Kandai Nozu1, Igor Vorechovsky2, Hiroshi Kaito3, Xue Jun Fu3, Koichi Nakanishi4, Yuya Hashimura3, Fusako Hashimoto3, Koichi Kamei5, Shuichi Ito5, Yoshitsugu Kaku6, Toshiyuki Imasawa7, Katsumi Ushijima8, Junya Shimizu9, Yoshio Makita10, Takao Konomoto11, Norishige Yoshikawa4, Kazumoto Iijima3. 1. Department of Pediatrics, Kobe University Graduate School of Medicine, Kobe, Japan; nozu@med.kobe-u.ac.jp. 2. Faculty of Medicine, University of Southampton, Southampton, United Kingdom; 3. Department of Pediatrics, Kobe University Graduate School of Medicine, Kobe, Japan; 4. Department of Pediatrics, Wakayama Medical University, Wakayama, Japan; 5. Division of Nephrology and Rheumatology, National Center for Child Health and Development, Tokyo, Japan; 6. Department of Nephrology, Fukuoka Children's Hospital, Fukuoka, Japan; 7. Kidney Center, National Hospital Organization Chiba-East Hospital, Chiba, Japan; 8. Department of Pediatrics, Yokkaichi Municipal Hospital, Mie, Japan; 9. Department of Pediatrics, National Hospital Organization Okayama Medical Center, Okayama, Japan; 10. Education Center, Asahikawa Medical University, Hokkaido, Japan; and. 11. Department of Pediatrics, Faculty of Medicine, University of Miyazaki, Miyazaki, Japan.
Abstract
BACKGROUND AND OBJECTIVES: X-linked Alport syndrome is caused by mutations in the COL4A5 gene. Although many COL4A5 mutations have been detected, the mutation detection rate has been unsatisfactory. Some men with X-linked Alport syndrome show a relatively mild phenotype, but molecular basis investigations have rarely been conducted to clarify the underlying mechanism. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: In total, 152 patients with X-linked Alport syndrome who were suspected of having Alport syndrome through clinical and pathologic investigations and referred to the hospital for mutational analysis between January of 2006 and January of 2013 were genetically diagnosed. Among those patients, 22 patients had suspected splice site mutations. Transcripts are routinely examined when suspected splice site mutations for abnormal transcripts are detected; 11 of them showed expected exon skipping, but others showed aberrant splicing patterns. The mutation detection strategy had two steps: (1) genomic DNA analysis using PCR and direct sequencing and (2) mRNA analysis using RT-PCR to detect RNA processing abnormalities. RESULTS: Six splicing consensus site mutations resulting in aberrant splicing patterns, one exonic mutation leading to exon skipping, and four deep intronic mutations producing cryptic splice site activation were identified. Interestingly, one case produced a cryptic splice site with a single nucleotide substitution in the deep intron that led to intronic exonization containing a stop codon; however, the patient showed a clearly milder phenotype for X-linked Alport syndrome in men with a truncating mutation. mRNA extracted from the kidney showed both normal and abnormal transcripts, with the normal transcript resulting in the milder phenotype. This novel mechanism leads to mild clinical characteristics. CONCLUSIONS: This report highlights the importance of analyzing transcripts to enhance the mutation detection rate and provides insight into genotype-phenotype correlations. This approach can clarify the cause of atypically mild phenotypes in X-linked Alport syndrome.
BACKGROUND AND OBJECTIVES:X-linked Alport syndrome is caused by mutations in the COL4A5 gene. Although many COL4A5 mutations have been detected, the mutation detection rate has been unsatisfactory. Some men with X-linked Alport syndrome show a relatively mild phenotype, but molecular basis investigations have rarely been conducted to clarify the underlying mechanism. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: In total, 152 patients with X-linked Alport syndrome who were suspected of having Alport syndrome through clinical and pathologic investigations and referred to the hospital for mutational analysis between January of 2006 and January of 2013 were genetically diagnosed. Among those patients, 22 patients had suspected splice site mutations. Transcripts are routinely examined when suspected splice site mutations for abnormal transcripts are detected; 11 of them showed expected exon skipping, but others showed aberrant splicing patterns. The mutation detection strategy had two steps: (1) genomic DNA analysis using PCR and direct sequencing and (2) mRNA analysis using RT-PCR to detect RNA processing abnormalities. RESULTS: Six splicing consensus site mutations resulting in aberrant splicing patterns, one exonic mutation leading to exon skipping, and four deep intronic mutations producing cryptic splice site activation were identified. Interestingly, one case produced a cryptic splice site with a single nucleotide substitution in the deep intron that led to intronic exonization containing a stop codon; however, the patient showed a clearly milder phenotype for X-linked Alport syndrome in men with a truncating mutation. mRNA extracted from the kidney showed both normal and abnormal transcripts, with the normal transcript resulting in the milder phenotype. This novel mechanism leads to mild clinical characteristics. CONCLUSIONS: This report highlights the importance of analyzing transcripts to enhance the mutation detection rate and provides insight into genotype-phenotype correlations. This approach can clarify the cause of atypically mild phenotypes in X-linked Alport syndrome.
Authors: Mir Reza Bekheirnia; Berenice Reed; Martin C Gregory; Kim McFann; Alireza Abdollah Shamshirsaz; Amirali Masoumi; Robert W Schrier Journal: J Am Soc Nephrol Date: 2010-04-08 Impact factor: 10.121
Authors: P Martin; N Heiskari; J Zhou; A Leinonen; T Tumelius; J M Hertz; D Barker; M Gregory; C Atkin; U Styrkarsdottir; H Neumann; J Springate; T Shows; E Pettersson; K Tryggvason Journal: J Am Soc Nephrol Date: 1998-12 Impact factor: 10.121
Authors: Emanuele Buratti; Martin Chivers; Jana Královicová; Maurizio Romano; Marco Baralle; Adrian R Krainer; Igor Vorechovsky Journal: Nucleic Acids Res Date: 2007-06-18 Impact factor: 16.971