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Using multipoint linkage analysis in 20 families segregating for X-linked retinitis pigmentosa (XLRP), the lod scores on a map of eight RFLP loci were obtained. Our results indicate that under the hypothesis of homogeneity the maximal multipoint lod score supports one disease locus located slightly distal to OTC at Xp21.1. Heterogeneity testing for two XLRP loci suggested that a second XLRP locus may be located 8.5 cM proximal to DXS28 at Xp21.3. Further heterogeneity testing for three disease loci failed to detect a third XLRP locus proximal to DXS7 in any of our 20 XLRP families.

A change in visual acuity of seven letters or more on the standardized Early Treatment Diabetic Retinopathy Study charts may be considered important in patients with retinitis pigmentosa. For these patients with minor lens opacity, visual acuity measurements obtained with undilated and dilated pupils were similar. These findings help to establish guidelines for monitoring the response of visual acuity during any future therapeutic intervention trials or for determining substantial changes in visual acuity over time when the course of visual acuity loss in such patients is monitored.