Role of the Pro23Leu mutation in a family affected by retinitis pigmentosa in the Basque Country

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Role of the Pro23Leu mutation in a family affected by retinitis pigmentosa in the Basque Country
  Clin Genet  1999: 56: 407–408  Printed in Ireland  .  All rights reser  ed  Letter to the Editor Role of the Pro23Leu mutation in a familyaffected by retinitis pigmentosa in theBasque Country Retinitis pigmentosa (RP) is a degenerative disor-der localized in the outer part of the retina thatleads mainly to night blindness and loss of periph-eral visual field.We screened RP patients for mutations in therhodopsin gene (1) using polymerase chain reac-tion (PCR), denaturing gradient gel electrophore-sis, restriction analysis and sequencing.One of these patients (II 1) (66 years old) wasinitially classified as a sporadic case (SCRP) (Fig.1). He suffered from bad night vision since he wasbetween 5 and 8 years old with slow progression.His brother (II 2) was not ophthalmologically ex-amined, but did not have any RP symptoms, onlysome optic defects. None of III 1, III 2 and III 3(in their 20’s or 30’s) showed any RP symptoms,but they all had optic defects; one had also am-bliopy. III 2 and III 3 were examined electrophysi-ologically. Whereas III 3 had a normalelectroretinogram, the answer to flashes of bluelight in III 2, presented a b-wave amplitude in asubnormal range with values of 14.4 for his righteye and 12.8 for his left eye. The values in III 3were 105 and 103, respectively. In the cone re-sponse to big stimuli under scotopic conditions,the b-wave amplitude was 85 and 70 in III 2compared to 121 and 135 in III 3.We found a heterozygous C-T transition in thesecond nucleotide of codon 23 causing a Pro-line23Leucine (Pro23Leu) mutation in II 1, III 1,III 2 and III 3.Dryja et al. (2) reported this mutation as respon-sible for one case of autosomal dominant RP(ADRP) but unfortunately without clinical de-scription. In our case, only II 1 had clear signs of RP.Interestingly, b-wave amplitude is the first signof a rod dysfunction and is used as an indication of early diagnosis even without retinal degenerationor abnormal fundus. We cannot determine at thispoint to what extent this could mean a rod dys-function in III 2. A continuous follow-up will benecessary for the next few years to answer this.We could be facing a dominant form of RP withincomplete penetrance and variable expression in-stead of the SCRP. The lack of symptoms inindividuals carrying this Pro23Leu mutation makesus speculate with the presence of some other inter-nal and / or external factors (3) which could alsoinfluence in the onset. This patient did not visit anophthalmologist until he was 36 years old and hewas diagnosed with RP at 55 years of age. Thisseems to represent a late onset and none of hisoffspring have reached that age yet. In addition,they take precautions such as wearing sunglassesor protecting themselves against the sunlight etc.Cases of ADRP with incomplete penetrance andmarked variation in their expressivity have alreadybeen reported (4, 5).In conclusion, we think the mutation Pro23Leufound here is related to RP, although a clinicalfollow-up will be necessary to confirm the role of this mutation in this case. Ana I Al   arezEsteban Arostegui Rosa MartinManuel MolinaMercedes DuranMaria I Tejada Fig  .  1 . Pedigree of the family. Individuals II 1, III 1, III 2 andIII 3 carry the Pro23Leu mutation. Individual II 2 is not acarrier. 407  Letter to the Editor  Acknowledgements We would like to thank the Foundation ONCE / NationalFederation for the RP affected people as well as thepatients and relatives, especially the family described here.This work was also supported by the Fondo de Investiga-ciones Cientificas (FIS 94 / 0854). References 1. Alvarez AI, Arostegui E, Martin R, Duran M, On-aindia ML, Molina M, Tejada MI. Molecular studyof the rhodopsin gene in retinitis pigmentosa patientsin the Basque Country. J Med Genet 1998: 35: 387– 390.2. Dryja TP, Hahn LB, Cowley GS, McGee TL, Berson EL.Mutation spectrum of the rhodopsin gene among patientswith autosomal dominant retinitis pigmentosa. Proc NatlAcad Sci USA 1991: 88: 9370–9374.3. Barkur S, Shastry BS. Retinitis pigmentosa and relateddisorders: phenotypes of rhodopsin and peripherin / RDSmutations. Am J Med Genet 1994: 52: 467–474.4. Berson EL, Simonoff EA. Dominant retinitis pigmentosawith reduced penetrance: further studies of the elec-troretinogram. Arch Ophthalmol 1979: 97 (7): 1286–1291.5. Moore AT, Fitzke F, Jay M, Arden GB, Inglehearn CF,Keen TJ, Bhattacharya SS, Bird AC. Autosomal dominantretinitis pigmentosa with apparent incomplete penetrance: aclinical, electrophysiological, psychophysical and moleculargenetic study. Br J Ophthalmol 1993: 77 (8): 473–479. Correspondence :  Dr Maria I TejadaGenetics UnitBasurto HospitalAvda Montevideo18, E-48013 BilbaoSpain 408
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