Four novel and two recurrent mutations of the ADAR1 gene in Chinese patients with dyschromatosis symmetrica hereditaria

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.

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 P53/POMC/Gαs/SASH1 autoregulatory feedback loop activates mutated SASH1 to cause pathologic hyperpigmentation

p53-Transcriptional-regulated proteins interact with a large number of other signal transduction pathways in the cell, and a number of positive and negative autoregulatory feedback loops act upon the p53 response. P53 directly controls the POMC/α-MSH productions induced by ultraviolet (UV) and is associated with UV-independent pathological pigmentation. When identifying the causative gene of dyschromatosis universalis hereditaria (DUH), we found three mutations encoding amino acid substitutions in the gene SAM and SH3 domain containing 1 (SASH1), and SASH1 was associated with guanine nucleotide-binding protein subunit-alpha isoforms short (Gαs). However, the pathological gene and pathological mechanism of DUH remain unknown for about 90 years. We demonstrate that SASH1 is physiologically induced by p53 upon UV stimulation and SASH and p53 is reciprocally induced at physiological and pathophysiological conditions. SASH1 is regulated by a novel p53/POMC/α-MSH/Gαs/SASH1 cascade to mediate melanogenesis. A novel p53/POMC/Gαs/SASH1 autoregulatory positive feedback loop is regulated by SASH1 mutations to induce pathological hyperpigmentation phenotype. Our study demonstrates that a novel p53/POMC/Gαs/SASH1 autoregulatory positive feedback loop is regulated by SASH1 mutations to induce pathological hyperpigmentation phenotype.

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.

Acromelanosis albo-punctata: a distinct inherited dermatosis with acral spotty dyspigmentation without systemic involvement

We describe an otherwise healthy 7-year-old boy who developed confetti-like hypopigmented macules on the dorsal aspects of the hands and feet, spreading to the palms and soles a few months after birth. In 1964 Siemens introduced the term acromelanosis albo-punctata to describe the skin features of a patient who has remained the only reported case in the literature so far and who strongly resembles our patient. By genetic testing we excluded mutations in genes known to be involved in diseases with acral hypo- or hyperpigmentation. We review the differential diagnosis of acral localized spotty dyspigmentation and conclude that acromelanosis albo-punctata may represent a distinct entity.

Identification of two novel splice mutations of the ADAR1 gene in two Chinese families with dyschromatosis symmetrica hereditaria

Dyschromatosis symmetrica hereditaria (DSH) is a rare, autosomal dominant dermatosis, characterized by a mixture of hyperpigmented and hypopigmented macules on the dorsa of the hands and feet. The DSH locus has been mapped to chromosome 1q21, and in 2003, pathogenic mutations were identified in the ADAR1 (adenosine deaminase acting on RNA1) gene. In this study, we performed mutation detection of the ADAR1 gene in two Chinese families with DSH. PCR and direct sequencing of the ADAR1 gene were used to identify and confirm the mutations in the two families. Furthermore, we analysed the RNA transcripts by reverse transcriptase (RT)-PCR. Two aberrant splice products were confirmed with RT-PCR and DNA direct sequence analysis. These novel findings further extend our understanding of the role of ADAR1 in DSH.