Adeno-associated virus vectors are able to restore fatty aldehyde dehydrogenase-deficiency. Implications for gene therapy in Sjogren-Larsson syndrome

New developments in the molecular treatment of ichthyosis: review of the literature

Ichthyosis covers a wide spectrum of diseases affecting the cornification of the skin. In recent years, new advances in understanding the pathophysiology of ichthyosis have been made. This knowledge, combined with constant development of pathogenesis-based therapies, such as protein replacement therapy and gene therapy, are rather promising for patients with inherited skin diseases. Several ongoing trials are investigating the potency of these new approaches and various studies have already been published. Furthermore, a lot of case series report that biological therapeutics are effective treatment options, mainly for Netherton syndrome and autosomal recessive congenital ichthyosis. It is expected that some of these new therapies will prove their efficacy and will be incorporated in the treatment of ichthyosis.

Current Strategies for the Gene Therapy of Autosomal Recessive Congenital Ichthyosis and Other Types of Inherited Ichthyosis

Mutations in genes such as transglutaminase-1 (TGM1), which are responsible for the formation and normal functioning of a lipid barrier, lead to the development of autosomal recessive congenital ichthyosis (ARCI). ARCIs are characterized by varying degrees of hyperkeratosis and the presence of scales on the body surface since birth. The quality of life of patients is often significantly affected, and in order to alleviate the manifestations of the disease, symptomatic therapy with moisturizers, keratolytics, retinoids and other cosmetic substances is often used to improve the condition of the patients' skin. Graft transplantation is commonly used to correct defects of the eye. However, these approaches offer symptomatic treatment that does not restore the lost protein function or provide a long-term skin barrier. Gene and cell therapies are evolving as promising therapy for ARCIs that can correct the functional activity of altered proteins. However, these approaches are still at an early stage of development. This review discusses current studies of gene and cell therapy approaches for various types of ichthyosis and their further prospects for patient treatment.

Gene Therapy and its Application in Dermatology

Gene therapy is an experimental technique to treat genetic diseases. It is based on the introduction of nucleic acid with the help of a vector, into a diseased cell or tissue, to correct the gene expression and thus prevent, halt, or reverse a pathological process. It is a promising treatment approach for genetic diseases, inherited diseases, vaccination, cancer, immunomodulation, as well as healing of some refractory ulcers. Both viral and nonviral vectors can be used to deliver the correct gene. An ideal vector should have the ability for sustained gene expression, acceptable coding capacity, high transduction efficiency, and devoid of mutagenicity. There are different techniques of vector delivery, but these techniques are still under research for assessment of their safety and effectiveness. The major challenges of gene therapy are immunogenicity, mutagenicity, and lack of sustainable therapeutic benefit. Despite these constraints, therapeutic success was obtained in a few genetic and inherited skin diseases. Skin being the largest, superficial, easily accessible and assessable organ of the body, may be a promising target for gene therapy research in the recent future.

Sjogren-Larsson Syndrome: Mechanisms and Management

Sjogren Larsson syndrome (SLS) is a rare autosomal recessive inborn error of lipid metabolism due to mutations in the ALDH3A2 that result in a deficiency of fatty aldehyde dehydrogenase (FALDH). The syndrome has a high prevalence in Sweden where it was first described, but now known to occur worldwide. The classical triad of ichthyosis, mental retardation and spasticity characterizes clinical features. Preterm birth is common. “Glistening white dots” in the retina is a pathognomic clinical feature. Magnetic resonance imaging of the brain demonstrates leukoencephalopathy predominant in the periventricular region. Cerebral MR spectroscopy reveals a characteristic abnormal lipid peak at 1.3ppm and a small peak at 0.9ppm. The primary role of FALDH is oxidation of medium and long-chain aliphatic aldehydes derived from fatty alcohol, phytanic acid, ether glycerolipids and sphingolipids. The diagnosis is based on the typical phenotype, demonstration of the enzyme deficiency and presence of biallelic mutations in the ALDH3A2. The management of SLS largely remains symptomatic currently. However, several potential therapeutic options are being developed, keeping in view of the fundamental metabolic defects or correcting the genetic defect. This review aims to summarize the clinical, genetic and biochemical findings, pathogenetic mechanisms and the current therapeutic options, in SLS.

A rare case of Sjogren-Larsson syndrome with recurrent pneumonia and asthma

Sjogren-Larsson syndrome (SLS) is a rare autosomal recessive neurocutaneous disorder with worldwide incidence of 0.4 per 100,000 people. It is characterized by the triad of congenital ichthyosis, spastic diplegia or quadriplegia, and mental retardation. Herein we report a 2-year-old male child with SLS, asthma, and recurrent pneumonia. SLS was confirmed by a molecular genetics study that revealed a deletion mutation in the ALDH3A2 gene. An ALDH3A2 gene mutation results in dysfunction of the microsomal enzyme fatty aldehyde dehydrogenase and impaired metabolism and accumulation of leukotriene B4, which is a key molecule and a pro-inflammatory mediator in developing allergic diseases, especially asthma. An increased level of leukotriene B4 has been reported in SLS patients. As far as we are aware, this is the first report of SLS associated with asthma and recurrent pneumonia. In conclusion, pediatricians should be aware of and evaluate patients with SLS for possible associated asthma and allergic disorders.

Genetics and prospective therapeutic targets for Sjögren-Larsson Syndrome

INTRODUCTION

Sjögren-Larsson syndrome (SLS) is a rare neurocutaneous disease characterized by ichthyosis, spasticity, intellectual disability and a distinctive retinopathy. It is caused by inactivating mutations in ALDH3A2, which codes for fatty aldehyde dehydrogenase (FALDH) and results in abnormal metabolism of long-chain aliphatic aldehydes and alcohols. The potential disease mechanisms leading to symptoms include 1) accumulation of toxic fatty aldehydes that form covalent adducts with lipids and membrane proteins; 2) physical disruption of multi-lamellar membranes in skin and brain; 3) abnormal activation of the JNK cell signaling pathway; and 4) defective farnesol metabolism resulting in abnormal PPAR-α dependent gene expression. Currently, no effective pathogenesis-based therapy is available.

AREAS COVERED

The clinical, pathologic and genetic features of SLS are summarized. The biochemical abnormalities caused by deficient activity of FALDH are reviewed in the context of proposed pathogenic mechanisms and potential therapeutic interventions.

EXPERT OPINION

The most promising pharmacologic approach to SLS involves blocking the formation of potentially harmful fatty aldehyde adducts using aldehyde scavenging drugs, currently in phase 2 clinical trials. Other approaches needing further investigation include: 1) ALDH-specific activator drugs and PPAR-α agonists to increase mutant FALDH activity; 2) inhibitors of the JNK phosphorylation cascade; 3) antioxidants to decrease aldehyde load; 4) dietary lipid modification; and 5) gene therapy.

Gene therapy for skin diseases

The skin possesses qualities that make it desirable for gene therapy, and studies have focused on gene therapy for multiple cutaneous diseases. Gene therapy uses a vector to introduce genetic material into cells to alter gene expression, negating a pathological process. This can be accomplished with a variety of viral vectors or nonviral administrations. Although results are promising, there are several potential pitfalls that must be addressed to improve the safety profile to make gene therapy widely available clinically.

A very rare neurocutaneous disorder in 2 siblings: Sjögren-Larsson syndrome

Sjögren-Larsson syndrome is an autosomal-recessive hereditary disorder involving congenital ichthyosis, mental retardation, and spastic diplegia or tetraplegia. It is caused by the deficient activity of fatty aldehyde dehydrogenase. In this report, the authors describe 2 siblings with Sjögren-Larsson syndrome. Both the patients had generalized ichthyosis, and the older one had spastic paraplegia and mental retardation, and the fundus examination revealed foveal and parafoveal glistening dots. The authors report the large kinship with Sjögren-Larsson syndrome, which is a rare and most probably underdiagnosed syndrome.

Sjögren-Larsson syndrome

Sjögren-Larsson syndrome is a recessively inherited syndrome caused by deficiency of fatty aldehyde dehydrogenase. The most common symptoms and signs are described, especially ichthyosis, spastic diplegia, and severe learning difficulties; but also other less frequent ones. Special investigations include sensory evoked potentials, electromyography, and proton magnetic resonance spectroscopy. Post-mortem examination shows, in particular, an accumulation of lipid substances in specific regions of the brain. The diagnosis depends on the measurement of fatty aldehyde dehydrogenase in cultured fibroblasts from skin biopsies, and by identifying known mutations by allele-specific polymerase chain reaction assay. Prenatal diagnosis is possible by using the same technique. The disorder is located on gene 17, and many mutations have been identified. Most mutations are unique to an affected family, but clinical variations may be due to unknown genetic and environmental factors. The deficiency of the enzyme impairs the oxidation of medium and long chain fatty aldehydes, and this may explain the link between the brain and skin disorders. The treatment of affected children needs input from a number of specialists, and their contributions are discussed.

Restoration of fatty aldehyde dehydrogenase deficiency in Sjögren-Larsson syndrome

Sjögren-Larsson syndrome (SLS) is an autosomal recessive neurocutaneous disorder caused by mutation in the ALDH3A2 gene that codes for human fatty aldehyde dehydrogenase (FALDH). Sjögren-Larsson syndrome patients lack FALDH, which catalyzes the oxidation of long-chain aliphatic aldehydes to fatty acids. The impaired FALDH activity leads to congenital ichthyosis, mental retardation and spasticity. The current lack of treatment is an impetus to develop gene therapy strategies by introducing functional FALDH into defective cells. We delivered human FALDH into keratinocytes of SLS patients using recombinant adeno-associated virus-2 vectors. Transduction of SLS keratinocytes resulted in an augmentation of FALDH activity comparable to phenotypically normal heterozygous carriers. Toxicity of long-chain aldehydes for FALDH-deficient cells decreased almost to the level of unaffected keratinocytes. Three-dimensional culture of corrected SLS keratinocytes revealed an ameliorated FALDH expression. These studies demonstrate the restoration of FALDH in human SLS cells supporting the concept of gene therapy as a potential future treatment option for SLS.