Diagnosis of autosomal recessive lamellar ichthyosis with mutations in the TGM1 gene

Transglutaminases: part I-origins, sources, and biotechnological characteristics

The transglutaminases form a large family of intracellular and extracellular enzymes that catalyze cross-links between protein molecules. Transglutaminases crosslinking properties are widely applied to various industrial processes, to improve the firmness, viscosity, elasticity, and water-holding capacity of products in the food and pharmaceutical industries. However, the extremely high costs of obtaining transglutaminases from animal sources have prompted scientists to search for new sources of these enzymes. Therefore, research has been focused on producing transglutaminases by microorganisms, which may present wider scope of use, based on enzyme-specific characteristics. In this review, we present an overview of the literature addressing the origins, types, reactions, and general characterizations of this important enzyme family. A second review will deal with transglutaminases applications in the area of food industry, medicine, pharmaceuticals and biomaterials, as well as applications in the textile and leather industries.

Expanding the Genotypic Spectrum of Bathing Suit Ichthyosis

Importance

Bathing suit ichthyosis (BSI) is a rare congenital disorder of keratinization characterized by restriction of scale to sites of relatively higher temperature such as the trunk, with cooler areas remaining unaffected. Fewer than 40 cases have been reported in the literature. Bathing suit ichthyosis is caused by recessive, temperature-sensitive mutations in the transglutaminase-1 gene (TGM1). Clear genotype-phenotype correlations have been difficult to establish because several of the same TGM1 mutations have been reported in BSI and other forms of congenital ichthyosis. We identify novel and recurrent mutations in 16 participants with BSI.

Objective

To expand the genotypic spectrum of BSI, identifying novel TGM1 mutations in patients with BSI, and to use BSI genotypes to draw inferences about the temperature sensitivity of TGM1 mutations.

Design, Setting, and Participants

A total of 16 participants with BSI from 13 kindreds were identified from 6 academic medical centers. A detailed clinical history was obtained from each participant, including phenotypic presentation at birth and disease course. Each participant underwent targeted sequencing of TGM1.

Main Outcomes and Measures

Phenotypic and genotypic characteristics in these patients from birth onward.

Results

Of the 16 participants, 7 were male, and 9 were female (mean age, 12.6 years; range, 1-39 years). We found 1 novel TGM1 indel mutation (Ile469_Cys471delinsMetLeu) and 8 TGM1 missense mutations that to our knowledge have not been previously reported in BSI: 5 have been previously described in non-temperature-sensitive forms of congenital ichthyosis (Arg143Cys, Gly218Ser, Gly278Arg, Arg286Gln, and Ser358Arg), and 3 (Tyr374Cys, Phe495Leu, and Ser772Arg) are novel mutations. Three probands were homozygous for Arg264Trp, Arg286Gln, or Arg315Leu, indicating that these mutations are temperature sensitive. Seven of 10 probands with a compound heterozygous TGM1 genotype had a mutation at either arginine 307 or 315, providing evidence that mutations at these sites are temperature sensitive and highlighting the importance of these residues in the pathogenesis of BSI.

Conclusions and Relevance

Our findings expand the genotypic spectrum of BSI and the understanding of temperature sensitivity of TGM1 mutations. Increased awareness of temperature-sensitive TGM1 genotypes should aid in genetic counseling and provide insights into the pathophysiology of TGM1 ichthyoses, transglutaminase-1 enzymatic activity, and potential therapeutic approaches.

al mena: a comprehensive resource of human genetic variants integrating genomes and exomes from Arab, Middle Eastern and North African populations

Middle East and North Africa (MENA) encompass very unique populations, with a rich history and encompasses characteristic ethnic, linguistic and genetic diversity. The genetic diversity of MENA region has been largely unknown. The recent availability of whole-exome and whole-genome sequences from the region has made it possible to collect population-specific allele frequencies. The integration of data sets from this region would provide insights into the landscape of genetic variants in this region. We integrated genetic variants from multiple data sets systematically, available from this region to create a compendium of over 26 million genetic variations. The variants were systematically annotated and their allele frequencies in the data sets were computed and available as a web interface which enables quick query. As a proof of principle for application of the compendium for genetic epidemiology, we analyzed the allele frequencies for variants in transglutaminase 1 (TGM1) gene, associated with autosomal recessive lamellar ichthyosis. Our analysis revealed that the carrier frequency of selected variants differed widely with significant interethnic differences. To the best of our knowledge, al mena is the first and most comprehensive repertoire of genetic variations from the Arab, Middle Eastern and North African region. We hope al mena would accelerate Precision Medicine in the region.

Transglutaminase regulation of cell function

Transglutaminases (TGs) are multifunctional proteins having enzymatic and scaffolding functions that participate in regulation of cell fate in a wide range of cellular systems and are implicated to have roles in development of disease. This review highlights the mechanism of action of these proteins with respect to their structure, impact on cell differentiation and survival, role in cancer development and progression, and function in signal transduction. We also discuss the mechanisms whereby TG level is controlled and how TGs control downstream targets. The studies described herein begin to clarify the physiological roles of TGs in both normal biology and disease states.

Autosomal recessive congenital ichthyosis

The term autosomal recessive congenital ichthyosis (ARCI) refers to a group of rare disorders of keratinization classified as nonsyndromic forms of ichthyosis. This group was traditionally divided into lamellar ichthyosis (LI) and congenital ichthyosiform erythroderma (CIE) but today it also includes harlequin ichthyosis, self-healing collodion baby, acral self-healing collodion baby, and bathing suit ichthyosis. The combined prevalence of LI and CIE has been estimated at 1 case per 138 000 to 300 000 population. In some countries or regions, such as Norway and the coast of Galicia, the prevalence may be higher due to founder effects. ARCI is genetically highly heterogeneous and has been associated with 6 genes to date: TGM1, ALOXE3, ALOX12B, NIPAL4, CYP4F22, and ABCA12. In this article, we review the current knowledge on ARCI, with a focus on clinical, histological, ultrastructural, genetic, molecular, and treatment-related aspects.

Transglutaminase-1 mutations in Omani families with lamellar ichthyosis

OBJECTIVE

To determine the molecular basis of familial ichthyosis in three Omani families.

SUBJECTS AND METHODS

Nine patients from three consanguineous families, A, B, and C, were born with typical features of lamellar ichthyosis subtype including collodion membrane and maintained ectropion, and epidermal scaling through their childhood. The 4 patients from family B had more severe symptoms requiring neonatal critical care and subsequent regular treatment with emollients, eye lubricants, and low-dose acitretin. DNA was extracted from peripheral blood by standard methods. The samples were initially genotyped to screen known loci linked to recessive ichthyosis on chromosomes 2q33-32 (ABCA12), 14q11 (TGM1), and 19p12-q12 using commercially supplied polymorphic fluorescent microsatellite markers. TGM1 was analyzed by direct sequencing for disease-associated mutations.

RESULTS

Two known pathogenic mutations in TGM1 were detected: p.Gly278Arg in families A and B and p.Arg396His in family C. These two mutations were segregating in an autosomal recessive mode of inheritance.

CONCLUSION

Two known pathogenic TGM1 mutations were detected in three large consanguineous Omani families with lamellar ichthyosis. This study confirmed the geographic distribution of known mutations to an apparently unrelated population.

Transglutaminase-1 gene mutations in autosomal recessive congenital ichthyosis: summary of mutations (including 23 novel) and modeling of TGase-1

Autosomal recessive congenital ichthyosis (ARCI) is a heterogeneous group of rare cornification diseases. Germline mutations in TGM1 are the most common cause of ARCI in the United States. TGM1 encodes for the TGase-1 enzyme that functions in the formation of the cornified cell envelope. Structurally defective or attenuated cornified cell envelop have been shown in epidermal scales and appendages of ARCI patients with TGM1 mutations. We review the clinical manifestations as well as the molecular genetics of ARCI. In addition, we characterized 115 TGM1 mutations reported in 234 patients from diverse racial and ethnic backgrounds (Caucasion Americans, Norwegians, Swedish, Finnish, German, Swiss, French, Italian, Dutch, Portuguese, Hispanics, Iranian, Tunisian, Moroccan, Egyptian, Afghani, Hungarian, African Americans, Korean, Japanese and South African). We report 23 novel mutations: 71 (62%) missense; 20 (17%) nonsense; 9 (8%) deletion; 8 (7%) splice-site, and 7 (6%) insertion. The c.877-2A>G was the most commonly reported TGM1 mutation accounting for 34% (147 of 435) of all TGM1 mutant alleles reported to date. It had been shown that this mutation is common among North American and Norwegian patients due to a founder effect. Thirty-one percent (36 of 115) of all mutations and 41% (29 of 71) of missense mutations occurred in arginine residues in TGase-1. Forty-nine percent (35 of 71) of missense mutations were within CpG dinucleotides, and 74% (26/35) of these mutations were C>T or G>A transitions. We constructed a model of human TGase-1 and showed that all mutated arginines that reside in the two beta-barrel domains and two (R142 and R143) in the beta-sandwich are located at domain interfaces. In conclusion, this study expands the TGM1 mutation spectrum and summarizes the current knowledge of TGM1 mutations. The high frequency of mutated arginine codons in TGM1 may be due to the deamination of 5' methylated CpG dinucleotides.

Novel transglutaminase-1 mutations and genotype-phenotype investigations of 104 patients with autosomal recessive congenital ichthyosis in the USA

BACKGROUND

Autosomal recessive congenital ichthyosis (ARCI) is a rare hereditary disorder of cornification. Mutations in the transglutaminase-1 (TGM1) gene, which encodes for the epidermal enzyme transglutaminase-1 (TGase-1), are one of the causes of ARCI.

METHODS

The TGM1 mutation spectrum was characterised and genotype-phenotype correlations investigated in 104 patients with ARCI ascertained through the National Registry for Ichthyosis and Related Disorders in the USA. Methods: Germline mutations in TGM1 were identified in 55% (57/104) of patients with ARCI. Arginine residues in TGase-1 were mutated in 39% (22/57) of patients overall and 54% (20/37) of those with missense mutations. In total, 55% (12/22) of missense mutations were within CpG dinucleotides and 92% (11/12) of these mutations were C-->T or G-->A transitions. The genotype-phenotype investigation found that ARCI with TGM1 mutations was significantly associated with presence of collodion membrane at birth (p = 0.006), ectropion (p = 0.001), plate-like scales (p = 0.005) and alopecia (p = 0.001). Patients who had at least one mutation predicted to truncate TGase-1 were more likely to have more severe hypohidrosis (p = 0.001) and overheating (p = 0.0007) at onset of symptoms than were those with exclusively TGM1 missense mutations. A logistic model was developed, which predicted that individuals with collodion membrane, alopecia and/or eye problems are about four times more likely to have TGM1 mutations than patients without these findings.

CONCLUSION

This is the largest investigation of patients with ARCI to date. It expands the TGM1 mutation spectrum and confirms that despite genetic and phenotypic heterogeneity in ARCI, TGM1 is the main causative gene for this disorder. The high frequency of mutated arginine codons in TGM1 may be due to the deamination of CpG dinucleotides.

Bathing suit ichthyosis is caused by transglutaminase-1 deficiency: evidence for a temperature-sensitive phenotype

Bathing suit ichthyosis (BSI) is a striking and unique clinical form of autosomal recessive congenital ichthyosis characterized by pronounced scaling on the bathing suit areas but sparing of the extremities and the central face. Here we report on a series of 10 BSI patients. Our genetic, ultrastructural and biochemical investigations show that BSI is caused by transglutaminase-1 (TGase-1) deficiency. Altogether, we identified 13 mutations in TGM1-among them seven novel missense mutations and one novel nonsense mutation. Structural modeling for the Tyr276Asn mutation reveals that the residue is buried in the hydrophobic interior of the enzyme and that the hydroxyl side chain of Tyr276 is exposed to solvent in a cavity of the enzyme. Cryosections of healthy skin areas demonstrated an almost normal TGase activity, in contrast to the affected BSI skin, which only showed a cytoplasmic and clearly reduced TGase-1 activity. The distribution of TGase-1 substrates in the epidermis of affected skin corresponded to the situation in TGase-1 deficiency. Interestingly, the expression of TGase-3 and cathepsin D was reduced. Digital thermography validated a striking correlation between warmer body areas and presence of scaling in patients suggesting a decisive influence of the skin temperature. In situ TGase testing in skin of BSI patients demonstrated a marked decrease of enzyme activity when the temperature was increased from 25 to 37 degrees C. We conclude that BSI is caused by TGase-1 deficiency and suggest that it is a temperature-sensitive phenotype.

Structural changes in epidermal scale and appendages as indicators of defective TGM1 activity

Defective transglutaminase 1 (TGM1) is a causative factor in some cases of lamellar ichthyosis (LI) and congenital ichthyosiform erythroderma (CIE) despite large differences in the phenotype between these conditions. In some of these individuals, defective cornified envelopes (CEs) have been reported by light or electron microscopic examination in epidermal scale, nail and/or hair. These findings suggest that assessment of such defects could have a diagnostic utility in distinguishing TG1-deficient versus non-deficient cases of autosomal recessive ichthyosis (ARI) . Present work (a) examines the integrity of CEs in epidermal scale and appendages in a case of TGM1-deficient CIE, (b) assesses the utility of hair/nail versus scale analysis in the diagnosis of TGM1 deficiency in vivo and (c) helps characterize the consequences of the V518M mutation in TGM1, about which conflicting reports have appeared. To this end, epidermal scale or callus, nail and hair samples from a patient with TGM1-deficient CIE, his asymptomatic family members and control subjects were extracted vigorously in sodium dodecyl sulfate and dithiothreitol and examined by light (phase contrast) and electron microscopy. Both epidermal scale and nail from the index case lacked the prominent cell borders that were visible by phase contrast microscopy after detergent extraction of control samples. (By contrast, abundant envelope structures were visible in extracted epidermal scale from patients with ichthyosis vulgaris, loricrin keratoderma and epidermolytic hyperkeratosis.) Electron microscopy confirmed the paucity of intact CEs, and revealed further that hair cuticle cells from the same subject also lacked the marginal bands that are visible in control hair samples. Such aberrations were evident neither in the samples from asymptomatic relatives of the index case nor in the hair-cuticle cells of numerous normal individuals, evidence that this defect is not a common polymorphism. These studies extend our prior work on TGM1-deficient LI to the full spectrum of TGM1-deficient patients, showing that the CIE phenotype, when attributable to a V518M heterozygous mutation in TGM1 in combination with an inactive allele, confers a cross-linking deficiency in a variety of keratinizing epithelia, as previously shown for TGM1-negative LI. These results further suggest that a non-invasive assessment of scale, nail and hair could be of diagnostic utility in distinguishing patients across a full range of phenotypes with deficiency in TGM1-encoded transglutaminase activity from other causes of ARI.

Disruption of the suprabasal keratin network by mutation M150T in the helix initiation motif of keratin 10 does not affect cornified cell envelope formation in human epidermis

Keratin 10 (K10) is known to be tightly bound to the cornified cell envelope (CCE) and this binding is thought to play an important role in enhancing the structural integrity of the cornified cells. Bullous congenital ichthyosiform erythroderma (BCIE) is a genetic disorder of keratinization caused by gene mutations in the conserved sequences of keratin 1 (K1) or K10, which leads to abnormal suprabasal keratin network assembly. In BCIE patients' skin, the keratin network abnormalities make the upper spinous and granular keratinocytes fragile and result in blister formation. However, the exact pathomechanism of the hyperkeratosis seen in BCIE is still unknown. The involvement of the CCE in the pathomechanism of hyperkeratosis in BCIE is controversial. Abnormal CCE assembly may cause hyperkeratosis as reported in cases of lamellar ichthyosis. Binding of K10 to CCE is thought to be a vital connection between the suprabasal keratin filament network and CCE. We hypothesize that abnormal suprabasal keratin assembly caused by either K1 or K10 mutations can disrupt CCE formation, resulting in the hyperkeratosis observed in BCIE. To clarify whether K10 and keratin network defects affect CCE formation in vivo, the ultrastructural and immunohistological features of CCE were studied in the epidermis of two Japanese BCIE patients from two independent families carrying an identical missense mutation M150T in the helix initiation motif of K10. Ultrastructurally, a 15-nm-thick, dense, normal-appearing CCE was formed at the cell periphery of the keratinized epidermal cells. Light and electron microscopic immunolabeling revealed that the major CCE precursor proteins, involucrin and loricrin, were normally distributed and restricted to CCE of the epidermis. Immunofluorescent labeling showed that epidermal TGases, TGase 1, TGase 2 and TGase 3, were expressed normally in the epidermis. These findings suggest that a normal CCE is formed during the process of human epidermal keratinization, even if the suprabasal keratin filament network is disrupted as with this particular K10 mutation, M150T in BCIE.

Identification of two novel nonsense mutations in the transglutaminase 1 gene in a Hungarian patient with congenital ichthyosiform erythroderma

Congenital ichthyosiform erythroderma (CIE) belongs together with lamellar ichthyosis (LI) to the group of autosomal recessive congenital ichthyoses (ARCI). Mutations in the transglutaminase (TGase) 1 gene (TGM1) have been identified in several families with LI and in some families with CIE. We report a case of CIE with two new nonsense mutations: a C7780G transversion in exon 11 resulting in a premature stop codon at aminoacid residue Y503X and a C8533G transversion in exon 13 leading to a nonsense mutation at S669X. These mutations were also identified in a heterozygous pattern in the unaffected parents. These two termination-codons result in the translation of a truncated protein at the C-terminal end domain of the TGM 1 molecule. B.C1 monoclonal antibody failed to detect TGase 1 in the patient's skin sample, and TGase activity measured by monodansyl cadaverine-incorporation showed the reduced TGase activity at the distribution of TGase 1 in the epidermis.

The clinical spectrum of nonbullous congenital ichthyosiform erythroderma and lamellar ichthyosis

Until about 20 years ago, the term lamellar ichthyosis (LI) represented all nonbullous autosomal recessive ichthyoses except for harlequin ichthyosis and ichthyosis syndromes. Since the 1980s, nonbullous autosomal recessive ichthyoses have been divided into two major clinical entities, nonbullous congenital ichthyosiform erythroderma (NBCIE) and LI. The nature of scaling and intensity of erythroderma are important clinical features that distinguish between NBCIE and LI. However, a considerable number of cases show an intermediate phenotype between the two classic clinical features. Histologically, parakeratosis and inflammatory cell infiltration are seen more frequently in NBCIE than in LI and the stratum corneum is usually thicker in LI than in NBCIE. However, neither histopathological findings nor ultrastructural features seem to help clearly distinguish between NBCIE and LI. Mutations in any of the three known causative genes, TGM1, ALOXE3 or ALOX12B, can lead either to NBCIE or LI. Candidate genes specific to either NBCIE or LI alone have not been identified. Based on these facts, it might be better to consider NBCIE and LI as variations of a single keratinization disorder, although the classification of these autosomal recessive congenital ichthyosis patients into NBCIE or LI depending on their clinical features is still useful for practical patient management.

Self-healing collodion baby: a dynamic phenotype explained by a particular transglutaminase-1 mutation

Spontaneous healing with no or only very mild ichthyosis distinguishes the "self-healing collodion baby" from other congenital ichthyoses. In two self-healing collodion baby siblings with markedly diminished epidermal transglutaminase 1 activity we found the compound heterozygous transglutaminase 1 mutations G278R and D490G. Molecular modeling and biochemical assays of mutant proteins under elevated hydrostatic pressure suggest significantly reduced activity in G278R and a chelation of water molecules in D490G that locks the mutated enzyme in an inactive trans conformation in utero. After birth these water molecules are removed and the enzyme is predicted to isomerize back to a partially active cis form, explaining the dramatic improvement of this skin condition.

Collodion baby: a follow-up study of 17 cases

Seventeen cases of collodion baby are reported. Clinical aspects, complications, treatment, final outcome and family history were studied. We did not observe any clinical features in the collodion baby that could serve as a clue in predicting the final diagnosis. Infections were observed in nine, hypothermia in five and hypernatraemic dehydration in four cases. Skin infection mainly occurred in babies treated with emollients (petrolatum, lanolin and cetomacrogolis cream were used). We therefore recommend treating the collodion baby in a humidified incubator, if necessary with intravenous rehydration, but not to use emollients. The final outcome of these study patients was erythrodermic autosomal recessive lamellar ichthyosis in seven cases (41%), non-erythrodermic autosomal recessive lamellar ichthyosis in three cases (18%), Sjögren-Larsson in one case (6%), epidermolytic hyperkeratosis in one case (6%), acute neonatal variant of Gaucher disease in one case (6%) and normal skin in four cases (24%).