Genome-wide scan of additional Jewish families confirms linkage of a myopia susceptibility locus to chromosome 22q12

PURPOSE

A genome-wide scan was previously reported for myopia in Ashkenazi Jews. In order to confirm the previous linkage peaks, a collection of DNA samples from 19 new Ashkenazi Jewish families were tested for linkage in a genome wide scan.

METHODS

Families were ascertained from an Orthodox Ashkenazi Jewish community through mailings. Myopia was defined as equal to or greater than -1 diopter in both meridians in both eyes. The genome wide scan used markers from a modified Cooperative Human Linkage Center version 9 (402 markers). Parametric two-point linkage was calculated with FASTLINK while multipoint linkage was calculated with GENEHUNTER.

RESULTS

The results for the 19 families demonstrated several regions of suggestive linkage on chromosomes 7, 1, 17, and 22. A combined analysis of the 19 families and 44 previously reported families demonstrated an increase in the LOD score to 4.73 for the chromosome 22 locus.

CONCLUSIONS

Multiple chromosomal regions have exhibited some evidence of linkage to a myopia susceptibility gene in this Ashkenazi Jewish population. The strongest evidence of linkage to such a susceptibility gene in these data is on chromosome 22.

Correlations in refractive errors between siblings in the Singapore Cohort Study of Risk factors for Myopia

BACKGROUND

The prevalence of myopia in parts of South East Asia has risen dramatically over the past 1-2 generations, suggesting that environmental factors may be particularly important determinants of refractive development in these populations.

AIM

To assess the contribution of familial factors (shared genes and/or shared family environment) to refractive error and ocular component dimensions of school-aged children in Singapore.

METHODS

Data were available for 315 children who had one or more siblings also participating in the Singapore Cohort Study of the Risk factors for Myopia (SCORM). Refractive error and ocular biometric parameters were measured under cycloplegia at baseline when children were 7-9 years, and at yearly follow-up sessions for the next 3 years, using consistent clinical procedures. The time children spent performing a variety of nearwork-related tasks was obtained from questionnaires. Familial influences were assessed by calculating between-sibling correlations.

RESULTS

After adjusting for age and sex, the between-sibling correlation in refractive error was 0.447 (95% CI 0.314 to 0.564), suggesting that familial factors account for 63-100% of the variation in the cohort. The between-sibling correlation for 1-year change in refractive error was similarly high, at 0.420 (95% CI 0.282 to 0.543). All ocular component dimensions were correlated significantly between siblings, especially for corneal curvature and vitreous chamber depth--the major structural determinants of refraction. The amount of time siblings spent engaged in nearwork tasks (reading, watching TV, playing video games, computing) and in outdoor activities was also highly correlated between siblings (p<0.001).

CONCLUSION

Shared genes and/or shared environment are important factors in the refractive development of children in Singapore. Because the time spent in nearwork tasks is highly correlated between siblings, epidemiological studies will benefit from precise, quantitative measures of refractive error in parents and more distant relatives in order to begin to dissociate genetic and environmental sources of variation.

Expression of Collagen-Binding Integrin Receptors in the Mammalian Sclera and Their Regulation during the Development of Myopia

PURPOSE

The sclera has a collagen-rich extracellular matrix that undergoes significant biochemical and biomechanical remodeling during myopic eye growth. The integrin family of cell surface receptors play critical roles in extracellular matrix and biomechanical remodeling in connective tissues. This study identified the major collagen-binding integrin receptors in the mammalian sclera and investigated their mRNA expression during the development of and recovery from experimental myopia.

METHODS

The presence of the alpha1, alpha2, and beta1 integrin subunits was examined by using tree-shrew-specific primers and RT-PCR. Scleral expression of alpha1beta1 and alpha2beta1 receptor proteins was further investigated by using Western blot analysis and immunocytochemistry. Myopia was induced monocularly by occluding pattern vision and scleral tissue collected after 24 hours and 5 days. In a subset of the 5-day treatment group, vision was restored for 24 hours before tissue was isolated. Total RNA was extracted, and integrin subunit expression levels were assessed with quantitative real-time PCR.

RESULTS

The presence of the major collagen-binding integrin subunits alpha1, alpha2, and beta1 was confirmed by RT-PCR in both scleral tissue and cultured scleral fibroblasts. Both the alpha1 and alpha2 integrin subunit proteins were identified in tree shrew scleral tissues, and integrin receptor expression was localized to scleral fibroblast focal adhesions. After only 24 hours of myopia induction, a time when no structural elongation has occurred, significant decreases were observed in the expression of the alpha1 (-36%) and beta1 (-44%) integrin subunits. After 5 days of myopia induction, alpha1 integrin expression had returned to baseline levels, whereas the alpha2 subunit showed a significant decrease in expression (-52%). The 5-day integrin profiles were maintained during recovery from the induced myopia, with only alpha2 integrin showing a statistically significant relative decrease in expression (-41%).

CONCLUSIONS

The mammalian sclera expresses the major collagen-binding integrin subunits. The alpha1 and beta1 subunit expression was decreased early during the development of myopia, whereas the regulation of alpha2 integrin occurred at a later time point. The differential regulation of alpha1beta1 and alpha2beta1 during the development of myopia may reflect specific roles for these receptors in the scleral extracellular matrix and biomechanical remodeling that accompanies myopic eye growth.

Analysis of single nucleotide polymorphisms at 13 loci within the transforming growth factor-induced factor gene shows no association with high myopia in Japanese subjects

A previous study in China first indicated that the transforming growth factor-induced factor (TGIF) is a probable candidate gene for high myopia. The purpose of our study was to investigate whether there are significant associations between high myopia and single nucleotide polymorphism (SNP) variants in the TGIF gene of Japanese subjects. Genomic DNA was collected from 330 Japanese subjects with high myopia and at a level refractive error was less than -9.25 Dsph and 330 randomized controls without high myopia. Thirteen SNPs were detected by polymerase chain reaction (PCR) and primer extension or by PCR and SNP-specific fluorogenic probes in all of the cases and controls. Thirteen SNPs were found within the TGIF genes of the cases and controls. Two of the SNPs were monomorphic and none of the 13 SNPs showed a significant result. The pairwise linkage disequilibrium (LD) mapping confirmed that these alleles have a comparatively strong LD index of >0.8 for D' and >0.4 for r(2). We found no statistical association between any of the 13 SNPs located on the TGIF gene and high myopia in Japanese subjects. Based on our study using Japanese subjects and the previous studies of TGIF gene polymorphism in Chinese and northern European subjects with myopia, there is no convincing evidence to prove a connection between nucleotide sequence variations in TGIF and high myopia.

Refractive errors in twin studies

It is estimated that 1.6 billion people worldwide have myopia, a refractive error, and this number is expected to increase to approximately 2.5 billion by the year 2020. It is now well established that both the environment and genetics play a role in the development of myopia. However, the exact contribution of each of these components to myopia development has yet to be completely determined. Twin studies (classical twin model) are commonly used to determine the weighting of genetic and environmental components in disease. Over the last century, twin studies have investigated the heritability of refractive errors in different sample populations and have collectively supported a genetic basis to refractive errors. However, different sample populations and methods of data collection have produced a wide range of heritability estimates ranging from .5 to .9. This article will review those twin studies that have investigated refractive error, particularly myopia, as well as biometric measures linked to refractive error, to compare heritability estimates and methodology designs.

Evaluation of MMP3 and TIMP1 as candidate genes for high myopia in young Taiwanese men

PURPOSE

We studied the relationship between high myopia and the MMP3 and TIMP1 genes.

DESIGN

Case-control study.

METHODS

We enrolled 150 high myopic individuals (< or = -6 diopters) and 262 controls (> or = -1.5 diopters) initially, and another 216 cases and 474 controls were enrolled for genotyping promising polymorphisms for replication. Thirteen polymorphisms were genotyped in the initial data. Logistic regression was used to test for genetic effects. Subset analyses were performed according to the education level and family history.

RESULTS

There was no significant association between any polymorphism and high myopia in the initial data. Among the highly educated subjects, the 5A/6A polymorphism at the MMP3 gene suggested a potential relationship with high myopia, and it was genotyped in the follow-up samples. However, this polymorphism failed to show any significant results in the overall subjects.

CONCLUSIONS

The two genes may not play a crucial role for high myopia in young Taiwanese men.

A new autosomal recessive form of Stickler syndrome is caused by a mutation in the COL9A1 gene

Stickler syndrome is characterized by ophthalmic, articular, orofacial, and auditory manifestations. It has an autosomal dominant inheritance pattern and is caused by mutations in COL2A1, COL11A1, and COL11A2. We describe a family of Moroccan origin that consists of four children with Stickler syndrome, six unaffected children, and two unaffected parents who are distant relatives (fifth degree). All family members were clinically investigated for ear, nose, and throat; ophthalmologic; and radiological abnormalities. Four children showed symptoms characteristic of Stickler syndrome, including moderate-to-severe sensorineural hearing loss, moderate-to-high myopia with vitreoretinopathy, and epiphyseal dysplasia. We considered the COL9A1 gene, located on chromosome 6q13, to be a candidate gene on the basis of the structural association with collagen types II and XI and because of the high expression in the human inner ear indicated by cDNA microarray. Mutation analysis of the coding region of the COL9A1 gene showed a homozygous R295X mutation in the four affected children. The parents and four unaffected children were heterozygous carriers of the R295X mutation. Two unaffected children were homozygous for the wild-type allele. None of the family members except the homozygous R295X carriers had any signs of Stickler syndrome. Therefore, COL9A1 is the fourth identified gene that can cause Stickler syndrome. In contrast to the three previously reported Stickler syndrome-causing genes, this gene causes a form of Stickler syndrome with an autosomal recessive inheritance pattern. This finding will have a major impact on the genetic counseling of patients with Stickler syndrome and on the understanding of the pathophysiology of collagens. Mutation analysis of this gene is recommended in patients with Stickler syndrome with possible autosomal recessive inheritance.

The association of single nucleotide polymorphisms in the 5'-regulatory region of the lumican gene with susceptibility to high myopia in Taiwan

PURPOSE

To study the relationships between single nucleotide polymorphisms (SNPs) of lumican, decorin, and DSPG3 genes and high myopia.

METHODS

One hundred and twenty adult patients with high myopia (< -10.0 D) and 137 controls were used to study the relationships between the decorin, lumican, and DSPG genes and high myopia. All subjects were free of ocular diseases, other than myopia, as well as of other systemic genetic diseases. Genotyping was performed by direct sequencing after PCR amplification of chromosomal DNA. Allele frequencies were tested for Hardy-Weinberg disequilibrium. The chi(2) or Fisher test was conducted to investigate the genotypic and allelic distribution between the high myopia and control groups.

RESULTS

The genotyping success rate was 100%. Univariate analysis revealed significant differences between patients and control subjects with respect to one of the SNPs (rs3759223, C->T) of the lumican gene, with a p value of 0.000283. There was no significant relationship between other SNPs of lumican, decorin, and DSPG genes and high myopia.

CONCLUSIONS

Our results indicate that an SNP (rs3759223), which is located in the promoter region of the lumican gene, may be worth further investigation to determine its association with development of high myopia.

Novel locus for X linked recessive high myopia maps to Xq23-q25 but outside MYP1

BACKGROUND

High myopia is a common genetic variation in most cases, affecting 1-2% of people, and is the fourth most common disorder causing blindness worldwide. Six autosomal dominant loci and one X-linked recessive locus have been reported, but no genes responsible for high myopia have been identified.

OBJECTIVE

To report a Chinese family in which six males presented with high myopia consistent with an X linked recessive trait.

RESULTS

Affected individuals shared three common features: high myopia, reduced visual acuity, and fundal changes of high myopia. Protan and deutan were observed in the family, but they did not co-segregate with the high myopia phenotype. X-chromosome-wide linkage analysis mapped the high myopia locus to a 25 cM (14.9 Mb) region on Xq23-q25 between DXS1210 and DXS8057, with maximum two point lod scores at theta = 0 of 2.75 and 2.29 for DXS1001 and DXS8059, respectively.

CONCLUSIONS

This new myopia locus is outside the linked region of the first high myopia locus (MYP1). Refinement of the linkage region with additional families and screening candidate genes for mutation may lead to the identification of the defect gene.

Mutational spectrum of COH1 and clinical heterogeneity in Cohen syndrome

Cohen syndrome (CS) is an autosomal recessive disorder with variability in the clinical manifestations, characterised by mental retardation, postnatal microcephaly, facial dysmorphism, pigmentary retinopathy, myopia, and intermittent neutropenia. Mutations in the gene COH1 have been found in an ethnically diverse series of patients. Brief clinical descriptions of 24 patients with CS are provided. The patients were from 16 families of different ethnic backgrounds and between 2.5 and 60 years of age at assessment. DNA samples from all patients were analysed for mutations in COH1 by direct sequencing. Splice site mutations were characterised using reverse transcriptase PCR analysis from total RNA samples. In this series, we detected 25 different COH1 mutations; 19 of these were novel, including 9 nonsense mutations, 8 frameshift mutations, 4 verified splice site mutations, 3 larger in frame deletions, and 1 missense mutation. We observed marked variability of developmental and growth parameters. The typical facial gestalt was seen in 23/24 patients. Early onset progressive myopia was present in all the patients older than 5 years. Widespread pigmentary retinopathy was found in 12/14 patients assessed over 5 years of age. We present evidence for extended allelic heterogeneity of CS, with the vast majority of mutations leading to premature termination codons in COH1. Our data confirm the broad clinical spectrum of CS with some patients lacking even the characteristic facial gestalt and pigmentary retinopathy at school age.

The TGFbeta1 gene codon 10 polymorphism contributes to the genetic predisposition to high myopia

PURPOSE

Transforming growth factor-beta (TGFbeta), a multifunctional growth factor that plays a key role in the remodeling of scleral tissue, may be involved in the predisposition and pathophysiology of high myopia. Our aim was to examine the association between myopia and the polymorphisms within codon 10 of the TGFbeta1 gene.

METHODS

This was a case control study. The study group contained participants who had high myopia and a spherical equivalent greater than -6.00 D. The control group was composed of medical students whose spherical equivalent was less then -0.5 D. All volunteers in this study were over 16 years old and had never undergone ocular surgery. Genotyping was conducted by restriction fragment length polymorphism, and the results were compared between myopia patients and control subjects.

RESULTS

The frequency of the CC genotype in TGFbeta1 codon 10 differed significantly between patients in the high myopia group (n=201) and individuals in the control group (n=86; p<0.001). People with either the CT or TT genotype had a lower probability of having high myopia with a spherical equivalent greater than -6.00 D than those with the CC genotype. Furthermore, there was a higher frequency of the C allele in the high myopia group than with the control group (p<0.001, OR=1.83, CI=1.27-2.63).

CONCLUSIONS

The frequency of the CC homozygote in the high myopia group was much higher than in the control group, indicating people with the CC homozygote may be at a higher risk of developing high myopia. Varied expression of this gene may contribute to the genetic predisposition to high myopia in Chinese Taiwanese.

Ophthalmic manifestations of Danon disease

PURPOSE

To describe the ophthalmic findings in patients with Danon disease, an X-linked condition causing cardiomyopathy in males and females.

DESIGN

Retrospective case series.

PARTICIPANTS

Patients with genetically proven Danon disease.

METHODS

Retrospective chart review of complete eye examinations including electroretinogram, visual fields, and fluorescein angiography.

RESULTS

Five females (4 affected) and 2 affected males were examined. The 4 affected females demonstrated a peripheral pigmentary retinopathy. Lens changes, myopia, abnormal electroretinogram and visual fields were also found. The males demonstrated a near-complete loss of pigment in the retinal pigment epithelium.

CONCLUSION

We report the first description of a characteristic retinopathy in patients with Danon disease and the first extracardiac manifestations in affected females. Retinopathy potentially could be used to identify asymptomatic carriers.

High myopia and congenital myopathy with partial pachygyria in cutis laxa syndrome

PURPOSE

Several types of inborn errors of the O-glycan biosynthesis are known, leading to clinically very distinct phenotypes. Children with O-mannosyl glycan biosynthesis defects commonly present as a severe form of congenital muscular dystrophy with decreased alpha-dystroglycan staining, congenital eye anomalies, and brain migration defects. Alpha-dystroglycan is an O-mannosylated glycoprotein with additional mucin type O-glycans.

METHODS

Based on overlapping clinical features with O-mannosyl glycan defects, especially with muscle-eye-brain disease, the authors performed a muscle biopsy in a child with severe congenital hypotonia, high myopia, partial pachygyria, mental retardation, cutis laxa, and an inborn error affecting the biosynthesis of both mucin type O-glycans and N-linked glycans.

RESULTS

The histology showed no signs of muscle dystrophy, but a mild myopathy with slight increase in the muscle fiber diameter variability and type I fiber predominance. No significant decrease in the alpha-dystroglycan staining was detected; therefore, in spite of the phenotypic similarities the authors could not confirm the role of abnormal dystroglycan in the etiology of the muscle weakness and the developmental anomalies.

CONCLUSIONS

High myopia, muscle weakness, and cortical neuronal migration abnormalities are common in disorders of O-mannosylation and also observed in the authors' patient. However, compared to the severe generalized defect observed in mannosyl glycan defects, in this child the cerebral white matter and cerebellum were spared, and no muscle dystrophy could be confirmed. This is the first description of high myopia in cutis laxa syndrome in combination with congenital disorders of glycosylation.

CSNB1 in Chinese families associated with novel mutations in NYX

X-linked congenital stationary night blindness (CSNB) and NYX mutation have not been reported in Chinese. Here, two Chinese families with the complete form of CSNB (CSNB1) are presented. Linkage analysis of one family mapped the disease to Xp11-Xq13 where NYX is located. Sequence analysis of NYX identified two novel mutations, c.281G>C and c.302T>C, which would result in missense changes of p.Arg94Pro and p.Ile101Thr in the encoded protein. These two mutations were not found in 96 controls. The c.281G>C mutation cosegregated with nyctalopia and myopia. Our results expand the mutation spectrum of NYX and enrich the clinical information related to NYX mutation. The importance of associated myopia with NYX mutations is discussed.

Ophthalmologic findings in Cornelia de Lange syndrome: a genotype-phenotype correlation study

OBJECTIVE

To evaluate individuals with Cornelia de Lange syndrome previously screened for mutations in the NIPBL gene for genotype-phenotype correlations with regard to severity of ophthalmologic findings.

METHODS

Fifty-four patients with Cornelia de Lange syndrome (26 mutation positive and 28 mutation negative) with varying extent and severity of ophthalmologic findings participated in the study. We conducted a retrospective analysis of ophthalmologic data obtained through survey responses and medical records. The severity of nasolacrimal duct obstruction, myopia, ptosis, and strabismus was classified. The severity of eye findings was compared relative to the presence vs the absence of mutations in the coding region of NIPBL and relative to mutations predicted to result in a truncated protein (nonsense and frameshift mutations) vs missense mutations. Fisher exact test was used to determine the significance of these correlations.

RESULTS

A trend toward increased ptosis severity was found among individuals with truncating (nonsense and frameshift) mutations compared with individuals with missense mutations (P = .07).

CONCLUSION

NIPBL may be directly involved in ptosis pathogenesis.

CLINICAL RELEVANCE

Elucidating the pathogenetic mechanisms of ophthalmologic morbidities in patients with de Lange syndrome may lead to more effective treatment.

Marked discordance for myopia in female monozygotic twins

Female monozygotic twins aged 54 years discordant for myopia are reported. One twin presented with bilateral high myopia (right eye = -6.00/+0.50 x 5 degrees , left eye = -6.00/+0.50 x 45 degrees ) and her identical twin had no significant refractive error (right eye = -0.50/plano, left eye = -0.50/+0.75 x 40 degrees ). An explanation for the striking refractive discordance seen in this case report is yet to be determined.

[Myopia and genetics]

The physiological manifestation of myopia is error of refraction. The incidence of myopia in Asian population is increasing much more rapidly compared with several decades ago. Most of the people in the relatively developed Chinese cities are developing or have developed myopia. Recently, researches reported six loci related to myopia. Viewing from the modern civilization and development of China, the sharp increase of the size of the population with myopia and the unbalanced change could not be explained only by gene mutation or any model of Mendelian inheritance. The comparison of the disparity of the economic and educational levels between in urban and rural areas showed that the onset of myopia might be influenced by both environmental and genetic factors. Special attention should be paid to myopia now to prevent severe physical problem in the Chinese urban population.

Novel mutations in GJA8 associated with autosomal dominant congenital cataract and microcornea

PURPOSE

The purpose of this study was to estimate the importance of mutations in the connexin50 gene (GJA8) as a cause of congenital or developmental cataracts in the Indian population and to identify novel mutations in GJA8 that cause cataract in this population.

METHODS

The coding region of GJA8 was analyzed for mutation by single strand conformational polymorphism in 60 probands affected with congenital or developmental cataract of which 11 probands' corneal diameter measured less than 11.00 mm. Direct sequencing was performed for samples that displayed an abnormal electrophoresis pattern. The segregation of the change with the diseased phenotype was analyzed in the entire pedigree by restriction fragment length polymorphism (RFLP) analysis.

RESULTS

Molecular analysis of GJA8 revealed two novel missense mutations V44E and R198Q, in the population screened. The mutations cosegregated with the diseased phenotype in an autosomal dominant manner and were absent in 400 normal control chromosomes analyzed. GJA8 mutations were seen in two of the 60 unrelated probands with cataracts. Affected individuals in both of whose families also had microcornea and variable myopia.

CONCLUSIONS

This is the first report of mutations in GJA8 to be associated with autosomal dominant cataract and microcornea. Mutations in GJA8 cause 3.3% of congenital cataracts in the population of India.

Form deprivation modulates retinal neurogenesis in primate experimental myopia

Juvenile primates develop myopia when their visual experience is degraded by lid fusion. In response to this abnormal visual input, retinal neural networks cause an excessive growth of the postequatorial segment of the eye, but the mechanism underlying this axial elongation is unknown. After fusion of the lids in one eye of juvenile rhesus macaques and green monkeys, we combined cDNA subtractions, microarray profiling, and real-time PCR to compare gene expression in the retinas of the closed and open eyes. This molecular analysis showed up-regulation of a number of genes associated with cell division in the retina of the closed eye and differential expression of six genes localized to chromosomal loci linked to forms of human hereditary myopia. In addition, it substantiated a previous observation, based on immunocytochemistry, that synthesis of vasoactive intestinal polypeptide was increased upon lid fusion. Injection of 5-bromo-2'-deoxyuridine and immunocytochemistry showed that the primate retinal periphery harbors mitotically active neuroprogenitor cells that increase in number when the visual experience is altered by lid fusion. Furthermore, the number of dividing cells is highly correlated with axial elongation of the eye and the resulting myopic refractive error. Thus, the retina undergoes active growth during the postnatal development of the primate eye. This growth is modulated by the visual input and accelerates considerably when the eye develops axial myopia. Vasoactive intestinal polypeptide may be the molecule that stimulates retinal growth.

Clinical and molecular characterization of a patient with an interstitial deletion of chromosome 12q15-q23 and peripheral corneal abnormalities

PURPOSE

To describe the ocular features of a patient with an interstitial deletion of chromosome 12 and to determine the molecular boundaries of the deletion.

DESIGN

Observational case report and laboratory investigation.

METHODS

A patient with an interstitial deletion of chromosome 12 was clinically examined for ocular abnormalities. DNA samples were used for molecular studies to define the deletion boundaries.

RESULTS

Ocular examination showed abnormalities of the anterior segment consistent with a diagnosis of cornea plana. Molecular analyses showed the deletion included the KERA gene, the SLRP (small leucine repeat protein) gene cluster, the genetic loci for autosomal-dominant (CNA1) and autosomal-recessive (CNA2) cornea plana, and a portion of the mapped locus for high myopia (MYP3).

CONCLUSIONS

These results, combined with previous genetic linkage studies, identifies a 3-cM region located between microsatellite markers D12S82 and D12S351 that is likely to contain a gene responsible for CNA1.

Myopia as a latent phenotype of a pleiotropic gene positively selected for facilitating neurocognitive development, and the effects of environmental factors in its expression

Myopia has become an almost pandemic problem in many populations. There are compelling evidence to suggest that myopia is a hereditary condition. However, myopia would constitute a definite selection disadvantage during most stages of human evolution, which is incompatible with its moderate to high prevalence in most modern populations. The rapid upsurge of myopia over just a few decades also implies that its inheritance does not follow any of the usual patterns, and environmental factors may have an important role in precipitating its occurrence in those who are genetically predisposed. Previous studies showed that myopes were, on average, more intelligent than non-myopes, and this association had been attributed to a biological link between eye growth and brain development. We propose a pleiotropic genetic model to explain the atypical epidemiologic and inheritance pattern of myopia and its relationship with neurocognitive development. This pleiotropic gene was positively selected for its facilitation of human intelligence. The myopic component is a latent phenotype; myopia will not be expressed unless some novel external factors are encountered (i.e. a "quirk" phenomenon). Therefore, the myopic component was selectively neutral in our ancestral environment. The net gain in Darwinian fitness enables the pleiotropic gene to attain a high frequency in the human population, as reflected by our current prevalence of myopia.

Eye growth changes in myopic children in Singapore

AIMS

To assess the longitudinal changes in biometric parameters and associated factors in young myopic children aged 7--9 years followed prospectively in Singapore.

METHODS

Children aged 7--9 years from three Singapore schools were invited to participate in the SCORM (Singapore Cohort study Of the Risk factors for Myopia) study. Yearly eye examinations involving biometry measures were performed in the schools. Only myopic children (n=543) with 3 year follow up data were included in this analysis.

RESULTS

The 3 year increases in axial length, anterior chamber depth, lens thickness, vitreous chamber depth, and corneal curvature were 0.89 mm, -0.02 mm, -0.01 mm, 0.92 mm, and 0.01 mm, respectively. Children who were younger, female, and who had a parental history of myopia were more likely to have greater increases in axial length. After adjustment for school, age, sex, race, parental myopia and reading in books per week, the age (p<0.001), sex (p=0.012), and parental myopia (p=0.027) remained significantly associated with the 3 year change in axial length. Reading in books per week, however, was not associated with axial length change. Children with faster rates of progression of myopia had greater increases in axial length (Pearson correlation coefficient (r)=-0.69) and vitreous chamber depth (r=-0.83).

CONCLUSIONS

The 3 year change in axial length of Singapore children aged 7--9 years at baseline was high and greater in younger children, females, and children with a parental history of myopia. Myopia progression was driven largely by vitreous chamber depth increase.

Changes in scleral MMP-2, TIMP-2 and TGFbeta-2 mRNA expression after imposed myopic and hyperopic defocus in chickens

Induction of myopia leads to a decreased glycosaminoglycan synthesis and smaller collagen fibrillar diameters, increased levels of gelatinase-A (MMP-2) and decreased amounts of tissue inhibitor of matrix metalloproteinase-2 (TIMP-2) in the fibrous sclera of both chicks and tree shrews. Another factor found to be involved in altered eye growth is the transforming growth factor beta-2 (TGFbeta-2). The aim of the current study was to measure MMP-2, TIMP-2 and TGFbeta-2 mRNA expression changes separately in the two scleral layers of chicks, following myopic and hyperopic defocus. Chicks were treated unilaterally with positive and negative lenses for different time periods. All contralateral eyes wore plano lenses and additional controls, treated binocularly with plano lenses, were included. Real-time PCR was used to measure MMP-2, TIMP-2 and TGFbeta-2 mRNA levels. Few changes in MMP-2 and TIMP-2 mRNA levels were measured following treatment with plus and minus lenses for up to 3 days. The mRNA levels of MMP-2 and TIMP-2 were either unchanged or co-regulated in both eyes, even though only the eye with the powered lens actually displayed changes in growth. In contrast, TGFbeta-2 mRNA was significantly up-regulated in the cartilaginous layer following treatment with plus lenses after 24 hr, compared to all other groups. These changes were confined to the eyes that also displayed reduced growth, suggesting a role of TGFbeta-2 in the final steps of visual eye growth regulation.