Ceramide profiling of stratum corneum in Sjögren-Larsson syndrome.

BACKGROUND: Sjögren-Larsson syndrome (SLS) is a neurocutaneous disorder whose causative gene is the fatty aldehyde dehydrogenase ALDH3A2 and of which ichthyosis is the major skin symptom. The stratum corneum contains a variety of ceramides, among which ω-O-acylceramides (acylceramides) and protein-bound ceramides are essential for skin permeability barrier formation. OBJECTIVES: To determine the ceramide classes/species responsible for SLS pathogenesis and the enzymes that are impaired in SLS. METHODS: Genomic DNA was collected from peripheral blood samples from an SLS patient and her parents, and whole-genome sequencing and Sanger sequencing were performed. Lipids were extracted from stratum corneum samples from the SLS patient and healthy volunteers and subjected to ceramide profiling via liquid chromatography coupled with tandem mass spectrometry. RESULTS: A duplication (c.55_130dup) and a missense mutation (p.Lys447Glu) were found in the patient's ALDH3A2 gene. The patient had reduced levels of all acylceramide classes, with total acylceramide levels at 25 % of healthy controls. Reductions were also observed for several nonacylated ceramides: ceramides with phytosphingosine or 6-hydroxysphingosine in the long-chain base moiety were reduced to 24 % and 41 % of control levels, respectively, and ceramides with an α-hydroxy fatty acid as the fatty acid moiety were reduced to 29 %. The fatty acid moiety was shortened in many nonacylated ceramide classes. CONCLUSION: These results suggest that reduced acylceramide levels are a primary cause of the ichthyosis symptoms of SLS, but reductions in other ceramide classes may also be involved.

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.

Novel ALDH3A2 mutations in structural and functional domains of FALDH causing diverse clinical phenotypes in Sjögren-Larsson syndrome patients.

Mutations in ALDH3A2 cause Sjögren-Larsson syndrome (SLS), a neuro-ichthyotic condition due to the deficiency of fatty aldehyde dehydrogenase (FALDH). We screened for novel mutations causing SLS among Indian ethnicity, characterized the identified mutations in silico and in vitro, and retrospectively evaluated their role in phenotypic heterogeneity. Interestingly, asymmetric distribution of nonclassical traits was observed in our cases. Nerve conduction studies suggested intrinsic-minus-claw hands in two siblings, a novel neurological phenotype to SLS. Genetic testing revealed five novel homozygous ALDH3A2 mutations in six cases: Case-1-NM_000382.2:c.50C>A, NP_000373.1:p.(Ser17Ter); Case-2-NM_000382.2:c.199G>T, NP_000373.1:p.(Glu67Ter); Case-3-NM_000382.2:c.1208G>A, NP_000373.1:p.(Gly403Asp); Case-4-NM_000382.2:c.1325C>T, NP_000373.1:p.(Pro442Leu); Case-5 and -6 NM_000382.2:c.1349G>A, NP_000373.1:p.(Trp450Ter). The mutations identified were predicted to be pathogenic and disrupt the functional domains of the FALDH. p.(Pro442Leu) at the C-terminal α-helix, might impair the substrate gating process. Mammalian expression studies with exon-9 mutants confirmed the profound reduction in the enzyme activity. Diminished aldehyde-oxidizing activity was observed with cases-2 and 3. Cases-2 and 3 showed epidermal hyperplasia with mild intracellular edema, spongiosis, hypergranulosis, and perivascular-interstitial lymphocytic infiltrate and a leaky eosinophilic epidermis. The presence of keratin-containing milia-like lipid vacuoles implies defective lamellar secretion with p.(Gly403Asp). This study improves our understanding of the clinical and mutational diversity in SLS, which might help to fast-track diagnostic and therapeutic interventions of this debilitating disorder.

Sjogren-Larsson Syndrome: A case series of five members from an extended family with a novel mutation.

BACKGROUNDD: Sjogren-Larsson syndrome (SLS) is a rare autosomal recessive disorder, characterized by a triad of spastic tetraplegia or diplegia, congenital ichthyosis, and intellectual disability. METHODS: We report a seven-years-old female born to consanguineous parents who presented with erythematous dry scaly skin all over the body sparing the face, without collodion membrane which started since birth. There were associated with global developmental delay and seizure disorder. SLS was suspected and hence sequence analysis of the ALDH3A2 gene by next-generation sequencing was performed for the patient. RESULTS: A novel nucleotide exchange in homozygous state at position c.1320 in exon 9 of the ALDH3A2 gene (c.1320T>A), leading to a stop of the protein sequence (p.Tyr440) was detected in the patient. Genetic testing of the patient's extended family revealed another four affected family members with the same mutation. CONCLUSIONS: SLS should be suspected in any patient with a triad of ichthyosis, intellectual disability and spastic di/tetraplegia. Molecular genetic testing of the ALDH3A2 gene should be performed to confirm the diagnosis. Extended family screening is highly recommended.

1-O-Alkylglycerol accumulation reveals abnormal ether glycerolipid metabolism in Sjögren-Larsson syndrome.

Sjögren-Larsson syndrome (SLS) is an inherited metabolic disease characterized by ichthyosis, spasticity, intellectual disability and deficient oxidation and accumulation of of fatty aldehydes and alcohols. We investigated whether excess fatty alcohols in SLS are diverted into biosynthesis of ether glycerolipids (eGLs) by measuring the 1-O-alkylglycerol (AG) backbone of eGLs in stratum corneum, plasma and red blood cells (RBCs). In all tissues, saturated and monounsaturated AGs were detected. In stratum corneum from SLS patients, saturated AGs (C15-C20) were increased 97-fold (range: 86- to 169-fold) compared to controls. AGs were largely (67 ± 9%) derived from neutral esterified eGLs (i.e. alkyl-diacylglyerol) and free non-esterified AGs (28 ± 10%), but very little from plasmalogens (3 ± 5%). Plasma from SLS patients had 2-fold more C18:0-AG (p < 0.005) and 40% less C16:1-AG (p < 0.01) than controls but the total concentration of AGs was not increased, and the AG profile in RBCs from SLS subjects was normal. All AGs were profoundly reduced in plasma and RBCs from patients with Zellweger spectrum disorder, who have impaired eGL (i.e. plasmalogen) synthesis. The striking accumulation of AGs in stratum corneum of SLS patients constitutes a novel lipid biomarker for this disease, and may contribute to the pathogenesis of the ichthyosis. Measurement of AGs is a simple and convenient method to assess global synthesis of eGLs and potentially identify patients with defects in their metabolism.

Disturbed brain ether lipid metabolism and histology in Sjögren-Larsson syndrome.

Sjögren-Larsson syndrome (SLS) is a rare neurometabolic syndrome caused by deficient fatty aldehyde dehydrogenase. Patients exhibit intellectual disability, spastic paraplegia, and ichthyosis. The accumulation of fatty alcohols and fatty aldehydes has been demonstrated in plasma and skin but never in brain. Brain magnetic resonance imaging and spectroscopy studies, however, have shown an abundant lipid peak in the white matter of patients with SLS, suggesting lipid accumulation in the brain as well. Using histopathology, mass spectrometry imaging, and lipidomics, we studied the morphology and the lipidome of a postmortem brain of a 65-year-old female patient with genetically confirmed SLS and compared the results with a matched control brain. Histopathological analyses revealed structural white matter abnormalities with the presence of small lipid droplets, deficient myelin, and astrogliosis. Biochemically, severely disturbed lipid profiles were found in both white and gray matter of the SLS brain, with accumulation of fatty alcohols and ether lipids. Particularly, long-chain unsaturated ether lipid species accumulated, most prominently in white matter. Also, there was a striking accumulation of odd-chain fatty alcohols and odd-chain ether(phospho)lipids. Our results suggest that the central nervous system involvement in SLS is caused by the accumulation of fatty alcohols leading to a disbalance between ether lipid and glycero(phospho)lipid metabolism resulting in a profoundly disrupted brain lipidome. Our data show that SLS is not a pure leukoencephalopathy, but also a gray matter disease. Additionally, the histopathological abnormalities suggest that astrocytes and microglia might play a pivotal role in the underlying disease mechanism, possibly contributing to the impairment of myelin maintenance.

Macular crystalline inclusions in Sjögren-Larsson syndrome are dynamic structures that undergo remodeling.

BACKGROUND: Sjögren-Larsson syndrome (SLS) is a rare genetic neurocutaneous disease caused by mutations in ALDH3A2 that results in deficiency of fatty aldehyde dehydrogenase and accumulation of fatty aldehydes and alcohols. The disease is associated with ichthyosis, spasticity, and intellectual disability. Patients exhibit a characteristic retinopathy with macular crystalline inclusions that first appear in early childhood and increase with age. Once formed, the inclusions are thought to be inert and irreversible. We sought to document how the crystalline inclusions change over time. MATERIALS AND METHODS: Serial retinal photographs of 4 SLS subjects (9-23 years old) were taken over a period of 1-3 years. Images were compared by visual inspection and analyzed using ImageJ/Fiji software to observe changes. RESULTS: Visual inspection of retinal photographs of SLS subjects taken over time demonstrated distinctive changes in crystalline inclusions. New inclusions were formed and some established inclusions regressed. These changes were conveniently demonstrated with software-based photographic image analysis. CONCLUSIONS: We conclude that macular inclusions in SLS are not simply inert deposits, but are dynamic structures that form over time and are subject to remodeling. This conclusion provides new insight into the interplay between the metabolic defect and retinal pathology in SLS, and raises the potential for new therapeutic approaches to reverse some aspects of the maculopathy.

Next-generation sequencing through multi-gene panel testing for diagnosis of hereditary ichthyosis in Chinese.

Inherited ichthyoses are a heterogeneous group of rare disorders related to over 40 genes. To identify underlying molecular causes in inherited ichthyosis among Chinese and to correlate genotype and phenotype, 35 probands clinically diagnosed inherited ichthyosis, except ichthyosis vulgaris and X-linked ichthyosis, were included in our study. Molecular analysis was performed using next-generation sequencing (NGS) through multi-gene panel testing targeting all ichthyosis-related genes. Genetic variants causative for the ichthyosis were identified in 32 of 35 investigated patients. In all, 43 causative mutations across 12 genes were disclosed, including 16 novel variants. Thirteen keratinopathic ichthyosis, fourteen autosomal recessive congenital ichthyosis (ARCI) including one caused by mutations in SDR9C7, and five syndromic ichthyoses were confirmed. Four probands, with presumptive ARCI, turned out to be keratinopathic ichthyosis (2), neutral lipid storage disease (1), and Sjogren-Larsson syndrome (1), respectively. Next-generation technology has been demonstrated to be an effective tool in diagnosing inherited ichthyosis constituting a diverse group of cornification disorders. Our study further expands mutation spectrum and clinical phenotype associated with inherited ichthyosis in Chinese.

Sjögren-Larsson syndrome: a complex metabolic disease with a distinctive ocular phenotype.

Purpose: Sjögren-Larsson Syndrome (SLS) is a rare genetic disorder characterized by a distinctive crystalline maculopathy, congenital ichthyosis, spasticity and intellectual disability. We review the genetic, biochemical and clinical aspects of SLS with a particular focus on the ophthalmologic features of the disease.Methods: Published reports of SLS are combined with clinical experience to provide an overview of this disease.Results: SLS is caused by bi-allelic mutations in ALDH3A2, which codes for fatty aldehyde dehydrogenase, a key enzyme needed for the metabolism of long-chain aliphatic aldehydes and alcohols. SLS patients display perifoveal crystalline inclusions (glistening white dots) that appear in early childhood, vary from sparse to florid and are located in the inner retina. Other findings include retinal thinning, cystic macular degeneration, retinal pigment epithelium atrophy and deficiency of macular pigment. Photophobia is common. Visual evoked potentials are often absent or delayed, whereas electroretinography studies are usually normal. Mild-moderate deficits in visual acuity are common but vision is usually preserved into adulthood. The maculopathy is thought to be due to the accumulation of fatty aldehydes and/or alcohols, which alter membrane function. Defective macular pigment metabolism may also contribute to a unique susceptibility to photo-oxidative damage in the retina.Conclusions: The distinctive retinal phenotype, together with the neurologic and cutaneous symptoms, allows the ophthalmologist to reliably diagnose SLS. Although no effective treatment exists for the ocular symptoms, emerging insight into the pathogenic mechanisms at play in the eye promises to bring effective therapy for SLS in the future.

Genotype and phenotype variability in Sjögren-Larsson syndrome.

The Sjögren-Larsson syndrome (SLS) is a rare autosomal recessive disorder caused by pathogenic variants in the ALDH3A2 gene, which codes for fatty aldehyde dehydrogenase (FALDH). FALDH prevents the accumulation of toxic fatty aldehydes by converting them into fatty acids. Pathogenic ALDH3A2 variants cause symptoms such as ichthyosis, spasticity, intellectual disability, and a wide range of less common clinical features. Interpreting patient-to-patient variability is often complicated by inconsistent reporting and negatively impacts on establishing robust criteria to measure the success of SLS treatments. Thus, with this study, patient-centered literature data was merged into a concise genotype-based, open-access database (www.LOVD.nl/ALDH3A2). One hundred and seventy eight individuals with 90 unique SLS-causing variants were included with phenotypic data being available for more than 90%. While the three lead symptoms did occur in almost all cases, more heterogeneity was observed for other frequent clinical manifestations of SLS. However, a stringent genotype-phenotype correlation analysis was hampered by the considerable variability in reporting phenotypic features. Consequently, we compiled a set of recommendations of how to generate comprehensive SLS patient descriptions in the future. This will be of benefit on multiple levels, for example, in clinical diagnosis, basic research, and the development of novel treatment options for SLS.

Clinical, biochemical, and genetic aspects of Sjögren-Larsson syndrome.

Sjögren-Larsson syndrome (SLS) is caused by an autosomal recessive mutation in ALDH3A2, which encodes the fatty aldehyde dehydrogenase responsible for the metabolism of long-chain aliphatic aldehydes and alcohols. The pathophysiologic accumulation of aldehydes in various organs, including the skin, brain, and eyes, leads to characteristic features of ichthyosis, intellectual disability, spastic di-/quadriplegia, and low visual acuity with photophobia. The severity of the clinical manifestations thereof can vary greatly, although most patients are bound to a wheelchair due to contractures. To date, correlations between genotype and phenotype have proven difficult to document due to low disease incidence and high heterogenetic variability in mutations. This review summarizes the clinical characteristics of SLS that have been found to contribute to the prognosis thereof, as well as recent updates from genetic and brain imaging studies. In addition, the differential diagnoses of SLS are briefly illustrated, covering cerebral palsy and other genetic or neurocutaneous syndromes mimicking the syndrome.

PNPLA1 is a transacylase essential for the generation of the skin barrier lipid ω-O-acylceramide.

Lipids are the primary components of the skin permeability barrier, which is the body's most powerful defensive mechanism against pathogens. Acylceramide (ω-O-acylceramide) is a specialized lipid essential for skin barrier formation. Here, we identify PNPLA1 as the long-sought gene involved in the final step of acylceramide synthesis, esterification of ω-hydroxyceramide with linoleic acid, by cell-based assays. We show that increasing triglyceride levels by overproduction of the diacylglycerol acyltransferase DGAT2 stimulates acylceramide production, suggesting that triglyceride may act as a linoleic acid donor. Indeed, the in vitro analyses confirm that PNPLA1 catalyses acylceramide synthesis using triglyceride as a substrate. Mutant forms of PNPLA1 found in patients with ichthyosis exhibit reduced or no enzyme activity in either cell-based or in vitro assays. Altogether, our results indicate that PNPLA1 is directly involved in acylceramide synthesis as a transacylase, and provide important insights into the molecular mechanisms of skin barrier formation and of ichthyosis pathogenesis.

Disruption of the Sjögren-Larsson Syndrome Gene Aldh3a2 in Mice Increases Keratinocyte Growth and Retards Skin Barrier Recovery.

The fatty aldehyde dehydrogenase (FALDH) ALDH3A2 is the causative gene of Sjögren Larsson syndrome (SLS). To date, the molecular mechanism underlying the symptoms characterizing SLS has been poorly understood. Using Aldh3a2(-/-) mice, we found here that Aldh3a2 was the major FALDH active in undifferentiated keratinocytes. Long-chain base metabolism was greatly impaired in Aldh3a2(-/-) keratinocytes. Phenotypically, the intercellular spaces were widened in the basal layer of the Aldh3a2(-/-) epidermis due to hyperproliferation of keratinocytes. Furthermore, oxidative stress-induced genes were up-regulated in Aldh3a2(-/-) keratinocytes. Upon keratinocyte differentiation, the activity of another FALDH, Aldh3b2, surpassed that of Aldh3a2 As a result, Aldh3a2(-/-) mice were indistinguishable from wild-type mice in terms of their whole epidermis FALDH activity, and their skin barrier function was uncompromised under normal conditions. However, perturbation of the stratum corneum caused increased transepidermal water loss and delayed barrier recovery in Aldh3a2(-/-) mice. In conclusion, Aldh3a2(-/-) mice replicated some aspects of SLS symptoms, especially at the basal layer of the epidermis. Our results suggest that hyperproliferation of keratinocytes via oxidative stress responses may partly contribute to the ichthyosis symptoms of SLS.

Changes in the Submandibular Salivary Gland Epithelial Cell Subpopulations During Progression of Sjögren's Syndrome-Like Disease in the NOD/ShiLtJ Mouse Model.

Sjögren's syndrome (SS), an autoimmune exocrinopathy, is associated with dysfunction of the secretory salivary gland epithelium, leading to xerostomia. The etiology of SS disease progression is poorly understood as it is typically not diagnosed until late stage. Since mouse models allow the study of disease progression, we investigated the NOD/ShiLtJ mouse to explore temporal changes to the salivary epithelium. In the NOD/ShiLtJ model, SS presents secondary to autoimmune diabetes, and SS disease is reportedly fully established by 20 weeks. We compared epithelial morphology in the submandibular salivary glands (SMG) of NOD/ShiLtJ mice with SMGs from the parental strain at 12, 18, and 22 weeks of age and used immunofluorescence to detect epithelial proteins, including the acinar marker, aquaporin 5, ductal cell marker, cytokeratin 7, myoepithelial cell marker, smooth muscle α-actin, and the basal cell marker, cytokeratin 5, while confirming immune infiltrates with CD45R. We also compared these proteins in the labial salivary glands of human SS patients with control tissues. In the NOD/ShiLtJ SMG, regions of lymphocytic infiltrates were not associated with widespread epithelial tissue degradation; however, there was a decrease in the area of the gland occupied by secretory epithelial cells in favor of ductal epithelial cells. We observed an expansion of cells expressing cytokeratin 5 within the ducts and within the smooth muscle α-actin(+) basal myoepithelial population. The altered acinar/ductal ratio within the NOD/ShiLtJ SMG likely contributes to salivary hypofunction, while the expansion of cytokeratin 5 positive-basal cells may reflect loss of function or indicate a regenerative response.

Method to simultaneously determine the sphingosine 1-phosphate breakdown product (2E)-hexadecenal and its fatty acid derivatives using isotope-dilution HPLC-electrospray ionization-quadrupole/time-of-flight mass spectrometry.

Sphingosine 1-phosphate (S1P), a bioactive lipid involved in various physiological processes, can be irreversibly degraded by the membrane-bound S1P lyase (S1PL) yielding (2E)-hexadecenal and phosphoethanolamine. It is discussed that (2E)-hexadecenal is further oxidized to (2E)-hexadecenoic acid by the long-chain fatty aldehyde dehydrogenase ALDH3A2 (also known as FALDH) prior to activation via coupling to coenzyme A (CoA). Inhibition or defects in these enzymes, S1PL or FALDH, result in severe immunological disorders or the Sjögren-Larsson syndrome, respectively. Hence, it is of enormous importance to simultaneously determine the S1P breakdown product (2E)-hexadecenal and its fatty acid metabolites in biological samples. However, no method is available so far. Here, we present a sensitive and selective isotope-dilution high performance liquid chromatography-electrospray ionization-quadrupole/time-of-flight mass spectrometry method for simultaneous quantification of (2E)-hexadecenal and its fatty acid metabolites following derivatization with 2-diphenylacetyl-1,3-indandione-1-hydrazone and 1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide. Optimized conditions for sample derivatization, chromatographic separation, and MS/MS detection are presented as well as an extensive method validation. Finally, our method was successfully applied to biological samples. We found that (2E)-hexadecenal is almost quantitatively oxidized to (2E)-hexadecenoic acid, that is further activated as verified by cotreatment of HepG2 cell lysates with (2E)-hexadecenal and the acyl-CoA synthetase inhibitor triacsin C. Moreover, incubations of cell lysates with deuterated (2E)-hexadecenal revealed that no hexadecanoic acid is formed from the aldehyde. Thus, our method provides new insights into the sphingolipid metabolism and will be useful to investigate diseases known for abnormalities in long-chain fatty acid metabolism, e.g., the Sjögren-Larsson syndrome, in more detail.

Fatty aldehyde and fatty alcohol metabolism: review and importance for epidermal structure and function.

Normal fatty aldehyde and alcohol metabolism is essential for epidermal differentiation and function. Long-chain aldehydes are produced by catabolism of several lipids including fatty alcohols, sphingolipids, ether glycerolipids, isoprenoid alcohols and certain aliphatic lipids that undergo α- or ω-oxidation. The fatty aldehyde generated by these pathways is chiefly metabolized to fatty acid by fatty aldehyde dehydrogenase (FALDH, alternately known as ALDH3A2), which also functions to oxidize fatty alcohols as a component of the fatty alcohol:NAD oxidoreductase (FAO) enzyme complex. Genetic deficiency of FALDH/FAO in patients with Sjögren-Larsson syndrome (SLS) results in accumulation of fatty aldehydes, fatty alcohols and related lipids (ether glycerolipids, wax esters) in cultured keratinocytes. These biochemical changes are associated with abnormalities in formation of lamellar bodies in the stratum granulosum and impaired delivery of their precursor membranes to the stratum corneum (SC). The defective extracellular SC membranes are responsible for a leaky epidermal water barrier and ichthyosis. Although lamellar bodies appear to be the pathogenic target for abnormal fatty aldehyde/alcohol metabolism in SLS, the precise biochemical mechanisms are yet to be elucidated. Nevertheless, studies in SLS highlight the critical importance of FALDH and normal fatty aldehyde/alcohol metabolism for epidermal function. This article is part of a Special Issue entitled The Important Role of Lipids in the Epidermis and their Role in the Formation and Maintenance of the Cutaneous Barrier. Guest Editors: Kenneth R. Feingold and Peter Elias.

Sjögren-Larsson syndrome: importance of early diagnosis and aggressive physiotherapy.

Sjögren-Larsson syndrome (SLS) is a congenital ichthyotic disorder with spasticity. We describe a case of a 5-year-old boy with SLS diagnosed clinically based on congenital ichythosis, quadriplegia, and mental retardation. The child responded well to emollients and antihistamines. His quadriplegia was managed by aggressive physiotherapy and mental retardation by stimulation techniques. After a 3-year follow up, significant improvement was seen in his motor and mental disability. This case highlights the importance of clinical diagnosis and early intervention for such a disabling disorder.

Studying fatty aldehyde metabolism in living cells with pyrene-labeled compounds.

The lack of fatty aldehyde dehydrogenase function in Sjögren Larsson Syndrome (SLS) patient cells not only impairs the conversion of fatty aldehydes into their corresponding fatty acid but also has an effect on connected pathways. Alteration of the lipid profile in these cells is thought to be responsible for severe symptoms such as ichtyosis, mental retardation, and spasticity. Here we present a novel approach to examine fatty aldehyde metabolism in a time-dependent manner by measuring pyrene-labeled fatty aldehyde, fatty alcohol, fatty acid, and alkylglycerol in the culture medium of living cells using HPLC separation and fluorescence detection. Our results show that in fibroblasts from SLS patients, fatty aldehyde is not accumulating but is converted readily into fatty alcohol. In control cells, in contrast, exclusively the corresponding fatty acid is formed. SLS patient cells did not display a hypersensitivity toward hexadecanal or hexadecanol, but 3-fold lower concentrations of the fatty alcohol than the corresponding fatty aldehyde were needed to induce toxicity in SLS patient and in control cells.

Abnormal barrier function in the pathogenesis of ichthyosis: therapeutic implications for lipid metabolic disorders.

Ichthyoses, including inherited disorders of lipid metabolism, display a permeability barrier abnormality in which the severity of the clinical phenotype parallels the prominence of the barrier defect. The pathogenesis of the cutaneous phenotype represents the consequences of the mutation for epidermal function, coupled with a "best attempt" by affected epidermis to generate a competent barrier in a terrestrial environment. A compromised barrier in normal epidermis triggers a vigorous set of metabolic responses that rapidly normalizes function, but ichthyotic epidermis, which is inherently compromised, only partially succeeds in this effort. Unraveling mechanisms that account for barrier dysfunction in the ichthyoses has identified multiple, subcellular, and biochemical processes that contribute to the clinical phenotype. Current treatment of the ichthyoses remains largely symptomatic: directed toward reducing scale or corrective gene therapy. Reducing scale is often minimally effective. Gene therapy is impeded by multiple pitfalls, including difficulties in transcutaneous drug delivery, high costs, and discomfort of injections. We have begun to use information about disease pathogenesis to identify novel, pathogenesis-based therapeutic strategies for the ichthyoses. The clinical phenotype often reflects not only a deficiency of pathway end product due to reduced-function mutations in key synthetic enzymes but often also accumulation of proximal, potentially toxic metabolites. As a result, depending upon the identified pathomechanism(s) for each disorder, the accompanying ichthyosis can be treated by topical provision of pathway product (eg, cholesterol), with or without a proximal enzyme inhibitor (eg, simvastatin), to block metabolite production. Among the disorders of distal cholesterol metabolism, the cutaneous phenotype in Congenital Hemidysplasia with Ichthyosiform Erythroderma and Limb Defects (CHILD syndrome) and X-linked ichthyosis reflect metabolite accumulation and deficiency of pathway product (ie, cholesterol). We validated this therapeutic approach in two CHILD syndrome patients who failed to improve with topical cholesterol alone, but cleared with dual treatment with cholesterol plus lovastatin. In theory, the ichthyoses in other inherited lipid metabolic disorders could be treated analogously. This pathogenesis (pathway)-driven approach possesses several inherent advantages: (1) it is mechanism-specific for each disorder; (2) it is inherently safe, because natural lipids and/or approved drugs often are utilized; and (3) it should be inexpensive, and therefore it could be used widely in the developing world.