Chi-Fan Yang

PSORS2 Is Due to Mutations in CARD14

Psoriasis is a common, immune-mediated genetic disorder of the skin and is associated with arthritis in approximately 30% of cases. Previously, we localized PSORS2 (psoriasis susceptibility locus 2) to chromosomal region 17q25.3-qter after a genome-wide linkage scan in a family of European ancestry with multiple cases of psoriasis and psoriatic arthritis. Linkage to PSORS2 was also observed in a Taiwanese family with multiple psoriasis-affected members. In caspase recruitment domain family, member 14 (CARD14), we identified unique gain-of-function mutations that segregated with psoriasis by using genomic capture and DNA sequencing. The mutations c.349G>A (p.Gly117Ser) (in the family of European descent) and c.349+5G>A (in the Taiwanese family) altered splicing between CARD14 exons 3 and 4. A de novo CARD14 mutation, c.413A>C (p.Glu138Ala), was detected in a child with sporadic, early-onset, generalized pustular psoriasis. CARD14 activates nuclear factor kappa B (NF-kB), and compared with wild-type CARD14, the p.Gly117Ser and p.Glu138Ala substitutions were shown to lead to enhanced NF-kB activation and upregulation of a subset of psoriasis-associated genes in keratinocytes. These genes included chemokine (C-C motif) ligand 20 (CCL20) and interleukin 8 (IL8). CARD14 is localized mainly in the basal and suprabasal layers of healthy skin epidermis, whereas in lesional psoriatic skin, it is reduced in the basal layer and more diffusely upregulated in the suprabasal layers of the epidermis. We propose that, after a triggering event that can include epidermal injury, rare gain-of-function mutations in CARD14 initiate a process that includes inflammatory cell recruitment by keratinocytes. This perpetuates a vicious cycle of epidermal inflammation and regeneration, a cycle which is the hallmark of psoriasis.

A Promoter Sequence Variant of ZNF750 Is Linked with Familial Psoriasis

We previously mapped a psoriasis-susceptibility gene to a 3.8-Mb region of the 17q terminus in a five-generation Chinese family with autosomal-dominant psoriasis. To identify the mutations responsible for the psoriasis in this family, we sequenced 78 genes within the region and found four gene variants, p.Ala201Val in CD7, c.-625A>C in zinc-finger protein 750 (ZNF750), p.Asp189Asn in C17orf56, and p.Ala568Thr in AATK cosegregated with the disease. The latter two variants were not studied further in the absence of disease segregation in other familial psoriasis and presence of variants in normal subjects. Functional analyses of CD7 did not support CD7 as a disease-causing gene. In contrast, the c.-625A>C mutation in ZNF750 resulted in a 42% reduction of the promoter activity, and the electrophoretic mobility shift assay showed binding of nuclear protein(s) to the mutant C allele. The c.-625A>C mutation was found in another sporadic psoriasis patient but was absent in 188 normal controls. Together, the mutation accounts for 1.7% (confidence interval: 0.2-5.84%) of psoriasis in the Chinese population. This report suggests that ZNF750 mutations could contribute to psoriasis susceptibility.

Molecular analysis of Wilson disease in Taiwan: Identification of one novel mutation and evidence of haplotype-mutation association

AbstractWilson disease (WND) is caused by a deficiency of the copper-transporting enzyme, P-type ATPase (ATP7B). Twelve different mutations have previously been identified in Taiwan Chinese with Wilson disease. We, herein, report another 4 missense mutations, 1 of which is novel. We did haplotype analysis of Taiwanese WND chromosomes, using three well characterized short tandem repeat markers (haplotype was assigned in the order of D13S314-D13S301-D13S316). Association correlation was found between the mutations and their respective haplotypes. Haplotype-deduced pedigree analysis was shown to be helpful in the mutation analysis of WND chromosomes and in the molecular assessment of both pre-symptomatic WND patients and carriers. Given the complexity and heterogeneity of the mutation spectrum of ATP7B, we suggest that haplotype analysis should be performed before full-scale mutation analysis.

Insertion/deletion mutations of type I oculocutaneous albinism in chinese patients from Taiwan.

Type I oculocutaneous albinism (OCA1) is an autosomal recessive disorder, which is caused by the reduction or the absence of tyrosinase activity in melanocytes of the skin, hair and eyes. Although tyrosinase mutations of OCA1 have been extensively analyzed in most populations worldwide, there is no systemic study of OCA1 mutation in Chinese patients. By use of single strand conformation polymorphism and direct sequencing, we had detected 21 mutant alleles out of 24 OCA1 chromosomes screened (87.5%). Detected mutant alleles include one splicing site, three insertion/deletion and five missense mutations, of which the splicing site nucleotide alteration (IVS 1‐3C>G) and two each of the insertion/deletion (232‐233 ins GGG and 861‐862 del TT) and missense mutations (Cys 289 Gly and Trp 400 Leu) are novel. The ins/del mutations accounts for about 37.5% in Chinese OCA1 alleles. The 232‐233 ins GGG, one of the novel mutations, was found to be most frequent (25%) among the OCA1 alleles in Chinese. Through this study, we found that while some of the OCA mutant alleles were identified in other populations, ethnic difference still exists. Hum Mutat 14:542, 1999.

Pharmacogenetics of dipeptidyl peptidase 4 inhibitors in a Taiwanese population with type 2 diabetes

Dipeptidyl peptidase-4 (DPP-4) inhibitors are oral anti-hyperglycemic drugs enabling effective glycemic control in type 2 diabetes (T2D). Despite DPP-4 inhibitors’ advantages, the patients’ therapeutic response varies. In this retrospective cohort study, 171 Taiwanese patients with T2D were classified as sensitive or resistant to treatment based on the mean change in HbA1c levels. Using an assumption-free genome-wide association study, 45 single nucleotide polymorphisms (SNPs) involved in the therapeutic response to DPP-4 inhibitors (P < 1 × 10-4) were identified at or near PRKD1, CNTN3, ASK, and LOC10537792. A SNP located within the fourth intron of PRKD1 (rs57803087) was strongly associated with DPP-4 inhibitor response (P = 3.2 × 10-6). This is the first pharmacogenomics study on DPP-4 inhibitor treatment for diabetes in a Taiwanese population. Our data suggest that genes associated with β-cell function and apoptosis are involved in the therapeutic effect of DPP-4 inhibitors, even in the presence of additional oral anti-diabetic drugs. Our findings provide information on how genetic variants influence drug response and may benefit the development of personalized medicine.

Homozygosity Mapping and Whole-Genome Sequencing Links a Missense Mutation in POMGNT1 to Autosomal Recessive Retinitis Pigmentosa

PURPOSE To identify the genetic cause in five families with autosomal recessive retinitis pigmentosa, a genetic disorder involving retinal degeneration and visual loss with high genetic heterogeneity. METHODS We performed whole-genome single nucleotide polymorphism genotyping on 35 members from the five families to map the region of homozygosity shared by all patients. Whole-genome sequencing was then conducted on one of the patients and a novel variant was identified in POMGNT1 from the homozygous region, which was confirmed by Sanger sequencing and sequenced in all family members. Mutant and wild-type POMGNT1 were expressed in heterologous cells to assess enzyme activity. RESULTS A 1.8-Mb homozygous region was identified at 1p34-p33 shared by all 17 patients. Whole-genome sequencing revealed a novel missense mutation in POMGNT1 (c.359A>C, p.Leu120Arg) from this homozygous region, which was shown to co-segregate with disease phenotype. The mutant protein carrying this missense mutation showed an approximately 80% decrease in POMGNT1 enzyme activity compared with the wild type. CONCLUSIONS We identified a novel mutation in POMGNT1 that causes nonsyndromic autosomal recessive retinitis pigmentosa, adding to the genetic heterogeneity of this retinal disease. POMGNT1 encodes a glycosyltransferase in O-mannosyl glycosylation and was previously found to be responsible for a group of congenital muscular dystrophies called dystroglycanopathies. Our discovery suggests the involvement of O-mannosyl glycosylation in retinitis pigmentosa and presents an instance of POMGNT1 mutation that does not involve muscular dystrophy.

Loss of GPNMB Causes Autosomal-Recessive Amyloidosis Cutis Dyschromica in Humans

Amyloidosis cutis dyschromica (ACD) is a distinct form of primary cutaneous amyloidosis characterized by generalized hyperpigmentation mottled with small hypopigmented macules on the trunks and limbs. Affected families and sporadic case subjects have been reported predominantly in East and Southeast Asian ethnicities; however, the genetic cause has not been elucidated. We report here that the compound heterozygosity or homozygosity of GPNMB truncating alleles is the cause of autosomal-recessive ACD. Six nonsense or frameshift mutations were identified in nine individuals diagnosed with ACD. Immunofluorescence analysis of skin biopsies showed that GPNMB is expressed in all epidermal cells, with the highest staining observed in melanocytes. GPNMB staining is significantly reduced in the lesional skin of affected individuals. Hyperpigmented lesions exhibited significantly increased amounts of DNA/keratin-positive amyloid deposits in the papillary dermis and infiltrating macrophages compared with hypo- or depigmented macules. Depigmentation of the lesions was attributable to loss of melanocytes. Intracytoplasmic fibrillary aggregates were observed in keratinocytes scattered in the lesional epidermis. Thus, our analysis indicates that loss of GPNMB, which has been implicated in melanosome formation, autophagy, phagocytosis, tissue repair, and negative regulation of inflammation, underlies autosomal-recessive ACD and provides insights into the etiology of amyloidosis and pigment dyschromia.

Skeletal Dysplasia Caused by FGFR3 Mutation in Taiwanese Patients

Background. The identification of a missense mutation (G380R) in the fibroblast growth factor receptor 3 (FGFR3) gene in patients with achondroplasia was followed by the detection of common FGFR3 mutations in two clinically related occurrences of skeletal dysplasia.: hypochondroplasia, and thanatophoric dysplasia. In this study, we investigated the FGFR3 mutation of achondroplasia, hypochondroplasia, and thanatophoric dysplasia in Taiwanese patients. Methods: There were 28 patients with achondroplasia, 18 with hypochondroplasia and two with thanatophoric dysplasia type I included in this study. Polymerase chain reaction (PCR), direct sequencing, and amplification created restriction site (ACRS) tests were performed to analyze the mutations on FGFR3 in these patients. Results: Genetic homogeneity of achondroplasia was demonstrated as recurrent G380R mutations in all patients hitherto reported. Although all detected mutations of hypochondroplasia were accounted for by a recurrent N540K mutation in the first tyrosine kinase domain of the receptor, a significant portion (45%) of our patients did not harbor the N540K mutation. Two patients with type I thanatophoric dysplasia were found to carry the R248C mutation. Conclusions: We used either a natural restriction enzyme site or ACRS to detect the recurrent G380R mutation of achondroplasia. The use of the ACRS was found to be more cost-effective and efficient than the use of the natural restriction enzyme digest.