Novel truncating mutations of the CHM gene in Chinese patients with choroideremia.
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.
Yip
Shea Ping
SP
Department of Health Technology and Informatics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong SAR, China. shea.ping.yip@polyu.edu.hk
Cheung
Tsz Shan
TS
Chu
Man Yu
MY
Cheung
Suk Chun
SC
Leung
Kam Wah
KW
Tsang
Kin Ping
KP
Lam
Stephen T S
ST
To
Chi Ho
CH
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
D048868:Adaptor Proteins, Signal Transducing; C081787:CHM protein, human