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.

Genetic homogeneity for inherited congenital microcoria loci in an Asian Indian pedigree

PURPOSE

Congenital microcoria is a rare autosomal dominant developmental disorder of the iris associated with myopia and juvenile open angle glaucoma. Linkage to the chromosomal locus 13q31-q32 has previously been reported in a large French family. In the current study, a three generation Asian Indian family with 15 congenital microcoria (pupils with a diameter <2 mm) affected members was studied for linkage to candidate microsatellite markers at the 13q31-q32 locus.

METHODS

Twenty-four members of the family were clinically examined and genomic DNA was extracted. Microsatellite markers at 13q31-q32 were PCR amplified and run on an ABI Prism 310 genetic analyzer and genotyped with the GeneScan analysis. Two point and multipoint linkage analyses were performed using the MLINK and SUPERLINK programs.

RESULTS

Peak two point LOD scores of 3.5, 4.7, and 5.3 were found co-incident with consecutive markers D13S154, DCT, and D13S1280. Multipoint analysis revealed a 4 cM region encompassing D13S1300 to D13S1280 where the LOD remains just over 6.0 Thus we confirm localization of the congenital microcoria locus to chromosomal locus 13q31-q32. In addition, eight individuals who had both microcoria and glaucoma were screened for glaucoma genes: myocilin (MYOC), optineurin (OPTN) and CYP1B1. Using direct sequencing a point mutation (144 G>A) resulting in a Q48H substitution in exon 1 of the MYOC gene was observed in five of the eight glaucoma patients, but not in unaffected family members and 100 unrelated controls.

CONCLUSIONS

We have confirmed the localization of the congenital microcoria locus (MCOR) to 13q31-q32 in a large Asian Indian family and conclude that current information suggests this is a single locus disorder and genetically homogeneous. When combined with the initial linkage paper our haplotype and linkage data map the MCOR locus to a 6-7 cM region between D13S265 and D13S1280. The DCT locus, a member of the tyrosinase family involved in pigmentation, maps within this region. Data presented here supports the hypothesis that congenital microcoria is a potential risk factor for glaucoma, although this observation is complicated by the partial segregation of MYOC Q48H (1q24.3-q25.2), a mutation known to be associated with glaucoma in India. Fine mapping and candidate gene analysis continues with the hope that characterizing the micocoria gene will lead to a better understanding of microcoria and glaucoma causation. The relationship between microcoria, glaucoma, and the MYOC Q48H mutation in this family is discussed.

The effect of parental history of myopia on eye size of pre-school children: a pilot study

PURPOSE

To evaluate parental history of myopia as a predictor of refractive error and eye size in Chinese pre-school children.

METHODS

A total of 514 pre-school children (aged 2.3--6.4 years) were examined. Parental history of myopia, amount of near work performed, refractive status and ocular biometry were recorded.

RESULTS

There was no significant difference in spherical equivalent refraction (SER) among children with no myopic parents (mean+0.94+/-0.05 D), one myopic parent (mean+0.77+- 0.07 D) and two myopic parents (mean+0.79+/- 0.12 D) (p=0.102) after controlling for age and amount of near work. Further, children with more myopic parents did not have longer eyeballs (p=0.335).

CONCLUSIONS

In this study in Chinese pre-school children, parental history of myopia was not found to be associated with a myopic refractive error or increased eyeball length. Further studies with larger sample sizes would help to confirm these results.

Genome-wide scan for myopia in the Old Order Amish

PURPOSE

To identify myopia susceptibility genes influencing common myopia in 34 Old Order Amish families, a genetically well-defined founder population.

DESIGN

A prospective study of families with myopia consisting of a minimum of two individuals affected with myopia.

METHODS

Extended families consisting of at least two siblings affected with myopia were ascertained. A genome-wide linkage scan using 387 markers was conducted by the Center for Inherited Disease Research (CIDR). Linkage analyses were conducted with parametric (autosomal dominant, fixed penetrance model) and nonparametric methods. Model-free linkage analysis was also performed maximizing over penetrance and over dominance (that is, fitting a wide range of both dominant and recessive models).

RESULTS

Under the fixed penetrance model, the maximum two-point heterogeneity LOD score (HLOD) was 1.59 at D20S451 and the maximum multipoint HLOD was 1.92 at D6S1021. The nonparametric maximum multipoint (NPL) at D3S2427 had a P-value of .0005. Under the model-free analysis, multipoint heterogeneity LOD scores of 2.03 were observed on both chromosomes 8 (under a recessive model between D8S1130 and D8S1106) and X (under a recessive model between DXS6800 and DXS6789). Reanalyses of chromosomes 3, 6, 8, 20, and X using the best penetrance models resulted in maximum multipoint HLODs of 1.84 at D3S3053; 1.84 at D3S2427; 2.04 at D8S1130; and 2.34 at DXS6800.

CONCLUSIONS

The locus on chromosome 8p23 independently confirms a report by Hammond and associates mapping a myopia quantitative trait loci (QTL) to this region.

Identification of a novel locus on 2q for autosomal dominant high-grade myopia

PURPOSE

Myopia, or nearsightedness, is a visual disorder of high and growing prevalence in the United States and in other countries. Pathologic high myopia, or myopia of </=-6.00 D, predisposes individuals to retinal detachment, macular degeneration, cataracts, and glaucoma. Autosomal dominant (AD) nonsyndromic high-grade myopia has been mapped to loci on 18p11.31, 12q21-q23, 17q21-q23, and 7q36. This is the report of significant linkage to a novel locus on the long arm of chromosome 2 in a large, multigenerational family with AD high-grade myopia.

METHODS

The family contains 31 participating members (14 affected). The average spherical refractive error for affected individuals was -14.46 D (range, -7.25 to -27.00). Before a genome screening was undertaken, linkage to intragenic or flanking markers for the myopic genetic syndromes of Stickler syndrome types I, II, and III; Marfan syndrome; and juvenile glaucoma were ruled out. In addition, no linkage was found to the known AD high-grade myopia loci listed above. A full genome screen of the family was performed with 382 microsatellite markers with an average intermarker distance of 10 cM. SimWalk2 software was used for multipoint linkage analysis based on an AD model with a penetrance of 90% and a disease allele frequency of 0.01.

RESULTS

Fine-point mapping with an additional nine custom-made and five commercial markers yielded a maximum two-point lod score of 5.67 at marker D2S2348. Results of multipoint analysis indicate that the 1-unit support intervals for this new locus spans approximately 9.1 cM from (238.7 to 247.8 cM) on the chromosome 2 genetic map at q37.1.

CONCLUSIONS

A novel locus for AD high-grade myopia has been determined, providing further evidence of genetic heterogeneity for this disorder.

X-Linked Cone Dysfunction Syndrome with Myopia and Protanopia

PURPOSE

To perform a detailed clinical, psychophysical, and molecular assessment of members of 4 families with an unusual X-linked cone dysfunction syndrome associated with myopia.

PARTICIPANTS

Affected and unaffected members of 4 British nonconsanguineous families.

METHODS

Subjects underwent both detailed clinical examination and psychophysical testing. After informed consent was obtained, blood samples were taken for DNA extraction, and molecular genetic analysis was performed. The strategy for molecular analysis was to amplify the coding regions of the long and middle wavelength-sensitive cone opsin genes and the upstream locus control region by polymerase chain reaction and to examine these fragments for mutations by sequencing of DNA.

RESULTS

The phenotype was almost identical in all 4 families, consisting of moderate to high myopia, astigmatism, moderately reduced acuity, and normal fundi. Electroretinography showed abnormal cone but normal rod responses. Psychophysical testing showed a selective impairment of long cones in combination with well-preserved middle cone and short cone function. There was no evidence to suggest that the phenotype was progressive. Molecular analysis of the X-linked opsin gene array in the 4 families indicated that affected males have inherited the same X-chromosome from their mother. In 2 families, a long/middle hybrid gene was detected. In a third family, the commonly described deleterious Cys203Arg amino acid substitution was identified in both the long and middle opsin genes. In the fourth family, the only abnormality was absence of a middle opsin exon 2; the cause of the protanopia in this family is uncertain.

CONCLUSIONS

The X-linked cone dysfunction syndrome associated with myopia and dichromacy described here has many similarities to Bornholm eye disease, a condition previously mapped to Xq28. Except for the Cys203Arg substitution in one family, no alterations in the opsin gene array were identified that could underlie the cone dysfunction. It is therefore possible that the cone dysfunction may have a genetic origin different from that of the dichromacy.

Birthweight and adult health in a population-based sample of Norwegian twins

Population-based twin data were used to test (a) whether lower birthweight confers a greater risk of adult health disorders, and (b) whether within-pair birthweight differences in twins explain discordance for health outcomes. The sample consisted of 1201 monozygotic (MZ) male twins, 1048 dizygotic (DZ) male twins, 1679 MZ female twins, 1489 DZ female twins, and 2423 opposite-sex DZ twins, born in Norway between 1967 and 1979. The relationship between birthweight and self-reported health outcomes were studied using multivariable logistic regression. In the full sample (n = 7840), birthweight was negatively associated with risk for nearsightedness (odds ratio OR = 0.76, 95% CI: 0.65 - 0.92) and minimal brain disorder (OR = 0.27, 95% CI: 0.16-0.44) when adjusted for gestational age, sex, zygosity, age, education and body mass index after correction for intraclass correlations and multiple comparisons. Within-pair analysis of 159 MZ and 224 DZ pairs revealed that myopic twins were on average 2 g (p = .966) and 64 g (p = .040) lighter than nonmyopic twins in MZ and DZ pairs respectively, suggesting that genetic factors may play an important role in the associations between birthweight and nearsightedness. Within-pair analysis of twins discordant for a minimal brain disorder indicated that affected twins were 80 g (p = .655) and 85 g (p = .655) lighter than their healthy co-twins in MZ and DZ pairs respectively, although there were only 2 MZ and 2 DZ discordant pairs.

Heritability of refractive error and familial aggregation of myopia in an elderly American population

PURPOSE

To determine the heritability of refractive error and the familial aggregation of myopia in an older population.

METHODS

Seven hundred fifty-nine siblings (mean age, 73.4 years) in 241 families were recruited from the Salisbury Eye Evaluation (SEE) Study in eastern Maryland. Refractive error was determined by noncycloplegic subjective refraction (if presenting distance visual acuity was < or =20/40) or lensometry (if best corrected visual acuity was >20/40 with spectacles). Participants were considered plano (refractive error of zero) if uncorrected visual acuity was >20/40. Preoperative refraction from medical records was used for pseudophakic subjects. Heritability of refractive error was calculated with multivariate linear regression and was estimated as twice the residual between-sibling correlation after adjusting for age, gender, and race. Logistic regression models were used to estimate the odds ratio (OR) of myopia, given a myopic sibling relative to having a nonmyopic sibling.

RESULTS

The estimated heritability of refractive error was 61% (95% confidence interval [CI]: 34%-88%) in this population. The age-, race-, and sex-adjusted ORs of myopia were 2.65 (95% CI: 1.67-4.19), 2.25 (95% CI: 1.31-3.87), 3.00 (95% CI: 1.56-5.79), and 2.98 (95% CI: 1.51-5.87) for myopia thresholds of -0.50, -1.00, -1.50, and -2.00 D, respectively. Neither race nor gender was significantly associated with an increased risk of myopia.

CONCLUSIONS

Refractive error and myopia are highly heritable in this elderly population.

Evaluation of Lipin 2 as a candidate gene for autosomal dominant 1 high-grade myopia

The first autosomal dominant high-grade myopia locus has been mapped to chromosome 18p11.31 between markers D18S59 and D18S1138 by haplotype analysis. Refinement of the region by transmission disequilibrium testing suggests that a candidate gene (or genes) for this locus named myopia 2 (MYP2) is likely in an interval between markers D18S63 and D18S52. Lipin 2 (LPIN2), a candidate gene for lipodystrophy, maps in proximity to this locus. Our purpose in this study was to identify mutations and polymorphisms in the LPIN2 gene in myopic patients and control subjects. Expression studies of this gene by reverse transcription-polymerase chain reaction (RT-PCR) showed that LPIN2 was ubiquitously expressed in various tissues, such as brain, kidney, lung, heart, and skeletal muscles. It was also expressed in cornea, lens, retina, optic nerve, and sclera. Direct sequencing of the LPIN2 gene revealed 11 single nucleotide polymorphisms (SNPs) in myopia and unaffected individuals. Eight of them were novel. Among the 11 SNPs detected in this study, 2 exonic variants (G2950692A and C2924436T) were synonymous and do not lead to changes in amino acid of the translated protein product. Two transversions in intron 1 (T2951033A homozygote and heterozygote, C2951049A) and one transversions in intron 7 (G2924536C homozygote and heterozygote), 5 nucleotide variants (A 2909606T, del2909343T, G2907798C, T2907425G, T2907152C) in the 3'-untranslated region (3'-UTR), and TATTAA nucleotide deletions (homozygote and heterozygote) at 2950970-5 in intron 1 were also detected. Although LPIN2 gene was excluded as a candidate for MYP2, the SNPs detected in this study will aid in future mapping and association studies involving this gene.

The Association of Astigmatism and Spherical Refractive Error in a High Myopia Cohort

PURPOSE

The purposes of this study were to determine whether the degree of myopia influences the presence and degree of total astigmatism, and to assess risk factors of astigmatism in patients with familial nonsyndromic severe myopia.

METHODS

We performed a retrospective study of 217 subjects from families with two or more subjects from successive generations with a myopic spherical refractive error of at least -5 D or greater in one eye. Mean myopic spherical equivalent was -10 D and the mean age of myopia onset was 7 years. Refractive error measurements were obtained and the association between the degree of myopia and cylinder power was examined by correlation analysis.

RESULTS

The prevalence of astigmatism (1.0 D of cylinder) was 36.1%. With-the-rule astigmatism was most common (55.8%), and the majority of astigmats had between 1.0 and 2.5 D of cylinder (77.6%). Statistically significant associations were found between the presence of astigmatism and risk factors of age and the age of myopia onset. In those patients with astigmatism, however, there was a moderate correlation between the degree of spherical equivalent and cylinder power (r = -0.34, p < 0.0001). Younger age (<16 years) (p = 0.03) was associated with higher cylinder power.

CONCLUSIONS

In severely myopic patients, there is a high prevalence of astigmatism that is predominantly with-the-rule. The degree of myopic spherical refractive error is correlated with astigmatism severity but is not a risk factor for the presence of astigmatism.

A genetic perspective on myopia

Myopia is a refractive error of the eye that has a significant socioeconomic impact due to its increasing prevalence and the fact that it causes visual impairment. Its aetiology is complex and is likely to involve the interaction of environmental and genetic influences. Tight environmental influence is exemplified by defocus-induced myopia produced in animal models, while genetic factors predominate in familial occurrence of myopia with a Mendelian inheritance pattern. The involvement of numerous mediators, such as cytokines, neurotransmitters and transcription factors, in myopia development has been indicated through various lines of investigation, particular interest focussing on scleral extracellular matrix proteins and developmental genes of the eye. As high-throughput technology for large-scale genotyping and RNA expression analysis enters the field of myopia research, a productive avenue will open up for deciphering the aetiological heterogeneity of myopia and the biological pathways underlying its development.

How genetic is school myopia?

Myopia is of diverse aetiology. A small proportion of myopia is clearly familial, generally early in onset and of high level, with defined chromosomal localisations and in some cases, causal genetic mutations. However, in economically developed societies, most myopia appears during childhood, particularly during the school years. The chromosomal localisations characterised so far for high familial myopia do not seem to be relevant to school myopia. Family correlations in refractive error and axial length are consistent with a genetic contribution to variations in school myopia, but potentially confound shared genes and shared environments. High heritability values are obtained from twin studies, but rest on contestable assumptions, and require further critical analysis, particularly in view of the low heritability values obtained from parent-offspring correlations where there has been rapid environmental change between generations. Since heritability is a population-specific parameter, the values obtained on twins cannot be extrapolated to define the genetic contribution to variation in the general population. In addition, high heritability sets no limit to the potential for environmentally induced change. There is in fact strong evidence for rapid, environmentally induced change in the prevalence of myopia, associated with increased education and urbanisation. These environmental impacts have been found in all major branches of the human family, defined in modern molecular terms, with the exception of the Pacific Islanders, where the evidence is too limited to draw conclusions. The idea that populations of East Asian origin have an intrinsically higher prevalence of myopia is not supported by the very low prevalence reported for them in rural areas, and by the high prevalence of myopia reported for Indians in Singapore. A propensity to develop myopia in "myopigenic" environments thus appears to be a common human characteristic. Overall, while there may be a small genetic contribution to school myopia, detectable under conditions of low environmental variation, environmental change appears to be the major factor increasing the prevalence of myopia around the world. There is, moreover, little evidence to support the idea that individuals or populations differ in their susceptibility to environmental risk factors.

[Pedigree study of pathological myopia]

90 pedigrees including 1822 individuals were investigated and analyzed to find out the genetic mode of pathological myopia in Chinese population. 169 screened nuclear pedigrees from the total were divided into two groups according to mating mode, Affected * Normal or Normal * Normal. Simple segregation analysis on A * N and N * N pedigrees was performed respectively. The results showed that A * N pedigrees fit the autosomal dominant inheritance, with segregation ratio 0.6033 and sporadic proportion 13.8%, while N * N pedigrees fit autosomal recessive inheritance, with segregation ratio 0.235245 and sporadic proportion 16.3%, although autosomal dominant inheritance could not be rejected. In complex segregation analysis,SAGE-REGD software was used to fit several genetic model, including Mendelian inheritance (major gene, dominant, recessive, codominant) and non-Mendelian inheritance (non-transmitted, environment, general), and at last all Mendelian inheritances including major gene, dominant, recessive, codominant inheritance were accepted, while codominant inheritance with minimus AIC was best fitted. Our study manifests that pathological myopia in Chinese population fits autosomal dominant and autosomal recessive inheritance with certain sporadic proportion, which demonstrates the high genetic heterogeneity of pathological myopia.

Pediatric ophthalmologic findings of Cohen syndrome in twins

We present the clinical findings and follow-up data of male twins with Cohen syndrome. The most characteristic ophthalmologic findings were down-slanting eyelids, lens opacities, chorioretinal dystrophy, pigmentary retinal deposits, pale disk, and bull's eye maculae.

Exclusion of lumican and fibromodulin as candidate genes in MYP3 linked high grade myopia

PURPOSE

The proteoglycans lumican and fibromodulin regulate collagen fibril assembly and show expression in ocular tissues. A recent mouse knockout study implicates lumican and fibromodulin as functional candidate genes for high myopia. Lumican maps within the chromosome 12q21-q23 autosomal dominant high grade myopia-3 (MYP3) interval, and fibromodulin maps to chromosome 1q32. We screened individuals for lumican and fibromodulin sequence alterations from the original MYP3 family, and from a second high grade myopia pedigree that showed suggestive linkage to both the MYP3 interval and to chromosome 1q32.

METHODS

A total of 10 affected (average spherical refractive error was -16.13 D) and 5 unaffected individuals from the 2 families were screened by direct DNA sequencing. Six primer pairs spanning intron-exon boundaries and coding regions were designed for the 3-exon 1804 base pair (bp) lumican gene. Two primer pairs for the 2-exon 2863 bp fibromodulin gene were designed. Polymerase chain reaction products were sequenced and analyzed using standard fluorescent methods. Sequences were quality scored and aligned for polymorphic analysis.

RESULTS

Direct DNA sequencing of lumican amplicons yielded the expected sequence with no evidence of polymorphism or pathologic mutation. Sequencing of fibromodulin amplicons revealed 6 polymorphisms, 1 of which was novel. One polymorphism was a silent mutation, and five were in the 3' untranslated region. No polymorphism segregated with high myopia.

CONCLUSIONS

Although null and double null Lum and Fmod mouse models have been developed for high myopia, our human cohort did not show affected status association with these genes. Sequencing of the human lumican and fibromodulin genes has excluded them as candidate genes for MYP3 associated high grade myopia.

Clinical description and genome wide linkage study of Y-sutural cataract and myopia in a Chinese family

PURPOSE

To describe the clinical characteristics of a Y-sutural cataract associated with myopia in a large Chinese family and to identify the causative gene and mutation.

METHODS

An autosomal dominant Y-sutural cataract and myopia were identified in members of a large family of Han ethnicity living in southern China. Ophthalmological examinations were performed and a medical history was taken. Blood samples were collected for DNA isolation. A genome wide scan was performed using markers spaced at about 10 cM intervals for genotyping and two point linkage analysis. Candidate genes were sequenced.

RESULTS

Bilateral lens opacities, the only sign of cataract in early childhood and the most prominent sign in all affected individuals, involved the entire anterior Y and posterior inverted Y sutures, showing a feather duster like appearance. The Y-sutural cataract in this family mapped to an 11.4 cM (13.5 Mb) region between D3S3606 and D3S1309 on chromosome 3q22 with a maximum lod score of 5.7 at theta=0 for D3S1292. Sequence analysis of the beaded filament structural protein 2 (BFSP2) gene identified a previously described c.697_699delGAA (E233del) mutation which was present in all individuals with Y-sutural cataract but not in unaffected individuals and controls. Myopia, observed in 10 out of 12 cataract patients and significantly higher than that in unaffected offspring and siblings (1 out of 8), was independently mapped to a 61.2 cM (59 Mb) region between D3S3606 and D3S1262 on 3q21.3-q27.2 with maximum lod score of 3.79.

CONCLUSIONS

This Y-sutural cataract is caused by an E233del mutation in BFSP2 which provides additional evidence supporting mutations in BFSP2 as a cause for cataract and demonstrates phenotypic variability in cataracts caused by BFSP2. The Y-sutural opacity in the lens might be the typical and earliest sign for cataract caused by the BFSP2 mutation. In addition, these results demonstrate a myopia susceptibility locus in this region, which might also be associated with the mutation in BFSP2.

Persistence of fetal vasculature in a patient with Knobloch syndrome: potential role for endostatin in fetal vascular remodeling of the eye

OBJECTIVE

To report a child with Knobloch syndrome (KS) with features of persistent fetal vasculature (PFV) and to discuss the possible role of endostatin in vascular remodeling of the fetal eye.

DESIGN

Case report with enzyme-linked immunosorbent assay (ELISA) analysis of serum endostatin.

MAIN OUTCOME MEASURES

Ocular examination, fluorescein angiography, echography, ELISA analysis of serum endostatin, and typing for pathogenic mutations in COL18A1.

RESULTS

Slit-lamp examination in the left eye disclosed numerous findings of PFV, including an extensive persistent pupillary membrane, scarcity of iris crypts, and pigmented epicapsular stellate remnants on the anterior lens surface. Dilated fundus examination revealed a total posterior vitreous detachment, despite the young age of the patient, with numerous white intragel opacities that were compatible with remnants of the vasa hyaloidea propria. The fundus had a tesselated appearance with angiographically visible large choroidal vessels. There was a retinochoroidal staphyloma inferotemporal to the optic disc. There were no retinal vessels visible temporally, and there was no macular differentiation or foveal pit. Competitive ELISA analysis disclosed no detectable serum endostatin. None of the 8 reported pathogenic mutations in the COL18A1 gene was found in the patient.

CONCLUSIONS

Persistent fetal vasculature may be a clinical and important manifestation in some patients with KS and can be explained by a deficiency in endostatin. Endostatin deficiency may result in reduced or delayed regression of fetal blood vessels in the eye (including the intravitreal compartment), thereby resulting in incomplete development of the normal vasculature in the retina. Our typing results for the reported COL18A1 mutations confirm the genetic heterogeneity of KS.

Linkage analysis of the genetic loci for high myopia on 18p, 12q, and 17q in 51 U.K. families

PURPOSE

To determine the extent to which high myopia in a cohort of 51 U.K. families can be attributed to currently identified genetic loci.

METHODS

The families comprised 245 subjects with phenotypic information and DNA available, of whom 170 were classified as affected. Subjects were genotyped for microsatellite markers spanning approximately 40cM regions on 18p (MYP2), 12q (MYP3) and 17q, together with markers flanking COL2A1, COL11A1, and FBN1. Two-point linkage analyses were performed using the same disease gene segregation model as was used in the original publications, followed by nonparametric and multipoint analyses using Genehunter (http://linkage.rockefeller.edu/soft/gh/ provided in the public domain by Rockefeller University, New York, NY), with additional maximization over the parameter alpha, the proportion of linked families.

RESULTS

Evidence of linkage was found for the MYP3 locus on 12q (two-point Zmax = 2.54, P = 0.0003 and multipoint hLOD = 1.08 at alpha = 0.24, P = 0.023 for marker D12S332; nonparametric linkage [NPL] = 1.49, P = 0.07 for marker D12S1607). For the 17q locus there was weak evidence of excess allele sharing and linkage under a recessive model (NPL = 1.34, P = 0.09 for marker D17S956; two-point hLOD = 1.24 at alpha = 0.30 for marker D17S1795; multipoint hLOD = 1.24 at alpha = 0.17, P = 0.014 for marker at 77.68 cM, between markers D17S956 and D17S1853). No significant linkage was found to the MYP2 locus on 18p, or to the COL2A1, COL11A1, and FBN1 genes.

CONCLUSIONS

These results suggest that the MYP3 locus on 12q could be responsible for high myopia in approximately 25% of the U.K. families showing apparent autosomal dominant transmission, but that the loci on 18p and 17q are less common causes. Thus, additional loci for high myopia are likely to be the cause of the majority of cases of high myopia in the United Kingdom.

Family aggregation of high myopia: estimation of the sibling recurrence risk ratio

PURPOSE

To estimate the sibling recurrence risk (KS) and the sibling recurrence risk ratio (lambda(S)) for high myopia in a cohort in the United Kingdom.

METHOD

The recurrence risks for myopia and high myopia were estimated in the siblings of 296 randomly selected high myopes ascertained from an optometric practice population. A model using an age of onset of spectacle wear for myopia of 9.1 +/- 0.7 years or younger was developed as a surrogate for high myopia. The influence of parental myopia on the sibling recurrence risk for high myopia was also evaluated.

RESULTS

KS was estimated (95% confidence limits) to be 10.0% (5.9, 14.8) and lambdaS to be 4.9 (2.8, 7.6). High myopes without myopic parents were surprisingly common ( approximately 40%) and were less likely to have highly myopic siblings (KS approximately 6%) than those with at least one myopic parent (KS approximately 14%).

CONCLUSIONS

The sibling recurrence risk ratio reported herein (lambdaS approximately 4.9) implies that the high penetrance autosomal dominant loci for high myopia identified to date account for only a minority of cases of high myopia in the United Kingdom. Furthermore, high-penetrance autosomal dominant inheritance or even high-penetrance recessive inheritance, per se, cannot account for most cases of high myopia. Instead, it may be necessary to consider high myopia as a "complex disease" resulting from the influence of either alleles of reduced penetrance ("susceptibility genes"), environmental factors, or both.

Impact of Family History of High Myopia on Level and Onset of Myopia

PURPOSE

To investigate the impact of a positive family history of high myopia on the level and onset of myopia and its ocular components.

METHODS

A cross-sectional study was conducted. The participants (aged 17 to 45 years) were categorized into four groups: normal, mild, moderate, and high myopia. The age of first glasses for myopia was used as the onset of myopia. The impact of the family history on the level and the onset of myopia was quantified. Parental effect on corneal curvature (CC), anterior chamber depth (ACD), and axial length (AXL) was analyzed.

RESULTS

The study included 185 normal subjects, 170 mild, 140 moderate, and 392 high myopes. Family history was strongly associated with the probands' status (P < 6 x 10(-12)). When there was >or=1 highly myopic parent, the odds ratios (ORs) of developing mild or moderate myopia were between 2.5 and 3.7 (95% CI: 1.1-6.5) and the ORs of having high myopia were > 5.5 (95% CI: 3.2-12.6). A strong association (P = 2 x 10(-6)) between parental myopic state and the AXL in the subjects was also found, but there was no statistical relationship for ACD or CC. There was an association between high myopia in parents and the onset of myopia in children. Siblings had a weaker association with the level of myopia and had no effect on the onset of myopia.

CONCLUSIONS

This study found strong familial effects on the level and onset of myopia even after adjusting for environmental factors. The parental effect on ocular components in their offspring was primarily on AXL.

Genomewide linkage scan for myopia susceptibility loci among Ashkenazi Jewish families shows evidence of linkage on chromosome 22q12

Mild/moderate (common) myopia is a very common disorder, with both genetic and environmental influences. The environmental factors are related to near work and can be measured. There are no known genetic loci for common myopia. Our goal is to find evidence for a myopia susceptibility gene causing common myopia. Cycloplegic and manifest refraction were performed on 44 large American families of Ashkenazi Jewish descent, each with at least two affected siblings. Individuals with at least -1.00 diopter or lower in each meridian of both eyes were classified as myopic. Microsatellite genotyping with 387 markers was performed by the Center for Inherited Disease Research. Linkage analyses were conducted with parametric and nonparametric methods by use of 12 different penetrance models. The family-based association test was used for an association scan. A maximum multipoint parametric heterogeneity LOD (HLOD) score of 3.54 was observed at marker D22S685, and nonparametric linkage analyses gave consistent results, with a P value of.0002 at this marker. The parametric multipoint HLOD scores exceeded 3.0 for a 4-cM interval, and significant evidence of genetic heterogeneity was observed. This genomewide scan is the first step toward identifying a gene on chromosome 22 with an influence on common myopia. At present, we are following up our linkage results on chromosome 22 with a dense map of >1,500 single-nucleotide-polymorphism markers for fine mapping and association analyses. Identification of a susceptibility locus in this region may eventually lead to a better understanding of gene-environment interactions in the causation of this complex trait.