Homogeneity of kerato-epithelin codon 124 mutations in Japanese patients with either of two types of corneal stromal dystrophy

A recognition survey of granular corneal dystrophy type 2 genetic detection in China

AIM

To evaluate the feasibility of promoting genetic detection for granular corneal dystrophy type 2 (GCD₂) by a questionnaire conducted among citizens in five cities in China.

METHODS

The data were collected by questionnaire, and analyzed by Chi-square test and one-tailed t test in IBM SPSS statistics.

RESULTS

Based on the survey data on the awareness of GCD₂ genetic detection in this study and the positive predictive analysis report of the citizens in five cities in China, the vast majority (84.2%) of respondents had never heard of it and did not know that GCD₂ patients have been prohibited from performing excimer surgery that can deteriorate GCD₂ patients' condition even leading to blindness. Though 3.4% of patients understood GCD₂ very much, they have no idea that GCD₂ could not be 100% accuracy diagnosed by the conventional inspection methods.

CONCLUSION

It is feasible and necessary to use GCD₂ genetic detection as an excimer preoperative examination project. In order to promote the development of detection project, a few improvements should be carried out in terms of the promoting efforts, costs, and research progress.

Mutation update: TGFBI pathogenic and likely pathogenic variants in corneal dystrophies

Human transforming growth factor β-induced (TGFBI), is a gene responsible for various corneal dystrophies. TGFBI produces a protein called TGFBI, which is involved in cell adhesion and serves as a recognition sequence for integrins. An alteration in cell surface interactions could be the underlying cause for the progressive accumulation of extracellular deposits in different layers of the cornea with the resulting changes of refractive index and transparency. To this date, 69 different pathogenic or likely pathogenic variants in TGFBI have been identified in a heterozygous or homozygous state in various corneal dystrophies, including a novel variant reported here. All disease-associated variants were inherited as autosomal-dominant traits but one; this latter was inherited as an autosomal recessive trait. Most corneal dystrophy-associated variants are located at amino acids Arg124 and Arg555. To keep the list of corneal dystrophy-associated variant current, we generated a locus-specific database for TGFBI (http://databases.lovd.nl/shared/variants/TGFBI) containing all pathogenic and likely pathogenic variants reported so far. Non-disease-associated variants are described in specific databases, like gnomAD and ExAC but are not listed here. This article presents the most recent up-to-date list of disease-associated variants.

Polymorphic fibrillation of the destabilized fourth fasciclin-1 domain mutant A546T of the Transforming growth factor-β-induced protein (TGFBIp) occurs through multiple pathways with different oligomeric intermediates

Mutations in the transforming growth factor β-induced protein (TGFBIp) are linked to the development of corneal dystrophies in which abnormal protein deposition in the cornea leads to a loss of corneal transparency and ultimately blindness. Different mutations give rise to phenotypically distinct corneal dystrophies. Most mutations are located in the fourth fasciclin-1 domain (FAS1-4). The amino acid substitution A546T in the FAS1-4 domain is linked to the development of lattice corneal dystrophy with amyloid deposits in the superficial and deep stroma, classifying it as an amyloid disease. Here we provide a detailed description of the fibrillation of the isolated FAS1-4 domain carrying the A546T substitution. The A546T substitution leads to a significant destabilization of FAS1-4 and induces a partially folded structure with increased surface exposure of hydrophobic patches. The mutation also leads to two distinct fibril morphologies. Long straight fibrils composed of pure β-sheet structure are formed at lower concentrations, whereas short and curly fibrils containing a mixture of α-helical and β-sheet structures are formed at higher concentrations. The formation of short and curly fibrils is preceded by the formation of a small number of oligomeric species with high membrane permeabilization potential and rapid fibril formation. The long straight fibrils are formed more slowly and through progressively bigger oligomers that lose their membrane permeabilization potential as fibrillation proceeds beyond the lag phase. These different fibril classes and associated biochemical differences may lead to different clinical symptoms associated with the mutation.

TGFBI gene mutation analysis in a Chinese pedigree of Avellino corneal dystrophy

AIM

To analyze phenotype and genotype of a Chinese pedigree with Avellino corneal dystrophy (ACD).

METHODS

Complete ophthalmic examinations were performed on all the family members. Exons of TGFBI were amplified by polymerase chain reaction, sequenced, and compared with a reference database.

RESULTS

A single heterozygous G>A (R124H) point mutation was identified in exon 4 of TGFBI in three affected members and two unaffected children who were offsprings of the affected members, but not in the other family members.

CONCLUSION

Mutation R124H in TGFBI was identified in this pedigree and appeared to be the disease causing mutation. Atypical phenotype and low penetrance was observed in this pedigree.

Molecular genetics of Chinese families with TGFBI corneal dystrophies

PURPOSE

To identify clinical features and mutations within the transforming growth factor-beta-induced (TGFBI) gene in three Chinese families with Granular corneal dystrophy, type 1 (GCD1) and Granular corneal dystrophy, type 2 (GCD2).

METHODS

Clinical features of GCD1 and GCD2 in three Chinese families were studied with slit-lamp and in vivo laser scanning confocal microscopy (LSCM). Molecular genetic analysis was performed on nine patients and fifteen unaffected individuals from these families. All exons of TGFBI were amplified by polymerase chain reaction (PCR) and sequenced.

RESULTS

Morphological changes in the cornea among affected individuals from three Chinese families examined by in vivo LSCM were almost the same. A heterozygous mutation C>T (R555W) was identified in exon 12 of TGFBI in patients of family A with GCD1. Another heterozygous mutation G>A (R124H) was found in exon 4 of TGFBI in affected members of family B and C with GCD2.

CONCLUSIONS

Mutations R555W and R124H in TGFBI were identified in three Chinese families with GCD. Even though there are a variety of mutations in TGFBI of GCD, the different subtypes of GCD (GCD1, GCD2, and GCD3) are in fact the same disorder. Our work supports the hypothesis that corneal dystrophies with the common genetic basis in TGFBI should be grouped together as TGFBI corneal dystrophies.

Reduced penetrance in familial Avellino corneal dystrophy associated with TGFBI mutations

PURPOSE

To characterize the clinical phenotype, histopathological features, and molecular genetic basis of an Avellino corneal dystrophy (ACD) in a Chinese family.

METHODS

A complete ophthalmologic examination was performed in 21 individuals (6 affected and 15 unaffected) of the four-generation family. DNA was obtained from peripheral blood leukocytes of each participant. Genetic analysis included TGFBI polymerase chain reaction (PCR) amplification and automated nucleotidic sequenceing of all 17 exons of genomic DNA. Histological analysis of corneal tissue from the proband was performed after a penetrating keratoplasty. One hundred Chinese controls were scanned for the presence of the R124H mutation by amplifying TGFBI exon 4 and then by direct sequencing of PCR products.

RESULTS

The proband of the pedigree had phenotypic features consistent with diagnosis of ACD. He was homozygous for the same R124H mutation in TGFBI as previously reported in Japan and European countries. In addition, 4 affected and 7 unaffected individuals carried the same variation in the heterozygous state were identified. None of the 100 control subjects was positive for this mutation. Moreover, a variable expressivity and an apparent non-penetrance were observed in the individuals with heterozygous R124H mutation in our pedigree. After excluding the missed diagnosis or a late onset, it could be interpreted as a reduced penetrance.

CONCLUSIONS

We reported a novel ACD family which exhibited a reduced penetrance of phenotype in northern China. This outcome supports that although the R124H mutation is one of the genetic causes of the disease, different genetic and environmental factors may influence the expressivity and the penetrance. Uncovering the mechanism may facilitate us to inhibit the occurrence of the corneal dystrophy caused by the R124H mutation in TGFBI, irrespective of the homozygous and heterozygous mutation.

TGFBI gene mutations in corneal dystrophies

The lattice corneal dystrophies (LCD) and granular corneal dystrophies (GCD) are autosomal dominant disorders of the corneal stroma. They are bilateral, progressive conditions characterized by the formation of opacities arising due to the deposition of insoluble material in the corneal stroma leading to visual impairment. The LCDs and GCDs are distinguished from each other and are divided into subtypes on the basis of the clinical appearance of the opacities, clinical features of the disease, and on histopathological staining properties of the deposits. The GCDs and most types of LCD arise from mutations in the transforming growth factor beta-induced (TGFBI) gene on chromosome 5q31. Over 30 mutations causing LCD and GCD have been identified so far in the TGFBI. There are two mutation hotspots corresponding to arginine residues at positions 124 and 555 of the transforming growth factor beta induced protein (TGFBIp) and they are the most frequent sites of mutation in various populations. Mutations at either of these two hotspots result in specific types of LCD or GCD. The majority of identified mutations involve residues in the fourth fasciclin-like domain of TGFBIp.

First genetic analysis of lattice corneal dystrophy type I in a family from Bulgaria

PURPOSE

To report a new family belonging to a previously non-investigated geographic are a with a rare form of lattice corneal dystrophy (LCD).

METHODS

Detailed ophthalmologic analysis was carried out on a Bulgarian woman, enrolled for perforating keratoplasty. In order to obtain a final diagnosis both histology and genetic analysis were performed.

RESULTS

Upon transplantation, histologic analysis of the dystrophic cornea revealed the typical staining pattern and amyloid deposits of lattice corneal dystrophies. Genetic analysis of the subject and her daughter confirmed the presence of an autosomal dominant R124C mutation within exon 4 of the BIGH3 gene, encoding for keratoepithelin, while showing no abnormalities in her son.

CONCLUSIONS

The identification of this mutation allows the unambiguous classification of this corneal dystrophy as LCD type I. A first case of LCD I in a family from Eastern Europe could help to better clarify the molecular epidemiology of the disease.

Genetic variation of the renin-angiotensin system and chronic kidney disease progression in black individuals in the atherosclerosis risk in communities study

The renin-angiotensin system (RAS) regulates BP and may affect chronic kidney disease (CKD) through induction of tissue growth and fibrosis. The angiotensinogen (AGT) promoter G(-6) allele lowers transcription and is inversely associated with hypertension. In white individuals, the A1166C 3'-UTR variant of angiotensin II type 1 receptor (AT1R) has been associated with CKD. CKD associations with these RAS genes are uncertain in high-risk black populations. A prospective population-based study of CKD risk was conducted among 3706 black individuals without severe renal dysfunction at baseline (serum creatinine > or =177 micromol/L [2.0 mg/dl] for men, > or =159 micromol/L [1.8 mg/dl] for women) to examine associations with AGT and AT1R. Incident CKD progression was defined as kidney disease hospitalization or increase in serum creatinine level > or =35 micromol/L (0.4 mg/dl) above baseline. During mean follow-up of 10.2 yr, CKD progression incidence rate (per 1000 person-years) was 8.2 (n = 312 cases). Risk was lower for AGT G(-6) carriers compared with A(-6) (incidence 6.9 versus 9.0; log-rank P = 0.03) and nonsignificantly higher among AT1R C1166 carriers. Adjusting for hypertension and major CKD risk factors, AGT G(-6)decreased risk (relative risk 0.75; 95% confidence interval 0.57 to 0.98). AT1R C1166 increased risk only among those with hypertension (relative risk 1.65; 95% confidence interval 1.14 to 2.39). The AGT G(-6)A polymorphism may play a role in CKD progression in black individuals, consistent with in vitro effects on AGT levels and renal remodeling but independent of BP. The AT1R C1166 allele may increase susceptibility but only in the presence of hypertension.

A clinical and molecular genetic study of autosomal-dominant stromal corneal dystrophy in British population

AIMS

To identify the underlying mutations in our British families and sporadic patients with different types of corneal dystrophies (CDs) and to establish a phenotype-genotype correlation.

METHODS

Twenty-nine patients, 9 sporadic and 20 patients from 7 families were subjected to both clinical and genetic examination. Slit lamp examination was performed for all patients who participated in the study to assess their corneal phenotype. Genomic DNA was extracted from 10 ml venous blood, and the BIGH3 gene was amplified exon by exon to perform heteroduplex analysis. Exons that displayed double bands were then analysed by direct bi-directional sequencing and restriction digest analyses.

RESULTS

Clinically our patients showed three distinct phenotypes of CD: 16 with Thiel-Behnke corneal dystrophy or corneal dystrophy of Bowman layer type 2 (CDB2), 8 with granular CD (GCD), and 5 with lattice CD type I (LCDI). Three different missense mutations have been detected in the coding region of BIGH3 gene, R555Q, in 16 CDB2 patients, R555W in 8 GCD patients, and R124C in 5 LCDI patients. These mutations were the same as to those previously reported in patients from other ethnic origins. Also,we identified seven nucleotide substitutions that did not change the amino acid sequence of the encoded protein of which four were novel.

CONCLUSIONS

In our patients of British origin, each phenotype of CD has been linked to a particular point mutation of the BIGH3 gene. Our study also highlights the importance of codons 124 and 555 as mutation hot spots in the BIGH3 gene in the British population.

Rapid genotyping for most common TGFBI mutations with real-time polymerase chain reaction

Recent studies of the corneal dystrophies (CDs) have shown that most cases of granular CD, Avellino CD, and lattice CD type I are caused by mutations in the human transforming growth factor beta-induced (TGFBI) gene. The aim of this study was to develop a rapid diagnostic assay to detect mutations in the TGFBI gene. Sixty-six patients from 64 families with TGFBI-associated CD were studied. A primer probe set was designed to examine the genome from exons 4 and 12 of the TGFBI gene in order to identify mutant and wild-type alleles. A region spanning the mutations was amplified by the polymerase chain reaction (PCR) in a commercial cycler. Mutations were then identified by melting curve analysis of the hybrid formed between the PCR product and a specific fluorescent probe. Using this system, we clearly distinguished each CD genotype (homozygous and heterozygous 418G-->A, heterozygous 417C-->T, heterozygous 1710C-->T, and wild-type) of all the patients by means of the clearly distinct melting peaks at different temperatures. One thermal cycling took approximately 54 min, and all results were completely in concordance with the genotypes determined by conventional DNA sequencing. Thus, the technique is accurate and can be used for routine clinical diagnosis. We expect that our new method will help in making precise diagnoses of patients with atypical CDs and aid the revision of the clinical classification of inherited corneal diseases based on the genetic pathogenesis.

BIGH3 mutation in a Bangladeshi family with a variable phenotype of LCDI

AIMS

To report a Bangladeshi family displaying intrafamilial phenotypic heterogeneity of lattice corneal dystrophy type I (LCDI) and to identify the causative mutation.

METHODS

Molecular genetic analysis was performed on DNA extracted from all members of the family. Exons of BIGH3 gene were amplified by polymerase chain reaction. Gene mutation and polymorphisms were identified by heteroduplex and sequence analyses. Segregation of the mutation in the family was confirmed by restriction digestion of amplified gene fragments.

RESULTS

A heterozygous C --> T transition at the first nucleotide position of codon 124 of the BIGH3 gene was detected in the three affected members and not in the unaffected members of the family.

CONCLUSIONS

This is the first report of BIGH3 gene mutation in a Bangladeshi family with phenotypic heterogeneity. This study confirms that BIGH3 gene screening should be undertaken for proper classification of corneal dystrophy, especially in the absence of histopathological examination.

A new mutation (Leu569Arg) within exon 13 of the TGFBI (BIGH3) gene causes lattice corneal dystrophy type I

PURPOSE

To describe an American family with lattice corneal dystrophy type I, which associates with a novel mutation, Leu569Arg, of the TGFBI (BIGH3) gene.

DESIGN

Experimental study.

METHODS

Genomic DNA was extracted from buccal epithelial cells of four affected members of an American family with lattice corneal dystrophy type I. All 17 exons of the TGFBI gene were evaluated by PCR amplification and direct sequencing. Clinical and histologic data were also collected.

RESULTS

Three generations of this family have been positively diagnosed with lattice corneal dystrophy, indicating autosomal dominant inheritance. We identified a heterozygous point mutation that associates with the disease phenotype. The single base-pair substitution (T1753G) results in an amino acid substitution (Leu569Arg) in exon 13 of the TGFBI gene.

CONCLUSIONS

Substitution of arginine for leucine at position 569 of the TGFBI gene results in a form of lattice corneal dystrophy that is phenotypically similar to other genetically distinct forms of type I disease. This is the first report of disease correlated with changes in exon 13 of the TGFBI gene.

Allelic homogeneity due to a founder mutation in Japanese patients with lattice corneal dystrophy type IIIA

Lattice corneal dystrophies (LCDs) are caused by mutations of the transforming growth factor beta-induced gene (TGFBI, formerly betaig-h3). LCD type IIIA (LCDIIIA) has been reported mostly from Japan. In this study, we demonstrate allelic homogeneity for Japanese patients with LCDIIIA, using intragenic polymorphic markers. When exon 11 of TGFBI was analyzed, all 18 patients examined were found to be heterozygous for both a P501T mutation and an IVS10-3C --> T variation. On the other hand, none of 54 normal Japanese control subjects had the P501T, and 5 of the controls were heterozygous for IVS10-3C --> T. Haplotype analysis of the patients revealed that both P501T and IVS10-3C --> T were located on the same chromosome, and a significant linkage disequilibrium (P < 0.001, Fisher's exact probability test) was observed between LCDIIIA (P501T) and IVS10-3C --> T. When exon 8 of the gene was analyzed, all these patients possessed the "G allele" of a 1028G/A polymorphism. A significant linkage disequilibrium (P < 0.003; chi-square test) was also observed between P501T and the G allele in the patients. These results suggest that allelic homogeneity seen in Japanese patients with LCDIIIA may result from a single founder mutation.

The changing face of the genetics of corneal dystrophies

Modern molecular genetics has had a profound effect on our understanding of corneal dystrophies. Mutations in the BIGH3 gene are responsible for four autosomal dominant corneal dystrophies. The mutation spectrum reveals the phenotypically diverse possibilities stemming from mutations of a single gene. Dystrophies have been grouped together in a "stamp-collector" fashion. Classification has been based on clinical description of disease. With better appreciation of molecular genetics, classifications can be based on underlying genetic cause. In fact, classification schema based on the gene or molecular defect responsible for the dystrophy have been introduced. Different phenotypes are determined by different genotypes. Clinicians must become more adept at understanding the molecular genetics of corneal dystrophies as genetics is increasingly important in the long-term diagnostic and therapeutic approach to dystrophies.

Loss-of-function polymorphism of the human kallikrein gene with reduced urinary kallikrein activity

Kallikrein is synthesized in the distal tubules and produces kinins, which are involved in the regulation of vascular tone in the kidney. Urinary kallikrein activity has been reported to be partly inherited and to be reduced in essential hypertension. In a systematic search for molecular variants of the human kallikrein gene, nine single-nucleotide polymorphisms were identified. Five of those polymorphisms, including two nonsynonymous substitutions in exon 3, i.e., Arg53His (allelic frequency in Caucasian subjects, 0.03) and Gln121Glu (allelic frequency, 0.33), were studied in a normotensive group and two independent hypertensive groups for which 24-h urinary kallikrein activity had been measured. A significant decrease in urinary kallikrein activity was observed for the subjects who were heterozygous for the Arg53His polymorphism, compared with the other subjects. This finding was consistent in the two hypertensive groups and was observed with several kallikrein enzymatic assays. The Gln121Glu polymorphism and the other polymorphisms were not associated with changes in urinary kallikrein activity. None of the polymorphisms was associated with hypertension. Recombinant kallikrein variants were synthesized and enzymatically characterized, using native kininogen and kininogen-derived synthetic peptide substrates. No important effect was observed after Gln121 mutation, but there was a major decrease in enzyme activity when Arg53 was replaced by histidine. A model of kallikrein derived from crystallographic data suggested that Arg53 can affect substrate binding. The identification of a subset of subjects with genetically reduced kallikrein activity as a result of an amino acid mutation could facilitate analysis of the role of the kallikrein-kinin system in renal and vascular diseases.

Differential occurrence of mutations causative of eye diseases in the Chinese population

Ethnic differences and geographic variations affect the frequencies and nature of human mutations. In the literature, descriptions of causative mutations of eye diseases in the Chinese population are few. In this paper we attempt to reveal molecular information on genetic eye diseases involving Chinese patients from published and unpublished works by us and other groups. Our studies on candidate genes of eye diseases in the Chinese population in Hong Kong include MYOC and TISR for primary open angle glaucoma, RHO and RP1 for retinitis pigmentosa, ABCA4 and APOE for age-related macular degeneration, RB1 for retinoblastoma, APC for familial adenomatous polyposis with congenital hypertrophy of retinal pigment epithelium, BIGH3/TGFBI for corneal dystrophies, PAX6 for aniridia and Reiger syndrome, CRYAA and CRYBB2 for cataracts, and mtDNA for Leber hereditary optic neuropathy. We have revealed novel mutations in most of these genes, and in RHO, RP1, RB1, BIGH3, and PAX6 we have reported mutations that contribute to better understanding of the functions and properties of the respective gene products. We showed absence of MYOC does not necessarily cause glaucoma. No disease causative mutations have been identified in MYOC or ABCA4. There are similarities in the patterns of sequence alterations and phenotype-genotype associations in comparison with other ethnic groups, while the MYOC, RB1, APC, and PAX6 genes have more Chinese-specific sequence alterations. Establishment of a mutation database specific for the Chinese is essential for identification of genetic markers with diagnostic, prognostic, or pharmacological values.

Power and replication in case-control studies

The case-control study design, a common staple of epidemiology, is increasingly used to test for genetic association. The simplicity of the design accounts for both its appeal and its limitations. Too often, however, apparent controversy arises for lack of appreciation of basic tenets underlying statistical testing. Power and replication are two concepts most commonly ignored in evaluating such studies. We review the basic principles of statistical testing, recall simple means to calculate power, and provide numerical examples pertaining to the association between angiotensinogen and essential hypertension.

BIGH3 gene mutations and rapid detection in Korean patients with corneal dystrophy

PURPOSE

Mutations in the BIGH3 gene on chromosome 5q31 cause four distinct autosomal dominant corneal dystrophies. We sought to determine whether the BIGH3 gene mutation was responsible for corneal dystrophy in Korean patients.

METHODS

Polymerase chain reaction single strand conformational polymorphism (PCR-SSCP) analysis was performed with the DNA from patients and healthy individuals. We sequenced the PCR products with the aberrant SSCP pattern to identify the mutation. Mutant-specific reverse primers were used to screen genomic DNA for the identified mutations.

RESULTS

We identified mutations R124C in the CDL1 family and R124H in four families with a granular dystrophy. We identified our granular dystrophy to be Avellino corneal dystrophy (ACD). Eighteen of 20 patients with a granular dystrophy contained the same R124H mutation, indicating that mutation R124H was very common in Korean patients with ACD. During this study, we identified a new polymorphism (T1667C, F540F).

CONCLUSIONS

This is the first report of mutations found in the BIGH3 gene in Korean families with corneal dystrophy. We report that the majority (90%) of ACD patients in Korea carry the R124H mutation. Mutant-specific reverse primers can be used to screen efficiently for CDL1 and ACD.

Characteristics of the human ocular surface epithelium

An appreciation of the biological characteristics of the human ocular surface epithelium affords us a great insight into the physiology of the human ocular surface in health and disease. Here, we review five important aspects of the human ocular surface epithelium. First, we recognize the discovery of corneal epithelial stem cells, and note how the palisades of Vogt have been suggested as a clinical marker of their presence. Second, we introduce the concept of the gene expression profile of the ocular surface epithelium as arrived at using a new strategy for the systematic analysis of active genes. We also provide a summary of several genes abundantly or uniquely expressed in the human corneal epithelium, namely clusterin, keratin 3, keratin 12, aldehyde dehydrogenase 3 (ALDH3), troponin-I fast-twitch isoform, ssig-h3, cathepsin L2 (cathepsin V), uroplakin Ib, and Ca(2+)-activated chloride channel. Genes related to limbal and conjunctival epithelia are also described. Third, we touch upon the genetic abnormalities thought to be involved with epithelial dysfunction in Meesmann's dystrophy, gelatinous drop-like corneal dystrophy, and the ssig-h3-mutated corneal dystrophies. Fourth, we provide an update regarding the current state of knowledge of the role of cytokines, growth factors and apoptosis in relation to ocular surface homeostasis and tissue reconstruction; the main factors being epidermal growth factor (EGF), keratinocyte growth factor (KGF), hepatocyte growth factor (HGF), transforming growth factor-ss (TGF-ss), and some inflammatory cytokines. Fifth, corneal epithelial barrier function and dysfunction as measured by fluorophotometry is remarked upon, with an explanation of the FL-500 fluorophotometer and its ability to detect corneal epithelial dysfunction at a subclinical level. The research described in this review has undoubtedly generated a complete understanding of corneal epithelial pathophysiology-an understanding that, directly or indirectly, has helped advance the development of new therapeutic modalities for ocular surface reconstruction.

Angiotensinogen in essential hypertension: from genetics to nephrology

There is general consensus that genetic variation accounts in part for individual susceptibilities to essential hypertension. In marked contrast to classic mendelian disorders, in which genetic alterations produce a gain or loss of function, genetic determinants of essential hypertension, high blood pressure of unknown cause, are expected to be small, achieving significance through the cumulative effects of environmental exposure over the course of a lifetime. Whether and how genetic factors that contribute to common diseases can be identified remain unclear. Research on a link between angiotensinogen and essential hypertension illustrates a path that began in genetics and is now leading toward nephrology. Various challenges encountered along the way may prove to be characteristic features of genetic investigations of the pathogenesis of common diseases. The implication of a gene by statistical analysis is only the beginning of a protracted process of functional analysis at increasing levels of biologic integration. The ultimate goal is to develop an understanding of the manner in which genetic variation at a locus can affect a physiologic parameter and to extract from this inference new knowledge of significance for the prevention or treatment of disease.

Altered frequency of a promoter polymorphism of the kinin B2 receptor gene in hypertensive African-Americans

Components of the kallikrein kinin system have been associated with the pathophysiology of hypertension in animal and human studies. In this study, we examined the distribution of four different polymorphisms of the kinin B1 and B2 receptor genes in a population of 120 normotensive and 77 hypertensive African-Americans. Allelic frequencies for three of the four polymorphisms were significantly different from those previously reported in Caucasian populations. Among the polymorphisms analyzed, a potentially functionally significant polymorphism in the core promoter of the kinin B2 receptor (C-58-->T transition) displayed an increased prevalence of the C-58 allele in the hypertensive patients as compared with the controls (0.75 v. 0.62, P = .009). Thus, this B2 receptor promoter polymorphism may represent a susceptibility marker for essential hypertension in African-Americans.

Six different mutations of TGFBI (betaig-h3, keratoepithelin) gene found in Japanese corneal dystrophies

PURPOSE

To investigate mutations of the human transforming growth factor beta-induced gene (TGFBI), transforming growth factor-beta-induced gene product (betaig-h3, keratoepithelin), in Japanese patients with Avellino corneal dystrophy (ACD), lattice corneal dystrophy (LCD), granular corneal dystrophy (GCD), and Reis-Bücklers corneal dystrophy (RBCD).

METHODS

Genomic DNA was extracted from the peripheral blood of 75 patients and 7 unaffected relatives from 60 families with ACD, 34 patients and 8 unaffected relatives from 21 families with LCD, 4 patients and 4 unaffected relatives from 4 families with GCD, and 4 patients and an unaffected relative from 3 families with RBCD. Fifty normal volunteers served as controls. Exons 4, 11, and 12 of the TGFBI gene were amplified by polymerase chain reaction and were directly sequenced.

RESULTS

Six different heterozygous missense mutations were detected in codons R124, L518, L527, and R555 of the TGFBI gene in the 117 patients from 88 families. A R124H mutation was detected in the patients with ACD. A R124C mutation was detected in the patients with LCD type 1 (LCD1), L518P was in atypical LCDI, and L527R in LCD with opacities deep in stroma. A R555W mutation was detected in the patients with GCD. A R555Q mutation was detected in the patients with RBCD.

CONCLUSIONS

We conclude that codons R124 and R555 of the TGFBI gene are also hot spots in Japanese patients with ACD, LCD, GCD, and RBCD. Many Japanese patients with CD had ACD with R124H mutation. GCD with R555W mutation was rare.

Genetics of the corneal dystrophies: what we have learned in the past twenty-five years

PURPOSE

To indicate important changes in our understanding of the corneal dystrophies.

METHODS

A review of the literature of the last quarter of a century.

RESULTS

The earliest clinical classifications of the corneal dystrophies were based on the application of clinical, biological, histochemical, and ultrastructural methods. Since then, the first great impetus to our understanding has come from the application of techniques to map disorders to specific chromosome loci, using polymorphic markers. More recently, using candidate gene and related approaches, it has been possible to identify genes causing several of the corneal dystrophies and the mutations responsible for their phenotypic variation. A notable success has been to show that several important "stromal" dystrophies result from mutations in the gene beta ig-h3, which encodes for the protein keratoepithelin (beta ig-h3).

CONCLUSIONS

For the corneal dystrophies, as with other inherited disorders, there is room for two sorts of classification system, one based mainly on clinical presentation and the other on an up-to-date understanding of the genetic mechanisms. They are not mutually exclusive. Some developmental corneal disorders are also discussed.

Advances in the molecular genetics of corneal dystrophies

PURPOSE

To improve our understanding of the role of specific genes on corneal transparency through a review of linkage to specific chromosomal loci and the identification of the mutant genes dealing with the corneal dystrophies.

METHOD

Relevant recent literature on the corneal dystrophies is reviewed.

RESULTS

Molecular genetic studies of the corneal dystrophies suggest that genes on at least 10 human chromosomes are involved in the maintenance of corneal transparency (chromosomes 1, 5, 9, 10, 12, 16, 17, 20, 21, and X). Within the 10 chromosomes to which corneal dystrophies have been mapped, specific genetic mutations in seven genes (GSN, BIGH3, KRT3, See also pp. 687-691. KRT12, MSS1, GLA, and ARSC1) have been identified in 15 corneal dystrophies. Some corneal dystrophies that are considered distinct clinicopathologic entities are actually caused by different mutations in the same gene. For example, lattice dystrophy types I and IIIA, granular corneal dystrophy types I, II (Avellino dystrophy), and III (Reis-Bucklers dystrophy), and Thiel-Behnke corneal dystrophy are the result of mutations in BIGH3. Mutations in three genes (GSN, BIGH3, MSS1) are associated with amyloid deposition in the cornea. A gene for keratoconus has been mapped to chromosome 21, which is noteworthy because of the established association of keratoconus in Down syndrome (trisomy 21).

CONCLUSION

Recent genetic studies on the corneal dystrophies provide insight into some of these disorders at a basic molecular level. Some corneal dystrophies that were previously believed to be distinct clinicopathologic entities are closely related at the molecular level with the different phenotypes resulting from distinct mutations in the same gene. This new knowledge is leading to a revised classification of the corneal dystrophies and to the development of animal models of corneal dystrophies. The latter will lead to a better understanding of the pathogenesis of the disorders and hence to novel therapeutic approaches to those dystrophies that cause significant visual impairment. Research of this nature is only in its infancy.

Leu518Pro mutation of the beta ig-h3 gene causes lattice corneal dystrophy type I

PURPOSE

To describe a Japanese family with lattice corneal dystrophy type I, which segregates with a novel mutation, Leu518Pro of the beta ig-h3 gene.

METHODS

DNA was extracted from leukocytes in four members (three affected and one unaffected) of a Japanese family with lattice corneal dystrophy type I. Exon 12 of the beta ig-h3 gene was amplified and analyzed with a molecular biologic method. Clinical data were also collected.

RESULTS

Three generations of this family have been positively diagnosed with lattice corneal dystrophy, indicating autosomal dominant inheritance. We found a heterozygous point mutation that segregates with the disease phenotype. It was a single base-pair transition (CTG to CCG, Leu to Pro).

CONCLUSION

Although it is extremely rare compared with the Arg124Cys mutation of the beta ig-h3 gene, Leu518Pro mutation of the beta ig-h3 also causes lattice corneal dystrophy type I.

Keio Mutation Database for eye disease genes (KMeyeDB)

A database of mutations in human eye disease genes has been constructed. This KMeyeDB employs a database software MutationView which provides graphical data presentation and analysis as a smooth user-interface. Currently, the KMeyeDB contains mutation data of 16 different genes for 18 eye diseases. The KMeyeDB is accessible through http://mutview.dmb.med.keio.ac.jp with advanced internet browsers.

Severe form of juvenile corneal stromal dystrophy with homozygous R124H mutation in the keratoepithelin gene in five Japanese patients

AIM

To confirm the mutation of the keratoepithelin gene in patients with a severe form of superficial juvenile granular corneal dystrophy (GCD).

METHODS

Five Japanese probands in whom GCD was diagnosed after histopathological examination and who developed severe manifestations of GCD in their first decade of life were investigated. Other affected family members of two probands were also examined. All probands were the offspring of consanguineous parents. DNA was extracted from their peripheral blood leucocytes and mutational analysis of the gene was performed by the polymerase chain reaction and direct sequencing.

RESULTS

Four of the five probands underwent their first keratectomy or keratoplasty in their teens and subsequently underwent a second or third keratoplasty. Each proband had a homozygous G-->A transition at codon 124, replacing Arg-->His, of the keratoepithelin gene. Their moderately affected family members were heterozygous for the mutation.

CONCLUSIONS

This finding suggests that the severity of the corneal phenotype depends on the dose effect of the mutant gene.

The classic form of granular corneal dystrophy associated with R555W mutation in the BIGH3 gene is rare in Japanese patients

PURPOSE

To identify the BIGH3 gene mutation in 10 unrelated Japanese individuals with granular corneal dystrophy.

METHODS

Genomic DNA was obtained from each patient's leukocytes. Exons 4 and 12 of the BIGH3 gene were amplified by polymerase chain reaction and were directly sequenced.

RESULTS

Nine of these patients were found to have the R124H mutation, whereas only one had the R555W mutation. Slit-lamp examination showed that the granular corneal dystrophy associated with each mutation is different.

CONCLUSIONS

These results, together with our previous findings, show that the classic form of granular corneal dystrophy associated with the R555W mutation is rare in Japanese patients, whereas granular corneal dystrophy accompanied by amyloid deposits and associated with the R124H mutation, Avellino corneal dystrophy, is more common. Direct examination may be insufficient in the proper diagnosis of corneal dystrophy, and BIGH3 mutation analysis may be required.