The molecular lesion is a T to A transversion at base pair 94,345,990 (v38) on chromosome 15 or base pair 119,429 in the GenBank genomic region NC_000081. This corresponds to nucleotide (nt) 2,116 in the mRNA sequence NM_177431 (isoform 1), within exon 13 of 39 total exons, and to nt 2,116 in the mRNA sequence NM_00164785 (isoform 2), within exon 13 of 28 total exons. The mutation results in a cysteine (C) to serine (S) substitution at amino acid position 619 (C619S) in both Adamts20 protein variants.