Impaired skin barrier function due to reduced ω- O -acylceramide levels in a mouse model of Sjögren–Larsson syndrome

Sjögren–Larsson syndrome (SLS) is an inherited neurocutaneous disorder whose causative gene encodes the fatty aldehyde dehydrogenase ALDH3A2. To date, the detailed molecular mechanism of the skin pathology of SLS has remained largely unclear. We generated double knockout (DKO) mice for Aldh3a2 and its homolog Aldh3b2 (a pseudogene in humans). These mice showed hyperkeratosis and reduced fatty aldehyde dehydrogenase activity and skin barrier function. The levels of ω- O -acylceramides (acylceramides), which are specialized ceramides essential for skin barrier function, in the epidermis of DKO mice were about 60% of those in wild type mice. In the DKO mice, levels of acylceramide precursors (ω-hydroxy ceramides and triglycerides) were increased, suggesting that the final step of acylceramide production was inhibited. A decrease in acylceramide levels was also observed in human immortalized keratinocytes lacking ALDH3A2 . Differentiated keratinocytes prepared from the DKO mice exhibited impaired long-chain base metabolism. Based on these results, we propose that the long-chain-base–derived fatty aldehydes that accumulate in DKO mice and SLS patients attack and inhibit the enzyme involved in the final step of acylceramide. Our findings provide insight into the pathogenesis of the skin symptoms of SLS, i.e., decreased acylceramide production, and its molecular mechanism.

A Neurodegenerative Phenotype Associated With Sjögren-Larsson Syndrome

Sjögren-Larsson syndrome (SLS) is a rare neurologic disorder caused by pathogenic sequence variants in ALDH3A2 and characterized by ichthyosis, spasticity, intellectual disability, and a crystalline retinopathy. Neurologic symptoms develop in the first 2 years of life. Except for worsening ambulation due to spastic diplegia and contractures, the neurologic disease has been considered static and a neurodegenerative course is distinctly unusual. We describe a young child with Sjögren-Larsson syndrome who exhibited an early and severely progressive neurologic phenotype that may have been triggered by a febrile rotavirus infection. Together with 7 additional published cases of these atypical patients, we emphasize that a neurodegenerative course can be an extreme outcome for a minority of patients with Sjögren-Larsson syndrome.

Retinal Diseases with Ciliopathies

Ciliopathies are a group of diseases that affects cells containing the cilia organel. Retinal involvement is frequent in ciliopathies. The outer segment of retinal photoreceptors is composed of the cilium. Functional defects limited to the photoreceptors cilia, in particular, are classified as non-syndromic ciliopathies like Leber congenital amaurosis and retinitis pigmentosa. Photoreceptor disease also manifests as a part of syndromic ciliopathies with the involvement of multiple tissues as Usher syndrome, Joubert syndrome, Meckel-Gruber syndrome, Senior-Loken syndrome, Sjögren-Larsson syndrome, Bardet-Biedl syndrome, and Alstrom syndrome. Underlying mechanisms of pathology remain largely unclear in these diseases. Symptoms are treated using current methods. This paper describes the pathogenesis, clinics, diagnosis, and treatment of retinal diseases occurring due to ciliopathy.

Muscle Tone Assessment under General Anesthesia for Sjögren-Larsson Syndrome and Spasticity

Introduction: Study of muscle tone in individuals with severe spasticity (Modified Asworth Scale – MAS:3) under general anesthesia can confirm or rule out the eventual necessity of the impending spasticity relieving ablative neurosurgery by observing the hypertonia reduction and passive range of motion expansion. Therefore, what we measure under muscle relaxants is practically a fixed deformity. Case Presentation: The study was performed on a girl with Sjögren-Larsson syndrome, presenting with icthyosis and spastic diplegia. Proposed intervention was Dorsal Rhizotomy. Under general anesthesia, with and without muscle relaxants, hypertonia was significantly reduced (MAS:1), but the angle of motion did not increase much. Conclusion: We decided not to perform such a neurosurgical procedure. In ambiguous situations, the proposed study can help in decision-making for spasticity treatment.

Nuclear receptor NHR-49 promotes peroxisome proliferation to compensate for aldehyde dehydrogenase deficiency in C. elegans

The intracellular level of fatty aldehydes is tightly regulated to minimize the formation of toxic aldehyde adducts of cellular components. Accordingly, deficiency of a fatty aldehyde dehydrogenase FALDH causes the neurologic disorder Sjögren-Larsson syndrome (SLS) in humans. However, cellular responses to unresolved, elevated fatty aldehyde levels are poorly understood. Based on lipidomic and imaging analysis, we report that the loss of endoplasmic reticulum-, mitochondria- and peroxisomes-associated ALH-4, the C. elegans FALDH ortholog, increases fatty aldehyde levels and reduces fat storage. ALH-4 deficiency in the intestine, cell-nonautonomously induces NHR-49/NHR-79-dependent hypodermal peroxisome proliferation. This is accompanied by the upregulation of catalases and fatty acid catabolic enzymes, as indicated by RNA sequencing. Such a response is required to counteract ALH-4 deficiency since alh-4; nhr-49 double mutant animals are not viable. Our work reveals unexpected inter-tissue communication of fatty aldehyde levels, and suggests pharmacological modulation of peroxisome proliferation as a therapeutic strategy for SLS.