Yoshinori Miyamura

Oculocutaneous Albinism Type 4 Is One of the Most Common Types of Albinism in Japan

Oculocutaneous albinism (OCA) is a complex genetic disease with great clinical heterogeneity. Four different types of OCA have been reported to date (OCA1, OCA2, OCA3, and OCA4). MATP was recently reported in a single Turkish OCA patient as the fourth pathological gene, but no other patients with OCA4 have been reported. Here, we report the mutational profile of OCA4, determined by genetic analysis of the MATP gene in a large Japanese population with OCA. Of 75 unrelated patients that were screened, 18 individuals (24%) were identified as having OCA4; they harbored seven novel mutations, including four missense mutations (P58S, D157N, G188V, and V507L) and three frameshift mutations (S90CGGCCA-->GC, V144insAAGT, and V469delG), showing that MATP is the most frequent locus for tyrosinase-positive OCA in Japanese patients. We discuss the functional melanogenic activity of each mutant allele, judging from the relationship between the phenotypes and genotypes of the patients. This is the first report on a large group of patients with OCA4.

Characterization of the human RAB38 and RAB7 genes: exclusion of new major pathological loci for Japanese OCA.

BACKGROUND Oculocutaneous albinisms (OCAs) are due to various gene mutations that cause a disruption of melanogenesis in the melanocyte. Four different genes associated with human OCA have been reported, however, not all of OCA patients can be classified according to these four genes. We have sought to find a new major locus for Japanese OCA. Recently two genes, RAB38 and RAB7, were reported to play an important role in melanogenesis in the melanocyte, suggesting that these two genes could be good candidates for new OCA loci. OBJECTIVE To determine the structures of the human RAB38 and RAB7 genes, and examine if the two genes are new major loci for Japanese OCA. METHODS We screened mutations in these genes of 25 Japanese OCA patients who lacked mutations in the OCA1 and OCA2 genes with SSCP/heteroduplexes method. RESULTS We determined the both genes, and their genomic organizations to design the primers for SSCP/heteroduplexes method. And then we screened mutations, but no mutation was detected. CONCLUSION Neither of the genes is a new major locus for Japanese OCA.

A Splicing Mutation of the Tyrosinase Gene Causes Yellow Oculocutaneous Albinism in a Japanese Patient with a Pigmented Phenotype

Background: Yellow oculocutaneous albinism (OCA) that is caused by tyrosinase gene mutations shows two characteristics: extreme hypopigmentation at birth and the eventual development of yellow or blond hair. Objective: We studied a Japanese girl who had brown hair, a lighter skin color than her unaffected family and brown eyes at 9 months of age. Methods: We performed direct sequencing analyses of the tyrosinase gene in her genomic DNA. Results: The patient was a compound heterozygote for the +ΔC310 mutation (known to result in absent melanogenic activity) and a second t→a transition at the 3′ end of intron 2. Conclusion: The t→a transition has previously been reported as a splicing mutation in other Caucasian patients with a typical yellow OCA phenotype. However, this patient showed much more pigmentation than that reported in Caucasians. Therefore, we estimate that the mild phenotype results from her genetic pigment background.

High frequency of the Ala481Thr mutation of the P gene in the Japanese population

P-gene-related oculocutaneous albinism (OCA2) (MIM#203200) is an autosomal recessive disorder that results from mutations of the P gene [Rinchik et al., 1993; Rosemblat et al., 1994], the human homologue to the mouse pink-eyed dilution gene. The function of the P gene product has not been clarified yet, although several potential functions have been proposed, e.g., a membrane transporter of a substrate [Rosemblat et al., 1998], a stabilizer of a melanosomal protein complex [Manga and Orlow, 2001], a regulator of melanosomal pH [Brilliant, 2001], or a sorter of tyrosinase to melanosome [Puri et al., 2000]. OCA2 is the most common type of albinism and accounts for approximately 50% of OCA worldwide. More than fifty different mutations of the P gene have been reported [Oetting and King, 1999; Passmore et al., 1999]. One of them is a missense substitution at codon 481 in which threonine (ACC) is substituted for alanine (GCC) (A481T) in the predicted luminal (or extracellular) loop of the P protein [Rinchik et al., 1993]. The A481T substitution is a relatively commonmutant allele of thePgene in theCaucasianpopulation (1/50, q1⁄4 0.01) and is associated with a very mild phenotype with no distinctive skin manifestations, clinically classified as ‘‘autosomal recessive ocular albinism,’’ rather than as OCA2 [Lee et al., 1994]. Transfection experiments of p null mouse melanocytes with the A481T mutant P cDNA showed that the A481T allele had approximately 70% function in melanogenesis compared with that of thewild-type humanP cDNA [Sviderskaya et al., 1997], which is consistent with this being a relatively mild OCA2 mutant allele. We report here that the A481T mutant allele is much more frequently found in Japanese than inCaucasians, i.e., approximately 10%of OCA patients and 12% of normally-pigmented people (Table I). One hundred and four unrelated normally-pigmented Japanese volunteers and40JapaneseOCApatientswho had no mutation detected in their tyrosinase gene were enrolled in this study for analysis of the P gene in this report. The twenty-four coding exons of the human P gene plus adjacent noncoding sequences were amplified from genomic DNA by PCR using the primers described previously [Lee et al., 1995]. The amplified segments were then screened for mutations by SSCP and heteroduplex method [Spritz et al., 1992]. Exon segments that yielded aberrant patterns were independently reamplified from genomic DNA and sequenced directly. This study was approved by the Ethical Committee of Nagoya University School of Medicine. We found that sixOCApatientswereheterozygous for the A481T allele and one was homozygous (Table I). Then,wedetermined the frequency of themutatedallele in 104 unrelated normally-pigmented Japanese. As shown in Table I, twenty of these 104 normal subjects were heterozygous and two were homozygous for the mutation allele, and the allele frequency of A481T in normally-pigmented Japanese was 0.12. Two homozygotes appeared entirely normal in terms of the biosynthesis ofmelanin pigment of the skin, eyes, and hair. These findings are totally consistent with the fact that the A481T allele had approximately 70% function in melanogenesis compared with that of the wild-type human P cDNA [Sviderskaya et al., 1997]. Because, generally speaking, less than 50% loss of function doesn’t cause symptoms in case of an autosomal recessive disorder. The A481T mutant allele does not cause OCA2 by itself even in homozygotes, but does cause a mild type of OCA2 when in combination with a null or almost null mutant allele. Only one Japanese OCA2 patient has been reported, and the patient was hemizygous for A481T [Saitoh et al., 2000], supporting the

Sequence-Based Diagnosis of Tyrosinase-Related Oculocutaneous Albinism: Successful Sequence Analysis of the Tyrosinase Gene from Blood Spots Dried on Filter Paper

Background: A large number of mutations of the tyrosinase gene result in oculocutaneous albinism (OCA). Therefore, at present, sequence analysis of the tyrosinase gene has become necessary to diagnose OCA patients and their relatives. Objective: The aim of this study was to facilitate the sequence-based diagnosis of tyrosinase-related OCA by using small amounts of the patient’s blood. Methods: Blood spots dried on filter papers were used as sources of genomic DNA. The exons and flanking regions of the tyrosinase gene were amplified by polymerase chain reaction (PCR) and were directly sequenced in both directions. Results: We successfully amplified all exons of the tyrosinase gene by PCR and were able to characterize compound heterozygous mutations of R278X and +ΔC310 in the patient’s gene. Conclusion: Recent advances of PCR-related technology allowed us to use fairly limited samples of blood for sequence analysis of the tyrosinase gene.

A novel mutation of the tyrosinase gene causing oculocutaneous albinism type 1 (OCA1)

Tyrosinase is a rate-limiting enzyme in the melanin biosynthetic pathway and a complete defect of the enzyme activity caused by homozygous mutations of the tyrosinase gene is well known to result in tyrosinase-negative oculocutaneous albinism (OCA1A) patients who never develop any melanin pigment in the skin, hair and eyes throughout life. In this paper, we report a novel missense substitution, R239W(CGG --> TGG) of the tyrosinase gene in a patient with tyrosinase-negative OCA.

Exclusion of linkage between dyschromatosis symmetrica hereditaria and chromosome 9

Dyschromatosis symmetrica hereditaria (DSH) is an autosomal dominant pigmentary disorder, first reported by Toyama in 1910. It is characterized by a mixture of hypopigmented and hyperpigmented macules of various sizes on the backs of the hands and feet. The disease gene of DSH and its chromosomal localization have not yet been identified. A family with DSH and idiopathic torsion dystonia (ITD), a rare neurological disease, was recently reported. Therefore, we speculated that there was a linkage between the DSH gene and the ITD gene, named DYT1 and localized on chromosome 9, and performed linkage analysis between DSH and microsatellite markers on chromosome 9 in three Japanese DSH families (36 patients in total). We obtained a LOD score of < -2 over the whole region of chromosome 9 encompassing DYT1. Thus, we conclude that there is no linkage between DSH and DYT1 as well as any region of chromosome 9.

Sunlight is merely a temporary modifier of dyschromatosis symmetrica hereditaria

251 DPP-4 inhibitors are reportedly associated with BP [6]. Median time for BP onset is 10 months with a wide range (eight days to 37 months) [1]. Topical and oral steroids are used for treatment, but DPP-4 inhibitor discontinuation is necessary to achieve remission [7]. Bene et al. reported a patient with partial response to topical steroid treatment despite DPP-4 inhibitor continuation [8]; in this case, the disease recurred after three months, and discontinuation of DPP-4 inhibitor improved the patient’s condition [8]. DPP-4 inhibitor-induced BP is characterized clinically by generalized blisters without oedematous erythema, sparse infiltration of eosinophils in perilesional skin [9], and autoantibodies that recognize epitopes other than the BP180 NC16a domain. In our patient, LBP recurred under continuous sitaglipitin treatment despite the response to ointment, however, no subsequent recurrence was observed after linagliptin discontinuation. Furthermore, a localized blister without oedematous erythema and BP180 autoantibodies targeting non-NC16a areas were observed, as well as scant eosinophilic infiltration in perilesional skin on microscopic examination. The differential diagnosis of blisters that DM patients develop under treatment include bullosis diabeticorum and bullous fixed drug eruption; in this patient, laboratory tests and histopathological findings suggested that LBP was associated with linagliptin. Several medications taken by our patient have been reported to cause BP [5], however, we concluded that these medications were not responsible for blister formation because BP did not recur despite the continuation of these medications. Our case illustrates the association between LBP and DPP4 inhibitors. DPP-4-associated bullous disease is recurrent without DPP-4 inhibitor discontinuation. Clinicians should therefore consider this for DM patients receiving DPP-4 inhibitors with a localized single blister .