Exome sequencing identifies a novel TTC37 mutation in the first reported case of Trichohepatoenteric syndrome (THE-S) in South Africa

Trichohepatoenteric Syndrome: A Report of Two Children From Bahrain With a Novel Mutation and a Literature Review

Trichohepatoenteric syndrome (THES) is a rare genetic disorder inherited in an autosomal recessive manner. THES primarily leads to neonatal enteropathy, typically manifesting as severe, persistent diarrhea, distinctive facial features such as frontal bossing and a broad flat nasal bridge, woolly and fragile hair, immunodeficiency resulting in recurrent infections, failure to thrive (FTT), and liver complications including fibrosis or cirrhosis. This multisystem disorder is linked to mutations in the tetratricopeptide repeat domain 37 (TTC37) gene, also known as superkiller complex (SKIC) protein 3, responsible for THES type 1, and the Ski2-like ribonucleic acid (RNA) helicase (SKIV2L) gene, also known as SKIC2, responsible for THES type 2. This case report describes two far-related pediatric patients from Bahrain diagnosed with THES type 1. Although both patients exhibited typical symptoms of this syndrome, the first patient had more severe symptoms. Diagnostic genetic evaluations confirmed THES. Patient 1 had three homozygous variants in the TTC37 gene, while Patient 2 had two variants in the same gene. Both of our patients had a novel homozygous variant. The treatment focused on supportive care and infection management. Despite these efforts, patients did not reach their growth potential. This report underscores the necessity for early identification of THES to facilitate appropriate management and genetic counseling.

Macrocephaly and Finger Changes: A Narrative Review

Macrocephaly, characterized by an abnormally large head circumference, often co-occurs with distinctive finger changes, presenting a diagnostic challenge for clinicians. This review aims to provide a current synthetic overview of the main acquired and genetic etiologies associated with macrocephaly and finger changes. The genetic cause encompasses several categories of diseases, including bone marrow expansion disorders, skeletal dysplasias, ciliopathies, inherited metabolic diseases, RASopathies, and overgrowth syndromes. Furthermore, autoimmune and autoinflammatory diseases are also explored for their potential involvement in macrocephaly and finger changes. The intricate genetic mechanisms involved in the formation of cranial bones and extremities are multifaceted. An excess in growth may stem from disruptions in the intricate interplays among the genetic, epigenetic, and hormonal factors that regulate human growth. Understanding the underlying cellular and molecular mechanisms is important for elucidating the developmental pathways and biological processes that contribute to the observed clinical phenotypes. The review provides a practical approach to delineate causes of macrocephaly and finger changes, facilitate differential diagnosis and guide for the appropriate etiological framework. Early recognition contributes to timely intervention and improved outcomes for affected individuals.

Trichohepatoenteric syndrome and cytomegalovirus infection: Case report and literature summary

Trichohepatoenteric syndrome is a rare autosomal recessive genetic disease caused by TTC37 (also known as SKIC3) or SKIV2L gene variant. We present a severely affected 2-month-old male infant with recurrent fever and unexplained diarrhea. Additionally, clinical data of 11 patients with trichohepatoenteric syndrome in China from 1 to 60 days of onset was presented. The infant's condition was not substantially relieved after cefotaxime sulbactam and meropenem treatment. Whole-exome sequencing revealed compound heterozygous variants (c.1708C>T and c.3342-9T>G) in TTC37 of the child whose parents were heterozygous carriers of the corresponding locus. The c.3342-9T>G variant originated from his mother and was reported for the first time. Combined with the clinical manifestations, the infant was diagnosed with trichohepatoenteric syndrome and treated with ganciclovir antiviral, intravenous nutritional support, and liver function protection. The infant was discharged with no fever and high stool frequency, but his condition improved. Therefore, trichohepatoenteric syndrome should be considered for recurrent fever and unexplained diarrhea.

SKI complex: A multifaceted cytoplasmic RNA exosome cofactor in mRNA metabolism with links to disease, developmental processes, and antiviral responses

RNA stability and quality control are integral parts of gene expression regulation. A key factor shaping eukaryotic transcriptomes, mainly via 3'-5' exoribonucleolytic trimming or degradation of diverse transcripts in nuclear and cytoplasmic compartments, is the RNA exosome. Precise exosome targeting to various RNA molecules requires strict collaboration with specialized auxiliary factors, which facilitate interactions with its substrates. The predominant class of cytoplasmic RNA targeted by the exosome are protein-coding transcripts, which are carefully scrutinized for errors during translation. Normal, functional mRNAs are turned over following protein synthesis by the exosome or by Xrn1 5'-3'-exonuclease, acting in concert with Dcp1/2 decapping complex. In turn, aberrant transcripts are eliminated by dedicated surveillance pathways, triggered whenever ribosome translocation is impaired. Cytoplasmic 3'-5' mRNA decay and surveillance are dependent on the tight cooperation between the exosome and its evolutionary conserved co-factor-the SKI (superkiller) complex (SKIc). Here, we summarize recent findings from structural, biochemical, and functional studies of SKIc roles in controlling cytoplasmic RNA metabolism, including links to various cellular processes. Mechanism of SKIc action is illuminated by presentation of its spatial structure and details of its interactions with exosome and ribosome. Furthermore, contribution of SKIc and exosome to various mRNA decay pathways, usually converging on recycling of ribosomal subunits, is delineated. A crucial physiological role of SKIc is emphasized by describing association between its dysfunction and devastating human disease-a trichohepatoenteric syndrome (THES). Eventually, we discuss SKIc functions in the regulation of antiviral defense systems, cell signaling and developmental transitions, emerging from interdisciplinary investigations. This article is categorized under: RNA Turnover and Surveillance > Turnover/Surveillance Mechanisms RNA Turnover and Surveillance > Regulation of RNA Stability RNA Interactions with Proteins and Other Molecules > RNA-Protein Complexes.

Novel TTC37 mutations in a patient with Trichohepatoenteric syndrome: a case report and literature review

BACKGROUND

Trichohepatoenteric syndrome (THES) is a rare autosomal recessive genetic disease caused by pathogenic mutations in TTC37 or SKIV2L gene. The presentation is variable, including intractable diarrhea, woolly hair abnormality, immune dysfunction, intrauterine growth restriction (IUGR), facial dysmorphism, and sometimes liver and skin abnormalities. Although four Chinese children affected with THES syndrome 1 have been described in Singapore, Taiwan (China) and Malaysia, to our knowledge, this is the first report of a patient with THES in Mainland China, harboring classical platelets features, clinical course, and novel mutations in TTC37 gene.

CASE DESCRIPTION

The male infant had symmetrical IUGR, and was born at 37⁺¹ weeks with a birth weight of 1,480 g. He presented with feeding difficulties and vomiting from the 12^th day after birth during the stay in neonatal intensive care unit, and had excessive diarrhea from the 21st day after birth. From the 35^th day after birth, even slightly hypotonic oral rehydration solution caused watery stools. The blood glucose level was lower than 3.3 mmol/L even when the glucose infusion rate was up to 14 mg/kg/min on the parenteral alone, which has not been reported in previous literature. Normal α-granules were observed occasionally in THES platelets. Whole-exome sequencing analysis identified compound heterozygous mutations (c.4130C > G: p.S1377X) and (Exon11-13 del) in the TTC37 gene, which had been inherited from his father and mother, respectively. To our knowledge, the above mutations have not been described in any database or previous literature. Total parenteral nutrition was employed as mainstay of therapy, and hydrocortisone (1 mg/kg/dose, every 4 hours) was used to maintain blood glucose levels. The patient's final prognosis was poor after discharged from the hospital.

CONCLUSIONS

This case presented with mild platelet abnormality and intractable hypoglycemia, which extends the known mutation and phenotype of THES. The clinical features of Chinese patient are consistent with other ethnicity. Molecular diagnosis is useful for patients with unexplained intractable diarrhea, which puts an end to a long diagnostic odyssey.

Tricho-hepato-enteric syndrome: Retrospective multicenter experience in Saudi Arabia

BACKGROUND

Trichohepatoenteric syndrome (THES) is a very rare disorder that is characterized by intractable congenital diarrhea, woolly hair, intrauterine growth restriction, facial dysmorphism, and short stature. Our knowledge of THES is limited due to the small number of reported cases.

METHODS

Thirty patients diagnosed with THES, all molecularly confirmed by whole exome sequencing (WES) to have biallelic variants in TTC37 or SKIV2L, were included in the study. Clinical, biochemical, and nutritional phenotypes and outcome data were collected from all participants.

RESULTS

The median age of THES patients was 3.7 years (0.9-23 years). Diarrhea and malnutrition were the most common clinical features (100%). Other common features included hair abnormalities (96%), skin hyperpigmentation (87%), facial dysmorphic abnormalities (73%), psychomotor retardation (57%), and hepatic abnormalities (30%). Twenty-five patients required parenteral nutrition (83%) with a mean duration of 13.34 months, and nearly half were eventually weaned off. Parenteral nutrition was associated with a poor prognosis. The vast majority of cases (89.6%) had biallelic variants in SKIV2L, with biallelic variants in TTC37 accounting for the remaining cases. A total of seven variants were identified in TTC37 (n = 3) and SKIV2L (n = 4). The underlying genotype influenced some phenotypic aspects, especially liver involvement, which was more common in TTC37-related THES.

CONCLUSION

Our data helps define the natural history of THES and provide clinical management guidelines.

Early-onset inflammatory bowel disease as a model disease to identify key regulators of immune homeostasis mechanisms

Rare, monogenetic diseases present unique models to dissect gene functions and biological pathways, concomitantly enhancing our understanding of the etiology of complex (and often more common) traits. Although inflammatory bowel disease (IBD) is a generally prototypic complex disease, it can also manifest in an early-onset, monogenic fashion, often following Mendelian modes of inheritance. Recent advances in genomic technologies have spurred the identification of genetic defects underlying rare, very early-onset IBD (VEO-IBD) as a disease subgroup driven by strong genetic influence, pinpointing key players in the delicate homeostasis of the immune system in the gut and illustrating the intimate relationships between bowel inflammation, systemic immune dysregulation, and primary immunodeficiency with increased susceptibility to infections. As for other human diseases, it is likely that adult-onset diseases may represent complex diseases integrating the effects of host genetic susceptibility and environmental triggers. Comparison of adult-onset IBD and VEO-IBD thus provides beautiful models to investigate the relationship between monogenic and multifactorial/polygenic diseases. This review discusses the present and novel findings regarding monogenic IBD as well as key questions and future directions of IBD research.

Tricho-Hepato-Enteric Syndrome mutation update: Mutations spectrum of TTC37 and SKIV2L, clinical analysis and future prospects

Tricho-Hepato-Enteric syndrome (THES) is a very rare autosomal recessive syndromic enteropathy caused by mutations of either TTC37 or SKIV2L genes. Very little is known of these two gene products in mammals nor of the pathophysiology of the disease. Since the identification of the genes, we have set up the molecular diagnostic of THES in routine, gathering a large cohort with clinical and molecular data. Here, we report the phenotype and genotype analysis of this cohort together with an extensive literature review of THES cases worldwide, that is, 96 individuals harboring mutations in one gene or the other. We set up locus-specific databases for both genes and reviewed the type of mutation as well as their localization in the proteins. No hot spot is evidenced for any type of mutation. The phenotypic analysis was first made on the whole cohort but is limited due to heterogeneity in clinical descriptions. We then examined the lab diagnostic cohort in detail for clinical manifestations. For the first time, we are able to suggest that patients lacking SKIV2L seem more severely affected than those lacking TTC37, in terms of liver damage and prenatal growth impairment.

Arrhythmogenic cardiomyopathy: Identification of desmosomal gene variations and desmosomal protein expression in variation carriers

Arrhythmogenic cardiomyopathy (AC) is an inherited disorder that is predominantly present in the right ventricular myocardium. Mutations in the genes encoding the desmosomal protein are thought to underlie the pathogenesis of AC. Since AC is genetically heterogeneous and phenotypically diverse, modifier genes and environmental factors have an important role in disease expression. The aim of the present study was to identify AC-associated desmosomal gene variations, and examine the expression levels of intercalated disc proteins in AC patients who carry the variations (DSG2 p.Leu797Gln, PKP2 p.Ser249Thr and p.E808fsX30). The results of the present investigation provided information on the search for modifier genes and desmosomal gene mutations, and improved our understanding of the mechanism underlying these AC mutations. Genetic screening of five desmosomal genes (DSG2, DSC2, JUP, PKP2, and DSP) in 23 patients with AC who underwent heart transplantation was performed and the expression levels and localizations of intercalated disc proteins were assessed using western blotting and immunohistochemistry, respectively. The results enabled the identification of three desmosomal gene variations (DSG2 L797Q, PKP2 S249T, and E808fsX30), two of which are reported for the first time. DSG2 L797Q was identified in one patient. The protein expression levels of DSG2 in the L797Q carrier were unchanged compared with the healthy controls, and the expression levels of the other proteins (JUP and Cx43) in the intercalated disc were also similar between the healthy controls, the variation carrier and the case controls. Two variations (S249T and E808fsX30) in PKP2 were identified in one patient, the protein expression levels of PKP2 in this patient were significantly decreased, and the expression levels of the other proteins in the intercalated disc was also decreased. The data suggest that there may be modifier genes and other AC-associated mutations requiring identification, in order to further our understanding of the disease mechanism induced by these mutations.

The RNA exosome and RNA exosome-linked disease

The RNA exosome is an evolutionarily conserved, ribonuclease complex that is critical for both processing and degradation of a variety of RNAs. Cofactors that associate with the RNA exosome likely dictate substrate specificity for this complex. Recently, mutations in genes encoding both structural subunits of the RNA exosome and its cofactors have been linked to human disease. Mutations in the RNA exosome genes EXOSC3 and EXOSC8 cause pontocerebellar hypoplasia type 1b (PCH1b) and type 1c (PCH1c), respectively, which are similar autosomal-recessive, neurodegenerative diseases. Mutations in the RNA exosome gene EXOSC2 cause a distinct syndrome with various tissue-specific phenotypes including retinitis pigmentosa and mild intellectual disability. Mutations in genes that encode RNA exosome cofactors also cause tissue-specific diseases with complex phenotypes. How mutations in these genes give rise to distinct, tissue-specific diseases is not clear. In this review, we discuss the role of the RNA exosome complex and its cofactors in human disease, consider the amino acid changes that have been implicated in disease, and speculate on the mechanisms by which exosome gene mutations could underlie dysfunction and disease.

Management of syndromic diarrhea/tricho-hepato-enteric syndrome: A review of the literature

Syndromic diarrhea/tricho-hepato-enteric syndrome (SD/THE) is a rare disease linked to the loss of function of either TTC37 or SKIV2L, two components of the SKI complex. It is characterized by a combination of 9 signs (intractable diarrhea, hair abnormalities, facial dysmorphism, immune abnormalities, IUGR/SGA, liver abnormalities, skin abnormalities, congenital heart defect and platelet abnormalities). We present a comprehensive review of the management of SD/THE and tested therapeutic regimens. A review of the literature was conducted in May 2017: 29 articles and 2 abstracts were included describing a total of 80 patients, of which 40 presented with mutations of TTC37, 14 of SKIV2L. Parenteral nutrition was used in the management of 83% of the patients and weaned in 44% (mean duration of 14.97 months). Immunoglobulins were used in 33 patients, but data on efficacy was reported for 6 patients with a diminution of infection (n = 3) or diarrhea reduction (n = 2). Antibiotics (n = 11) provided no efficacy. Steroids (n = 17) and immunosuppressant drugs (n = 13) were used with little efficacy and mostly in patients with IBD-like SD/THE. Hematopoietic stem cell transplantation (HSCT) was performed in 4 patients: 2 died, for one it corrected the immune defects but not the other features and for the last one, it provided only a partial improvement. Finally, no specific diet was effective except for some contradictory reports for elemental formula. In conclusion, the management of SD/THE mainly involves parenteral nutrition and immunoglobulin supplementation. Antibiotics, steroids, immunosuppressants, and HSCT are not recommended as principle treatments since there is no evidence of efficacy.