Survival Motor Neuron (SMN) polymorphism in relation to congenital arthrogryposis in two Piedmont calves

The term arthrogryposis refers to a symptom complex that is characterised by congenital limb contractures. Arthrogryposis has been reported in man, in farm animals and in pets. Several forms have been reported to have a genetic origin in man. In Brown Swiss and Holstein Friesian cattle, congenital contractures have been recorded and classified as spinal muscular atrophy (SMA). The survival motor neuron gene (SMN) has been suggested as a candidate gene for SMA. In the last 20 years, the National Association of Piedmont Cattle have recorded arthrogryposis cases. We cloned and sequenced SMN cDNA extracted from the spinal cord samples of two animals: one Piedmont calf showing a severe clinical form of arthrogryposis and one normal Piedmont calf. In the affected calf, more than 50% of the 5′end clones showed a ATG > TTG single nucleotide polymorphism (SNP) in exon 1 that should determine a Met > Leu aminoacid change (single point mutation M3L). This mutation is associated with a 9 bp increase length of 5′UTR and to a TTC → TTT silent mutation in exon 1. No single point mutation or 5′end polymorphism was shown in healthy animals and in the remaining 50% of the clones from the affected calf. We hypothesise a possible pathogenic effect of the 5′end-exon 1 polymorphism.