Here we confirm this finding and identify a key role for MNS1 function in determining left–right body asymmetry and sperm flagella formation and function in humans by defining a homozygous founder frameshift variant in MNS1, in association with randomisation of left–right body asymmetry and male infertility, in four inter-related families of Amish descent, identified through a combination of homozygosity mapping and whole exome sequencing (WES). The gene discussed is MNS1; the disease is male infertility.