The molecular lesion is an A to T transversion at base pair 70,615,130 (v38) on chromosome 11, or base pair 4,501 in the GenBank genomic region NC_000077. The mutation is located within intron 11, two nucleotides from the next, and final, exon (exon 12). It is not yet known how the pip-squeak mutation affects splicing of the gene. The locations of putative cryptic acceptor sites within exon 12 are unknown.