title: Novel truncating mutations of the CHM gene in Chinese patients with choroideremia.
abstract: OBJECTIVE
  Choroideremia (CHM) is an X-linked retinal degenerative disorder caused by mutations in the CHM gene. The mutations result in malfunction of the Rab escort protein 1 (REP-1). In this study, mutational analysis of the CHM gene was performed on five Chinese families clinically diagnosed with CHM.
  
  
  METHODS
  Denaturing high performance liquid chromatography was used for mutation screening for all 15 exons and flanking intron regions of the CHM gene. Mutations were confirmed and characterized with DNA sequencing. Second samples were later collected for extraction of mRNA and proteins from leukocytes. A non-radioactive protein truncation test (PTT) was developed and used to characterize the truncating nature of the mutations. Immunoblot analysis of proteins extracted from leukocytes was also performed.
  
  
  RESULTS
  Five mutations were identified in these five families, each with one distinct mutation: three frameshift, one nonsense, and one splicing. Two of these were novel mutations: c.627dupA in exon 5 and c.703-1G>C in intron 5. The truncating nature of the mutations was experimentally proved by PTT for four families with second samples collected. In particular, c.703-1G>C spliced exon 5 directly to exon 7 and deleted the entire exon 6 from the transcript. Direct immunoblot analysis failed to detect REP-1 in males affected by CHM, but demonstrated its presence in female carriers and homozygous normal females.
  
  
  CONCLUSIONS
  This is the first study reporting mutations in the CHM gene in Chinese families. Mutational analysis was performed at the DNA, mRNA and protein levels. Five truncating mutations were found, and two of these were novel.
authors: Department of Health Technology and Informatics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong SAR, China. shea.ping.yip@polyu.edu.hk
authors: Shea Ping
authors: SP
authors: Yip
authors: Tsz Shan
authors: TS
authors: Cheung
authors: Man Yu
authors: MY
authors: Chu
authors: Suk Chun
authors: SC
authors: Cheung
authors: Kam Wah
authors: KW
authors: Leung
authors: Kin Ping
authors: KP
authors: Tsang
authors: Stephen T S
authors: ST
authors: Lam
authors: Chi Ho
authors: CH
authors: To
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics*; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D044466:Asian People / Q000235:genetics*; D002648:Child; D002675:Child, Preschool; D002681:China; D015794:Choroideremia / Q000235:genetics*; D002851:Chromatography, High Pressure Liquid; D004252:DNA Mutational Analysis; D005260:Female; D005820:Genetic Testing; D006801:Humans; D015151:Immunoblotting; D007962:Leukocytes / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D009154:Mutation / Q000235:genetics*; D009691:Nucleic Acid Denaturation; D010375:Pedigree
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C081787:CHM protein, human