Having a good idea of the map location of the gene responsible for this disorder in Brown Swiss cattle, Drögemüller et al. (2010) used sequence capture followed by resequencing to identify a single base insertion in the gene for sulfite oxidase (SUOX) as being causative for this disorder in this breed. The synthesis of sulfite oxidase is dependent upon molybdenum cofactor (Moco), whose synthesis is dependent upon two peptides (MOCS1A and MOCS1B) that are encoded (via consecutive reading frames) by the gene MOCS1. Consistent with their mapping results, Buitkamp et al. (2011) have shown that arachnomelia in Simmental cattle is due to a 2-bp deletion in the MOCS1 gene (see OMIA 001541). Thus we have an excellent example of mutations in two genes involved in the same biochemical pathway giving rise to the same biochemical deficiency and hence the same clinical signs. This is the first example of this type of genetic heterogeneity to be documented in cattle. As stated by Buitkamp et al. (2011), arachnomelia is thus the first example in cattle of an oligogenic disorder.
