Genomic context and consequences of FGFR2 mutations. A, Schematic representation of genomic region affected by c.1083A>G and c.1083A>T mutations (not to scale). IIIa, IIIb and IIIc denote exons of FGFR2 encoding the 3rd immunoglobulin-like domain; note that physiological skipping of exon IIIb normally occurs in blood mRNA.TM, exon encoding transmembrane domain. Sequencing of genomic DNA demonstrates heterozygosity for c.1083A>G (II-1, Family 1) or c.1083A>T (III-2, Family 2) mutation at the -2 position from the end of exon IIIc (indicated by dashed red line; the upper line in each trace shows the wild type sequence). Below the cartoon is shown the genomic sequence around the cryptic donor splice site within exon IIIc (marked with red asterisk). B, Amplified cDNA corresponding to c.1083A>G and c.1083A>T mutations (same individuals as for genomic analyses), demonstrates two additional smaller products (indicated with white arrows D and E), in addition to the normal (C) product. C, In the cDNA product coincident with the wild type band (II-1, Family 1), the mutant allele at the penultimate position of exon IIIc is not represented, indicating complete skipping of normal splicing. The consequences for splicing of the mutant allele (sequence traces illustrated are from III-1, Family 2) are either to activate the cryptic splice donor site within exon IIIc (D) or to skip exon IIIc completely (E).