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.