Prenatal diagnosis of congenital non-bullous ichthyosiform erythroderma (lamellar ichthyosis)

Epidermolytic hyperkeratosis: clinical update

Epidermolytic hyperkeratosis (EHK), earlier termed as bullous congenital ichthyosiform erythroderma is a skin disorder characterized as an autosomal dominant and rare disorder which has been observed to affect 1 in over 200,000 infants as a consequence of a significant mutation in the genes responsible for the keratin proteins, mostly keratin 1 and 10. The features present at birth include erythema and blistering. In adults, the hallmarks include hyperkeratosis, erosions, and blisters. The major symptoms including xerosis, pruritus, and painful fissuring lead not only to cosmetic problems but also stress, inferiority complex and other psychological conditions. While clinical inspection followed by confirmatory tests including histopathology and electron microscopic assessment is used for diagnosis, treatment modalities can be further improved for better diagnosis. This article reviews subtypes of ichthyosis, with a focus on EHK, genetics behind the disease, recently reported mutations, the existing diagnostics and treatments for the same and potential of new modalities in diagnosis/treatment.

Ultrastructural Features of Trafficking Defects Are Pronounced in Melanocytic Nevus in Hermansky–Pudlak Syndrome Type 1

Hermansky-Pudlak syndrome (HPS) is an autosomal recessive disorder characterized by oculocutaneous albinism, a bleeding disorder, and ceroid lipofuscinosis in the lungs and gut. HPS is genetically heterogeneous and the most common variant, HPS type 1, is caused by mutations in HPS1 gene. The protein encoded by HPS1 is considered to facilitate the trafficking of melanocyte-specific gene products into the premelanosome. We report the ultrastructural findings in a melanocytic nevus seen in a 17-y-old Japanese female patient with HPS1 who is a compound heterozygote of HPS1 mutations, including a novel mutation. Electron microscopy of a pinkish papule corresponding to the melanocytic nevus revealed markedly aberrant, immature melanosomes, large membranous structures, and giant melanosomes in the vicinity of trans-Golgi network, the characteristic abnormalities because of protein trafficking defects in HPS1. These ultrastructural features were far more clearly demonstrated in the nevus cells than in the epidermal melanocytes. Thus, ultrastructural analysis of nevus cells may be an additional diagnostic tool for HPS1 and could give us important clues to further understanding of the pathomechanisms of HPS.

Gap junction development in the human fetal hair follicle and bulge region

BACKGROUND

Gap junctions, composed of connexin (Cx) subunits, are channels that allow intercellular communication between adjacent cells and are thought to play a key role in the regulation of cell proliferation and differentiation. The Cx expression pattern and formation of gap junctions in human fetal hair follicles has yet to be clarified, including the prominent follicular bulge region that is believed to be a site rich in stem cells.

OBJECTIVES

To study the expression of two major Cxs, Cx26 and Cx43, in developing hair follicles in skin samples from a series of human fetuses of estimated gestational age (EGA) 88-163 days, and to determine quantitatively the presence of gap junctions.

METHODS

We used immunofluorescence labelling to investigate the sequential expression pattern of Cx26 and Cx43 in developing human hair follicles. Gap junction formation was observed by electron microscopy and the numbers of gap junctions were analysed quantitatively. Results Both Cx26 and Cx43 expression were observed at 88 days' EGA in the inner part of the hair peg. At 135 days' EGA, Cx26 was expressed in the outer root sheath (ORS) and the inner root sheath (IRS), while Cx43 was expressed chiefly in the IRS, hair matrix and sebaceous glands. At 163 days' EGA, Cx26 expression was most intense in the outermost layer of the ORS, in contrast to Cx43 expression which was in the inner part of the ORS. In the bulge region, only Cx43 was expressed in a subset of cells in the bulge. Ultrastructurally, gap junctions were observed at 102 days' EGA in the hair peg, and the number of gap junctions increased as the hair follicle matured. Gap junctions were also observed between the bulge cells in considerable numbers.

CONCLUSIONS

The changing expression patterns of Cx26 and Cx43 and the increasing gap junction numbers suggest a close association of Cx expression and gap junction formation with hair follicle morphogenesis. In addition, the present ultrastructural observations demonstrate that considerable numbers of the bulge cells, a putative site rich in hair follicle stem cells, form gap junctions during human hair follicle development.

Changes in gap junction distribution and connexin expression pattern during human fetal skin development

Gap junctions are intercellular channels composed of connexin subunits that mediate cell-cell communication. The functions of gap junctions are believed to be associated with cell proliferation and differentiation and to be important in maintaining tissue homeostasis. We therefore investigated the expression of connexins (Cx)26 and 43, the two major connexins in human epidermis, and examined the formation of gap junctions during human fetal epidermal development. By immunofluorescence, Cx26 expression was observed between 49 and 96 days' estimated gestational age (EGA) but was not present from 108 days' EGA onwards. Conversely, Cx43 expression was observed from 88 days' EGA onwards. Using electron microscopy, the typical structure of gap junctions was observed from 120 days' EGA. The number of gap junctions increased over time and they were more common in the upper layers, within the periderm and intermediate keratinocyte layers rather than the basal layer. Immunoelectron microscopy revealed Cx43 labeling on the gap junction structures after 105 days' EGA. Formation of gap junctions increased as skin developed, suggesting that gap junctions may play an important role in fetal skin development. Furthermore, the changing patterns of connexin expression suggest that Cx26 is important for early fetal epidermal development.

Formation of cornified cell envelope in human hair follicle development

BACKGROUND

Cornified cell envelope (CCE) formation is an important step in the final stage of keratinization, in which CCE precursor proteins including involucrin and loricrin are cross-linked by keratinocyte transglutaminases (TGases) to the inner surface of the plasma membrane of cornified cells, while the outer surface is coated with material derived from secreted lamellar granules.

OBJECTIVES

Skin samples from human fetuses of a series of estimated gestational age (EGA) (49-163 days) were studied for the prescence of precursor proteins. Methods TGase activity was studied by in situ TGase activity assay, and ultrastructural features of CCE formation were observed at each stage of hair follicle development. We used immunofluorescent labelling to investigate the time and site of expression of CCE precursor proteins involucrin and loricrin, TGases 1, 2 and 3, and a 25-kDa lamellar granule-associated protein (LGP) in developing human hair follicles.

RESULTS

In the hair germ (65-84 days EGA) (corresponding to the stages 1-2 of murine hair follicle morphogenesis), only TGase 2 was observed in the entire hair germ, where in situ TGase activity was weakly positive, although thickening of cell membrane was not seen ultrastructurally. In the hair peg (85-104 days EGA) (corresponding to the stage 3 of murine hair follicle morphogenesis), loricrin and TGase 2 were seen in cells of the upper part of the hair peg while TGase 1, 3 and LGP were observed in the inner cells of the hair peg. In situ TGase activity was weakly positive in the upper part and inner cells of the hair peg. In the bulbous hair peg (105-135 days EGA) (corresponding to the stages 4-6 of murine hair follicle morphogenesis) and differentiated lanugo hair follicle (> 135 days EGA) (corresponding to the stages 7-8 of murine hair follicle morphogenesis), immunoreactivities of involucrin, loricrin, TGase 1, 2, 3, in situ TGase activity and LGP were detected in the inner root sheath cells, hair canals and inner cells of the outer root sheath in the region of the isthmus. Ultrastructurally, thickening of cell membrane was already seen in the inner root sheath cells of the bulbous hair peg and electron-dense, thick CCE was observed in the hair cuticle and hair canal of differentiated lanugo hair follicle.

CONCLUSIONS

These data indicate that, in terms of CCE formation, certain portions of the developing human hair follicle have already been determined in differentiation of the hair canal and cuticle at the hair peg stage.

Changing patterns of localization of putative stem cells in developing human hair follicles

In rodents, the hair follicle stem cells lie in a well-defined bulge in the outer root sheath; however, the bulge as a stem cell site of human hair follicle epithelium is still controversial. Epidermal stem cells are thought to express high levels of beta1 integrin and low levels of E-cadherin and beta- and gamma-catenin. In order to clarify the ontogenic distribution of possible stem cells during hair follicle development, the expression patterns of beta1 integrin subunits, E-cadherin, and beta- and gamma-catenins in the skin samples from human fetuses of a series of estimated gestational ages (EGA) were examined. beta1 integrin-rich, E-cadherin-, and beta- and gamma-catenin-poor cells, possible stem cells, were localized to the entire hair germ (65-84 d EGA) and later to the outermost cells of hair peg (85-104 d EGA). In the bulbous hair peg (105-135 d EGA) and in the differentiated lanugo hair follicle (>135 d EGA), they were settled in the bulge and the outermost layer of the outer root sheath. This sequential localization was similar to that of cells rich in epidermal growth factor receptor expression and positive with keratin 19, a putative marker of epidermal stem cells. In addition, these beta1 integrin-rich, E-cadherin-, and beta- and gamma-catenin-poor cells showed similar, undifferentiated morphologic features by electron microscopy. This information of ontogenic localization of possible hair follicle stem cells contributes to the further understanding of mechanisms of human hair follicle morphogenesis and supports the idea that the human fetal hair follicle bulge is a site of stem cells for follicular epithelium.

Periderm cells form cornified cell envelope in their regression process during human epidermal development

Terminally differentiated stratified squamous epithelium forms a lining of the plasma membrane called the cornified cell envelope, a thick layer of several covalently cross-linked precursor proteins including involucrin, small proline-rich proteins, and loricrin. Their cross-linking isodipeptide bonds are formed by epidermal transglutaminases 1-3. Material from lamellar granules is attached on the extracellular surface of corneocytes during the keratinization process. The formation of cornified cell envelope and sequential expression of major cornified cell envelope precursor proteins, transglutaminases, and 25 kDa lamellar granule-associated protein were studied in human embryonic and fetal skin. Ultrastructurally, membrane thickening has already started in periderm cells of the two-layered epidermis and an electron-dense, thickened cell envelope similar to cornified cell envelope in adult epidermis is observed in periderm cells at the three-layered and later stages of skin development. In the two-layered epidermis (49-65 d estimated gestational age), immunoreactivities of involucrin, small proline-rich proteins, all the transglutaminases, and lamellar granule-associated protein were present only in the periderm. In the three-layered epidermis and thereafter (66-160 d estimated gestational age), loricrin became positive in the periderm cells, transglutaminases extended to the entire epidermis, and lamellar granule-associated protein was detected in intermediate cells as well as periderm cells. Immunoelectron microscopy demonstrated that both major cornified cell envelope precursor proteins, involucrin and loricrin, were restricted to the cornified cell envelope in periderm cells at this stage of development. After 160 d estimated gestational age, the periderm had disappeared and cornified cell envelope proteins and lamellar granule-associated proteins were expressed in the spinous, granular, and cornified cells and transglutaminases were detected in the entire epidermis. These findings indicate that cornified cell envelope precursor proteins, transglutaminases, and lamellar granule-associated proteins are expressed in coordination in periderm cells during human epidermal development and suggest that periderm cells form cornified cell envelope in the process of regression.

Prenatal exclusion of lamellar ichthyosis based on identification of two new mutations in the transglutaminase 1 gene

Lamellar ichthyosis is a severe, generalized, autosomal recessive genodermatosis characterized clinically by large, parchment-like scales and histologically by acanthosis and marked hyperkeratosis. Genetic heterogeneity in lamellar ichthyosis has been recognized with reports of two linked loci (on chromosomes 14q11 and 2q33-35). In a cohort of four small families with lamellar ichthyosis we found confirmatory evidence for linkage (p < or = 0.01) to D14S275, a microsatellite marker close to transglutaminase 1 on chromosome 14q11. We also identified two novel transglutaminase 1 mutations in an affected sibling pair from one of these families. The paternal mutation in exon 3, 1387insCAGC, causes a frameshift predicted to result in premature termination of translation within the same exon. The maternal mutation in exon 8, 4561delAC, also causes a frameshift and a premature stop codon in this exon. The mother of these siblings recently became pregnant with twins. Genotyping and direct sequencing of DNA isolated from fetal amniotic fluid cultures revealed the presence of the paternal but the absence of the maternal mutation, thus predicting a normal skin phenotype. Both twins were born with normal-appearing skin. Our findings demonstrate that mutations of both alleles of the transglutaminase 1 gene are the cause of lamellar ichthyosis in this family, and illustrate an emerging clinical application of molecular genetics in dermatology.

Topical application of viral vectors for epidermal gene transfer

Efficient gene transfer with extended gene expression is essential for successful treatment of skin diseases using gene therapy. Previously we evaluated a physical gene transfer method (gene gun delivery) for its ability to transfect the epidermis in vivo. In this study, we tested two viral vectors for their ability to transduce murine epidermis through topical application. Both an adenoviral vector and a herpes simplex virus (HSV) amplicon vector transduced murine epidermis with high efficiency after topical application. Differences in amount and duration of transgene expression were compared between these two vectors. Quantitative analysis of reporter lacZ gene expression showed that the viral vector-mediated gene transfers were superior to gene-gun delivery of plasmid DNA. Significant necrosis and cytotoxicity, however, were observed in the HSV-treated skin. In addition, we show that murine epidermis developed hyperkeratosis and acanthosis 4 d after an adenoviral vector containing a human TGF-alpha expression unit was applied topically. Finally we demonstrate the feasibility of transduction of fetal skin in utero by intraamniotic injection of an adenovirus vector.

Characteristic morphologic abnormality of harlequin ichthyosis detected in amniotic fluid cells

We have examined cells from amniotic fluid obtained at 17 and 21 weeks' gestation and fetal skin biopsy samples from a fetus at risk of harlequin ichthyosis by light and electron microscopy. Clumps of abnormally keratinized cells that had a large number of lipid droplets in the cytoplasm were seen within both the 17- and 21-week amniotic fluid cell pellets. The cells in these clumps were similar to the thick layers of keratinized cells observed in the skin biopsy and autopsy samples. Morphologic examination of the fetal skin biopsy samples obtained at 21 weeks gestation revealed the characteristic changes of harlequin ichthyosis. The intraepidermal portions of hair canals had an excessive number of layers of keratinized cells. Normal lamellar granules were absent but abundant membrane-bound vesicles of a similar size and a number of dense bodies were observed in the cells of the upper intermediate layers of the epidermis. Autopsy skin samples of the terminated fetus at the twenty-third week of gestation showed structural changes that corresponded to those of the amniotic fluid cells and the fetal skin biopsy samples, although the periderm was gone in all the regions. Our findings of amniotic fluid indicate that the characteristic epidermal abnormality of harlequin ichthyosis has been expressed at 17 weeks gestation in some parts of the body or structures of fetal skin (e.g., hair canals) that keratinize before interfollicular epidermis. Moreover, the results suggest that harlequin ichthyosis can be detected in utero by morphologic analysis of amniotic fluid cells obtained by amniocentesis.

All about ichthyosis

From "alligator people" to "porcupine boys," the ichthyoses have been a distinctly recognizable entity for thousands of years. Recent improvements in biochemical and genetic research have allowed more scientific delineation of this class of diseases. This article covers the latest in pathophysiology, the major classes of ichthyoses, many of the newer minor ones, prenatal diagnosis, and treatment options.

The expression of congenital ichthyosiform erythroderma in second trimester fetuses of the same family: morphologic and biochemical studies

The first born offspring of first-cousin parents was affected with a keratinization disorder thought to be nonbullous congenital ichthyosiform erythroderma (CIE). In each of three subsequent pregnancies, the parents elected to have prenatal diagnosis based on evaluation of fetal skin biopsies. The epidermis of fetus 1 was identical to normal 21-wk estimated gestation age (EGA) fetal epidermis, but because keratinization begins normally around 24 wk EGA, the procedure was repeated 4 wk later. A thin epidermis with a few layers of stratum corneum indicated a normal fetus and a healthy infant was born at term. Skin biopsy samples from fetus 2 gave conflicting results; the epidermis of one sample appeared normal but the second had 5-15 layers of incompletely keratinized cells superficial to basal and intermediate layers. The hair canals of both samples were hyperkeratotic. Pelleted amniotic fluid cells contained aggregates of incompletely keratinized epidermal cells and concentric rings of keratinized cells. The fetus was thought to be affected and the pregnancy terminated. Regional variation in epidermal thickness and keratinization was noted upon gross examination of the fetus and by histology of the skin. Marked hyperkeratinization of follicles was evident in all regions. No abnormal keratins were expressed in the affected epidermis but epidermal lipids analyzed from two body regions had a lower triglyceride content and a higher content of free sterols compared with age-matched, normal fetal epidermis. Immunolabeling for markers of differentiation revealed variable stages of epidermal differentiation according to region. Four structurally identical biopsy samples were obtained from a third fetus. The epidermis appeared normal for age and hair canals were keratinized to various extents. The pregnancy was continued and at 33 wk a male infant was born with a severe ichthyosis of the face and scalp and fine, white scaling on the body. The epidermis of both the severely and mildly affected regions of the newborn had a thick, compact stratum corneum and other features of CIE. Scars from all four fetal biopsies were identified on the trunk, in areas which appeared less affected clinically. This study reports, for the first time, the criteria for prenatal diagnosis of CIE and the variable expression of this disorder in the midtrimester fetus. More importantly, it demonstrates the risks and pitfalls of this in utero diagnosis based on epidermal morphology.

Label-retaining cells in human embryonic and fetal epidermis

Human embryonic and fetal epidermis was examined and labeling indices (LIs) for basal, intermediate, and periderm cells were determined. The LI for fetal basal cells was 8-11% and the LI for fetal intermediate cells was 7.5-9%. The total fetal epidermal LI was 16-20%, which equaled the basal LI for embryonic epidermis. After 21 days in organ culture, only basal cells in the fetal epidermis labeled with tritiated thymidine, while both basal and intermediate cells in the embryonic epidermis labeled and the total LI for fetal and embryonic epidermal cells was the same as the adult epidermal LI (7%). The LI for periderm decreased with increasing estimated gestational age (EGA) from 9.5% at 49 days EGA to 0.4% at 85 days EGA. A subpopulation of epithelial cells that retained tritiated thymidine label and that have some of the attributes associated with stem cells has been previously demonstrated in rodents. In order to examine human embryonic and fetal epidermis for the presence of such cells, epidermis from various gestational ages were labeled and grown in organ culture for 21 days. The mean percent label-retaining cells (LRCs) for embryonic and fetal epidermis was determined. Approximately 4% of the embryonic and 2% of the fetal epidermal cells retained label for 21 days in organ culture. Embryonic LRCs were found in the basal and suprabasal layers, but fetal LRCs were found only in the basal layer. The presence of LRCs in human embryonic and fetal epidermis suggests that epithelial cell proliferation in these tissues may be regulated via a stem cell pattern of proliferation.