X-linked reticulate pigmentary disorder with systemic manifestations: report of a third family and literature review

Filaggrin-Associated Atopic Skin, Eye, Airways, and Gut Disease, Modifying the Presentation of X-Linked Reticular Pigmentary Disorder (XLPDR)

BACKGROUND

X-linked reticular pigmentary disorder (XLPDR) is a rare condition characterized by skin hyperpigmentation, ectodermal features, multiorgan inflammation, and recurrent infections. All probands identified to date share the same intronic hemizygous POLA1 hypomorphic variant (NM_001330360.2(POLA1):c.1393-354A > G) on the X chromosome. Previous studies have supported excessive type 1 interferon (IFN) inflammation and natural killer (NK) cell dysfunction in disease pathogenesis. Common null polymorphisms in filaggrin (FLG) gene underlie ichthyosis vulgaris and atopic predisposition.

CASE

A 9-year-old boy born to non-consanguineous parents developed eczema with reticular skin hyperpigmentation in early infancy. He suffered recurrent chest infections with chronic cough, clubbing, and asthma, moderate allergic rhinoconjunctivitis with keratitis, multiple food allergies, and vomiting with growth failure. Imaging demonstrated bronchiectasis, while gastroscopy identified chronic eosinophilic gastroduodenitis. Interestingly, growth failure and bronchiectasis improved over time without specific treatment.

METHODS

Whole-genome sequencing (WGS) using Illumina short-read sequencing was followed by both manual and orthogonal automated bioinformatic analyses for single-nucleotide variants, small insertions/deletions (indels), and larger copy number variations. NK cell cytotoxic function was assessed using 51Cr release and degranulation assays. The presence of an interferon signature was investigated using a panel of six interferon-stimulated genes (ISGs) by QPCR.

RESULTS

WGS identified a de novo hemizygous intronic variant in POLA1 (NM_001330360.2(POLA1):c.1393-354A > G) giving a diagnosis of XLPDR, as well as a heterozygous nonsense FLG variant (NM_002016.2(FLG):c.441del, NP_0020.1:p.(Arg151Glyfs*43)). Compared to healthy controls, the IFN signature was elevated although the degree moderated over time with the improvement in his chest disease. NK cell functional studies showed normal cytotoxicity and degranulation.

CONCLUSION

This patient had multiple atopic manifestations affecting eye, skin, chest, and gut, complicating the presentation of XLPDR. This highlights that common FLG polymorphisms should always be considered when assessing genotype-phenotype correlations of other genetic variation in patients with atopic symptoms. Additionally, while the patient exhibited an enhanced IFN signature, he does not have an NK cell defect, suggesting this may not be a constant feature of XLPDR.

Inherited Reticulate Pigmentary Disorders

Reticulate pigmentary disorders (RPDs) are a group of inherited and acquired skin conditions characterized by hyperpigmented and/or hypopigmented macules. Inherited RPDs include dyschromatosis symmetrica hereditaria (DSH), dyschromatosis universalis hereditaria (DUH), reticulate acropigmentation of Kitamura (RAK), Dowling-Degos disease (DDD), dyskeratosis congenita (DKC), Naegeli-Franceschetti-Jadassohn syndrome (NFJS), dermatopathia pigmentosa reticularis (DPR), and X-linked reticulate pigmentary disorder. Although reticulate pattern of pigmentation is a common characteristic of this spectrum of disorders, the distribution of pigmentation varies among these disorders, and there may be clinical manifestations beyond pigmentation. DSH, DUH, and RAK are mostly reported in East Asian ethnicities. DDD is more common in Caucasians, although it is also reported in Asian countries. Other RPDs show no racial predilection. This article reviews the clinical, histological, and genetic variations of inherited RPDs.

Infections in DNA Repair Defects

DNA repair defects are heterogenous conditions characterized by a wide spectrum of clinical phenotypes. The common presentations of DNA repair defects include increased risk of cancer, accelerated aging, and defects in the development of various organs and systems. The immune system can be affected in a subset of these disorders leading to susceptibility to infections and autoimmunity. Infections in DNA repair defects may occur due to primary defects in T, B, or NK cells and other factors such as anatomic defects, neurologic disorders, or during chemotherapy. Consequently, the characteristics of the infections may vary from mild upper respiratory tract infections to severe, opportunistic, and even fatal infections with bacteria, viruses, or fungi. Here, infections in 15 rare and sporadic DNA repair defects that are associated with immunodeficiencies are discussed. Because of the rarity of some of these conditions, limited information is available regarding infectious complications.

DNA replication-associated inborn errors of immunity

Inborn errors of immunity are a heterogeneous group of monogenic immunologic disorders caused by mutations in genes with critical roles in the development, maintenance, or function of the immune system. The genetic basis is frequently a mutation in a gene with restricted expression and/or function in immune cells, leading to an immune disorder. Several classes of inborn errors of immunity, however, result from mutation in genes that are ubiquitously expressed. Despite the genes participating in cellular processes conserved between cell types, immune cells are disproportionally affected, leading to inborn errors of immunity. Mutations in DNA replication, DNA repair, or DNA damage response factors can result in monogenic human disease, some of which are classified as inborn errors of immunity. Genetic defects in the DNA repair machinery are a well-known cause of T^-B^-NK⁺ severe combined immunodeficiency. An emerging class of inborn errors of immunity is those caused by mutations in DNA replication factors. Considerable heterogeneity exists within the DNA replication-associated inborn errors of immunity, with diverse immunologic defects and clinical manifestations observed. These differences are suggestive for differential sensitivity of certain leukocyte subsets to deficiencies in specific DNA replication factors. Here, we provide an overview of DNA replication-associated inborn errors of immunity and discuss the emerging mechanistic insights that can explain the observed immunologic heterogeneity.

Congenital Diseases of DNA Replication: Clinical Phenotypes and Molecular Mechanisms

Deoxyribonucleic acid (DNA) replication can be divided into three major steps: initiation, elongation and termination. Each time a human cell divides, these steps must be reiteratively carried out. Disruption of DNA replication can lead to genomic instability, with the accumulation of point mutations or larger chromosomal anomalies such as rearrangements. While cancer is the most common class of disease associated with genomic instability, several congenital diseases with dysfunctional DNA replication give rise to similar DNA alterations. In this review, we discuss all congenital diseases that arise from pathogenic variants in essential replication genes across the spectrum of aberrant replisome assembly, origin activation and DNA synthesis. For each of these conditions, we describe their clinical phenotypes as well as molecular studies aimed at determining the functional mechanisms of disease, including the assessment of genomic stability. By comparing and contrasting these diseases, we hope to illuminate how the disruption of DNA replication at distinct steps affects human health in a surprisingly cell-type-specific manner.

Clinical Approach to Linear Hyperpigmentation: A Review Article

Linear hyperpigmentation is an unusual anatomical configuration in clinical dermatology. Owing to its rarity, consensus on the most effective method of classification is lacking. While linear hyperpigmentation generally follows Blaschko's lines, this is not universal. Clinical findings such as adherence to Blaschko's lines, associated morphological findings (including other cutaneous lesions), and systemic manifestations can be used to further characterize and diagnose variants of the disorder. Early detection of any underlying disease is vital, especially in cases with effective management, because the disorder may make it difficult to manage hyperpigmentation. Herein, we introduce a logical clinical diagnostic approach that represents a useful tool for dermatologists to efficiently evaluate patients presenting with linear hyperpigmentation. A simplified systematic and evidence-based approach is useful for this clinical condition owing to the heterogeneous causes and lack of specific diagnostic tools.

Immune Dysfunction in Mendelian Disorders of POLA1 Deficiency

POLA1 encodes the catalytic unit of DNA polymerase α, which together with the Primase complex launches the DNA replication process. While complete deficiency of this essential gene is presumed to be lethal, at least two conditions due to partial POLA1 deficiency have been described. The first genetic syndrome to be mapped to POLA1 was X-linked reticulate pigmentary disorder (XLPDR, MIM #301220), a rare syndrome characterized by skin hyperpigmentation, sterile multiorgan inflammation, recurrent infections, and distinct facial features. XLPDR has been shown to be accompanied by profound activation of type I interferon signaling, but unlike other interferonopathies, it is not associated with autoantibodies or classical autoimmunity. Rather, it is accompanied by marked Natural Killer (NK) cell dysfunction, which may explain the recurrent infections seen in this syndrome. To date, all XLPDR cases are caused by the same recurrent intronic mutation, which results in gene missplicing. Several hypomorphic mutations in POLA1, distinct from the XLPDR intronic mutation, have been recently reported and these mutations associate with a separate condition, van Esch-O'Driscoll syndrome (VEODS, MIM #301030). This condition results in growth retardation, microcephaly, hypogonadism, and in some cases, overlapping immunological features to those seen in XLPDR. This review summarizes our current understanding of the clinical manifestations of POLA1 gene mutations with an emphasis on its immunological consequences, as well as recent advances in understanding of its pathophysiologic basis and potential therapeutic options.

NK cell defects in X-linked pigmentary reticulate disorder

X-linked reticulate pigmentary disorder (XLPDR, Mendelian Inheritance in Man #301220) is a rare syndrome characterized by recurrent infections and sterile multiorgan inflammation. The syndrome is caused by an intronic mutation in POLA1, the gene encoding the catalytic subunit of DNA polymerase-α (Pol-α), which is responsible for Okazaki fragment synthesis during DNA replication. Reduced POLA1 expression in this condition triggers spontaneous type I interferon expression, which can be linked to the autoinflammatory manifestations of the disease. However, the history of recurrent infections in this syndrome is as yet unexplained. Here we report that patients with XLPDR have reduced NK cell cytotoxic activity and decreased numbers of NK cells, particularly differentiated, stage V, cells (CD3^–CD56^dim). This phenotype is reminiscent of hypomorphic mutations in MCM4, which encodes a component of the minichromosome maintenance (MCM) helicase complex that is functionally linked to Pol-α during the DNA replication process. We find that POLA1 deficiency leads to MCM4 depletion and that both can impair NK cell natural cytotoxicity and show that this is due to a defect in lytic granule polarization. Altogether, our study provides mechanistic connections between Pol-α and the MCM complex and demonstrates their relevance in NK cell function.

X-linked reticulate pigmentary disorder is associated with functional NK cell defect due to abnormal lytic granule polarization.

DNA polymerase-α regulates the activation of type I interferons through cytosolic RNA:DNA synthesis

Aberrant nucleic acids generated during viral replication are the main trigger for antiviral immunity, and mutations that disrupt nucleic acid metabolism can lead to autoinflammatory disorders. Here we investigated the etiology of X-linked reticulate pigmentary disorder (XLPDR), a primary immunodeficiency with autoinflammatory features. We discovered that XLPDR is caused by an intronic mutation that disrupts the expression of POLA1, which encodes the catalytic subunit of DNA polymerase-α. Unexpectedly, POLA1 deficiency resulted in increased production of type I interferons. This enzyme is necessary for the synthesis of RNA:DNA primers during DNA replication and, strikingly, we found that POLA1 is also required for the synthesis of cytosolic RNA:DNA, which directly modulates interferon activation. Together this work identifies POLA1 as a critical regulator of the type I interferon response.

X-linked reticulate pigmentary disorder with systemic manifestations: a new family and review of the literature

X-linked reticulate pigmentation disorder with systemic manifestations (XLPDR) is an extremely rare genodermatosis with recessive X-linked inheritance but unknown molecular basis. In males, cutaneous involvement is characterized by reticulate hyperpigmentation of the skin that is associated with a typical facies and severe systemic involvement. In the carrier females, manifestations are apparently limited to the skin with patchy linear hyperpigmentation following the lines of Blaschko that are similar to stage III incontinentia pigmenti. Thus far, only five families affected by this disorder have been described. We report on a new family with clinical features of XLPDR and compare it with those reported in the literature.

X-Linked reticulate pigmentary disorder in a female patient

BACKGROUND

X-linked reticulate pigmentary disorder is a very rare cutaneous condition characterized by different clinical manifestations according to sex.

METHODS

We report a 31-year-old woman with X-linked reticulate pigmentary disorder.

RESULTS

On examination, there were multiple, asymptomatic, brownish macules in linear and whorled patterns over the trunk, axillae, groin, and extremities. The woman had not experienced any systemic manifestations involving the gastrointestinal, pulmonary, or ocular systems. Her hair, teeth, and nails were normal on close observation. All laboratory data were within the normal range. A genetic study was not performed.

CONCLUSIONS

Although a genetic study was not performed, we believe that our patient can be diagnosed with X-linked reticulate pigmentary disorder according to the clinical and histopathologic findings.

Cryptogenic multifocal ulcerous stenosing enteritis (CMUSE) in a man with a diagnosis of X-linked reticulate pigmentary disorder (PDR)

Cryptogenic multifocal ulcerous stenosing enteritis (CMUSE) is a rare syndrome characterized by episodes of intestinal suboclusion caused by intestinal stenosis with superficial ulceration. Histological findings in the cases described in the literature are similar, even though they are not specific. The cause of the syndrome is as yet unknown. We report on the case of a 25-year-old male with a protein losing enteropathy (PLE) in the context of the CMUSE syndrome. At a later date the patient was also diagnosed with an X-linked recessive reticulate pigmentary disorder (PDR). The clinical features and tests which led to the diagnosis are described. The reported cases of CMUSE and of the gastrointestinal symptoms in the three families with PDR are reviewed in order to search for an association between these two entities. To date, there is no evidence to ascertain whether these two rare syndromes observed in the same patient are related or coincidental.

Refined mapping of X-linked reticulate pigmentary disorder and sequencing of candidate genes

X-linked reticulate pigmentary disorder with systemic manifestations in males (PDR) is very rare. Affected males are characterized by cutaneous and visceral symptoms suggestive of abnormally regulated inflammation. A genetic linkage study of a large Canadian kindred previously mapped the PDR gene to a greater than 40 Mb interval of Xp22-p21. The aim of this study was to identify the causative gene for PDR. The Canadian pedigree was expanded and additional PDR families recruited. Genetic linkage was performed using newer microsatellite markers. Positional and functional candidate genes were screened by PCR and sequencing of coding exons in affected males. The location of the PDR gene was narrowed to a approximately 4.9 Mb interval of Xp22.11-p21.3 between markers DXS1052 and DXS1061. All annotated coding exons within this interval were sequenced in one affected male from each of the three multiplex families as well as one singleton, but no causative mutation was identified. Sequencing of other X-linked genes outside of the linked interval also failed to identify the cause of PDR but revealed a novel nonsynonymous cSNP in the GRPR gene in the Maltese population. PDR is most likely due to a mutation within the linked interval not affecting currently annotated coding exons.

Poikiloderma, tendon contracture and pulmonary fibrosis: a new autosomal dominant syndrome?

Members of two generations of a South African family have a unique syndrome comprising poikiloderma, tendon contractures and progressive pulmonary fibrosis. The condition is clinically important as the skin changes, which involve the face, have considerable cosmetic impact, while lung involvement is potentially lethal in adulthood. Skin manifestations which facilitate diagnosis include facial telangiectasia, mottled hypo- and hyperpigmentation, papules and epidermal atrophy. The scalp, facial and body hair are fine and scanty. The tendon contractures lead to progressive digital flexion deformities and abnormalities of the ankles and feet, with disturbance of gait. Pulmonary involvement manifests as progressive dyspnoea. Pedigree data are compatible with an autosomal dominant mode of transmission. Poikiloderma of Weary is characterized by linear sclerotic and fibrous bands and not tendon contractures and is not associated with potentially lethal pulmonary fibrosis. Rather than name this disorder a variant of Weary syndrome, it might be prudent to use as an umbrella title one composed by Weary himself: 'hereditary sclerosing poikiloderma' (HSP), under which variants such as HSP Weary type, HSP with cardiac involvement (aortic stenosis described as inconsistently associated with Weary syndrome) and HSP with tendon/pulmonary involvement (current family) may be classified. The manifestations in this family differ from other poikilodermata and, to the best of our knowledge, have not been previously documented.