Reduction of stratum corneum ceramides in Neu-Laxova syndrome caused by phosphoglycerate dehydrogenase deficiency

Human genetic defects of sphingolipid synthesis

Sphingolipids are ubiquitous lipids, present in the membranes of all cell types, the stratum corneum and the circulating lipoproteins. Autosomal recessive as well as dominant diseases due to disturbed sphingolipid biosynthesis have been identified, including defects in the synthesis of ceramides, sphingomyelins and glycosphingolipids. In many instances, these gene variants result in the loss of catalytic function of the mutated enzymes. Additional gene defects implicate the subcellular localization of the sphingolipid-synthesizing enzyme, the regulation of its activity, or even the function of a sphingolipid-transporter protein. The resulting metabolic alterations lead to two major, non-exclusive types of clinical manifestations: a neurological disease, more or less rapidly progressive, associated or not with intellectual disability, and an ichthyotic-type skin disorder. These phenotypes highlight the critical importance of sphingolipids in brain and skin development and homeostasis. The present article reviews the clinical symptoms, genetic and biochemical alterations, pathophysiological mechanisms and therapeutic options of this relatively novel group of metabolic diseases.

PHGDH-related microcephalic dwarfism in two fetuses: Expanding the phenotypical spectrum of L-serine biosynthesis defect

Defects in L-serine biosynthesis are a group of autosomal recessive diseases resulting in a wide phenotypic spectrum ranging from viable to lethal presentations and caused by variants in the three genes encoding the L-serine biosynthesis enzymes, PHGDH, PSAT1, and PSPH. Neu-Laxova syndrome (NLS) is the fetal form of this group, characterized by multiple congenital anomalies including severe intrauterine growth retardation, cutaneous lesions extending from ichthyosis to severe restrictive dermopathy with ectropion and eclabion, edema, microcephaly, central nervous system abnormalities, and flexion contractures. Here we report on two unrelated fetuses with an attenuated phenotype of NLS, that initially evoked Taybi-Linder syndrome. They carry biallelic pathogenic variants in the PHGDH gene. These observations expand the phenotypic continuum of L-serine biosynthesis defects, and illustrate the phenotypic overlap between NLS and microcephalic primordial dwarfism.

KLK11 ichthyosis: large truncal hyperkeratotic pigmented plaques underscore a distinct autosomal dominant disorder of cornification

Recently, Gong et al. reported two substitutions, p.(Gly50Glu) and p.(Gly50Arg), located at the last amino acid of the estimated signal peptide in kallikrein11 (KLK11) in three independent ichthyosiform erythroderma or erythrokeratoderma pedigrees (Gong et al., Br J Dermatol, 2023). Here, we present a further case of autosomal dominant congenital ichthyosiform erythroderma caused by the p.(Gly50Glu) substitution in KLK11; the patient had sharply demarcated pigmented hyperkeratotic lesions. Thus, p.(Gly50Glu) in KLK11 might represent a recurrent variant underlying this recently reported autosomal dominant disorder of cornification, and the large hyperkeratotic pigmented plaques seen in all patients may represent a pathognomonic part of the phenotype.

Pathogenic PSAT1 Variants and Autosomal Recessive Axonal Charcot-Marie-Tooth Disease With Ichthyosis

BACKGROUND

Biallelic pathogenic phosphoserine aminotransferase 1 (PSAT1) variants generally cause a severe phenotype predominantly involving the central nervous system. Here, for the first time, we report two patients harboring pathogenic PSAT1 variants only manifested as polyneuropathy and ichthyosis.

METHODS

Two patients from unrelated families presenting with polyneuropathy and ichthyosis were enrolled. Whole exome sequencing was performed to identify possible disease-causing variants. Their clinical, electrophysiological, imaging, biochemical, and pathologic changes were in detail assessed and investigated.

RESULTS

Homozygous variant c.43G>C and compound heterozygous variants c.112A>C and c.43G>C in PSAT1 were identified in patients 1 and 2, respectively. Nerve conduction studies revealed preserved or mild slowing motor nerve conduction velocities of the median nerves in the two patients, whereas the compound motor action potential in patient 1 was severely decreased. Brain magnetic resonance imaging of the two patients found no abnormalities. Median nerve enlargement was observed on ultrasound in patient 1. Both patients had normal level of serine and glycine in plasma and cerebrospinal fluid. Sural nerve biopsy found severe loss of myelinated fibers. Electron microscopy revealed neurofilament accumulation and mitochondrial aggregation in axons. Both variants in PSAT1 were classified as likely pathogenic or pathogenic variants according to the standard guidelines.

CONCLUSIONS

Our study confirms that pathogenic PSAT1 variants can cause a mild phenotype, predominantly as autosomal recessive axonal Charcot-Marie-Tooth disease.

Mild phenotypes of phosphoglycerate dehydrogenase deficiency by a novel mutation of PHGDH gene: Case report and literature review

Phosphoglycerate dehydrogenase (PHGDH) deficiency is a rare autosomal recessive genetic disease of serine biosynthesis. Its typical features are congenital microcephaly, epileptic seizures, and psychomotor developmental delay. Here, we reported the first Chinese familial cases with genetically confirmed PHGDH deficiency and reviewed several previous reports. Two siblings in this family presented with microcephaly, psychomotor retardation, and epilepsy in early juvenile. Brain magnetic resonance imaging (MRI) showed only a slight change of enlarged ventricle. Biochemical investigations revealed low serum serine and glycine concentrations. The whole-exome sequencing (WES) results identified a missense variant in the PHGDH gene (NM_006623.4: exon11: c.1211T>A, p. Val404Asp). Although two patients in this Chinese family carried the same pathogenic mutation in the PHGDH, their symptoms and responses to treatment were not exactly the same. We found a novel variant in the PHGDH gene and expanded the genotypic and phenotypic spectrum of serine biosynthesis disorders.

Ceramide Analysis in Combination With Genetic Testing May Provide a Precise Diagnosis for Self-Healing Collodion Babies

Self-healing collodion baby (SHCB), also called "self-improving collodion baby", is a rare mild variant of autosomal recessive congenital ichthyosis and is defined as a collodion baby who shows the nearly complete resolution of scaling within the first 3 months to 1 year of life. However, during the neonatal period, it is not easy to distinguish SHCB from other inflammatory forms of autosomal recessive congenital ichthyosis, such as congenital ichthyosiform erythroderma. Here, we report a case study of two Japanese SHCB patients with compound heterozygous mutations, c.235G>T (p.(Glu79∗))/ c.1189C>T (p.(Arg397Cys)) and c.1295A>G (p.(Tyr432Cys))/ c.1138delG (p.(Asp380Thrfs∗3)), in CYP4F22, which encodes cytochrome P450, family 4, subfamily F, polypeptide 22 (CYP4F22). Immunohistochemically, inflammation with the strong expression of IL-17C, IL-36γ, and TNF-α was seen in the skin at birth. CYP4F22 is an ultra-long-chain FA ω-hydroxylase responsible for ω-O-acylceramide (acylceramide) production. Among the epidermal ceramides, acylceramide is a key lipid in maintaining the epidermal permeability barrier function. We found that the levels of ceramides with ω-hydroxy FAs including acylceramides and the levels of protein-bound ceramides were much lower in stratum corneum samples obtained by tape stripping from SHCB patients than in those from their unaffected parents and individuals without SHCB. Additionally, our cell-based enzyme assay revealed that two mutants, p.(Glu79∗) and p.(Arg397Cys), had no enzyme activity. Our findings suggest that genetic testing coupled with noninvasive ceramide analyses using tape-stripped stratum corneum samples might be useful for the early and precise diagnosis of congenital ichthyoses, including SHCB.

Stratum Corneum Ceramide Profiles Provide Reliable Indicators of Remission and Potential Flares in Atopic Dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease. Prevention of exacerbation of AD is a crucial issue for all physicians. However, exacerbation of AD often is seen during reduction of AD treatment, even with appropriate follow-up by tapered topical corticosteroids and daily topical moisturizers, indicating the need for good indicators of AD remission. We hypothesized that the presence of mutations in FLG or the stratum corneum ceramide profile on AD remission phase may predict the ease of AD exacerbation. This study examined the differences in the frequency of FLG mutations or stratum corneum ceramide profiles (stratum corneum levels and carbon chain length for 11 ceramide classes [ceramides containing nonhydroxy fatty acids and dihydrosphingosines; nonhydroxy fatty acids and sphingosines; nonhydroxy fatty acids and 6-hydroxysphingosines; nonhydroxy fatty acids and phytosphingosines; a-hydroxy fatty acids and dihydrosphingosines; a-hydroxy fatty acids and sphingosines; a-hydroxy fatty acids and 6-hydroxysphingosines; a-hydroxy fatty acids and phytosphingosines; ester-linked fatty acids, o-hydroxy fatty acids, and sphingosines; ester-linked fatty acids, o-hydroxy fatty acids, and 6-hydroxysphingosines; and ester-linked fatty acids, o-hydroxy fatty acids, and phytosphingosines]) at AD remission phase between the two AD study groups: subsequent exacerbation (‒) and (+) of AD. The frequency of FLG mutations did not differ between the study groups. On the other hand, the carbon chain lengths of ceramides containing nonhydroxy fatty acids and dihydrosphingosines, nonhydroxy fatty acids and sphingosines, and nonhydroxy fatty acids and 6-hydroxysphingosines were shorter in the exacerbated AD group than in the maintained-AD group. Thus, the stratum corneum ceramide profile at the remission phase of AD is a potential biomarker, predicting the likelihood of substantial AD remission or subsequent AD exacerbation.

Season- and facial site-specific skin changes due to long-term mask wearing during the COVID-19 pandemic

Background

As people have regularly worn facial masks due to the coronavirus disease 2019 (COVID‐19) pandemic, mask‐wear‐related adverse effects on the skin have been recognized. The aim of this study was to explore skin changes, their seasonal variations in the general population caused by commonly used masks and a possible mechanism underlying negative effects of mask‐wearing.

Materials and methods

Eighteen Japanese females participated in the study during summer and winter in Japan. Skin characteristics were measured in the non‐mask‐wearing preauricular area and the mask‐wearing cheek and perioral areas.

Results

Trans‐epidermal water loss (TEWL) on the cheek area tended to be increased in winter, which was positively correlated with skin scaliness on the same area. Ceramide (CER) content and composition in the mask‐covered stratum corneum (SC) were slightly changed between summer and winter, and CER [NP]/[NS] ratio was negatively correlated with the TEWL on the perioral skin in winter. Skin hydration and sebum secretion were higher on the cheek compared to the perioral area in summer. Skin redness was particularly high on the cheek in winter.

Conclusion

Mask‐wear‐related skin changes were season‐ and facial site‐specific, and alterations in SC CER may play a role in barrier‐related skin problems caused by mask use.

Microcephaly in Neurometabolic Diseases

Neurometabolic disorders are an important group of diseases that mostly occur in neonates and infants. They are mainly due to the lack or dysfunction of an enzyme or cofactors necessary for a specific biochemical reaction, which leads to a deficiency of essential metabolites in the brain. This, in turn, can cause certain neurometabolic diseases. Disruption of metabolic pathways, and the inhibition at earlier stages, may lead to the storage of reaction intermediates, which are often toxic to the developing brain. Symptoms are caused by the progressive deterioration of mental, motor, and perceptual functions. The authors review the diseases with microcephaly, which may be one of the most visible signs of neurometabolic disorders.

The efficacy of synthetic pseudo-ceramide for dry and rough lips

OBJECTIVE

Lips can easily become dry and rough, one reason being the characteristics of their ceramide (CER) profile. Lips have lower levels of total ceramides, higher percentages of CER[NS] and CER[AS], and lower percentages of CER[NP] and CER[NH] than skin in other regions of the body. The purpose of this study was to clarify the effects of synthetic pseudo‐ceramide (pCer; Cetyl‐PG hydroxyethyl palmitamide) to improve the dryness and roughness of the lips of healthy subjects in a formulation that exclude an occlusive effect.

METHODS

Thirty‐one Japanese female subjects with normal skin (age range 21–37 years; mean 28.6) were enrolled in this study. A four‐week continuous use test was conducted using samples with or without 0.5% or 2.0% pCer. The degree of lip roughness was scored, and values of capacitance, transepidermal water loss (TEWL) and lip surface elasticity were measured. Endogenous CER profiles and absorption levels of pCer in the stratum corneum (SC) were analysed in tape‐stripped skin specimens.

RESULTS

Treatment with the pCer‐2.0% sample significantly improved the visual roughness score after 2 and 4 weeks compared to 0 weeks and compared to the Blank. Moreover, an improvement in TEWL was observed after 4 weeks of treatment with the pCer‐2.0% sample. CER[NP] showed a significant increase in pCer‐2.0% treated lips after 4 weeks compared to the Blank. Both pCer‐0.5% and pCer‐2.0% were significantly absorbed after 2 weeks compared with the Blank.

CONCLUSION

The effect of the synthetic pseudo‐ceramide pCer to improve the roughness of lips was shown excluding the effect of occlusiveness derived from the formulation for the first time. Since the improvement of TEWL and absorption of pCer was observed, we concluded that pCer was first absorbed in rough lip areas, improved the ceramide profile and consequently restored the barrier function.

L-serine synthesis via the phosphorylated pathway in humans

L-serine is a nonessential amino acid in eukaryotic cells, used for protein synthesis and in producing phosphoglycerides, glycerides, sphingolipids, phosphatidylserine, and methylenetetrahydrofolate. Moreover, L-serine is the precursor of two relevant coagonists of NMDA receptors: glycine (through the enzyme serine hydroxymethyltransferase), which preferentially acts on extrasynaptic receptors and D-serine (through the enzyme serine racemase), dominant at synaptic receptors. The cytosolic "phosphorylated pathway" regulates de novo biosynthesis of L-serine, employing 3-phosphoglycerate generated by glycolysis and the enzymes 3-phosphoglycerate dehydrogenase, phosphoserine aminotransferase, and phosphoserine phosphatase (the latter representing the irreversible step). In the human brain, L-serine is primarily found in glial cells and is supplied to neurons for D-serine synthesis. Serine-deficient patients show severe neurological symptoms, including congenital microcephaly, psychomotor retardation, and intractable seizures, thus highlighting the relevance of de novo production of this amino acid in brain development and morphogenesis. Indeed, the phosphorylated pathway is strictly linked to cancer. Moreover, L-serine has been suggested as a ready-to-use treatment, as also recently proposed for Alzheimer's disease. Here, we present our current state of knowledge concerning the three mammalian enzymes of the phosphorylated pathway and known mutations related to pathological conditions: although the structure of these enzymes has been solved, how enzyme activity is regulated remains largely unknown. We believe that an in-depth investigation of these enzymes is crucial to identify the molecular mechanisms involved in modulating concentrations of the serine enantiomers and for studying the interplay between glial and neuronal cells and also to determine the most suitable therapeutic approach for various diseases.

SDR9C7 plays an essential role in skin barrier function by dehydrogenating acylceramide for covalent attachment to proteins

Among the components of the barrier structure of the stratum corneum in human skin, the corneocyte lipid envelope (CLE) is extremely important for the skin barrier. The importance of the CLE and esterified ω-hydroxy sphingosine (CerEOS), its main precursor, has been suggested from the fact that mutations in a number of genes involved in CerEOS synthesis and CLE formation have been identified as genetic causes of congenital ichthyoses, which are severe genetic skin disorders. However, the molecule/mechanism involved in the covalent binding of CerEOS to proteins on the outer surface of the cornified cell envelope had been a missing part. Very recently, we proposed new potential modes of protein binding by covalent reactions of CerEOS-epoxy-enone. We revealed the biochemical function of short-chain dehydrogenase/reductase family 9C member 7 (SDR9C7), encoded by SDR9C7, as catalyzing the dehydrogenation of the lipoxygenase products that are esterified in CerEOS. Epoxy-enone produced by SDR9C7 covalently binds to proteins on the outer extracellular surface of the cornified cell envelope. Importantly, our recent striking findings were derived from the detailed lipid analysis of only one ARCI patient with SDR9C7 mutation. The combination of detailed analyses of precious samples from a rare patient and the establishment of corresponding animal models is an effective and powerful tool for analyzing rare inherited diseases. This review summarizes this newly revealed mechanism in skin barrier formation, describes the characteristic features of patients with SDR9C7 mutations, and introduces the clinical value of non-invasive analyses for patients with very rare intractable skin diseases.

Reduced stratum corneum acylceramides in autosomal recessive congenital ichthyosis with a NIPAL4 mutation

BACKGROUND

NIPAL4, encoding the NIPA-like domain containing 4 protein (NIPAL4), is one of the causative genes of autosomal recessive congenital ichthyosis (ARCI). The physiological role of NIPAL4 and the pathogenetic mechanisms of ARCI caused by NIPAL4 mutations remain unclear.

OBJECTIVE

To clarify the changes of ceramide components in the lesional stratum corneum (SC) and the gene expression profile in the lesional skin of an ARCI patient with a novel frameshift mutation in NIPAL4.

METHODS

We performed ultrastructural and immunohistochemical analyses of the skin. We used RNA sequencing to determine the mRNA expression in the skin of the patient and healthy individuals. We investigated ceramide components using tape stripped SC samples from the patient.

RESULTS

mRNA expression profiling in the patient's skin showed significant upregulation of IL-17/TNFα-related genes (IL17C, IL36A, IL36G, S100A7A, S100A9) and psoriasis hallmark genes (VNN3, LCE3D, PLA2G4D), and significant downregulation of lipid-associated genes (GAL, HAO2, FABP7). Ceramide analysis in the patient's SC revealed amounts of CER[NS] with carbon chain-length (C) 32-52 were increased, while amounts of most acylceramide with C66:2 - C72:2 were reduced relatively to those in healthy individuals. After the retinoid treatment, CER[NS] with carbon chains C46-54, CER[EOH] and CER[EOP] increased.

CONCLUSION

IL-17C and IL-36 family cytokines might be involved in the pathogenetic process of ARCI with NIPAL4 mutations. Reduced amounts of the acylceramides in the SC are associated with the skin phenotype due to NIPAL4 mutations. Efficacy of the oral retinoid treatment might be due to restored amounts of CER[EOH] and CER[EOP] in the SC.