Models of Distal Arthrogryposis and Lethal Congenital Contracture Syndrome.

Distal arthrogryposis and lethal congenital contracture syndromes describe a broad group of disorders that share congenital limb contractures in common. While skeletal muscle sarcomeric genes comprise many of the first genes identified for Distal Arthrogyposis, other mechanisms of disease have been demonstrated, including key effects on peripheral nerve function. While Distal Arthrogryposis and Lethal Congenital Contracture Syndromes display superficial similarities in phenotype, the underlying mechanisms for these conditions are diverse but overlapping. In this review, we discuss the important insights gained into these human genetic diseases resulting from in vitro molecular studies and in vivo models in fruit fly, zebrafish, and mice.

MYH3-associated distal arthrogryposis zebrafish model is normalized with para-aminoblebbistatin.

Distal arthrogryposis (DA) is group of syndromes characterized by congenital joint contractures. Treatment development is hindered by the lack of vertebrate models. Here, we describe a zebrafish model in which a common MYH3 missense mutation (R672H) was introduced into the orthologous zebrafish gene smyhc1 (slow myosin heavy chain 1) (R673H). We simultaneously created a smyhc1 null allele (smyhc1- ), which allowed us to compare the effects of both mutant alleles on muscle and bone development, and model the closely related disorder, spondylocarpotarsal synostosis syndrome. Heterozygous smyhc1R673H/+ embryos developed notochord kinks that progressed to scoliosis with vertebral fusions; motor deficits accompanied the disorganized and shortened slow-twitch skeletal muscle myofibers. Increased dosage of the mutant allele in both homozygous smyhc1R673H/R673H and transheterozygous smyhc1R673H/- embryos exacerbated the notochord and muscle abnormalities, causing early lethality. Treatment of smyhc1R673H/R673H embryos with the myosin ATPase inhibitor, para-aminoblebbistatin, which decreases actin-myosin affinity, normalized the notochord phenotype. Our zebrafish model of MYH3-associated DA2A provides insight into pathogenic mechanisms and suggests a beneficial therapeutic role for myosin inhibitors in treating disabling contractures.

A missense variant in SLC39A8 is associated with severe idiopathic scoliosis.

Genetic factors predictive of severe adolescent idiopathic scoliosis (AIS) are largely unknown. To identify genetic variation associated with severe AIS, we performed an exome-wide association study of 457 severe AIS cases and 987 controls. We find a missense SNP in SLC39A8 (p.Ala391Thr, rs13107325) associated with severe AIS (P = 1.60 × 10-7, OR = 2.01, CI = 1.54-2.62). This pleiotropic SNP was previously associated with BMI, blood pressure, cholesterol, and blood manganese level. We replicate the association in a second cohort (841 cases and 1095 controls) resulting in a combined P = 7.02 × 10-14, OR = 1.94, CI = 1.63-2.34. Clinically, the minor allele of rs13107325 is associated with greater spinal curvature, decreased height, increased BMI and lower plasma manganese in our AIS cohort. Functional studies demonstrate reduced manganese influx mediated by the SLC39A8 p.Ala391Thr variant and vertebral abnormalities, impaired growth, and decreased motor activity in slc39a8 mutant zebrafish. Our results suggest the possibility that scoliosis may be amenable to dietary intervention.