Autosomal recessive colobomatous microphthalmia

IHH enhancer variant within neighboring NHEJ1 intron causes microphthalmia anophthalmia and coloboma

Genomic sequences residing within introns of few genes have been shown to act as enhancers affecting expression of neighboring genes. We studied an autosomal recessive phenotypic continuum of microphthalmia, anophthalmia and ocular coloboma, with no apparent coding-region disease-causing mutation. Homozygosity mapping of several affected Jewish Iranian families, combined with whole genome sequence analysis, identified a 0.5 Mb disease-associated chromosome 2q35 locus (maximal LOD score 6.8) harboring an intronic founder variant in NHEJ1, not predicted to affect NHEJ1. The human NHEJ1 intronic variant lies within a known specifically limb-development enhancer of a neighboring gene, Indian hedgehog (Ihh), known to be involved in eye development in mice and chickens. Through mouse and chicken molecular development studies, we demonstrated that this variant is within an Ihh enhancer that drives gene expression in the developing eye and that the identified variant affects this eye-specific enhancer activity. We thus delineate an Ihh enhancer active in mammalian eye development whose variant causes human microphthalmia, anophthalmia and ocular coloboma. The findings highlight disease causation by an intronic variant affecting the expression of a neighboring gene, delineating molecular pathways of eye development.

Clinical spectrum of non-syndromic microphthalmos, anophthalmos and coloboma in the paediatric population: a multicentric study from North India

AIMS

To describe the clinical features, visual acuity and causes of ocular morbidity in children (0-18 years) with microphthalmos, anophthalmos, and coloboma (MAC) from North India.

METHODS

A retrospective study conducted between October 2017 and September 2018 in three tertiary eye institutes, part of the Bodhya Eye Consortium with consensus led common pro formas. Children with complete clinical data and without syndromic/systemic involvement were included. The clinical phenotype was divided into isolated ocular coloboma (CB), coloboma with microcornea (CBMC), colobomatous microphthalmos (CBMO), non-colobomatous microphthalmos (MO) and anophthalmos (AO).

RESULTS

A total of 532 children with MAC were examined. Seventeen records were excluded due to incomplete data (0.2%). 515 children (845 eyes) were included: 54.4% males and 45.6% females. MAC was unilateral in 36% and bilateral in 64%. CB, CBMC, CBMO, MO and AO were seen in 26.4%, 31%, 22%, 8% and 12.5% of eyes, respectively. Nystagmus was found in 40%, strabismus in 23%, cataract in 18.7% and retinal detachment in 15%. Best-corrected visual acuity (BCVA) of <3/60 was seen in 62.4% eyes. Blindness (BCVA <3/60 in better eye) was seen in 42.8% of bilateral patients. Those with microcornea or microphthalmos with coloboma had worse BCVA (p<0.001). There were regional differences in the type of MAC phenotype presenting to the three institutes.

CONCLUSION

The MAC group of disorders cause significant ocular morbidity. The presence of microcornea or microphthalmos with coloboma predicts worse BCVA. The variation of the MAC phenotype with the district of origin of the patient raises questions of aetiology and is subject to further studies.

aldh7a1 regulates eye and limb development in zebrafish

Uveal coloboma is a potentially blinding congenital ocular malformation caused by failure of the optic fissure to close during development. Although mutations in numerous genes have been described, these account for a minority of cases, complicating molecular diagnosis and genetic counseling. Here we describe a key role of aldh7a1 as a gene necessary for normal eye development. We show that morpholino knockdown of aldh7a1 in zebrafish causes uveal coloboma and misregulation of nlz1, another known contributor to the coloboma phenotype, as well as skeletal abnormalities. Knockdown of aldh7a1 leads to reduced cell proliferation in the optic cup of zebrafish, delaying the approximation of the edges of the optic fissure. The aldh7a1 morphant phenotype is partially rescued by co-injection of nlz1 mRNA suggesting that nlz1 is functionally downstream of aldh7a1 in regulating cell proliferation in the optic cup. These results support a role of aldh7a1 in ocular development and skeletal abnormalities in zebrafish.

Anophthalmos, microphthalmos, and Coloboma in the United kingdom: clinical features, results of investigations, and early management

PURPOSE

To describe the clinical features of children with anophthalmos, microphthalmos, and typical coloboma (AMC).

DESIGN

Descriptive, observational, cross-sectional study of the United Kingdom.

PARTICIPANTS

A total of 135 children with AMC newly diagnosed over an 18-month period beginning in October 2006.

METHODS

Cases were identified using active surveillance through an established ophthalmic surveillance system. Eligible cases were followed up 6 months after first notification.

MAIN OUTCOME MEASURES

Phenotypic characteristics, both ocular and systemic, clinical investigations, causes, and interventions.

RESULTS

A total of 210 eyes (of 135 children) were affected by AMC, of which 153 had isolated coloboma or coloboma with microphthalmos. The most common colobomatous anomaly was a chorioretinal defect present in 109 eyes (71.2%). Some 44% of children were bilaterally visually impaired. Systemic abnormalities were present in 59.7% of children, with craniofacial anomalies being the most common. Children with bilateral disease had a 2.7 times higher odds (95% confidence interval, 1.3-5.5, P = 0.006) of having systemic involvement than unilaterally affected children. Neurologic imaging was the most frequent investigation (58.5%) performed. Less than one third (30.3%) of the children with microphthalmos had ocular axial lengths measured. Eight children had confirmed genetic mutations. Approximately half (49.2%) of the children required ocular intervention.

CONCLUSIONS

Colobomatous defects were the most common phenotype within this spectrum of anomalies in the United Kingdom. The high frequency of posterior segment colobomatous involvement means that a dilated fundal examination should be made in all cases. The significant visual and systemic morbidity in affected children underlines the importance of a multidisciplinary approach to management.

Unilateral Isolated Microphthalmia Inherited as an Autosomal Recessive Trait

PURPOSE

To report a family with unilateral isolated microphthalmia showing an autosomal recessive pattern of inheritance.

CASE REPORT

We report a family in which three out of four children, one male and monozygotic female twins, were born with unilateral isolated microphthalmia to healthy consanguineous parents. One twin additionally had a horseshoe kidney. Rare cases of familial isolated microphthalmia/anophthalmia have been previously described. This is the first report of a family with autosomal recessive isolated microphthalmia occurring unilaterally in all affected individuals. It remains unknown how this inherited genetic disease results in unilateral manifestation.

CONCLUSION

Mirror imaging of this condition in the monozygotic twins may help elucidate the underlying mechanism. The constellation of features in this family may contribute to solve remaining questions of research into symmetry and asymmetry.

Uveal coloboma: clinical and basic science update

PURPOSE OF REVIEW

To integrate knowledge on the embryologic and molecular basis of optic fissure closure with clinical observations in patients with uveal coloboma.

RECENT FINDINGS

Closure of the optic fissure has been well characterized and many genetic alterations have been associated with coloboma; however, molecular mechanisms leading to coloboma remain largely unknown. In the past decade, we have gained better understanding of genes critical to eye development; however, mutations in these genes have been found in few individuals with coloboma. CHD7 mutations have been identified in patients with CHARGE syndrome (coloboma, heart defects, choanal atresia, retarded growth, genital anomalies, and ear anomalies or deafness). Animal models are bringing us closer to a molecular understanding of optic fissure closure.

SUMMARY

Optic fissure closure requires precise orchestration in timing and apposition of two poles of the optic cup. The relative roles of genetics and environment on this process remain elusive. While most cases of coloboma are sporadic, autosomal dominant, autosomal recessive, and X-linked inheritance patterns have been described. Genetically, colobomata demonstrate pleiotropy, heterogeneity, variable expressivity, and reduced penetrance. Coloboma is a complex disorder with a variable prognosis and requires regular examination to optimize visual acuity and to monitor for potential complications.

Cataract surgery in the small adult eye

Microphthalmos is a rare condition that is often associated with several other ocular abnormalities. Given the considerable differences between microphthalmic and anatomically normal eyes, cataract surgery is technically demanding in these patients, and special attention must be given to adequate preoperative planning of these procedures. Furthermore, the unique nature of these surgeries creates a particular subset of intraoperative and postoperative complications. However, with the advent of piggyback intraocular lens placement, the visual outcomes of cataract surgery in small adult eyes have improved considerably over the past 20 years. This review discusses the nature of the microphthalmic eye, and addresses proper pre-, intra-, and postoperative care of the microphthalmic patient.

Heritable unilateral clinical anophthalmia

We examined a newborn child with unilateral right-sided clinical anophthalmos born to a mother with unilateral left-sided anophthalmos. Although rare, isolated nonsyndromic heritable unilateral anophthalmia and microphthalmia have been reported in the literature. We briefly review the genetics of such anomalies and discuss the importance of a full clinical genetics evaluation. Treatment of this patient's anophthalmic socket consists of progressive conformer expansion to be followed by placement of a self-inflating polymer expander.

The familial contribution to non-syndromic ocular coloboma in south India

AIMS

To identify the proportion of familial cases of isolated ocular colobomatous malformations in a case series from south India.

METHODS

Children with ocular coloboma without systemic features were recruited from multiple sources in Andhra Pradesh, India. Their families were traced, pedigrees drawn, and family members examined.

RESULTS

56 probands, 25 females (44.6%) and 31 males (57.4%) with a colobomatous malformation were identified. In 12 cases (21.4%) another family member was affected. The risk to siblings was 3.8%. The parents were consanguineous in 25 cases (44.6%).

CONCLUSIONS

21.4% of cases of isolated ocular coloboma in this highly consanguineous population of south India were familial, with both autosomal dominant and autosomal recessive mechanisms likely in different families.

Novel mutation in sonic hedgehog in non-syndromic colobomatous microphthalmia

Ocular (uveoretinal) colobomas occur in one in 10,000 individuals and present a substantive cause of congenital poor vision. The genetic bases of most forms of uveoretinal coloboma are elusive; mutations in PAX2 are found in only a few cases of coloboma of the retina and optic nerve that occur with renal anomalies as part of the renal-coloboma syndrome (MIM#120330; #167409). From experimental data that upstream expression of sonic hedgehog (SHH) controls Pax2 expression in mice and zebrafish, and from clinical experience that colobomas are observed frequently in patients with holoprosencephaly, we hypothesized that SHH could be a candidate for non-syndromic ocular colobomas (NSOC). We identified a three-generation family in which both a proband and his mother presented with iris and uveoretinal colobomas without optic nerve involvement. A novel 24 bp deletion in the gene SHH was identified in these affected family members, and cosegregated with the phenotype. This is the first report of the association of SHH mutations and uveoretinal coloboma.

Genetic mapping of a novel X-linked recessive colobomatous microphthalmia

Colobomatous microphthalmia is a common ocular malformation with a heterogeneous phenotype. The majority of cases without associated systemic abnormalities have an autosomal dominant inheritance pattern [McKusick, 1990: Mendelian inheritance in man]. A few isolated cases with autosomal recessive transmission have been described [Zlotogora et al., 1994: Am J Med Genet 49:261--262]. To our knowledge, no cases of X-linked colobomatous microphthalmia that are not a part of a syndrome or a multisystem disorder have been reported. In this study, we describe a genetic and clinical evaluation of a large pedigree in which colobomatous microphthalmia is segregating in an X-linked recessive fashion. Based on recombination breakpoint analysis, we have determined that the critical interval exists between markers DXS989 and DXS441, placing the disease locus on the proximal short arm or the proximal long arm of the X chromosome. Using linkage analysis, we obtained two-point lod scores of 2.71 at zero recombination with markers DXS1058, DXS6810, DXS1199, and DXS7132. Overlapping multipoint analysis established a broad maximum from marker DXS1068 to marker DXS7132, a region spanning approximately 28 cM. This study provides evidence for the presence of a new locus for colobomatous microphthalmia.

A locus for autosomal dominant colobomatous microphthalmia maps to chromosome 15q12-q15

Congenital microphthalmia is a common developmental ocular disorder characterized by shortened axial length. Isolated microphthalmia is clinically and genetically heterogeneous and may be inherited in an autosomal dominant, autosomal recessive, or X-linked manner. Here, we studied a five-generation family of Sephardic Jewish origin that included 38 members, of whom 7 have either unilateral or bilateral microphthalmia of variable severity inherited as an autosomal dominant trait with incomplete penetrance. After exclusion of several candidate loci, we performed a genome-scan study and demonstrated linkage to chromosome 15q12-q15. Positive LOD scores were obtained with a maximum at the D15S1007 locus (maximum LOD score 3.77, at recombination fraction 0.00). Haplotype analyses supported the location of the disease-causing gene in a 13.8-cM interval between loci D15S1002 and D15S1040.

Ocular colobomata

Ocular colobomata present diagnostic and therapeutic challenges in patients of all ages, but especially in young children. The "typical" coloboma, caused by defective closure of the fetal fissure, is located in the inferonasal quadrant, and it may affect any part of the globe traversed by the fissure from the iris to the optic nerve. Ocular colobomata are often associated with microphthalmia, and they may be idiopathic or associated with various syndromes. Types and severity of complications vary depending on the location and size of the colobomata. This article reviews the pathogeneses, categorization, genetic bases, differential diagnoses and management of ocular coloboma.

Phenotype of autosomal recessive congenital microphthalmia mapping to chromosome 14q32

BACKGROUND

Congenital microphthalmia (OMIM: 309700) may occur in isolation or in association with a variety of systemic malformations. Isolated microphthalmia may be inherited as an autosomal dominant, an autosomal recessive, or an X linked trait.

METHODS

Based on a whole genome linkage analysis, in a six generation consanguineous family with autosomal recessive inheritance, the first locus for isolated microphthalmia was mapped to chromosome 14q32. Eight members of this family underwent clinical examination to determine the nature of the microphthalmia phenotype associated with this locus.

RESULTS

All affected individuals in this family suffered from bilateral microphthalmia in association with anterior segment abnormalities, and the best visual acuity achieved was "perception of light". Corneal changes included partial or complete congenital sclerocornea, and the later development of corneal vascularisation and anterior staphyloma. Intraocular pressure, as measured by Schiotz tonometry, was greatly elevated in many cases.

CONCLUSIONS

This combination of ocular defects suggests an embryological disorder involving tissues derived from both the neuroectoderm and neural crest. Other families with defects in the microphthalmia gene located on 14q32 may have a similar ocular phenotype aiding their identification.

A locus for autosomal recessive congenital microphthalmia maps to chromosome 14q32

Congenital microphthalmia (CMIC) (OMIM 309700) may occur in isolation or in association with a variety of systemic malformations. Isolated CMIC may be inherited as an autosomal dominant, an autosomal recessive, or an X-linked trait. On the basis of a whole-genome linkage analysis, we have mapped the first locus for isolated CMIC, in a five-generation consanguineous family with autosomal recessive inheritance, to chromosome 14q32. All affected individuals in this family have bilateral CMIC. Linkage analysis gave a maximum two-point LOD score of 3.55 for the marker D14S65. Surrounding this marker is a region of homozygosity of 7.3 cM, between the markers D14S987 and D14S267, within which the disease gene is predicted to lie. The genes for several eye-specific transcription factors are located on human chromosome 14q and in the syntenic region of mouse chromosome 12. However, both CHX10 (14q24.3), mutations of which give rise to CMIC in mouse models, and OTX2 (14q21-22) can be excluded as candidates for autosomal recessive congenital microphthalmia (arCMIC), since they map outside the critical disease region defined by recombination events. This suggests that arCMIC is caused by defects in a novel developmental gene that may be important or even essential in eye development.

Hereditary disorders among Iranian Jews

Iranian Jews represent an ancient community with a very high degree of inbreeding. Although the community remained relatively isolated, it had strong ties with Babylonian Jewry in Iraq. Several genetic disorders have been reported to be frequent among Iranian Jews, in particular, corticosterone methyloxydase deficiency type II, polyglandular syndrome, and rimmed vacuole myopathy. Based on the data collected in our clinic, recessive and dominant deafness also appear to be frequent. Other diseases, such as beta-thalassemia, achromatopsia, colobomatous microphthalmia, Dubin-Johnson syndrome, and congenital myasthenia gravis, were frequent in both the Iranian and Iraqi Jewish communities. The place of origin of the families within Iran and the results of molecular studies suggest some reason(s) for the high frequency of these disorders among Iranian Jews. While the high frequency of some of the disorders, such as corticosterone methyloxydase deficiency type II, represents a founder effect, in other diseases (such as beta-thalassemia) it was secondary to heterozygote advantage.