Novel mutations of the FANCG gene causing alternative splicing in Japanese Fanconi anemia

Abstract

Fanconi anemia (FA), an autosomal recessive disorder characterized by a progressive pancytopenia associated with congenital anomalies and high predisposition to malignancies, is a genetically and clinically heterogeneous disease. At least eight complementation groups (FA-A to FA-H) have been identified. Previously, we studied mutations of the FANCA gene, responsible for FA-A, and found pathogenic mutations in 12 of 15 unclassified Japanese FA patients. Here, we further studied an additional 5 FA patients for sequence alterations of the FANCA gene and found pathogenic mutations in 2 of them. We further analyzed mutations of the FANCC and FANCG genes, responsible for FA-C and FA-G, respectively, in the remaining 6 FA patients. Although there was no alterations in the FANCC gene in these 6 patients, two novel mutations of the FANCG gene, causing aberrant RNA splicing, were detected in 2 FA patients. One was a base substitution from G to C of the invariant GT dinucleotides at the splice donor site of intron 3, resulting in the skipping of exon 3, as well as the skipping of exons 3 and 4. The other was a base substitution from C to T in exon 8, creating a nonsense codon (Q356X). This mutation resulted in the exclusion of a sequence of 18 nucleotides containing the mutation from the mRNA, without affecting the splicing potential of either the authentic or the cryptic splice donor site. Collectively, 14 of the 20 unclassified Japanese FA patients belong to the FA-A group, 2 belong to the FA-G group, and none belongs to the FA-C group.

Two common founder mutations of the fanconi anemia group g gene FANCG/XRCC9 in the Japanese population

“…Truncated products with partial function resulting from mutant alleles may be involved in phenotypic variation of FA (Yamashita et al, 1996). RT-PCR analysis of FANCG mRNA showed that IVS3+1G>C resulted in skipping of exon 3 or exons 3 and 4, whereas 1066C>T, generating a stop codon in exon 8, resulted in a deletion of 18 bp including the new stop codon, by activation of a cryptic splice site upstream from the normal IVS8 splice donor site (data not shown), as described (Yamada et al, 2000). Thus, IVS3+1G>C and 1066C>T arepredicted to yield truncated proteins with deletion of 44 amino acids (G59V+del 60-103) and 6 amino acids (del 354-359), respectively, whereas 91C>T and 194delC are predicted to produce no protein products (null-mutations).…”

“…Other investigators screened 20 Japanese patients and identified 12 patients with FANCA mutations and 2 patients with FANCG mutations, a homozygote for IVS3+1G>C and a compound heterozygote with IVS3+1G>C and 1066C>T (Tachibana et al, 1999;Yamada et al, 2000). In the present study, we further screened 45 unrelated FA families in Japan and identified 10 with biallelic mutations of FANCG.…”

Spectrum of sequence variation in theFANCG gene: An International Fanconi Anemia Registry (IFAR) study

“…In patient IFAR 8048, a single transcript was found in which exon 9 was deleted together with 18 bp from exon 8, creating a truncated protein. The splicing machinery used the same cryptic donor splice site (position 1058 in exon 8) seen in the Japanese patient with 1066C4T [Yamada et al, 2000]. In the subject IFAR 8056, two transcripts were found.…”

“…This mutation was only found in French-Acadian families in our study of IFAR families. The IVS3+1G4C mutation was found in two subjects, one homozygous (AP66P) and the other a compound heterozygote (AP02P), in a study of FA patients in Japan [Yamada et al, 2000]. Both subjects were reported to exhibit two aberrant transcripts, corresponding to the skipping of exon 3 and the skipping of exons 3 and 4, respectively.…”

Mutations in the Gene Encoding the E2 Conjugating Enzyme UBE2T Cause Fanconi Anemia

“…The AP65P individual has been reported as carrying no mutations in FANCA, FANCG, and FANCC. 18 We transformed the cells with human TERT (hTERT) and termed them AP65P-hTERT. Unfortunately, we were unable to immortalize bone marrow fibroblasts from PNGS-255.…”