A novel ELOVL4 variant, L168S, causes early childhood-onset Spinocerebellar ataxia-34 and retinal dysfunction: a case report

The Spinocerebellar Ataxia 34-Causing W246G ELOVL4 Mutation Does Not Alter Cerebellar Neuron Populations in a Rat Model

Spinocerebellar ataxia 34 (SCA34) is an autosomal dominant disease that arises from point mutations in the fatty acid elongase, Elongation of Very Long Chain Fatty Acids 4 (ELOVL4), which is essential for the synthesis of Very Long Chain-Saturated Fatty Acids (VLC-SFA) and Very Long Chain-Polyunsaturated Fatty Acids (VLC-PUFA) (28-34 carbons long). SCA34 is considered a neurodegenerative disease. However, a novel rat model of SCA34 (SCA34-KI rat) with knock-in of the W246G ELOVL4 mutation that causes human SCA34 shows early motor impairment and aberrant synaptic transmission and plasticity without overt neurodegeneration. ELOVL4 is expressed in neurogenic regions of the developing brain, is implicated in cell cycle regulation, and ELOVL4 mutations that cause neuroichthyosis lead to developmental brain malformation, suggesting that aberrant neuron generation due to ELOVL4 mutations might contribute to SCA34. To test whether W246G ELOVL4 altered neuronal generation or survival in the cerebellum, we compared the numbers of Purkinje cells, unipolar brush cells, molecular layer interneurons, granule and displaced granule cells in the cerebellum of wildtype, heterozygous, and homozygous SCA34-KI rats at four months of age, when motor impairment is already present. An unbiased, semi-automated method based on Cellpose 2.0 and ImageJ was used to quantify neuronal populations in cerebellar sections immunolabeled for known neuron-specific markers. Neuronal populations and cortical structure were unaffected by the W246G ELOVL4 mutation by four months of age, a time when synaptic and motor dysfunction are already present, suggesting that SCA34 pathology originates from synaptic dysfunction due to VLC-SFA deficiency, rather than aberrant neuronal production or neurodegeneration.

Potential Clinical Benefit of Very Long Chain Fatty Acid Supplementation in Spinocerebellar Ataxia Type 34

Spinocerebellar ataxia type 34 (SCA34) is a dominantly inherited disease that causes late-onset ataxia, in association with skin lesions in the form of erythrokeratodermia variabilis. It is caused by mutations in the ELOVL4 gene, which encodes for the ELOVL4 protein and has the function of lengthening very long chain (VLC) fatty acids (FA), which are important components of central myelin. The aim of this work was to review the medical literature on the biochemical abnormalities of SCA34, and based on the obtained information, to propose supplementation of deficient FAs. A review of the ad hoc medical literature was performed. Plasma levels of the ELOVL4 products C32, C34 and C36 FA have not been reported in SCA34 yet. However, pathogenic variants of ELOVL4 revealed deficient biosynthesis of C28, C30, C32, C34 and C36 FA compared to WT in cell cultures, and the levels of ceramides and phosphatidylcholines containing ≥ 34 C FA were decreased compared to WT in HeLa cells expressing mutant SCA34 proteins. Besides, a pathological study of SCA34 revealed myelin destruction and loss of oligodendrocytes in cerebral and cerebellar white matter. Levels of VLC-FA should be determined, to identify specifically deficient FAs in SCA34. Cerebellar ataxia could possibly be improved by administration of the deficient FAs, as found in SCA38 with supplementation of docosahexaenoic acid. The authors suggest investigators with access to SCA34, to take into consideration this therapeutic hypothesis, and try to verify the potential efficacy of administration of VLCFA in this disease.

Posterior Polar Annular Choroidal Dystrophy: Genetic Insights and Differential Diagnosis in Inherited Retinal Diseases

Posterior polar annular choroidal dystrophy (PPACD) is a rare ocular disorder and presents as symmetric degeneration of the retinal pigment epithelium (RPE) and the underlying choriocapillaris, encircling the retinal vascular arcades and optic disc. This condition distinctively preserves the foveal region, optic disc, and the outermost regions of the retina. Despite its distinct clinical presentation, due to the infrequency of its occurrence and the limited number of reported cases, the pathophysiology, and the genetic foundations of PPACD are still largely uncharted. This review aims to bridge this knowledge gap by investigating potential genetic contributors to PPACD, assessing current findings, and identifying genes that warrant further study. Emphasis is also placed on the crucial role of multimodal imaging in diagnosing PPACD, highlighting its importance in understanding disease pathophysiology. By analyzing existing case reports and drawing comparisons with similar retinal disorders, this paper endeavors to delineate the possible genetic correlations in PPACD, providing a foundation for future genetic research and the development of targeted diagnostic strategies.