Genetically distinct autosomal dominant posterior polar cataract in a four-generation Japanese family

Sideways sculpting - A novel technique in eyes with posterior polar cataracts

Posterior polar cataracts (PPCs) have long been a concern for cataract surgeons due to their natural proclivity for posterior capsule rupture. Although problems can be avoided, there is no surgical procedure that can completely eliminate the possibility of posterior capsular rupture. Research reports a higher percentage of capsule rupture and related complications post surgical intervention. The sideways sculpting technique is a novel method to alleviate unnecessary tension on the posterior capsule. To disseminate this novel technique to practicing ophthalmologists to reduce the risk of complications related to polar cataracts. This video presents the creation of sculpting or trench at the center of the nucleus, sideways movement of the phacotip trench, rotation of the nucleus, and phacoemulsification steps while operating a dense PPC. Step-by-step demonstration of sideways sculpting and an overview of its significance. Video Link: https://drive.google.com/file/d/17ukCjdr9DlEgguCgfh0DPAPYxCCEzirq/view?usp=sharing .

Charged multivesicular body protein 4b forms complexes with gap junction proteins during lens fiber cell differentiation

Charged multivesicular body protein 4b (CHMP4B) is a core sub-unit of the endosomal sorting complex required for transport III (ESCRT-III) machinery that serves myriad remodeling and scission processes of biological membranes. Mutation of the human CHMP4B gene underlies rare forms of early-onset lens opacities or cataracts, and CHMP4B is required for lens growth and differentiation in mice. Here, we determine the sub-cellular distribution of CHMP4B in the lens and uncover a novel association with gap junction alpha-3 protein (GJA3) or connexin 46 (Cx46) and GJA8 or Cx50. Immunofluorescence confocal microscopy revealed that CHMP4B localized to cell membranes of elongated fiber cells in the outer cortex of the lens-where large gap junction plaques begin to form-particularly, on the broad faces of these flattened hexagon-like cells in cross-section. Dual immunofluorescence imaging showed that CHMP4B co-localized with gap junction plaques containing Cx46 and/or Cx50. When combined with the in situ proximity ligation assay, immunofluorescence confocal imaging indicated that CHMP4B lay in close physical proximity to Cx46 and Cx50. In Cx46-knockout (Cx46-KO) lenses, CHMP4B-membrane distribution was similar to that of wild-type, whereas, in Cx50-KO lenses, CHMP4B localization to fiber cell membranes was lost. Immunoprecipitation and immunoblotting analyses revealed that CHMP4B formed complexes with Cx46 and Cx50 in vitro. Collectively, our data suggest that CHMP4B forms plasma membrane complexes, either directly and/or indirectly, with gap junction proteins Cx46 and Cx50 that are often associated with "ball-and-socket" double-membrane junctions during lens fiber cell differentiation.

A charged multivesicular body protein (CHMP4B) is required for lens growth and differentiation

Charged multivesicular body protein 4B (CHMP4B) functions as a core component of the endosome sorting complex required for transport-III (ESCRT-III) machinery that facilitates diverse membrane remodeling and scission processes in eukaryotes. Mutations in the human CHMP4B gene underlie rare, inherited forms of early-onset lens opacities or cataract. Here we have characterized the lens phenotypes of mutant (knock-in) mice harboring a human cataract-associated mutation (p.D129V) in CHMP4B (Chmp4b-mutant) and conditional knockdown mice deficient in lens CHMP4B (Chmp4b-CKD). In situ hybridization localized Chmp4b transcripts to lens epithelial cells and elongating fiber cells at the lens equator. Heterozygous Chmp4b-mutant (D/V) mice were viable and fertile with lenses grossly similar to those of wild-type. However, homozygous Chmp4b-mutant (V/V) mice died by embryonic day 15.5 (E15.5) with grossly abnormal eye and brain histology. Chmp4b-CKD mice displayed variable degrees of lens dysmorphology including lens ablation. Immuno-localization of aquaporin-0 (AQP0) revealed lens fiber cell degeneration in homozygous Chmp4b-mutant (V/V) mouse embryos and in embryonic and postnatal Chmp4b-CKD mice. DNA fragmentation (TUNEL) analysis revealed global cell death in homozygous Chmp4b-mutant (V/V) embryos, whereas, cell death was confined to the lens of Chmp4b-CKD mice. Immuno-localization of the monocyte/macrophage marker macrosialin (CD68) suggested that severe lens degeneration in Chmp4b-CKD mice resulted in an ocular immune cell response. Collectively, these mouse data suggest that (1) heterozygous, germ-line mutations in Chmp4b may not manifest as cataract, (2) homozygous, germ-line mutations in Chmp4b are embryonic lethal, and (3) conditional loss of Chmp4b results in arrest of lens growth and differentiation.

Managing the posterior polar cataract: An update

Posterior polar cataracts (PPC) have always been a challenge for cataract surgeons due to their inherently higher propensity for posterior capsule rupture. Over the years, several technical modifications have been suggested to enhance safety and reduce posterior capsule rupture rates in these polar cataracts. This review article tries to present the various techniques and strategies to published in literature to manage PPCs. It also discusses pearls for making surgery more reproducible and consistent, as well as the role of newer diagnostic and surgical technology based on the published literature on the subject.

A new locus in chromosome 2q37-qter is associated with posterior polar cataract

PURPOSE

To study the genetic basis of autosomal dominant posterior polar cataracts in two Chinese pedigrees.

MATERIALS AND METHODS

Peripheral blood samples were collected and genomic DNA was isolated. A genome-wide scan, using microsatellite markers at approximately 10-cm intervals and additional microsatellite markers for the positive region, was performed. Haplotype data were processed using Cyrillic software (version 2.1) to define the region of the disease gene. Mutation analysis was carried out for candidate genes. Sequencing data were analyzed with the software Sequence Scanner v1.0.

RESULTS

A maximum two-point LOD score (Z (max)) of 2.53 and 2.03 was obtained at marker D2S125 with recombination θ = 0.00 in the two families. The possible disease genes were located at approximately 8.44-cM between the marker D2S125 and the terminal of chromosome 2q, namely, 2q37-qter. Candidate genes, such as Gamma-crystallins (CRYGA-D), septin 2 (SEPT2), aquaporin 12B (AQP12B), and chemokine orphan receptor 7 (CXCR7), were sequenced but no causative mutations were found.

CONCLUSIONS

Our results suggest that an unidentified gene in chromosome 2q37-qter is associated with posterior polar cataract, which may have an implication in understanding the genetic and molecular mechanisms of cataracts.

Epidemiology and molecular genetics of congenital cataracts

Congenital cataract is a crystallin severe blinding disease and genetic factors in disease development are important. Crystallin growth is under a combination of genes and their products in time and space to complete the coordination role of the guidance. Congenital cataract-related genes, included crystallin protein gene (CRYAA, CRYAB, CRYBA1/A3, CRYBA4, CRYBB1, CRYBB2, CRYBB3, CRYGC, CRYGD, CRYGS), gap junction channel protein gene (GJA1, GJA3, GJA8), membrane protein gene (GJA3, GJA8, MIP, LIM2), cytoskeletal protein gene (BF-SP2), transcription factor genes (HSF4, MAF, PITX3, PAX6), ferritin light chain gene (FTL), fibroblast growth factor (FGF) and so on. Currently, there are about 39 genetic loci isolated to which primary cataracts have been mapped, although the number is constantly increasing and depends to some extent on definition. We summarized the recent advances on epidemiology and genetic locations of congenital cataract in this review.

Posterior polar cataract: A review

Posterior polar cataract is a rare form of congenital cataract. It is usually inherited as an autosomal dominant disease, yet it can be sporadic. Five genes have been attributed to the formation of this disease. It is highly associated with complications during surgery, such as posterior capsule rupture and nucleus drop. The reason for this high complication rate is the strong adherence of the opacity to the weak posterior capsule. Different surgical strategies were described for the handling of this challenging entity, most of which emphasized the need for gentle maneuvering in dealing with these cases. It has a unique clinical appearance that should not be missed in order to anticipate, avoid, and minimize the impact of the complications associated with it.

Inverse horse-shoe technique for the phacoemulsification of posterior polar cataract

OBJECTIVE

To study a new technique of controlled hydrodelineation followed by viscodelineation and viscodissection during phacoemulsification in eyes with posterior polar cataracts and to report its effectiveness in preserving the posterior capsule.

DESIGN

Prospective interventional study.

PARTICIPANTS

Twenty-eight eyes of 22 patients with posterior polar cataracts.

METHODS

All patients underwent phacoemulsification under topical anaesthesia with controlled hydrodelineation, viscodelineation, and viscodissection with minimal stress on the posterior capsule. Hydrodissection was not done. The preoperative complications and visual outcome were recorded.

RESULTS

The mean follow-up time was 8 months (range 2-24 months). Posterior capsule rupture occurred only in 2 eyes (7.1%); neither of the 2 had any vitreous prolapse, so anterior vitrectomy was not required. Mean visual acuity improved significantly after surgery (p = 0.0001, paired t test). The causes of the low postoperative visual acuity were amblyopia in 3 eyes (10.7%) and age-related macular degeneration in 1 (3.6%).

CONCLUSIONS

This inverse horse-shoe technique of controlled viscodelineation and viscodissection markedly reduced the risk of posterior capsule rupture. Moreover, if it occurred, the anterior vitreous face remained intact, so the IOL could be implanted in the sulcus without resorting to anterior vitrectomy.

Modified epinucleus pre-chop for the dense posterior polar cataract

A novel technique for the surgical management of dense posterior polar cataracts is described. In instances where hydrodelineation may be difficult to achieve due to the density of the nucleus, the anterior epinucleus is first pre-chopped in a piecemeal in situ maneuver before mobilizing, segmenting, and emulsifying the dense endonucleus. This is followed by the removal of the posterior epinucleus and the posterior polar plaque. Because the chopper is repositioned at different meridians in the mid-periphery of the anterior epinucleus, it stops short of the central posterior epinucleus, thus avoiding extension of the crack toward the posterior polar plaque and the posterior capsule.

CHMP4B, a novel gene for autosomal dominant cataracts linked to chromosome 20q

Cataracts are a clinically diverse and genetically heterogeneous disorder of the crystalline lens and a leading cause of visual impairment. Here we report linkage of autosomal dominant "progressive childhood posterior subcapsular" cataracts segregating in a white family to short tandem repeat (STR) markers D20S847 (LOD score [Z] 5.50 at recombination fraction [theta] 0.0) and D20S195 (Z=3.65 at theta =0.0) on 20q, and identify a refined disease interval (rs2057262-(3.8 Mb)-rs1291139) by use of single-nucleotide polymorphism (SNP) markers. Mutation profiling of positional-candidate genes detected a heterozygous transversion (c.386A-->T) in exon 3 of the gene for chromatin modifying protein-4B (CHMP4B) that was predicted to result in the nonconservative substitution of a valine residue for a phylogenetically conserved aspartic acid residue at codon 129 (p.D129V). In addition, we have detected a heterozygous transition (c.481G-->A) in exon 3 of CHMP4B cosegregating with autosomal dominant posterior polar cataracts in a Japanese family that was predicted to result in the missense substitution of lysine for a conserved glutamic acid residue at codon 161 (p.E161K). Transfection studies of cultured cells revealed that a truncated form of recombinant D129V-CHMP4B had a different subcellular distribution than wild type and an increased capacity to inhibit release of virus-like particles from the cell surface, consistent with deleterious gain-of-function effects. These data provide the first evidence that CHMP4B, which encodes a key component of the endosome sorting complex required for the transport-III (ESCRT-III) system of mammalian cells, plays a vital role in the maintenance of lens transparency.

Posterior polar cataract: minimizing risk of posterior capsule rupture

PURPOSE

To study a preferred technique of phacoemulsification in eyes with posterior polar cataract and report its outcome.

METHODS

Under topical anesthesia, phacoemulsification was carried out after hydrodelination in 23 cases (38 eyes) with ages ranging from 19 to 65 years (mean=33.5 years). Hydrodissection was not performed.

RESULTS

Mean duration of follow-up was 9.5 months. None of the eyes developed posterior capsule rupture, but seven eyes (18.4%) revealed posterior capsule plaque postoperatively, which needed neodymium : YAG laser capsulotomy. Mean visual acuity improved significantly after surgery (P=0.0001, paired t-test); In all, 34 eyes achieved a best-corrected visual acuity of 20/40 or more (89.4%). However, the postoperative visual acuity was less than 20/25 in 11 eyes (28.9%). The causes of the low acuity were amblyopia in eight eyes (21.0%) and macular degeneration due to retinitis pigmentosa in two others (5.2%).

CONCLUSION

Phacoemulsification is an effective and safe method to treat posterior polar cataract with gentle hydrodelination 'hydrodissection free phacoemulsification technique'. This is especially true when great attention is paid to the 'floppy' posterior capsule. Although previous amblyopia might interfere with excellent surgical outcome in patients with a unilateral or highly asymmetric bilateral cataract, visual acuity improved significantly in most cases.

Posterior polar cataract is the predominant consequence of a recurrent mutation in the PITX3 gene

BACKGROUND

The authors recently identified three large genetically unrelated families with an identical 17 base pair duplication mutation in exon 4 of the PITX3 gene. Here, they report the detailed clinical phenotype.

METHODS

Affected and unaffected individuals in the three families with autosomal dominant posterior polar cataract underwent full clinical examination and donated blood samples for DNA extraction and molecular genetic studies.

RESULTS

In all three families, an identical 17 base pair duplication mutation in PITX3 was identified which co-segregated with disease status in the family. All affected individuals had bilateral progressive posterior polar cataracts. In one family, posterior polar cataract was the only clinical abnormality but in the other two families, one of 10 affected individuals and four of 11 affected individuals also had anterior segment mesenchymal dysgenesis (ASMD).

CONCLUSION

Mutations in the PITX3 gene in humans result in posterior polar cataract and variable ASMD. The gene encodes a transcription factor which has a key role in lens and anterior segment development. The mechanism by which the mutant protein gives rise to such a regional pattern of lens opacity remains to be elucidated.

Outcomes of surgery for posterior polar cataract

PURPOSE

To report the preferred technique and the outcomes of surgery for posterior polar cataract.

SETTING

Hayashi Eye Hospital, Fukuoka, Japan.

METHODS

Medical records of 28 eyes of 20 consecutive patients with posterior polar cataract who had cataract surgery were reviewed. The surgical techniques used, intraoperative complications, preoperative and postoperative visual acuities, and the causes of impaired visual acuity after surgery were examined.

RESULTS

Of the 28 eyes, 25 (89.3%) with a small to medium posterior polar opacity had standard phacoemulsification or aspiration surgery. Two eyes (7.1%) with a large opacity and soft lens nucleus had pars plana lensectomy, and 1 eye (3.6%) with a large opacity and hard nucleus had intracapsular cataract extraction. Among the eyes having phacoemulsification or aspiration surgery, posterior capsule rupture occurred in 2 (7.1%). The mean visual acuity improved significantly after surgery (P <.0001); however, the postoperative visual acuity was worse than 20/20 in 7 eyes (25.0%). The cause of the low acuity was amblyopia in 4 eyes (14.3%), impaired foveal function after retinal detachment in 2 eyes (7.1%), and macular degeneration in 1 eye (3.6%).

CONCLUSION

Posterior polar cataracts can be safely extracted if the appropriate surgical technique is selected. Visual acuity improved significantly in most cases, although some patients with a unilateral cataract had previously developed amblyopia.