Research On Clinical Features And Molecular Genetic Mechanism Of Autosomal Dominant Dyschromatosis Universalis Hereditaria In A Chinese Han Family

Research on clinical features and molecular genetic mechanism of autosomal dominant dyschromatosis universalis hereditaria in a Chinese Han familyBackground Dyschromatosis universalis hereditaria(DUH) is a rare peculiar pigmentary genodermatosis first described by Ichikawa and Hiraga in 1933. According to the linkage region,DUH has been divided into three major types, namely DUH1(OMIM 127500) mapped to chromosome 6q24.2-q25.2,DUH2(OMIM 612715) with linkage to 12q21-q23 and DUH3(OMIM 615402) located on 2q35. DUH1 and DUH3 are autosomal dominant forms, while DUH2 transmits with autosomal recessive inheritance. Autosomal dominant DUH is characterized by generalized hyperpigmented and hypopigmented macules exhibiting variable patterns and color depths. This disorder always occurs in infancy or early childhood, and almost affects whole body. The lesions have no obvious change with age. Some patients also have other anomalies, including small stature, learning disability, high tone deafness, cataracts and epileptic seizures. Until now, the mutations in SASH1 or ABCB6 have been reported to be responsible for DUH.Objective(1) we investigate the clinical features of DUH by clinical studies on a case of autosomal dominant DUH in a Chinese Han family.(2)Mutation analysis of ABCB6 and SASH1 genes is performed in order to elucidate the pathogenesis of molecular genetics in this family.Methods(1) We obtained detailed clinical data in a non-consanguineous four-generation Chinese Han family with DUH from Henan Province. The proband was made by physical examination, reflectance confocal microscopy, histologicalexamination and melan-A stain. Then we carried out a genetic survey and clinical physical examination on other members in this family;(2)EDTA anticoagulated venous blood samples were collected from eight subjects of this family(five affected subjects and three unaffected subjects) and two hundred unrelated healthy individuals as controls. Genomic DNA was extracted using Flexi Gene DNA kits;(3)Primers to amplify all coding exons and the respective exon-intron boundaries of the SASH1 and ABCB6 genes were designed by Primer Premier 5.0 software. The purified products performed on a touchdown polymerase chain reaction(PCR) program were sequenced on an ABI Prism3730 XL automated sequencer;(4) Immunohistochemical study was performed to explore the expression level of SASH1 protein in the proband’s skin lesions.Results(1) An autosomal dominant mode of inheritance was suggested in this family. The pigmentary disturbance was first noticed during the age of 1 year, initially appeared on the face, then gradually spread to whole body in all affected individuals. The lesions had no obvious change with age. A great many of stellate shaped light brown to tanned hyperpigmented macules with 2-5mm in diameter were irregularly distributed on patients’ face, neck, trunk and extremities. The skin of other area appeared to be generally homogeneous hypopigmentation. All affected members had similar clinical features except the proband’s elder sister who presented with generalized hyperpigmented macules mingled with hypopigmented macules in a reticular pattern. Patients’ palms, soles, oral mucosa, nails, teeth, mentality and general health were all normal. RCM of hyperpigmentation on the proband showed a remarkably hyperrefractile hypermelanosis in basal layer, the morphologically-intact bright pigmentary rings structures were also observed. However, a marked decrease of pigment in the hypopigmented areas and half-rings or scalloped border-like features of the rings instead of normal intact pigmentary rings. Skin biopsy revealed hyper- or hypomelanosis in the basal layer of epidermis, and there was no unremarkable changein the dermis. Melan-A staining showed dendritic melanocytes in the epidermis of the proband’s hyperpigmented lesion were normal in number and distribution;(2) Sanger sequencing analysis revealed a novel heterozygous missense mutation c.2236C>G(p.Ser587Arg) of the SASH1 gene in five affected individuals, which was not identified in any of the three unaffected individuals or two hundred healthy controls. This point mutation was accepted as pathogenic by SIFT and probably damaging by Poly Phen-2. Structure modeling using Py Mol software illustrated that S587 R mutation leds to a β/α conformational transition in SH3 domain of SASH1. No causative mutation in the ABCB6 gene was found in this family;(3) Immunohistochemistry staining of SASH1 m Ab for proband’s biopsy specimens showed SASH1 protein positively expressed in the cytoplasm of some epithelial cells in the hyperpigmented lesion, but no staining in the hypopigmented lesion.Conclusion(1) Autosomal dominant DUH is a rare genodermatosis characterized by irregularly shaped hyperpigmented and hypopigmented macules almost involving the whole body, which appears in infancy or early childhood. The hypopigmentation is diffuse or mingles with hyperpigmented macules in a reticular pattern. Both RCM and histological examination showed increased pigmentation in the basal layer of epidermis in the hyperpigmented lesion, whereas decreased pigmentation in the hypopigmented area. However, the melan-A staining revealed the number and distribution of melanocytes were normal in the epidermis.(2) A novel heterozygous missense mutation c.2236C>G(p.Ser587Arg) of the SASH1 gene was identified as the pathogenic role in DUH of this Chinese family. This mutation might lead to abnormality in transporting melanin from melanocytes to neighbouring keratinocytes, thereby resulted in universal dyschromatosis.