Genome-Wide Linkage, Exome Sequencing and Functional Analyses Identify ABCB6 as the Pathogenic Gene of Dyschromatosis Universalis Hereditaria

Abstract

BackgroundAs a genetic disorder of abnormal pigmentation, the molecular basis of dyschromatosis universalis hereditaria (DUH) had remained unclear until recently when ABCB6 was reported as a causative gene of DUH.MethodologyWe performed genome-wide linkage scan using Illumina Human 660W-Quad BeadChip and exome sequencing analyses using Agilent SureSelect Human All Exon Kits in a multiplex Chinese DUH family to identify the pathogenic mutations and verified the candidate mutations using Sanger sequencing. Quantitative RT-PCR and Immunohistochemistry was performed to verify the expression of the pathogenic gene, Zebrafish was also used to confirm the functional role of ABCB6 in melanocytes and pigmentation.ResultsGenome-wide linkage (assuming autosomal dominant inheritance mode) and exome sequencing analyses identified ABCB6 as the disease candidate gene by discovering a coding mutation (c.1358C>T; p.Ala453Val) that co-segregates with the disease phenotype. Further mutation analysis of ABCB6 in four other DUH families and two sporadic cases by Sanger sequencing confirmed the mutation (c.1358C>T; p.Ala453Val) and discovered a second, co-segregating coding mutation (c.964A>C; p.Ser322Lys) in one of the four families. Both mutations were heterozygous in DUH patients and not present in the 1000 Genome Project and dbSNP database as well as 1,516 unrelated Chinese healthy controls. Expression analysis in human skin and mutagenesis interrogation in zebrafish confirmed the functional role of ABCB6 in melanocytes and pigmentation. Given the involvement of ABCB6 mutations in coloboma, we performed ophthalmological examination of the DUH carriers of ABCB6 mutations and found ocular abnormalities in them.ConclusionOur study has advanced our understanding of DUH pathogenesis and revealed the shared pathological mechanism between pigmentary DUH and ocular coloboma.

Updated review of genetic reticulate pigmentary disorders

“…Soon afterwards, Liu et al . also provided evidence that ABCB6 is involved in DUH and noticed the coexistence of pigmentation and ocular abnormalities in their patients with DUH . This result supports the opinion that the ABCB6 protein has an important effect on both pigmentation and ocular development …”

“…). Most patients with DUH show skin lesions on the trunk or extremities in infancy or early childhood; the lesions usually stop spreading before adolescence . Histologically, there is an increase or decrease of melanin pigmentation in the basal cells of hyperpigmented lesions or hypopigmented macules, respectively, and pigmentary incontinence can occasionally be observed by light microscopy .…”

Leishmania tarentolae as a host for heterologous expression of functional human ABCB6 transporter

“…Moreover, the identity of its physiological substrate, although accepted by most researchers to involve porphyrins or porphyrin-like molecules [5,29], is not entirely clear and is difficult to study due to the hydrophobic character of candidate compounds. Nevertheless, it is clear that human ABCB6 participates in and influences many physiological and pharmacological phenomena on cellular and tissue level: mutations in the ABCB6 gene have been implicated in hereditary forms of coloboma [11], dyschromatosis universalis [12] and pseudohyperkalemia [13]. It has also been suggested that ABCB6…”

ABCB6, an ABC Transporter Impacting Drug Response and Disease

“…ABCB6 has also been implicated in other genetic diseases such as to ocular colobama (a missing piece of tissue in the eye) and dyschromatosis universalis, which is a genetic disorder of abnormal pigmentation (48, 49). Reported variants associated with these disorders are found in Table 2.…”

“… * This table was curated from the following references: (16, 17, 48, 49, 54–59) ** Allele Frequencies MAF% were obtained from NHLBI GO Exome Sequencing Project (ESP) Exome VariantVariant Server (http://evs.gs.washington.edu/EVS/) accessed on August 14, 2017. …”