Monilethrix is a genetic hair shaft disorder that causes a dystrophic alopecia due to hair fragility. All mutations known to cause autosomal dominant monilethrix have been found in the highly conserved helix initiation motif (HIM) and helix termination motif (HTM) of the type II hair keratins K81, K83 and K86. Rare cases with recessive transmission have been linked to desmoglein 4 (DSG4), also expressed in hair cortex. We identified a large Tasmanian family with seemingly recessive transmission. Family members were clinically examined and hair samples were examined under the light microscope. We identified a new mutation located in the Coil 2 region of K86 with dominant transmission. This is the first mutation identified in a region other than the HIM or HTM of a hair keratin, suggesting that dominant mutations tend to occur in the extremities of hair keratins. We also investigated the phenotypic variation associated with monilethrix. Tensile strength studies demonstrated a reduction in strength and elasticity of non-beaded hairs (mean difference in tenacity of -2.140 cN/dtex p=0.018, and strain of 10.429% p<0.001) compared to unaffected controls from the same extended family. Thus both beaded and non-beaded monilethrix hairs demonstrate abnormal tensile properties that contribute to clinical severity.