Objective: To present evidence for a type IV collagen alpha5 chain (alpha5[IV]) abnormality in the anterior lens capsule of a patient with anterior lenticonus associated with Alport syndrome.
Methods: The anterior lens capsule obtained from a 54-year-old man with anterior lenticonus associated with Alport syndrome was examined ultrastructurally and stained immunohistochemically for the alpha chains of type IV collagen, alpha1(IV) to alpha6(IV). A search was also made for a mutation in the COL4A5 complementary DNA encoding the alpha5(IV) chain by reverse transcription-polymerase chain reaction of illegitimate transcripts.
Results: The anterior lens capsule of the patient was much thinner than that of normal subjects and lacked the alpha3(IV) to alpha6(IV) chains immunohistochemically, while control specimens stained positively for all of the alpha(IV) chains. The patient had a C-to-T transition at nucleotide 5231 causing a nonsense mutation, R1677X, in the COL4A5 complementary DNA.
Conclusion: Our findings demonstrated that normal anterior lens capsules express all of the alpha(IV) chains and that a patient with anterior lenticonus associated with Alport syndrome had a mutation in the COL4A5 gene resulting in the lack of immunoreactivity to alpha3(IV) to alpha6(IV) chains in the anterior lens capsule. Clinical Relevance This study showed abnormal composition of alpha(IV) chains in the anterior lens capsule of a patient with anterior lenticonus caused by a nonsense mutation in the COL4A5 gene. Further investigation of the phenotype-genotype relationship will provide a better understanding of the molecular pathogenesis of anterior lenticonus.