SPLICE-MEDIATED INSERTION OF AN ALU SEQUENCE IN THE COL4A3 MESSENGER-RNA CAUSING AUTOSOMAL RECESSIVE ALPORT SYNDROME

Alport syndrome is a mainly X-linked hereditary disease of basement me mbranes characterized by progressive renal failure, deafness, and ocul ar lesions. The alpha 3(1V) and alpha>4(IV) collagen genes have been r ecently shown to be involved in the less frequent autosomal recessive form. When screening lymphocyte COL4A3 mRNAs from Alport patients, we found a mutant whose transcripts were disrupted by a 74 bp insertion a t the junction of exons IV or V and VI. The insertion derives from an antisense Alu element in COL4A3 intron V, which has been spliced into the alpha 3(IV) mRMA due to a G to T transversion activating a cryptic acceptor splice site in this Alu element. There is complete segregati on of this mutation with the disease in the family. Our findings provi de the first evidence for the pathogenic role of abnormal splicing of COL4A3. Moreover, we demonstrate the superiority of mutation screening at the mRNA level to detect a hitherto poorly recognized mutation mec hanism in humans, splice-mediated insertion of an Alu fragment into a coding sequence.