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


OBJECTIVE
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.
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.
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Liu
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Jiang
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Liu
X-J
XJ
Kang
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Ao
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Sun
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Luo
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Song
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Lo
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Zhang
D000243:Adenosine Deaminase / Q000097:blood / Q000235:genetics*; D001483:Base Sequence; D004252:DNA Mutational Analysis / Q000379:methods; D005260:Female; D015870:Gene Expression; D006239:Haplotypes; D006801:Humans; D008297:Male; D020125:Mutation, Missense; D010375:Pedigree; D010859:Pigmentation Disorders / Q000201:enzymology / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics; D016601:RNA-Binding Proteins; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D012873:Skin Diseases, Genetic / Q000201:enzymology / Q000235:genetics*
D012333:RNA, Messenger; D016601:RNA-Binding Proteins; C567955:ADARB1 protein, human; D000243:Adenosine Deaminase