Identification of novel mutations in X-linked retinitis pigmentosa families and implications for diagnostic testing.
OBJECTIVE
The goal of this study was to identify mutations in X-chromosomal genes associated with retinitis pigmentosa (RP) in patients from Germany, The Netherlands, Denmark, and Switzerland.


METHODS
In addition to all coding exons of RP2, exons 1 through 15, 9a, ORF15, 15a and 15b of RPGR were screened for mutations. PCR products were amplified from genomic DNA extracted from blood samples and analyzed by direct sequencing. In one family with apparently dominant inheritance of RP, linkage analysis identified an interval on the X chromosome containing RPGR, and mutation screening revealed a pathogenic variant in this gene. Patients of this family were examined clinically and by X-inactivation studies.


RESULTS
This study included 141 RP families with possible X-chromosomal inheritance. In total, we identified 46 families with pathogenic sequence alterations in RPGR and RP2, of which 17 mutations have not been described previously. Two of the novel mutations represent the most 3'-terminal pathogenic sequence variants in RPGR and RP2 reported to date. In exon ORF15 of RPGR, we found eight novel and 14 known mutations. All lead to a disruption of open reading frame. Of the families with suggested X-chromosomal inheritance, 35% showed mutations in ORF15. In addition, we found five novel mutations in other exons of RPGR and four in RP2. Deletions in ORF15 of RPGR were identified in three families in which female carriers showed variable manifestation of the phenotype. Furthermore, an ORF15 mutation was found in an RP patient who additionally carries a 6.4 kbp deletion downstream of the coding region of exon ORF15. We did not identify mutations in 39 sporadic male cases from Switzerland.


CONCLUSIONS
RPGR mutations were confirmed to be the most frequent cause of RP in families with an X-chromosomal inheritance pattern. We propose a screening strategy to provide molecular diagnostics in these families.
Neidhardt
John
J
Division of Medical Molecular Genetics and Gene Diagnostics, Institute of Medical Genetics, University of Zurich, Switzerland. neidhardt@medgen.uzh.ch
Glaus
Esther
E
Lorenz
Birgit
B
Netzer
Christian
C
Li
Yün
Y
Schambeck
Maria
M
Wittmer
Mariana
M
Feil
Silke
S
Kirschner-Schwabe
Renate
R
Rosenberg
Thomas
T
Cremers
Frans P M
FP
Bergen
Arthur A B
AA
Barthelmes
Daniel
D
Baraki
Husnia
H
Schmid
Fabian
F
Tanner
Gaby
G
Fleischhauer
Johannes
J
Orth
Ulrike
U
Becker
Christian
C
Wegscheider
Erika
E
Nürnberg
Gudrun
G
Nürnberg
Peter
P
Bolz
Hanno Jörn
HJ
Gal
Andreas
A
Berger
Wolfgang
W
D005091:Exons / Q000235:genetics; D005136:Eye Proteins / Q000235:genetics; D005190:Family; D005260:Female; D019204:GTP-Binding Proteins; D005799:Genes, Dominant; D040181:Genetic Diseases, X-Linked / Q000175:diagnosis* / Q000235:genetics*; D006579:Heterozygote; D006801:Humans; D040582:Inheritance Patterns / Q000235:genetics; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics; D008297:Male; D008565:Membrane Proteins / Q000235:genetics; D009154:Mutation / Q000235:genetics*; D010375:Pedigree; D011110:Polymorphism, Genetic; D012174:Retinitis Pigmentosa / Q000175:diagnosis* / Q000235:genetics*; D017384:Sequence Deletion
D005136:Eye Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; C072178:RP2 protein, human; C099929:RPGR protein, human; D019204:GTP-Binding Proteins