Dyschromatosis symmetrica hereditaria with long hair on the forearms, hypo/hyperpigmented hair, and dental anomalies: report of a novel ADAR1 mutation

Identification of five novel variants of ADAR1 in dyschromatosis symmetrica hereditaria by next-generation sequencing

Background

Dyschromatosis symmetrica hereditaria (DSH) is a rare autosomal dominant inherited pigmentary dermatosis characterized by a mixture of hyperpigmented and hypopigmented freckles on the dorsal aspect of the distal extremities. To date, pathogenic mutations causing DSH have been identified in the adenosine deaminase acting on RNA1 gene (ADAR1), which is mapped to chromosome 1q21.

Objective

The present study aimed to investigate the underlying pathological mechanism in 14 patients with DSH from five unrelated Chinese families. Next-generation sequencing (NGS) and direct sequencing were performed on a proband with DSH to identify causative mutations. All coding, adjacent intronic, and 5'- and 3'-untranslated regions of ADAR1 were screened, and variants were identified.

Result

These mutations consisted of three missense mutations (NM_001025107: c.716G>A, NM_001111.5: c.3384G>C, and NM_001111.5: c.3385T>G), one nonsense mutation (NM_001111.5:c.511G>T), and one splice-site mutation (NM_001111.5: c.2080-1G>T) located in exon 2, exon 14, and the adjacent intronic region according to recommended Human Genome Variation Society (HGVS) nomenclature. Moreover, using polymerase chain reaction and Sanger sequencing, we identified five novel ADAR1 variants, which can be predicted to be pathogenic by in silico genome sequence analysis. Among the mutations, the missense mutations had no significant effect on the spatial structure of the protein, while the stop codon introduced by the nonsense mutation truncated the protein.

Conclusion

Our results highlighted that the advent of NGS has facilitated high-throughput screening for the identification of disease-causing mutations with high accuracy, stability, and specificity. Five novel genetic mutations were found in five unrelated families, thereby extending the pathogenic mutational spectrum of ADAR1 in DSH and providing new insights into this complex genetic disorder.

Genetic Analyses of Enamel Hypoplasia in Multiethnic Cohorts

Enamel hypoplasia causes reduction in the thickness of affected enamel and is one of the most common dental anomalies. This defect is caused by environmental and/or genetic factors that interfere with tooth formation, emphasizing the importance of investigating enamel hypoplasia on an epidemiological and genetic level. A genome-wide association of enamel hypoplasia was performed in multiple cohorts, overall comprising 7,159 individuals ranging in age from 7-82 years. Mixed-models were used to test for genetic association while simultaneously accounting for relatedness and genetic population structure. Meta-analysis was then performed. More than 5 million single-nucleotide polymorphisms were tested in individual cohorts. Analyses of the individual cohorts and meta-analysis identified association signals close to genome-wide significance (P < 510-8), and many suggestive association signals (510-8 < P < 510-6) near genes with plausible roles in tooth/enamel development. The strongest association signal (P = 1.5710-9) was observed near BMP2K in one of the individual cohorts. Additional suggestive signals were observed near genes with plausible roles in tooth development in the meta-analysis, such as SLC4A4 which can influence enamel hypoplasia. Additional human genetic studies are needed to replicate these results and functional studies in model systems are needed to validate our findings.

Analysis of genotype/phenotype correlations in Japanese patients with dyschromatosis symmetrica hereditaria

Dyschromatosis symmetrica hereditaria (DSH) is one of the genetic pigmentation disorders and shows characteristic mixture of hyper- and hypo-pigmented small macules on the extremities. Heterozygous mutations in the adenosine deaminase acting on RNA1 gene (ADAR1) cause DSH. In the present study, we report five cases of DSH and identify a distinct known mutation in each patient. Furthermore, we review previously described cases with the five ADAR1 mutations found in the present study. We reviewed clinical and molecular findings in the present and previously reported cases and found an identical mutation can result in various phenotypic severities, even in one family. We found novel phenotype-genotype correlations between the presence/absence of facial lesions and the ADAR1 mutation c.3286C>T. The absence of freckle-like macules in the face was found to be more commonly associated with the mutation c.3286C>T than with the other 4 ADAR1 mutations (odds ratio = 0.056 [95% CI: 0.007–0.47, p < 0.005]). We objectively evaluated the severity of skin manifestations in the extremities using our definition of severity levels for such manifestations. This is the first semi-quantitative evaluation of skin manifestations in DSH. Using our definition, we found that patients with facial lesions with or without hypopigmented macules tend to show more severe symptoms on the extremities than patients without facials lesions show. Furthermore, no significant difference in the severity of the skin lesions was observed between the upper and the lower extremities, suggesting that sun exposure does not affect significantly the pathogenesis of DSH skin lesions.

A novel missense mutation of ADAR1 gene in a Chinese family leading to dyschromatosis symmetrica hereditaria and literature review

Dyschromatosis symmetrica hereditaria (DSH) is a rare autosomal dominant pigmentary genodermatosis, which is characterized by a mixture of hyperpigmented and hypopigmented macules on the dorsal of the hands and feet, and on the face presented like freckle. Identification of RNA-specific adenosine deaminase 1 (ADAR1) gene results in DSH. This study was mainly to explore the pathogenic mutation of ADAR1 gene and provide genetics counselling and prenatal diagnostic testing for childbearing individuals.Mutational analysis of ADAR1 gene was performed by polymerase chain reaction (PCR) and electrophoretic separation of PCR products by 1.5% agarose gel electrophoresis. The coding exons and intron/exon flanking regions followed by bidirectional sequencing was performed on all participants. In this study, we found that a 28 year-old male patient harbouring a deleterious substitution of Leu1052Pro in the ADAR1 gene in a typical DSH family. His mother suffered from the DSH also owns the same mutation. This mutation, however, is not identified in the unaffected members in this family and those 200 normal controls. In summary, this new mutation Leu1052Pro reported here is pathogenic and detrimental for DSH. Our finding not only enriches mutation database and contributes to dissecting further the correlation between mutation position and phenotypical features of DSH, but also provides genetics counselling and prenatal diagnostic testing for childbearing couple.

Speckled acral hypopigmentation in an adolescent

We report a case of speckled acral hypopigmentation in a 12-year-old girl. She presented with asymptomatic hypopigmented macules on the hands and feet. This rare entity is a proposed variant of reticulate acropigmentation and of unknown etiology.

Clinical and Genetic Review of Hereditary Acral Reticulate Pigmentary Disorders

Reticulated pigmentation is a unique pigmentary change caused by a heterogeneous group of hereditary and acquired disorders. This pigmentation is characterized by a mottled appearance, with lesions that vary in size and pigmentary content. This review discusses the hereditary group of the reticulated pigmentation disorders, such as dyschromatosis symmetrica hereditaria, dyschromatosis universalis hereditaria, and reticulate acropigmentation of Kitamura. The clinical presentation and histopathological features often overlap, making diagnosis difficult. However, each of these hereditary conditions possesses a unique genetic mutation, and genetic analysis is thus more useful in the diagnosis of these conditions. This article delivers an update regarding the clinical features, detailed histopathological description, and genetic information concerning hereditary reticulate pigmentary disorders and aims to provide useful background for use by clinical dermatologists and histopathologists when approaching this group of hereditary disorders.

Diverse selective regimes shape genetic diversity at ADAR genes and at their coding targets

A-to-I RNA editing operated by ADAR enzymes is extremely common in mammals. Several editing events in coding regions have pivotal physiological roles and affect protein sequence (recoding events) or function. We analyzed the evolutionary history of the 3 ADAR family genes and of their coding targets. Evolutionary analysis indicated that ADAR evolved adaptively in primates, with the strongest selection in the unique N-terminal domain of the interferon-inducible isoform. Positively selected residues in the human lineage were also detected in the ADAR deaminase domain and in the RNA binding domains of ADARB1 and ADARB2. During the recent history of human populations distinct variants in the 3 genes increased in frequency as a result of local selective pressures. Most selected variants are located within regulatory regions and some are in linkage disequilibrium with eQTLs in monocytes. Finally, analysis of conservation scores of coding editing sites indicated that editing events are counter-selected within regions that are poorly tolerant to change. Nevertheless, a minority of recoding events occurs at highly conserved positions and possibly represents the functional fraction. These events are enriched in pathways related to HIV-1 infection and to epidermis/hair development. Thus, both ADAR genes and their targets evolved under variable selective regimes, including purifying and positive selection. Pressures related to immune response likely represented major drivers of evolution for ADAR genes. As for their coding targets, we suggest that most editing events are slightly deleterious, although a minority may be beneficial and contribute to antiviral response and skin homeostasis.

Five novel mutations in the ADAR1 gene associated with dyschromatosis symmetrica hereditaria

Background

Dyschromatosis symmetrica hereditaria (DSH) is an autosomal dominantly inherited skin disease associated with mutations of ADAR1, the gene that encodes a double-stranded RNA-specific adenosine deaminase. The purpose of this study was to investigate the potential mutations in ADAR1 in seven Chinese families with DSH.

Methods

All the coding exons including adjacent intronic as well as 5′ and 3′ untranslated region (UTR) of ADAR1 were screened by direct sequencing. Moreover, quantitative reverse-transcription polymerase chain (qRT-PCR) and Western blot were applied to determine the pathogenic effects associated with the mutations.

Results

Molecular genetic investigations detected five novel mutations (c.556C > T, c.3001C > T, c.1936_1937insTG, c.1065_1068delGACA and c.1601G > A resulting in p.Gln186X, p.Arg1001Cys, p.Phe646LeufsX16, p.Asp357ArgfsX47 and p.Gly471AspfsX30 protein changes, respectively) as well as two previously reported (c.2744C > T and c.3463C > T causing p.Ser915Phe and p.Arg1155Trp protein changes, respectively). Among them, we found that the substitution c.1601G > A at the last nucleotide of exon 2 compromised the recognition of the splice donor site of intron 2, inducing an aberrant transcript with 190-bp deletion in exon 2 and causing an approximately 50% reduction of ADAR1 mRNA level in affected individual. In addition, consistent with the predicted results, the expression patterns of other novel mutations were detected by Western blot.

Conclusion

We identified five novel and two recurrent mutations of the ADAR1 gene in seven Chinese families with DSH and investigated potential effects of the novel mutations in this study. Our study expands the database on mutations of ADAR1 and for the first time, demonstrates the importance of exonic nucleotides at exon-intron junctions for ADAR1 splicing.