先天赤緑色覚異常と錐体ジストロフィに伴う後天色覚異常の合併を遺伝子解析により診断した1例

A case of congenital red-green color blindness with acquired color vision defect secondary to cone dystrophy diagnosed by genetic analysis

要約　目的：先天赤緑色覚異常と錐体ジストロフィに伴う後天色覚異常が合併した症例の報告。症例：57歳男性が錐体ジストロフィの精査目的で受診した。所見：矯正視力は右0.4，左0.3で，両眼黄斑部に萎縮性病変を認めた。網膜電図で錐体系反応がより高度に障害されていた。パネルD-15は1型色覚と2型色覚の軸が混在し，アノマロスコープでは混色目盛値0～73で絶対等色し，その傾きは1型2色覚より急峻で，杆体1色覚（全色盲）より緩やかであった。遺伝子解析で単一のL-Mハイブリッド遺伝子が検出され，1型色覚（強度異常）の存在が確認された。結論：1型色覚に加え，錐体ジストロフィによる中心窩錐体機能低下を合併したため，1型2色覚よりも強度の色覚異常を呈した可能性が考えられた。

Abstract.　Purpose：To report a case who had congenital red-green color blindness and cone dystrophy with acquired color vision defect. Case：A 57-year-old male presented with photophobia and failing visual acuity. He and three males in the pedigree had been diagnosed with congenital color blindness. Findings：Corrected visual acuity was 0.4 right and 0.3 left. Both eyes showed macular atrophy. Full-field electroretinogram showed reduced cone responses. Farnsworth panel D-15 test showed mixed protan and deutan confusion lines. Nagel type Ⅰ anomaloscope showed red-green mixture with extended yellow-scale range at each matching point. Slopes of regression lines were those between protanopia and achromatopsia. Molecular genetic analysis showed that the patient had a single L-M hybrid gene that is present in protanopia or severe form of protanomaly. Conclusion：This patient showed severer dyschromatopsia than protanopia due to additional cone dysfunction.