H Syndrome: Recently Defined Genodermatosis With Distinct Histologic Features. A Morphological, Histochemical, Immunohistochemical, and Ultrastructural Study of 10 Cases

H syndrome with bilateral choroidal osteoma: Coincidence or association?

PURPOSE

To report a case with bilateral corneal arcus and bilateral choroidal osteoma associated with H syndrome.

METHODS

Descriptive case report.

RESULTS

A 16-year-old girl with H syndrome was followed up in the pediatric nephrology clinic for chronic renal failure and was consulted to the ophthalmology clinic. She had low vision for more than 5 years. Slit lamp examination revealed bilateral corneal arcus . Lens and iris were normal. Axial length was 19.99 mm in the right eye and 21.85 mm in the left eye. A bilateral orange-yellow plaque was noted in the posterior pole in the funduscopic examination. Fundus autofluorescence (FAF) showed a bilateral diffuse macular hipoautofluorescence area in correspondence with the decalcified portion of the mass. Optical coherence tomography (OCT) showed a bilateral choroidal mass with a dome-shaped pushing effect on the overlying retina and damage to the outer layers of the retina. Fluorescein angiography (FA) with bilateral patchy diffuse late hyperfluorescence and B scan ultrasonography showed a bilateral solid highly reflective choroidal mass with acoustic shadowing. Orbital computerized tomography (CT) scans showed bilateral hyperdense plaques in the posterior pole. A diagnosis of choroidal osteomas was made for both eyes.

CONCLUSIONS

This report presents a case with bilateral corneal arcus and bilateral choroidal osteoma associated with H syndrome that has not been previously reported in the literature. Patients diagnosed with this syndrome should undergo routine eye examination, and due to the progressive nature of histiocytosis, they should also be followed closely ophthalmologically.

Rheumatological manifestations of H syndrome

H syndrome (HS) is a rare autosomal recessive genodermatosis characterised by cutaneous hyperpigmentation, hypertrichosis, sclerodermatous thickening, and multisystemic involvement. It results from mutations in the SLC29A3 gene encoding the human equilibrative nucleoside transporter 3, leading to impaired histiocyte apoptosis and unchecked proliferation. We report the case of a 24-year-old Moroccan male who had a history of insulin-dependent diabetes mellitus. He developed hyperpigmented skin patches with hypertrichosis and induration. Musculoskeletal findings included bilateral hallux valgus, pes planus, reducible flexion contractures of the proximal interphalangeal joints, and restricted ankle dorsiflexion. Additional findings consist of lymphadenopathy, hepatomegaly, hypogonadism, and ophthalmic manifestations. Investigations showed elevated sedimentation rate, anaemia, and osteopaenia. Ankle ultrasound revealed calcaneal enthesopathy and subcutaneous infiltration. In reporting this case, we aim to highlight the significant rheumatological involvement that can arise in patients with H syndrome and explore potential treatment options to improve the musculoskeletal findings.

A novel start-loss mutation of the SLC29A3 gene in a consanguineous family with H syndrome: clinical characteristics, in silico analysis and literature review

BACKGROUND

The SLC29A3 gene, which encodes a nucleoside transporter protein, is primarily located in intracellular membranes. The mutations in this gene can give rise to various clinical manifestations, including H syndrome, dysosteosclerosis, Faisalabad histiocytosis, and pigmented hypertrichosis with insulin-dependent diabetes. The aim of this study is to present two Iranian patients with H syndrome and to describe a novel start-loss mutation in SLC29A3 gene.

METHODS

In this study, we employed whole-exome sequencing (WES) as a method to identify genetic variations that contribute to the development of H syndrome in a 16-year-old girl and her 8-year-old brother. These siblings were part of an Iranian family with consanguineous parents. To confirmed the pathogenicity of the identified variant, we utilized in-silico tools and cross-referenced various databases to confirm its novelty. Additionally, we conducted a co-segregation study and verified the presence of the variant in the parents of the affected patients through Sanger sequencing.

RESULTS

In our study, we identified a novel start-loss mutation (c.2T > A, p.Met1Lys) in the SLC29A3 gene, which was found in both of two patients. Co-segregation analysis using Sanger sequencing confirmed that this variant was inherited from the parents. To evaluate the potential pathogenicity and novelty of this mutation, we consulted various databases. Additionally, we employed bioinformatics tools to predict the three-dimensional structure of the mutant SLC29A3 protein. These analyses were conducted with the aim of providing valuable insights into the functional implications of the identified mutation on the structure and function of the SLC29A3 protein.

CONCLUSION

Our study contributes to the expanding body of evidence supporting the association between mutations in the SLC29A3 gene and H syndrome. The molecular analysis of diseases related to SLC29A3 is crucial in understanding the range of variability and raising awareness of H syndrome, with the ultimate goal of facilitating early diagnosis and appropriate treatment. The discovery of this novel biallelic variant in the probands further underscores the significance of utilizing genetic testing approaches, such as WES, as dependable diagnostic tools for individuals with this particular condition.

H syndrome: A histiocytosis-lymphadenopathy plus syndrome. A comprehensive review of the literature

H syndrome is a rare autosomal recessive genodermatosis that falls under the histiocytosis-lymphadenopathy plus syndrome. The term "H syndrome" includes manifestations such as hyperpigmentation, hypertrichosis, hepatosplenomegaly, heart anomalies, hearing loss, hypogonadism, low height, and occasionally hyperglycemia. The syndrome is associated with mutations in the SLC29A3 gene, which encodes the human equilibrative transporter 3 present in endosomes, lysosomes, and mitochondria. The generalized and ubiquitous presence of affected lysosomes and mitochondria contributes to the systemic and phenotypically heterogeneous manifestations of the syndrome. H syndrome manifestations are cutaneous, systemic, and organ-specific. The pathognomonic signs are hypertrichosis and hyperpigmentation in the inner thighs and shins. However, not all patients present with these symptoms. H syndrome management involves a multidisciplinary approach to address specific symptoms and complications. The prognosis of H syndrome depends on several factors, including the extent and severity of clinical manifestations, the presence of complications, and timely diagnosis and management. Further studies are needed to explore the association between prognosis and the different mutations encountered in H syndrome.

Equilibrative nucleotide transporter ENT3 (SLC29A3): A unique transporter for inherited disorders and cancers

As a crucial gene associated with diseases, the SLC29A3 gene encodes the equilibrative nucleoside transporter 3 (ENT3). ENT3 plays an essential regulatory role in transporting intracellular hydrophilic nucleosides, nucleotides, hydrophilic anticancer and antiviral nucleoside drugs, energy metabolism, subcellular localization, protein stability, and signal transduction. The mutation and inactivation of SLC29A3 are intimately linked to the occurrence, development, and prognosis of various human tumors. Moreover, many hereditary human diseases, such as H syndrome, pigmentary hypertrichosis and non-autoimmune insulin-dependent diabetes mellitus (PHID) syndrome, Faisalabad histiocytosis (FHC), are related to SLC29A3 mutations. This review explores the mechanisms of SLC29A3 mutations and expression alterations in inherited disorders and cancers. Additionally, we compile studies on the inhibition of ENT3, which may serve as an effective strategy to potentiate the anticancer activity of chemotherapy. Thus, the synopsis of genetics, permeant function and drug therapy of ENT3 provides a new theoretical and empirical foundation for the diagnosis, prognosis of evaluation and treatment of various related diseases.

H syndrome treated with Tocilizumab: two case reports and literature review

H syndrome is a rare autosomal recessive genetic disorder characterized by the following clinical features: cutaneous hyperpigmentation, hypertrichosis, hepatosplenomegaly, heart anomalies, hearing loss, hypogonadism, short stature, hallux valgus, hyperglycemia, fixed flexion contractures of the toe joints, and the proximal interphalangeal joints. In rare cases, autoinflammatory and lymphoproliferative manifestations have also been reported. This disorder is due to loss-of-function mutations in SLC29A3 gene, which encode the equilibrative nucleoside transporter ENT3. This deficiency leads to abnormal function and proliferation of histiocytes. H syndrome is part of the R-group of histiocytosis. We report two different cases, one was diagnosed in adulthood and the other in childhood. The first case reported is a 37-year-old woman suffering from H syndrome with an autoinflammatory systemic disease that begins in adulthood (fever and diffuse organ's infiltration) and with cutaneous, articular, auditory, and endocrinological manifestations since childhood. The second case reported is a 2-year-old girl with autoinflammatory, endocrine, and cutaneous symptoms (fever, lymphadenopathy, organomegaly, growth delay, and cutaneous hyperpigmentation). Homozygous mutations in SLC29A3 confirmed the diagnosis of H syndrome in both cases. Each patient was treated with Tocilizumab with a significant improvement for lymphoproliferative, autoinflammatory, and cutaneous manifestations. Both cases were reported to show the multiple characteristics of this rare syndrome, which can be diagnosed either in childhood or in adulthood. In addition, an overview of the literature suggested Tocilizumab efficiency.

OCT2 expression in histiocytoses

Diagnosis of histiocytosis can be difficult and one of the biggest challenges is to distinguish between reactive and neoplastic histiocytes on histology alone. Recently, OCT2 nuclear expression was reported in Rosai-Dorfman disease (RDD). Our purpose was to expand the testing of OCT2 on a broader variety of sporadic or H syndrome-related histiocytoses. Cases of histiocytoses were retrieved from the files of Ambroise Paré Pathology Department. All slides and molecular analyses were reviewed, and staining was completed with immunohistochemistry for OCT2. A total of 156 samples from different localizations were tested. Among sporadic cases, 52 patients had RDD, and 10 patients had mixed histiocytosis combining RDD with Erdheim Chester disease (ECD, n = 8), Langerhans cell histiocytosis (LCH, n = 2) or juvenile xanthogranuloma (JXG, n = 1). All these patients were positive for OCT2 in RDD characteristic histiocytes. Twenty-three patients had ECD and all but two (91% - 21/23) were negative for OCT2. By contrast, OCT2 was positive in 11/27 (41%) LCH and 6/16 (38%) JXG. Among the 10 samples of H syndrome-associated histiocytosis, 3 had typical RDD histology, 6 had unclassified histiocytosis, and one had mixed RDD-LCH; all were positive for OCT2. On 16 samples of granulomatous lymphadenitis, OCT2 was negative in epithelioid histiocytes. Our study shows that OCT2 has a sensitivity of 100% for RDD cases and mixed histiocytoses with an RDD component. It is negative in 92% of ECD but expressed in at least 38% of LCH, JXG, and C group histiocytoses. Finally, OCT2 is positive in all H syndrome-related histiocytoses, independent of their histology.

Case report of H-syndrome with a review from a rheumatological perspective

A woman in her 20s, symptomatic since the age of 4 with short stature, hearing loss, skin hyperpigmentation and induration over the medial aspect of the thigh, hypertrichosis, histiocytes on biopsy, lymphadenopathy, dilated scleral vessels, pancreatic exocrine deficiency, pericardial thickening, swelling of the eyelids and resistant retroperitoneal fibrosis. Whole-genome sequencing showed a mutation in SLC29A3, confirming 'H'-syndrome. She is on steroids and methotrexate. This case highlights the rheumatological mimics of this rare disorder.

Phenotypic intrafamilial variability including H syndrome and Rosai-Dorfman disease associated with the same c.1088G > A mutation in the SLC29A3 gene

Background

Mutations in the SLC29A3 gene, which encodes the nucleoside transporter hENT3, have been implicated in syndromic forms of histiocytosis including H syndrome, pigmented hypertrichosis with insulin-dependent diabetes, Faisalabad histiocytosis and Familial Rosai–Dorfman disease (RDD). Herein, we report five new patients from a single family who present with phenotypes that associate features of H syndrome and Familial Rosai–Dorfman disease.

Methods

We investigated the clinical, biochemical, histopathological and molecular findings in five Tunisian family members' diagnosed with Familial RDD and/or H syndrome. The solute carrier family 29 (nucleoside transporters), member 3 (SLC29A3) gene was screened for molecular diagnosis using direct Sanger sequencing.

Results

Genetic analysis of all affected individuals revealed a previously reported missense mutation c.1088 G > A [p.Arg363Gln] in exon 6 of the SLC29A3 gene. Four affected members presented with clinical features consistent with the classical H syndrome phenotype. While their cousin’s features were in keeping with Familial Rosai–Dorfman disease diagnosis with a previously undescribed cutaneous RDD presenting as erythematous nodular plaques on the face. This report underlines the clinical variability of SLC29A3 disorders even with an identical mutation in the same family.

Conclusion

We report a rare event of 5 Tunisian family members' found to be homozygous for SLC29A3 gene mutations but showing a different phenotype severity. Our study reveals that despite a single mutation, the clinical expression of the SLC29A3 disorders may be significantly heterogeneous suggesting a poor genotype–phenotype correlation for the disease.

Panniculitis in Children

Panniculitides form a heterogenous group of inflammatory diseases that involve the subcutaneous adipose tissue. These disorders are rare in children and have many aetiologies. As in adults, the panniculitis can be the primary process in a systemic disorder or a secondary process that results from infection, trauma or exposure to medication. Some types of panniculitis are seen more commonly or exclusively in children, and several new entities have been described in recent years. Most types of panniculitis have the same clinical presentation (regardless of the aetiology), with tender, erythematous subcutaneous nodules. Although the patient's age and the lesion site provide information, a histopathological assessment is sometimes required for a definitive diagnosis and classification of the disorder. In children, most panniculitides are lobular. At present, autoimmune inflammatory diseases and primary immunodeficiencies have been better characterised; panniculitis can be the presenting symptom in some of these settings. Unexplained panniculitis in a young child should prompt a detailed screen for monogenic immune disorders because the latter usually manifest themselves early in life. Here, we review forms of panniculitis that occur primarily in children, with a focus on newly described entities.

Pseudo-Meigs' Syndrome in Tunisian H Syndrome Female Patient: First Case Reported

H syndrome is an extremely rare autosomal recessive affection caused by biallelic mutations in the SLC29A3 gene encoding the human equilibrative nucleoside transporter hENT3. The hallmark signs are cutaneous consisting of hyperpigmentation and hypertrichosis patches. Besides, associated systemic manifestations are highly various reflecting phenotypic pleiotropism. Herein, we report a first case of pseudo-Meigs’ syndrome occurring in a young Tunisian H syndrome diagnosed patient with a novel homozygous frameshift mutation in exon 2 of the SLC29A3 gene: p.S15Pfs*86 inducing a premature stop codon. The patient developed ascites associated with left ovarian mass and she underwent surgery. After tumor resection, ascites disappeared rapidly. Histological examination showed serous cystadenoma of the ovary orienting the diagnosis towards pseudo-Meigs’ syndrome.

Inherited disorders of lysosomal membrane transporters

Disorders caused by defects in lysosomal membrane transporters form a distinct subgroup of lysosomal storage disorders (LSDs). To date, defects in only 10 lysosomal membrane transporters have been associated with inherited disorders. The clinical presentations of these diseases resemble the phenotypes of other LSDs; they are heterogeneous and often present in children with neurodegenerative manifestations. However, for pathomechanistic and therapeutic studies, lysosomal membrane transport defects should be distinguished from LSDs caused by defective hydrolytic enzymes. The involved proteins differ in function, localization, and lysosomal targeting, and the diseases themselves differ in their stored material and therapeutic approaches. We provide an overview of the small group of disorders of lysosomal membrane transporters, emphasizing discovery, pathomechanism, clinical features, diagnostic methods and therapeutic aspects. We discuss common aspects of lysosomal membrane transporter defects that can provide the basis for preclinical research into these disorders.

H syndrome with a novel homozygous SLC29A3 mutation in two sisters

H syndrome (OMIM 602782) is a recently defined autosomal recessive genodermatosis. Cutaneous findings of H syndrome include hyperpigmentation, hypertrichosis, and induration, while hearing loss, heart anomalies, hepatomegaly, hypogonadism, hyperglycemia (diabetes mellitus), low height (short stature), hallux valgus (flexion contractures), and hematological abnormalities are the extracutaneous abnormalities. We report a novel homozygous missense mutation, c.416T > C p.(Leu139Pro), in the SLC29A3 (NM_001174098.1) gene in two sisters with H syndrome presenting with different phenotypes.

H Syndrome retrospectively diagnosed: The importance of recognizing cutaneous signs

We present a case of a retrospectively diagnosed H syndrome in a man who died of a probable heart infarction. We highlight the importance of recognizing cutaneous hallmarks of this syndrome for better clinical management and prevention.

Rosai-Dorfman disease: an overview

CONTEXT

Rosai-Dorfman disease is an uncommon histiocytic disorder most frequently presenting as bilateral cervical lymphadenopathy in children and young adults. Extranodal disease occurs in a significant proportion of patients. It has been recently classified as part of the 'R group' of histiocytoses by the Histiocyte Society in 2016. Cutaneous Rosai-Dorfman disease is regarded as a separate disease entity that falls into the 'C group' of histiocytoses according to this classification system. The pathogenesis was previously poorly understood; however, recent evidence demonstrating clonality in a subset of cases raises the possibility of a neoplastic process. A possible association with IgG4-related disease remains controversial.

OBJECTIVES

To provide a comprehensive review of Rosai-Dorfman disease, including nodal, extranodal and cutaneous forms, with a particular emphasis on new insights into the possible clonal nature of the disease; to discuss the recently revised classification of the histiocytoses by the Histiocyte Society; and to summarise the findings from the literature regarding the controversial association with IgG4-related disease.

DATA SOURCES

This review is based on published peer-reviewed English literature.

CONCLUSIONS

Classic Rosai-Dorfman disease, which may be sporadic or familial, is considered a separate entity from cutaneous disease, which is reflected in the revised classification of histiocytoses. An increase in IgG4-positive plasma cells may be seen in Rosai-Dorfman disease. This finding in isolation is of limited significance and should be interpreted with caution. Studies investigating the molecular profile of the disease show that in at least a subset of cases the disease is a clonal process. The classification of Rosai-Dorfman disease is therefore likely to change as our understanding of the aetiopathogenesis evolves.

Clinical, Histochemical, and Molecular Study of Three Turkish Siblings Diagnosed with H Syndrome, and Literature Review

BACKGROUND

The term "H syndrome" was coined to denote the major clinical findings, which include hyperpigmentation, hypertrichosis, hearing loss, hepatosplenomegaly, hyperglycaemia, hypogonadism, hallux flexion contractures, and short height.

OBJECTIVE

To report the clinical, endocrinological, histochemical, and genetic findings of three siblings.

METHODS

Skin and liver biopsies were taken to investigate the histochemical characteristics of hyperpigmented hypertrichotic skin lesions and massive hepatomegaly. The levels of basal serum thyroid hormones, oestradiol, total testosterone, follicle-stimulating hormone, luteinising hormone, and stimulated growth hormone (GH) were measured to investigate the endocrine aspects of the syndrome. Mutation analysis was carried out in all six exons and exon-intron boundaries of SLC29A3 by direct sequencing.

RESULTS

Physical examination of the patients revealed common charac-teristic findings of H syndrome. Additional clinical findings were sectorial iris atrophy in the younger sister. Laboratory evaluation revealed microcytic anaemia, markedly increased erythrocyte sedimentation rate and C-reactive protein levels, and humoral immune deficiency in the younger siblings, who presented with recurrent fever and sinopulmonary infection. Two different GH stimulation tests revealed GH deficiency in the younger sister with short stature. Liver and skin biopsies revealed polyclonal lymphohistiocytic and plasma cell infiltration. Sequencing of SLC29A3 in the three siblings revealed a novel homozygous mutation in exon 6, which caused the transition of arginine to tryptophan.

CONCLUSION

This study not only extended the clinical and mutation spectrum of SLC29A3 in H syndrome, but also showed that short children should be assessed according to the guidelines for short stature in children.

Mutation in the SLC29A3 Gene in an Egyptian Patient with H Syndrome: A Case Report and Review of Literature

Histiocytosis-lymphadenopathy plus syndrome (H syndrome) is caused by mutations in the SLC29A3 gene that result in histiocytic infiltration of numerous organs. Patients suffering from this disorder can be easily mistaken for similar conditions such as Muckle-Wells syndrome. We present a 9.5-year-old boy, who is the offspring of a consanguineous marriage. He suffered from sensorineural hearing loss, dark hyperpigmented indurated dry areas on the medial thighs sparing the knees with hypertrichosis on the affected areas, and areas of hypopigmentation on the abdomen. The patient displayed mild dysmorphism including frontal bossing, synophrys, bilateral proptosis (with normal thyroid function), thick eyebrows, flat nose, long philtrum, and pectus excavatum. Formal intelligence testing showed that he was a slow learner. Laboratory findings included elevated serum amyloid-A, erythrocyte sedimentation rate, and total proteins in urine tests. Complete blood count showed mild microcytic hypochromic anemia. The molecular analysis was crucial to confirm the provisional clinical diagnosis. H syndrome is a rare autoinflammatory syndrome with pleiotropic manifestations that affect many organs and can be mistaken for other conditions. Our patient's description may expand the phenotype of H syndrome, as areas of hypopigmentation were observed on the abdomen. Molecular analysis of SLC29A3 -related diseases is essential to highlight the variability and increase the awareness of H syndrome aiming for early diagnosis and proper treatment.

H syndrome: Clinical, histological and genetic investigation in Tunisian patients

H syndrome is a rare autosomal recessive disorder with characteristic dermatological findings consisting of hyperpigmentation and hypertrichosis patches mainly located on the inner thighs and multisystemic involvement including hepatosplenomegaly, hearing loss, heart abnormalities and hypogonadism. The aim of this study was to conduct a clinical and genetic investigation in five unrelated Tunisian patients with suspected H syndrome. Hence, genetic analysis of the SLC29A3 gene was performed for four patients with a clinical diagnosis of H syndrome. We identified a novel frame-shift mutation in the SLC29A3 gene in a female patient with a severe clinical presentation. Furthermore, we report two mutations previously described, the p.R363Q mutation in a male patient and the p.P324L mutation in two patients of different age and sex. This paper extends the mutation spectrum of H syndrome by reporting a novel frame-shift mutation, the p.S15Pfs*86 in exon 2 of SLC29A3 gene and emphasizes the relevance of genetic testing for its considerable implications in early diagnosis and clinical management.

Tocilizumab for the Treatment of SLC29A3 Mutation Positive PHID Syndrome

Pigmentary hypertrichosis and non-autoimmune insulin-dependent diabetes mellitus (PHID) is associated with recessive mutations in SLC29A3, encoding the equilibrative nucleoside transporter hENT3 expressed in mitochondria, causing PHID and H syndromes, familial Rosai-Dorfman disease, and histiocytosis-lymphadenopathy-plus syndrome. Autoinflammation is increasingly recognized in these syndromes. We previously reported a 16-year-old girl with PHID syndrome associated with severe autoinflammation that was recalcitrant to interleukin-1 and tumor necrosis factor-α blockade. Tocilizumab is a humanized, monoclonal, anti-human interleukin-6 receptor antibody routinely used to treat arthritis in children and adults. Herein we report the first case of successful treatment of PHID syndrome using tocilizumab. Before commencing tocilizumab, there was evidence of significant systemic inflammation, and progressive sclerodermatous changes (physician global assessment [PGA] 7/10). Twelve weeks after starting tocilizumab (8 mg/kg every 2 weeks, intravenously) systemic inflammatory symptoms improved, and acute phase response markers normalized; serum amyloid A reduced from 178 to 8.4 mg/L. After a dose increase to 12 mg/kg every 2 weeks her energy levels, appetite, fevers, and night sweats further improved. Less skin tightness (PGA 5/10) was documented 12 months later. This excellent clinical and serological response was sustained over 48 months, and cutaneous sclerosis had improved further (PGA 3/10). Her height remained well below the 0.4th centile, and tocilizumab also had no impact on her diabetes or exocrine pancreatic insufficiency. Although the mechanism of autoinflammation of PHID remains uncertain, we suggest that tocilizumab should be the first choice when considering treatment of the autoinflammatory or cutaneous manifestations of this genetic disease.

Novel homozygous SLC29A3 mutations among two unrelated Egyptian families with spectral features of H-syndrome

OBJECTIVES

H syndrome and pigmented hypertrichosis with insulin-dependent diabetes mellitus (PHID) had been described as two autosomal recessive disorders. We aim to screen for pathogenic SLC29A3 mutations in two unrelated Egyptian families with affected siblings of these overlapping syndromes.

METHODS

Clinical, laboratory, histopathological, and radiological characteristics of individuals probably diagnosed as H and/or PHID syndrome were reported. Mutation analysis of SLC29A3 gene was performed for all members of the two Egyptian families.

RESULTS

All affected individuals were females; proband of family-I (A1961) displayed overlapping features of H syndrome and PHID, while her younger brother (A1962) was asymptomatic. A1961 presented with previously undescribed features; absent pectoralis major muscle and a supracondylar bony spur in left humerus. In family-II, probands (A1965 and A1966) had clinical features consistent with classical H syndrome with unique early onset of cutaneous phenomena at birth. Mutation analysis of SLC29A3 revealed homozygous mutation previously reported in literature c.1279G>A [p.G427S] in A1961 and unexpectedly in the asymptomatic A1962 of family-I. Probands of family-II were homozygous for a novel mutation c.401G>A [p.R134H], in the same codon that was published in an Indian boy [p.R134C].

CONCLUSIONS

We emphasize the inter- and intra-familial genetic heterogeneity among Egyptian patients with overlapping features of SLC29A3 disorders. This suggests the presence of other factors like regulatory genes or epigenetic factors that may explain variable disease manifestations and severity.

Ophthalmologic Findings in H Syndrome: A Unique Diagnostic Clue

BACKGROUND

H syndrome is an autosomal recessive histiocytosis with multisystemic involvement caused by mutations in the SLC29A3 gene. The term H syndrome was coined to denote the major clinical findings which include hyperpigmentation, hypertrichosis, hearing loss, hepatosplenomegaly, hypogonadism, hyperglycemia/diabetes mellitus and hallux valgus/flexion contractures. Almost 100 individuals affected with this disorder have been reported, however, a thorough evaluation of the ophthalmologic features of H syndrome has not yet been performed.

MATERIALS AND METHODS

Ophthalmic examination of a 50-year-old male with H syndrome. Mutation analysis of SLC29A3 was also performed in this patient.

RESULTS

Ophthalmic findings included; shallow orbits with exorbitism, bilateral pterygium, limbal thickening, corneal arcus and cortical cataract. We also review ophthalmologic findings in previously reported H syndrome patients.

CONCLUSIONS

The presence of dilated lateral scleral vessels, corneal arcus and shallow orbits should raise the suspicion of H syndrome, especially when seen in young age.

Emperipolesis: an additional common histopathologic finding in H syndrome and Rosai-Dorfman disease

H syndrome is a recently described autosomal recessive disorder characterized by indurated, hyperpigmented, and hypertrichotic cutaneous plaques, mainly involving the lower abdomen and lower extremities. Associated systemic manifestations include hepatosplenomegaly, heart anomalies, hearing loss, hypogonadism, low height, and hyperglycemia. H syndrome is caused by mutations in the gene SLC29A3, which encodes hENT3, a member of the human equilibrative nucleoside transporter family. Histopathologically, cutaneous lesions of H syndrome consist of dermal and subcutaneous fibrosis with inflammatory infiltrate mostly composed of large histiocytes, some plasma cells, and scattered lymphoid aggregates. Recently, histopathologic and immunohistochemical studies have demonstrated that the immunophenotype of the histiocytes infiltrating the skin of a patient with H syndrome is similar to that of the lesions of Rosai-Dorfman disease. Furthermore, mutations in SLC29A3 gene have also been demonstrated in patients described as having an inherited form of Rosai-Dorfman disease, named Faisalabad histiocytosis or familial Rosai-Dorfman disease. We describe emperipolesis in the cutaneous lesions of a patient with H syndrome, further supporting the relationship between Rosai-Dorfman disease and H syndrome.

A mild form of SLC29A3 disorder: a frameshift deletion leads to the paradoxical translation of an otherwise noncoding mRNA splice variant

We investigated two siblings with granulomatous histiocytosis prominent in the nasal area, mimicking rhinoscleroma and Rosai-Dorfman syndrome. Genome-wide linkage analysis and whole-exome sequencing identified a homozygous frameshift deletion in SLC29A3, which encodes human equilibrative nucleoside transporter-3 (hENT3). Germline mutations in SLC29A3 have been reported in rare patients with a wide range of overlapping clinical features and inherited disorders including H syndrome, pigmented hypertrichosis with insulin-dependent diabetes, and Faisalabad histiocytosis. With the exception of insulin-dependent diabetes and mild finger and toe contractures in one sibling, the two patients with nasal granulomatous histiocytosis studied here displayed none of the many SLC29A3-associated phenotypes. This mild clinical phenotype probably results from a remarkable genetic mechanism. The SLC29A3 frameshift deletion prevents the expression of the normally coding transcripts. It instead leads to the translation, expression, and function of an otherwise noncoding, out-of-frame mRNA splice variant lacking exon 3 that is eliminated by nonsense-mediated mRNA decay (NMD) in healthy individuals. The mutated isoform differs from the wild-type hENT3 by the modification of 20 residues in exon 2 and the removal of another 28 amino acids in exon 3, which include the second transmembrane domain. As a result, this new isoform displays some functional activity. This mechanism probably accounts for the narrow and mild clinical phenotype of the patients. This study highlights the 'rescue' role played by a normally noncoding mRNA splice variant of SLC29A3, uncovering a new mechanism by which frameshift mutations can be hypomorphic.

Accelerated coronary atherosclerosis and H syndrome

A 12-year-old boy with insulin dependent diabetes mellitus, presented with acute myocardial infarction. Intracoronary thrombolysis with urokinase restored TIMI III flow in the culprit vessel. After stabilisation with medical therapy, unusual clinical findings in the form of cutaneous hyperpigmentation and hypertrichosis, affecting the lower extremities, were appreciated. These and other phenotypic features were consistent with H syndrome, a recently described autosomal recessive genodermatosis, and confirmed by mutation analysis. Despite being on optimal medical therapy for coronary artery disease, the patient presented 3 months thereafter, with unstable angina which was successfully managed with percutaneous coronary intervention. An unusual occurrence of coronary artery disease with accelerated atherosclerosis in a child with H syndrome is presented herein. Identification of further patients with this novel disorder will clarify the possible association, suggested here, with increased risk for coronary or other vascular events.

Early-onset sensorineural hearing loss is a prominent feature of H syndrome

This case report describes two patients with H syndrome, a multisystemic autosomal recessive disorder, caused by mutations in the SLC29A3 gene. It is characterized by cutaneous hyperpigmentation, camptodactyly or flexion contractures and other features, among them hearing loss. The two patients had hearing loss as their presenting symptom, and had mutations in SLC29A3, one of them a novel mutation. The aim of this paper is to increase awareness to this recently described disorder, and to emphasize that H syndrome should be included in the differential diagnosis of congenital or acquired syndromic hearing loss in children.

H syndrome: novel and recurrent mutations in SLC29A3

The H syndrome (OMIM 612391) is a recently described autosomal recessive disorder characterized by cutaneous hyperpigmentation, hypertrichosis, hepatosplenomegaly, heart anomalies, hearing loss, hypogonadism, short stature (low height), hyperglycaemia/diabetes mellitus, hallux valgus, and fixed flexion contractures of the toe and finger joints.(1,2) Histologically, there is an inflammatory infiltrate consisting mainly of histiocytes, later replaced by fibrosis of the deep dermis and subcutis.(3) In total, 31 patients have been reported in the literature with the clinical phenotype characteristic of this syndrome.(1-7)