GED deletion (L700del) presenting with movement disorders and lacking severe infantile encephalopathy, consistent with an intermediate clinical phenotype. Patient-derived fibroblasts exhibited tubular peroxisomes and enlarged mitochondria, while Drosophila models demonstrated that DNM1LL700del has intermediate functional effects that were more pronounced than those of a GTPase-domain variant A192E but less severe than those of the middle-domain variant G350R. Comparison with another GED variant, Y691C, further demonstrated variant-specific differences in severity within the GED. Metabolic stress assays showed that L700del fibroblasts exhibited impaired growth under galactose conditions, consistent with increased vulnerability under conditions dependent on mitochondrial oxidative metabolism. Bezafibrate, a PPAR agonist that promotes mitochondrial biogenesis, partially rescued this growth defect. Together, these findings support a functional allelic spectrum in DNM1L-associated disease in which protein domain contributes to, but does not completely determine, functional severity. L700del represents an intermediate-strength allele associated with a movement-disorder phenotype and a pharmacologically modifiable metabolic vulnerability.

genetics↗

bioRxiv2022

Functional analysis of a novel de novo variant in PPP5C associated with microcephaly, seizures, and developmental delay

We describe a proband evaluated through the Undiagnosed Diseases Network (UDN) who presented with microcephaly, developmental delay, and refractory epilepsy with a de novo p.Ala47Thr missense variant in the protein phosphatase gene, PPP5C. This gene has not previously been associated with a Mendelian disease, and based on the population database, gnomAD, the gene has a low tolerance for loss-of-function variants (pLI=1, o/e=0.07). We functionally evaluated the PPP5C variant in C. elegans by knocking the variant into the orthologous gene, pph-5, at the corresponding residue, Ala48Thr. We employed assays in three different biological processes where pph-5 was known to function through opposing the activity of genes, mec-15 and sep-1. We demonstrated that, in contrast to control animals, the pph-5 Ala48Thr variant suppresses the neurite growth phenotype and the GABA signaling defects of mec-15 mutants, and the embryonic lethality of sep-1 mutants. The Ala48Thr variant did not display dominance and behaved similarly to the reference pph-5 null, indicating that the variant is likely a strong hypomorph or complete loss-of-function. We conclude that pph-5 Ala48Thr is damaging in C. elegans. By extension in the proband, PPP5C p.Ala47Thr is likely damaging, the de novo dominant presentation is consistent with haplo-insufficiency, and the PPP5C variant is likely responsible for one or more of the probands phenotypes.

genetics↗