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Two novel mutations and evidence for haploinsufficiency of the ADAR gene in dyschromatosis symmetrica hereditaria

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Summary  Background 

Dyschromatosis symmetrica hereditaria (DSH, MIM 127400) is a dominantly inherited skin disease associated with mutations in ADAR, the gene that encodes a double-stranded RNA-specific adenosine deaminase. We previously reported two novel ADAR mutations (p.Q513X and p.R916W) and confirmed the role of ADAR in Chinese patients with DSH. Both haploinsufficiency and a dominant-negative effect have been suggested as the potential mechanism by which ADAR mutations cause DSH. Objectives 

To identify ADAR mutations in two additional Chinese DSH families and to obtain insight into the pathogenic mechanism of heterozygous ADAR mutations. Methods 

For mutation detection, all ADAR exons and their flanking intronic sequences were amplified and sequenced. Mutations were further confirmed by restriction analysis. Direct sequencing of cDNA fragments produced by reverse transcription–polymerase chain reaction (RT–PCR) and real-time quantitative RT–PCR were used to examine the expression of ADAR in peripheral lymphocytes isolated from affected individuals. Results 

A small deletion, c.1555delT (p.C519fs), and a missense mutation, c.3116A>G (p.K1039R), were found in families A and B, respectively. In individuals carrying p.Q513X or p.C519fs, sequencing of cDNA fragments indicated almost total loss of mRNA expression from the mutant alleles, and real-time quantitative RT–PCR showed an approximately 50% reduction of ADAR expression. However, equal abundance of the wild-type and mutant cDNA sequences without reduction of ADAR expression was found in a patient with the missense p.R916W mutation. These results suggest that both the nonsense p.Q513X and frameshift p.C519fs mutations have generated null alleles probably by nonsense-mediated mRNA decay. Conclusions 

Two novel ADAR mutations were found in Chinese patients with DSH. Evidence for ADAR haploinsufficiency as a mechanism underlying the molecular pathogenesis of DSH was obtained.
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Keywords: ADAR; double-stranded RNA-specific adenosine deaminase; dyschromatosis symmetrica hereditaria; haploinsufficiency

Document Type: Research Article

Affiliations: 1: Department of Medical Genetics and National Key Laboratory of Medical Molecular Biology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences & Peking Union Medical College, 5 Dong Dan San Tiao, Beijing 100005, China 2: The Research Center for Medical Genomics, China Medical University, Shenyang, China 3: Department of Dermatology, Shenyang No. 7 People's Hospital, Shenyang, China

Publication date: 2006-04-01

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