Mutation Analysis And Functional Study Of U2HR In Chinese Patients With Marie Unna Hereditary Hypotrichosis

Background Marie Unna Hereditary Hypotrichosis (MUHH OMIM 146550) is a rare autosomal dominant hair loss disorder which was firstly described in 1925 by the German dermatologist Marie Unna in a seven-generation of North German family. Clinically, main features of MUHH include sparse or absent hair at birth, growth of coarse and wiry hair during childhood, and progressive hair loss at puberty. Most affected members usually have little or no body hair,eyelashes,eyebrows and secondary sexual hair. Apart from hair loss, there are no other associated abnormalities in MUHH,but the disorder was more severe in males than in females. Histological examination of skin biopsy shows a marked reduction of hair follicles which are often atrophic, and epidermis and dermis containing hair follicles without hair, no marked inflammatory cell infiltrate or fibrosis surrounding hair follicles. Electron microscopic studies show an irregularly twisted hair,longitudinal fractures,longitudinal split,irregular cross section,mild peeling and irregular hair shafts in MUHH. There is genetic heterogeneity. To date, two loci for this disorder have been mapped to chromosome 8p21 and 1p21.1–1q21.3. The locus at 8p21 has been confirmed by many different research groups. This interval contains the entire hairless gene (HR). A number of research groups performed mutation analysis on the HR gene, but no mutation responsible for MUHH has been identified. There are four uORFs in the HR 5′UTR,designated U1HR, U2HR, U3HR and U4HR, from 5′to 3′. U2HR is predicted to encode a 34 amino acid peptide that is highly conserved among mammals, which is an inhibitory uORF. Recently, one collaborating group identified a pathogenic initiation codon mutation in U2HR in a large Chinese Han family with MUHH, and established a spectrum of defects in U2HR from 18 additional families with a confirmed clinical diagnosis of MUHH, they identified 12 more mutations in U2HR. Functional analysis showed that these different classes of mutations all resulted in increased translation of the main HR physiologic ORF.Objective (1) To analyze the clinical features of three families and four sporadic cases with MUHH from Chinese Han population. (2) To identify the U2HR in HR mutations in Chinese patients with MUHH and to get more information for a relationship between genotype and phenotype, and further verify the new pathogenesis in the genetic diseases. (3) To analyze the relative mRNA expression and protein expression of the HR gene.Methods (1) The clinical features of MUHH patients were analyzed by family pedigree investigation, histological examination of skin biopsy and electron microscopic studies. (2) The U2HR in HR gene was amplified by polymerase chain reaction (PCR) using published primers, and we sequence the U2HR gene in one family and four sporadic cases with MUHH. (3) We searched for the mutation reports and papers about MUHH by Chinese Biology Medicine (CBM) disk and PubMed. The clinical features and mutation analysis of MUHH were summarized. (4) Relative mRNA expression of the HR gene was determined by Real-Time PCR on total RNA purified from human peripheral blood monouclear cells(PBMCs)in the mutant, other cases and healthy controls. (5) Protein expression of the HR gene was determined by Western-blot in the mutant, other cases and healthy controls.Results (1) MUHH is an autosomal dominant hair loss disorder. We did not observe obvious genotype-phenotype correlation in MUHH patients. (2) We identified one novel missense mutation (c.E26A) in a sporadic patient. The mutation was not detected in the patient′s unaffected father and in 100 normal controls. (3) The result of relative mRNA expression of HR gene showed no significant difference between the mutant and other patients or normal controls. (4) The result of western-blot showed the expression level of HR gene is significantly higher in the mutant than those in the other patients or normal controls.Conclusions: (1) We identified one novel missense mutation (c.E26A) in a sporadic patient. The mutation in the U2HR of HR gene seems to be the pathologic cause of the patient. This study contributes to expand the repertoire of U2HR mutations underlying MUHH. We summarized a total of 14 mutations of U2HR region with MUHH by previous reports and speculated that the mutation hotspots of U2HR region might be located in codons 24 to 28 of U2HR. However, our study suggested the genetic heterogeneity of MUHH. (2) We speculated mutation in U2HR may increase the expression of HR protein, and loss–of- function mutations in U2HR maybe associated with autosomal dominant MUHH. The higher level of HR protein is perhaps the important cause of hair loss.