Pitfalls of mapping a large Turkish consanguineous family with vertical monilethrix inheritance: Monilethrix, a rare autosomal dominant disease characterized by hair fragility and follicular hyperkeratosis, is caused by mutations in three type It hair cortex keratins. The human keratin family comprises 54 members, 28 type I and 26 type II. The phenotype shows variable penetrance and results ill hair fragility and patchy dystrophic alopecia. In our study, Monilethrix was diagnosed oil the basis of clinical characteristics and microscopic examination in a family with 11 affected members. Haplotype analysis was performed by three Simple Tandem Repeat markers (STR) and KRT86 gene was sequenced for the identification of the disease causing mutation. In the results of this, autosomal dominant mutation (E402K) in exon 7 of KRT86 gene was identified as a cause of Moniltherix in the large family from Turkey.