Carriers Of X-linked Retinitis Pigmentosa Research Articles

A family with RP3 type of X-linked retinitis pigmentosa: an association with ciliary abnormalities

The results of linkage analysis in a family with X-linked retinitis pigmentosa (XLRP) are presented. Probe M27B (DXS255), localized to Xp11.22, was only loosely linked to XLRP, whereas pHOC3 (OTC), in the more distal Xp21.1 region, was tightly linked. In this family, the conditional probability of an RP3 locus (in Xp21.1-p11.4) was found to be 0.978 compared with 0.021 for an RP2 locus (in Xp11.4-p11.2). Risk assessment showed that 2 out of 4 "at risk" females showing no clinical abnormality have a high probability of being genetic carriers of XLRP. Some affected males have recurrent respiratory infections as a result of a condition indistinguishable from the immotile cilia syndrome; indeed, there is an association between XLRP and susceptibility to respiratory infections in the majority of affected males. The possibility that previously observed ciliary abnormalities in XLRP patients might be associated specifically with an RP3 locus abnormality is discussed.

Vitreous fluorophotometry in carriers of choroideremia and X-linked retinitis pigmentosa.

The status of the blood-retinal barrier (BRB) in carriers of choroideremia and X-linked retinitis pigmentosa (XLRP) was determined by vitreous fluorophotometry (VF) and compared with that in female control subjects. Electroretinographic (ERG) amplitudes were measured to determine the overall functional integrity of retinal rods and cones. Comparison of the VF results showed an abnormal BRB in at least some carriers of XLRP, particularly those with peripheral fundus pigmentary changes, but not in carriers of choroideremia with even moderately extensive pigmentary changes. The abnormal BRB in XLRP carriers, with or without peripheral fundus pigmentary changes, was associated with at least moderate to moderately extensive reduction in scotopic ERG amplitudes, while the normal VF results in choroideremia carriers were associated with normal scotopic ERG amplitudes. However, in XLRP carriers, mild to modest reductions in ERG scotopic responses were seen in the presence of normal VF findings.

Rod and Cone Dysfunction in Carriers of X-linked Retinitis Pigmentosa

Carriers of X-linked retinitis pigmentosa were studied using electroretinographic and psychophysical procedures. Under both dark- and lightadapted (cone-isolated) conditions, electroretinogram (ERG) a-waves of carriers were reduced in amplitude but normal in implicit time, whereas b-waves were reduced in amplitude and delayed in implicit time. Reductions in b-wave amplitudes of the carriers as a group were equivalent for the rod and cone systems. Luminance-response functions for both dark-adapted and cone-isolated b-waves were fit by the Naka-Rushton equation and demonstrated a selective reduction of Rmax; the semi-saturation constant (K) and the slope parameter (n) were normal. Electroretinograms recorded using the brightest stimulus flashes were most effective at distinguishing carriers from normals. Absolute thresholds of the carriers were elevated significantly across the central 40° of the visual field. As a group, the threshold elevations of the carriers were approximately equal for the rod and cone systems

Carriers of X-linked retinitis pigmentosa. A fluorophotometric determination of the permeability of the blood-retinal barrier.

The blood-retinal barrier permeability to fluorescein was studied in a single family with X-linked retinitis pigmentosa by an elaborate vitreous fluorophotometric method. Affected males showed a ten times increase of permeability compared with normals. In a group of seven obligate carriers the mean permeability was significantly increased by 45% compared with the mean permeability in a group of normals. Five of the seven carriers had permeabilities higher than the normal mean permeability + 2 SD, while two carriers had a permeability within the normal mean +/- 2 SD. Thus, this study supported that carriers of X-linked retinitis pigmentosa show deterioration of the blood-retinal barrier. However, the phenomenon is not present in all carriers and the permeability cannot be used as a completely safe indicator of the carrier state.