A novel mutation in the fatty acid transport protein 4 gene in a patient initially described as affected by self-healing congenital verruciform hyperkeratosis

[Syndromes with scales and keratosis]

Approximately 9000 different phenotypes are known in medicine. The definition phenotype includes both manifest diseases as well as features without any disease value and the pure genetic disposition to develop a disease (e.g. tumors or complex diseases); however, most phenotypes are rare monogenic hereditary diseases. Approximately 6400 of these phenotypes have so far been elucidated by molecular genetics and are caused by mutations in 4064 different genes. Of all genetic diseases, an estimated one third are associated with skin symptoms. Genodermatoses are the phenotypes predominantly related to the skin, of which approximately 600 are familiar to dermatologists. The syndromes with scaling and keratosis include cornification disorders where the symptoms are not limited to the skin. They are associated with skin symptoms such as ichthyosis, erythroderma and palmoplantar keratoderma but show additional symptoms from other organ groups. The typical combination of symptoms may be unique to a syndrome and therefore seminal for the diagnosis.

[Ichthyosis prematurity syndrome: Two new cases]

BACKGROUND

Ichthyosis prematurity syndrome is a rare syndromic form of ichthyosis caused by mutations in FATP4, which plays a central role in the transport and activation of fatty acids in the epidermis and in epidermal barrier function. Despite stereotypical clinical presentation in the neonatal period, the diagnosis is not well known by clinicians. Herein we report two new cases.

PATIENTS AND METHODS

Case no. 1: a boy born prematurely (33weeks of gestation) to non-consanguineous French parents presented at birth with respiratory distress necessitating admission to intensive care. His skin was covered by a thick caseous vernix, especially on the scalp, eyebrows and 4 limbs. At the age of 4years, the boy's skin appeared normal. Case no. 2: a boy born prematurely to consanguineous Moroccan parents (34weeks of gestation) presented at birth with respiratory distress requiring admission to intensive care. At clinical examination, he had a whitish thick skin giving an impression of vernix caseosa, with involvement of the scalp, forehead, 4 limbs and abdomen. At the age of 2 years, his skin was normal.

CONCLUSION

The clinical presentation of this syndrome is typical. It is important to make the diagnosis to enable genetic counseling and planning of adequate neonatal care in the event of future pregnancies.

Identification of novel FATP4 mutations in a Japanese patient with ichthyosis prematurity syndrome

Ichthyosis prematurity syndrome (IPS) is a rare autosomal recessive disorder characterized by prematurity, a thick caseous scale at birth and lifelong atopic diathesis. Here, we describe the first Japanese case of IPS and report novel compound heterozygous mutations (p.C403Y and p.R510H) in fatty acid transport protein 4 (FATP4). She is the first reported patient of Asian origin, entirely distinct from the Scandinavian population, in whom the heterozygote carrier frequency is very high.

Ichthyosis prematurity syndrome: a case report and review of known mutations

Ichthyosis prematurity syndrome (IPS; Mendelian Inheritance in Man 608649) is classified as a syndromic autosomal recessive ichthyosis. Here we describe two siblings with IPS and report a recurrent homozygous mutation (c.1430T>A) that is predicted to lead to a p.Val477Asp substitution in fatty acid transport protein 4. This mutation has arisen for the second time in an entirely distinct population from the Scandinavian population where it was first described.

A spontaneous Fatp4/Scl27a4 splice site mutation in a new murine model for congenital ichthyosis

Congenital ichthyoses are life-threatening conditions in humans. We describe here the identification and molecular characterization of a novel recessive mutation in mice that results in newborn lethality with severe congenital lamellar ichthyosis. Mutant newborns have a taut, shiny, non-expandable epidermis that resembles cornified manifestations of autosomal-recessive congenital ichthyosis in humans. The skin is stretched so tightly that the newborn mice are immobilized. The genetic defect was mapped to a region near the proximal end of chromosome 2 by SNP analysis, suggesting Fatp4/Slc27a4 as a candidate gene. FATP4 mutations in humans cause ichthyosis prematurity syndrome (IPS), and mutations of Fatp4 in mice have previously been found to cause a phenotype that resembles human congenital ichthyoses. Characterization of the Fatp4 cDNA revealed a fusion of exon 8 to exon 10, with deletion of exon 9. Genomic sequencing identified an A to T mutation in the splice donor sequence at the 3'-end of exon 9. Loss of exon 9 results in a frame shift mutation upstream from the conserved very long-chain acyl-CoA synthase (VLACS) domain. Histological studies revealed that the mutant mice have defects in keratinocyte differentiation, along with hyperproliferation of the stratum basale of the epidermis, a hyperkeratotic stratum corneum, and reduced numbers of secondary hair follicles. Since Fatp4 protein is present primarily at the stratum granulosum and the stratum spinosum, the hyperproliferation and the alterations in hair follicle induction suggest that very long chain fatty acids, in addition to being required for normal cornification, may influence signals from the stratum corneum to the basal cells that help to orchestrate normal skin differentiation.

The expression and function of fatty acid transport protein-2 and -4 in the murine placenta

Background

The uptake and trans-placental trafficking of fatty acids from the maternal blood into the fetal circulation are essential for embryonic development, and involve several families of proteins. Fatty acid transport proteins (FATPs) uniquely transport fatty acids into cells. We surmised that placental FATPs are germane for fetal growth, and are regulated during hypoxic stress, which is associated with reduced fat supply to the fetus.

Methodology/Principal Findings

Using cultured primary term human trophoblasts we found that FATP2, FATP4 and FATP6 were highly expressed in trophoblasts. Hypoxia enhanced the expression of trophoblastic FATP2 and reduced the expression of FATP4, with no change in FATP6. We also found that Fatp2 and Fatp4 are expressed in the mouse amnion and placenta, respectively. Mice deficient in Fatp2 or Fatp4 did not deviate from normal Mendelian distribution, with both embryos and placentas exhibiting normal weight and morphology, triglyceride content, and expression of genes related to fatty acid mobilization.

Conclusions/Significance

We conclude that even though hypoxia regulates the expression of FATP2 and FATP4 in human trophoblasts, mouse Fatp2 and Fatp4 are not essential for intrauterine fetal growth.

Ichthyosis prematurity syndrome: clinical evaluation of 17 families with a rare disorder of lipid metabolism

BACKGROUND

Ichthyosis prematurity syndrome (IPS) is classified as a syndromic congenital ichthyosis based on the presence of skin changes at birth, ultrastructural abnormalities in the epidermis, and extracutaneous manifestations. Recently, mutations in the fatty acid transporter protein 4 gene have been identified in patients with IPS.

OBJECTIVE

We sought to perform a detailed clinical evaluation of patients with IPS identified in Norway.

METHODS

Clinical examination and follow-up of all patients (n = 23) and light and electron microscopic examination of skin biopsy specimens were performed.

RESULTS

IPS was characterized prenatally by ultrasound findings of polyhydramnios, separation of membranes, echogenic amniotic fluid, and clear chorionic fluid. All patients were born prematurely with sometimes life-threatening neonatal asphyxia; this was likely caused by aspiration of corneocyte-containing amniotic fluid as postmortem examination of lung tissue in two patients revealed keratin debris filling the bronchial tree and alveoli. The skin appeared erythrodermic, swollen, and covered by a greasy, thick vernix caseosa-like "scale" at birth, and evolved rapidly to a mild chronic ichthyosis. Many patients subsequently had chronic, severe pruritus. Histopathologic and ultrastructural examination of skin biopsy specimens showed hyperkeratosis, acanthosis, dermal inflammation, and characteristic aggregates of curved lamellar structures in the upper epidermis. Peripheral blood eosinophilia was invariably present and most patients had increased serum immunoglobulin E levels. Over 70% of the patients had a history of respiratory allergy and/or food allergy.

LIMITATIONS

The study included only 23 patients because of the rarity of the disease.

CONCLUSION

IPS is characterized by defined genetic mutations, typical ultrastructural skin abnormalities, and distinct prenatal and postnatal clinical features.

Role of fatty acid transporters in epidermis: Implications for health and disease

Skin epidermis is an active site of lipid synthesis. The intercellular lipids of human stratum corneum (SC) are unique in composition and quite different from the lipids found in most biological membranes. The three major lipids in the SC are free fatty acids, cholesterol and ceramides. Fatty acids can be synthesized by keratinocytes de novo and, in addition, need to be taken up from the circulation. The latter process has been shown to be protein mediated, and several fatty acid transporters are expressed in skin. Recent studies of transgenic and knockout animal models for fatty acid transporters and the identification of fatty acid transport protein 4 (FATP4 or SLC27A4) mutations as causative for Ichthyosis Prematurity Syndrome highlight the vital roles of fatty acid transport and metabolism in skin homeostasis. This review provides an overview of our current understanding of the role of fatty acids and their transporters in cutaneous biology, including their involvement in epidermal barrier generation and skin inflammation.

FATP4 missense and nonsense mutations cause similar features in Ichthyosis Prematurity Syndrome

Background

Ichthyosis Prematurity Syndrome (IPS) is an autosomal recessive disorder characterized by premature birth, non-scaly ichthyosis and atopic manifestations. The disease was recently shown to be caused by mutations in the gene encoding the fatty acid transport protein 4 (FATP4) and a specific reduction in the incorporation of very long chain fatty acids (VLCFA) into cellular lipids.

Findings

We screened probands from five families segregating IPS for mutations in the FATP4 gene. Four probands were compound heterozygous for four different mutations of which three are novel. Four patients were heterozygous and one patient homozygous for the previously reported non-sense mutation p.C168X (c.504c > a). All patients had clinical characteristics of IPS and a similar clinical course.

Conclusions

Missense mutations and non-sense mutations in FATP4 are associated with similar clinical features suggesting that missense mutations have a severe impact on FATP4 function. The results broaden the mutational spectrum in FATP4 associated with IPS for molecular diagnosis of and further functional analysis of FATP4.