Choroideremia; clinical and genetic aspects.

(1) HISTORICAL.-In the fully-developed state, choroideremia presents a characteristic and unmistakable picture of which Fig. 1 and Colour Plate 1(a and b) may be taken as examples. The almost total lack of choroidal vessels strongly suggests a developmental anomaly. In fact most of the early writers on, the subject, such as Mauthner (1872) and Koenig (1874), stressed the likeness to choroidal coloboma. As cases accumulated, less extreme pictures were observed, and these raised the possibility that choroideremia was a progressive affection and not a congenital anomaly-a view that gained some support from the fact that, apart from showing some choroidal vessels, these less extreme cases also showed pigmentary changes, sometimes reminiscent of retinitis pigmentosa (Zorn, 1920; Beckershaus, 1926; Werkle, 1931). Furthermore, the recognition of gyrate atrophy as a separate entity (Cutler, 1895) fitted in well with such a reading. The patches of atrophy seen in that affection could well be visualized as an early stage of the generalized atrophy seen in choroideremia, and since there was some evidence that gyrate atrophy was itself a variant of retinitis pigmentosa-for the affection is reputed to have been observed in families diagnosed as suffering from retinitis pigmentosa (see Usher, 1935)-the suggestion emerged that choroideremia, far from being a congenital stationary affection, was an extreme variant of retinitis pigmentosa. The occurrence of nightblindness as a cardinal symptom in all three affections appeared to lend additional support to the idea of their unity-a view still further supported by the fact that retinitis pigmentosa had been recorded in families with choroideremia by Smith and Usher (1916) and by Beckershaus (1926). Three possible readings of choroideremia therefore emerged. At the one extreme it was regarded as an independent, congenital, stationary affection; in sharp contrast to this view it was regarded as an extreme variant of retinitis pigmentosa with its abiotrophic character; thirdly it figured as an independent affection, possibly congenital, but undoubtedly progressive. These difficulties, which could not be resolved by the case reports, have been cleared up in recent years by genetic studies. It is now established that choroideremia is an independent affection unrelated to retinitis pigmentosa. Whether the