C to A transversion at base pair 103,471,232 (v38) on chromosome 15, or base pair 17,450 in the GenBank genomic region NC_000081 encoding Nckap1l. The mutation corresponds to residue 1,000 in the mRNA sequence NM_153505.4 (c.1000C>A) within exon 10 of 31 total exons. The mutation results in substitution of tyrosine 315 for a premature stop codon (p.Y315*) in the HEM1 protein.