Novel mutations in the NRL gene and associated clinical findings in patients with dominant retinitis pigmentosa.

OBJECTIVES

To search for mutations in the neural retina leucine zipper (NRL) gene in patients with dominant retinitis pigmentosa and to compare the severity of disease in these patients with that observed previously in patients with dominant rhodopsin mutations.

METHODS

Single-strand conformation analysis was used to survey 189 unrelated patients for mutations. The available relatives of index patients with mutations were also evaluated. In our clinical examination of patients, we measured visual acuity, final dark-adaptation threshold equivalent visual field diameter, and electroretinogram amplitudes among other parameters of visual function. We compared the clinical findings with those obtained earlier from similar evaluations of a group of 39 patients with the dominant rhodopsin mutation Pro23His and a group of 25 patients with the dominant rhodopsin mutation Pro347Leu.

RESULTS

We identified 3 novel missense mutations in a total of 4 unrelated patients with dominant retinitis pigmentosa: Ser50Pro, Ser50Leu (2 patients), and Pro51Thr. Each mutation cosegregated with dominant retinitis pigmentosa. None of these mutations were found among 91 unrelated control individuals. The visual acuities among the 4 index patients and 3 relatives with NRL mutations who were clinically evaluated ranged from 20/20 (in a 9-year-old patient) to 20/200 (in a 73-year-old patient). All patients had bone-spicule pigment deposits in their fundi. Average rod-plus-cone and cone-isolated electroretinogram amplitudes were both decreased by 99% or more compared with normal amplitudes. The dark-adaptation thresholds, equivalent visual field diameters, and electroretinogram amplitudes (all corrected for age and refractive error) indicated that the disease caused by the NRL mutations was more severe than that caused by the dominant rhodopsin mutation Pro23His and was similar in severity to that produced by the rhodopsin mutation Pro347Leu.

CONCLUSION

The 3 novel NRL mutations we discovered bring the total number of reported mutations in this gene to 6. Five of the 6 mutations affect residues 50 or 51, suggesting that these residues are important in a structural or functional domain of the encoded protein.

CLINICAL RELEVANCE

Rod and cone function is affected to a similar degree in patients with these mutations. The disease caused by NRL mutations found in this study appears to be more severe than that caused by the rhodopsin mutation Pro23His and is similar in severity to that caused by the rhodopsin mutation Pro347Leu, even after correcting for age.