Altered chromatin topologies caused by balanced chromosomal translocation lead to central iris hypoplasia.

Despite the advent of genomic sequencing, molecular diagnosis remains unsolved in approximately half of patients with Mendelian disorders, largely due to unclarified functions of noncoding regions and the difficulty in identifying complex structural variations. In this study, we map a unique form of central iris hypoplasia in a large family to 6q15-q23.3 and 18p11.31-q12.1 using a genome-wide linkage scan. Long-read sequencing reveals a balanced translocation t(6;18)(q22.31;p11.22) with intergenic breakpoints. By performing Hi-C on induced pluripotent stem cells from a patient, we identify two chromatin topologically associating domains spanning across the breakpoints. These alterations lead the ectopic chromatin interactions between APCDD1 on chromosome 18 and enhancers on chromosome 6, resulting in upregulation of APCDD1. Notably, APCDD1 is specifically localized in the iris of human eyes. Our findings demonstrate that noncoding structural variations can lead to Mendelian diseases by disrupting the 3D genome structure and resulting in altered gene expression.

Heterocromia de íris: uma revisão das condições que podem afetar a pigmentação iridiana / Heterochromia: a review of conditions that may affect iris pigmentation

RESUMO A íris é responsável pela cor dos olhos. Ela ainda realiza o controle da quantidade de luz que penetra no olho pela pupila. Variações nos genes de cada indivíduo, além da quantidade e da qualidade de melanina na íris, determinam a cor dos olhos. A heterocromia é caracterizada por diferenças na coloração da íris de um mesmo indivíduo, sendo, na maioria das vezes, benigna. Existem basicamente três tipos de heterocromia de íris: central, setorial e completa. A heterocromia de íris pode ter como causa alterações genéticas e congênitas, relacionadas ou não a síndromes específicas, como a de Sturge-Weber, a de Waardenburg, a de Parry-Romberg e a de Horner congênita. Há também causas adquiridas, como doenças ou lesões, trauma ocular e corpos estranhos intraoculares, uso de certas medicações tópicas, siderose ocular, irites ou uveítes como a síndrome uveítica de Fuchs, dentre outras. Diante de um paciente com heterocromia de íris, deve-se entender o contexto e o curso clínico desse sinal, pois pode se tratar de uma alteração de pigmentação benigna ou existir uma doença base em curso, que requer terapêutica específica. Este artigo de revisão de literatura visa abordar as principais etiologias relacionadas à heterocromia de íris, além de discorrer sobre a anatomia e a fisiologia da coloração iridiana e sobre a fisiopatologia de suas possíveis alterações.

ABSTRACT The iris is responsible for eye color and controls the amount of light that enters the eye through the pupil. Variation in each individual's genes, besides the quantity and quality of melanin in the iris, determine eye color. Heterochromia is characterized by different colors of irises in the same individual, and it is benign in most cases. There are basically three types of heterochromia: central, partial and complete. Heterochromia can be caused by genetic and congenital alterations, which may or may not be related to specific conditions, such as Sturge-Weber syndrome, Waardenburg syndrome, Parry-Romberg syndrome and congenital Horner syndrome. It may be associated to acquired causes like diseases or injuries, such as eye trauma and intraocular foreign bodies, use of some topical medications, ocular siderosis, iritis or uveitis, such as Fuchs´ uveitis, among others. When assessing a patient with heterochromia, one must understand the context and clinical course of this signal, since it may be a benign pigmentation disorder or there may be an underlying disease, which requires specific therapy. This literature review article was set out to address the main etiologies related to heterochromia, in addition to describing the anatomy and physiology of the iris color and the pathophysiology of possible alterations.

Genome-wide association studies for iris pigmentation and heterochromia patterns in Large White pigs.

Eye colour genetics have been extensively studied in humans since the rediscovery of Mendel's laws. This trait was first interpreted using simplistic genetic models but soon it was realised that it is more complex. In this study, we analysed eye colour variability in a Large White pig population (n = 897) and report the results of GWASs based on several comparisons including pigs having four main eye colour categories (three with both pigmented eyes of different brown grades: pale, 17.9%; medium, 14.8%; and dark, 54.3%; another one with both eyes completely depigmented, 3.8%) and heterochromia patterns (heterochromia iridis - depigmented iris sectors in pigmented irises, 3.2%; heterochromia iridum - one whole eye iris of depigmented phenotype and the other eye with the iris completely pigmented, 5.9%). Pigs were genotyped with the Illumina PorcineSNP60 BeadChip and GEMMA was used for the association analyses. The results indicated that SLC45A2 (on chromosome 16, SSC16), EDNRB (SSC11) and KITLG (SSC5) affect the different grades of brown pigmentation of the eyes, the bilateral eye depigmentation defect and the heterochromia iridis defect recorded in this white pig population respectively. These genes are involved in several mechanisms affecting pigmentation. Significant associations for the eye depigmented patterns were also identified for SNPs on two SSC4 regions (including two candidate genes: NOTCH2 and PREX2) and on SSC6, SSC8 and SSC14 (including COL17A1 as candidate gene). This study provided useful information to understand eye pigmentation mechanisms, further valuing the pig as animal model to study complex phenotypes in humans.

A novel mutation of the StAR gene with congenital adrenal hyperplasia and its association with heterochromia iridis: a case report.

BACKGROUND: We report a novel mutation within the StAR gene, causing congenital adrenal hyperplasia, with the so far unreported association with heterochromia iridis. CASE PRESENTATION: In a now 15-year-old girl (born at 41 + 6 weeks of gestation) adrenal failure was diagnosed in the neonatal period based on the clinical picture with spontaneous hypoglycaemia, hyponatremia and an extremely elevated concentration of ACTH (3381 pmol/l; ref. level 1,1-10,1 pmol/l), elevated renin (836 ng/l; ref. level 5-308 ng/l), and a decreased concentration of aldosterone (410 pmol/l; ref. level 886-3540 pmol/l). In addition to hyperpigmented skin the patient exhibited sectorial heterochromia iridis. Sequence analysis of the steroidogenic acute regulatory protein (StAR) gene showed a novel homozygous mutation (c.652G > A (p.Ala218Thr), which was predicted in-silico to be possibly damaging. Under daily steroid substitution her electrolyte levels are balanced while she became obese. Puberty occurred spontaneously. CONCLUSION: A novel mutation in the StAR gene was identified in a patient with severe adrenal hypoplasia and sectorial heterochromia iridis. We discuss a causal relationship between these two rare phenotypes, i.e. whether very high levels of ACTH and alpha-MSH during early development might have disturbed early differentiation and distribution of uveal melanocytes. If confirmed in additional cases, discolorization of the iris might be considered as an additional phenotypical feature in the differential diagnosis of congenital adrenal insufficiency.

Bilateral asymmetrical partial heterochromia of iris and fundus in Waardenburg syndrome type 2A with a novel MITF gene mutation.

A 3-year-old girl presented with bilateral asymmetrical partial heterochromia of iris and fundus. The parents also complained of bilateral hearing loss in the child. Suspecting an auditory-pigmentary syndrome, systemic and genetic evaluation was performed. The child had profound sensory-neural hearing loss. Targeted gene sequencing revealed a novel nonsense variation in exon 9 of the MITF gene (chr3:70008440A>T) that was pathogenic for Waardenburg syndrome (WS) type 2A. This case highlights the characteristics of the iris and fundus hypochromia, which may provide a clue toward the diagnosis of WS.

Direct-to-consumer DNA testing of 6,000 dogs reveals 98.6-kb duplication associated with blue eyes and heterochromia in Siberian Huskies.

Consumer genomics enables genetic discovery on an unprecedented scale by linking very large databases of personal genomic data with phenotype information voluntarily submitted via web-based surveys. These databases are having a transformative effect on human genomics research, yielding insights on increasingly complex traits, behaviors, and disease by including many thousands of individuals in genome-wide association studies (GWAS). The promise of consumer genomic data is not limited to human research, however. Genomic tools for dogs are readily available, with hundreds of causal Mendelian variants already characterized, because selection and breeding have led to dramatic phenotypic diversity underlain by a simple genetic structure. Here, we report the results of the first consumer genomics study ever conducted in a non-human model: a GWAS of blue eyes based on more than 3,000 customer dogs with validation panels including nearly 3,000 more, the largest canine GWAS to date. We discovered a novel association with blue eyes on chromosome 18 (P = 1.3x10-68) and used both sequence coverage and microarray probe intensity data to identify the putative causal variant: a 98.6-kb duplication directly upstream of the Homeobox gene ALX4, which plays an important role in mammalian eye development. This duplication is largely restricted to Siberian Huskies, is strongly associated with the blue-eyed phenotype (chi-square P = 5.2x10-290), and is highly, but not completely, penetrant. These results underscore the power of consumer-data-driven discovery in non-human species, especially dogs, where there is intense owner interest in the personal genomic information of their pets, a high level of engagement with web-based surveys, and an underlying genetic architecture ideal for mapping studies.

De novo apparent loss-of-function mutations in PRR12 in three patients with intellectual disability and iris abnormalities.

PRR12 encodes a proline-rich protein nuclear factor suspected to be involved in neural development. Its nuclear expression in fetal brains and in the vision system supports its role in brain and eye development more specifically. However, its function and potential role in human disease has not been determined. Recently, a de novo t(10;19) (q22.3;q13.33) translocation disrupting the PRR12 gene was detected in a girl with intellectual disability and neuropsychiatric alterations. Here we report on three unrelated patients with heterozygous de novo apparent loss-of-function mutations in PRR12 detected by clinical whole exome sequencing: c.1918G>T (p.Glu640*), c.4502_4505delTGCC (p.Leu1501Argfs*146) and c.903_909dup (p.Pro304Thrfs*46). All three patients had global developmental delay, intellectual disability, eye and vision abnormalities, dysmorphic features, and neuropsychiatric problems. Eye abnormalities were consistent among the three patients and consisted of stellate iris pattern and iris coloboma. Additional variable clinical features included hypotonia, skeletal abnormalities, sleeping problems, and behavioral issues such as autism and anxiety. In summary, we propose that haploinsufficiency of PRR12 is associated with this novel multisystem neurodevelopmental disorder.

Ocular findings in Loeys-Dietz syndrome.

BACKGROUND: Loeys-Dietz syndrome (LDS), an autosomal-dominant connective tissue disorder, is characterised by systemic manifestations including arterial aneurysm and craniofacial dysmorphologies. Although ocular involvement in LDS has been reported, detailed information on those manifestations is lacking. METHODS: Retrospective chart review of patients with diagnosed LDS and comparison with age-matched control patients. RESULTS: Mean age was 37.8±14.6 years (patients with LDS) and 38.4±13.5 years (controls). Patients with LDS less frequently had iris transillumination, cataract and glaucoma compared with controls. Scleral and retinal vascular abnormalities were not found in any of the LDS eyes. Ectopia lentis was found in one patient with LDS. The eyes of patients with LDS tended to be more myopic (spherical equivalent, -2.47±2.70 dioptres (dpt) vs -1.30±2.96dpt (controls); P=0.08) and longer (24.6±1.7mm vs 24.1±1.5mm (controls); P=0.10). Central corneal thickness was significantly reduced in LDS eyes (521±48µm vs 542±37µm (controls); P=0.02). Corneal curvature (43.06±1.90dpt (LDS) versus 43.00±1.37dpt (controls); P=0.72) and interpupillary distance (65.0±6.0mm (LDS) vs 64.3±4.8mm (controls); P=0.66) did not differ significantly between both groups. Visual acuity was similar between both groups (0.03±0.09logarithm of the minimum angle of resolution (logMAR) for LDS eyes and 0.05±0.17logMAR for control eyes, P=0.47). CONCLUSIONS: Ocular features of LDS include decreased central corneal thickness and mild myopia. Ectopia lentis may be slightly more common than in controls but appears less common than in Marfan syndrome. Hypertelorism, scleral and retinal vascular abnormalities were not features of LDS.

A genome-wide association study reveals a locus for bilateral iridal hypopigmentation in Holstein Friesian cattle.

BACKGROUND: Eye pigmentation abnormalities in cattle are often related to albinism, Chediak-Higashi or Tietz like syndrome. However, mutations only affecting pigmentation of coat color and eye have also been described. Herein 18 Holstein Friesian cattle affected by bicolored and hypopigmented irises have been investigated. RESULTS: Affected animals did not reveal any ophthalmological or neurological abnormalities besides the specific iris color differences. Coat color of affected cattle did not differ from controls. Histological examination revealed a reduction of melanin pigment in the iridal anterior border layer and stroma in cases as cause of iris hypopigmentation. To analyze the genetics of the iris pigmentation differences, a genome-wide association study was performed using Illumina BovineSNP50 BeadChip genotypes of the 18 cases and 172 randomly chosen control animals. A significant association on bovine chromosome 8 (BTA8) was identified at position 60,990,733 with a -log10(p) = 9.17. Analysis of genotypic and allelic dependences between cases of iridal hypopigmentation and an additional set of 316 randomly selected Holstein Friesian cattle controls showed that allele A at position 60,990,733 on BTA8 (P = 4.0e-08, odds ratio = 6.3, 95% confidence interval 3.02-13.17) significantly increased the chance of iridal hypopigmentation. CONCLUSIONS: The clinical appearance of the iridal hypopigmentation differed from previously reported cases of pigmentation abnormalities in syndromes like Chediak-Higashi or Tietz and seems to be mainly of cosmetic character. Iridal hypopigmentation is caused by a reduced content of melanin pigment in the anterior border layer and iridal stroma. A single genomic position on BTA8 was detected to be significantly associated with iridal hypopigmentation in examined cattle. To our knowledge this is the first report about this phenotype in Holstein Friesian cattle.

YBR/EiJ mice: a new model of glaucoma caused by genes on chromosomes 4 and 17.

A variety of inherited animal models with different genetic causes and distinct genetic backgrounds are needed to help dissect the complex genetic etiology of glaucoma. The scarcity of such animal models has hampered progress in glaucoma research. Here, we introduce a new inherited glaucoma model: the inbred mouse strain YBR/EiJ (YBR). YBR mice develop a form of pigmentary glaucoma. They exhibit a progressive age-related pigment-dispersing iris disease characterized by iris stromal atrophy. Subsequently, these mice develop elevated intraocular pressure (IOP) and glaucoma. Genetic mapping studies utilizing YBR as a glaucoma-susceptible strain and C57BL/6J as a glaucoma-resistant strain were performed to identify genetic loci responsible for the iris disease and high IOP. A recessive locus linked to Tyrp1(b) on chromosome 4 contributes to iris stromal atrophy and high IOP. However, this is not the only important locus. A recessive locus on YBR chromosome 17 causes high IOP independent of the iris stromal atrophy. In specific eyes with high IOP caused by YBR chromosome 17, the drainage angle (through which ocular fluid leaves the eye) is largely open. The YBR alleles of genes on chromosomes 4 and 17 underlie the development of high IOP and glaucoma but do so through independent mechanisms. Together, these two loci act in an additive manner to increase the susceptibility of YBR mice to the development of high IOP. The chromosome 17 locus is important not only because it causes IOP elevation in mice with largely open drainage angles but also because it exacerbates IOP elevation and glaucoma induced by pigment dispersion. Therefore, YBR mice are a valuable resource for studying the genetic etiology of IOP elevation and glaucoma, as well as for testing new treatments.

Iris transillumination defect and its gene modulators do not correlate with intraocular pressure in the BXD family of mice.

PURPOSE: Intraocular pressure (IOP) is currently the only treatable phenotype associated with primary open angle glaucoma (POAG). Our group has developed the BXD murine panel for identifying genetic modulators of the various endophenotypes of glaucoma, including pigment dispersion, IOP, and retinal ganglion cell (RGC) death. The BXD family consists of the inbred progeny of crosses between the C57BL/6J (B6) strain and the glaucoma-prone DBA/2J (D2) strain that has mutations in Tyrp1 and Gpnmb. The role of these genes in the iris transillumination defect (TID) has been well documented; however, their possible roles in modulating IOP during glaucoma onset and progression are yet not well understood. METHODS: We used the IOP data sets and the Eye M430v2 (Sep08) RMA Database available on GeneNetwork to determine whether mutations in Tyrp1 and Gpnmb or TIDs have a direct role in the elevation of IOP in the BXD family. We also determined whether TIDs and IOP are coregulated. RESULTS: As expected, Tyrp1 and Gpnmb expression levels showed a high degree of correlation with TIDs. However, there was no correlation between the expression of these genes and IOP. Moreover, unlike TIDs, IOP did not map to either the Tyrp1 or Gpnmb locus. Although the Tyrp1 and Gpnmb mutations in BXD strains are a prerequisite for the development of TID, they are not required for or associated with elevated IOP. CONCLUSIONS: Genetic modulators of IOP thus may be independently identified using the full array of BXD mice without concern for the presence of TIDs or mutations in Typr1 and/or Gpnmb.

Ocular Findings in Patients with the Hermansky-Pudlak Syndrome (Types 1 and 3).

PURPOSE: To describe and compare ocular findings in patients with Hermansky-Pudlak syndrome (HPS) type 1 and 3. METHODS: This is a retrospective case series of 64 patients with HPS from 1999 to 2009 evaluated at an outpatient private ophthalmologic clinic. Patients underwent genetic analysis of selected albinism (Tyrosine and P gene) and HPS genes (HPS-1 and HPS-3) by screening for common mutations and exon sequencing with DNA screening. Descriptive and non-parametric statistical analyses were carried out. RESULTS: Nearly 70% of the patients were homozygous for common Puerto Rican mutations leading to the HPS1 gene (16-BP DUP, 53.6%), while 30% had the 3904-BP DEL HPS3 gene mutation. Best corrected visual acuity (BCVA) was poorer in patients with type 1 HPS than in patients with type 3 HPS (p < 0.001), esotropia was more common among type 1 HPS patients (p < 0.018), while exotropia was more common among patients with type 3 HPS. Total iris transillumination was more common in patients with type 1 HPS and minimal iris transillumination in patients with type 3 HPS (p < 0.001). The maculae were translucent in patients with type 1 HPS, while patients with type 3 HPS had opaque maculae (p < 0.001). CONCLUSIONS: Patients with type 1 HPS had poorer BCVA, increased incidence of esotropia, lighter iris and macular appearance. In contrast, patients with type 3 HPS had more exotropia. In addition, to our knowledge this is the largest series type 3 HPS ever reported.

Ocular Alterations in a Rare Case of Segmental Neurofibromatosis Type 1 with a Non-Classified Mutational Variant of the NF-1 Gene.

BACKGROUND: Neurofibromatosis type 1 (NF-1) is an autsomal dominant disorder which can occasionally result from somatic mosaicism and manifest as segmental forms of the disease. METHODS: A 37-year-old woman with ascertained NF-1, based on clinical diagnostic criteria and genetic analysis, was referred for ophthalmological evaluation. Genetic analysis, magnetic resonance imaging (MRI), complete ophthalmological examination, and near infrared reflectance (NIR) images at 815 nm of the retina were obtained. RESULTS: Genetic analysis revealed a non-classified mutational variant of the NF-1 gene identified as NM_000267.3:c2084T > C (p.Leu695Pro.T). MRI demonstrated non-symptomatic bilateral optic nerve gliomas. The only cutaneous sign was a subcutaneous neurofibroma of the posterior cervical region. Slit-lamp examination showed bilateral Lisch nodules. NIR images of the retina did not show any choroidal hamartomas. DISCUSSION: We report a rare case of segmental neurofibromatosis with a non-classified mutational variant of the NF-1 gene described in only one previous case in the literature. The patient presented with clinical features of NF-1 localized to the head and neck region, compatible with diagnosis of segmental NF-1. Interestingly, ocular manifestations included bilateral optic nerve gliomas and Lisch nodules, but no choroidal hamartomas.

Iris pigmentation as a quantitative trait: variation in populations of European, East Asian and South Asian ancestry and association with candidate gene polymorphisms.

In this study, we present a new quantitative method to measure iris colour based on high-resolution photographs. We applied this method to analyse iris colour variation in a sample of individuals of East Asian, European and South Asian ancestry. We show that measuring iris colour using the coordinates of the CIELAB colour space uncovers a significant amount of variation that is not captured using conventional categorical classifications, such as 'brown', 'blue' or 'green'. We tested the association of a selected panel of polymorphisms with iris colour in each population group. Six markers showed significant associations with iris colour in the European sample, three in the South Asian sample and two in the East Asian sample. We also observed that the marker HERC2 rs12913832, which is the main determinant of 'blue' versus 'brown' iris colour in European populations, is also significantly associated with central heterochromia in the European sample.

Loss-of-Function SOX10 Mutation in a Patient with Kallmann Syndrome, Hearing Loss, and Iris Hypopigmentation.

BACKGROUND: Kallmann syndrome (KS) is a clinically and genetically heterogeneous disorder consisting of hypogonadotropic hypogonadism and anosmia. KS is occasionally associated with deafness. Recently, mutations in SOX10, a well-known causative gene of Waardenburg syndrome (WS) characterized by deafness, skin/hair/iris hypopigmentation, Hirschsprung disease, and neurological defects, have been identified in a few patients with KS and deafness. However, the current understanding of the clinical consequences of SOX10 mutations remains fragmentary. CASE REPORT: A Japanese male patient presented with sensory deafness, blue irises, and anosmia, but no hair/skin hypopigmentation, Hirschsprung disease, or neurological abnormalities. He showed no pubertal sex development at 15.1 years of age. Blood examinations revealed low levels of FSH and testosterone. RESULTS: Molecular analysis detected a de novo p.Leu145Pro mutation in SOX10, which has previously been reported in a patient with WS and Hirschsprung disease. The mutation was predicted to be probably damaging. The mutant protein barely exerted in vitro transactivating activity. CONCLUSIONS: These results highlight the significance of SOX10 haploinsufficiency as a genetic cause of KS with deafness. Importantly, our data imply that the same SOX10 mutations can underlie both typical WS and KS with deafness without skin/hair hypopigmentation, Hirschsprung disease, or neurological defects.

Iris Flocculi as an ocular marker of ACTA2 mutation in familial thoracic aortic aneurysms and dissections.

Non-syndromic familial thoracic aortic aneurysms and dissections (TAAD) are inherited in an autosomal dominant manner. We report a missense mutation in the smooth muscle α-actin (ACTA2; MIM*102620) gene in a 3 generational family from Northern Ireland in which iris flocculi were an ocular marker of the disease.