Galactokinase deficiency induced cataracts in Indian infants: identification of 4 novel mutations in GALK gene

Elongated axial length and myopia-related fundus changes associated with the Arg130Cys mutation in the LIM2 gene in four Chinese families with congenital cataracts

Background

Congenital cataract (CC) is a congenital abnormality characterized by lens opacity present at birth and is associated with highly heterogeneous clinical manifestations. Lens-specific integral membrane protein (LIM2) gene expression is localized to tight junctional domains of different lens fiber membranes. To date, only four mutations in LIM2 have been reported to be associated with congenital or presenile cataracts. Due to the rarity of variants detected in the gene, there is limited progress in understanding the correlation between the genotype and phenotype of patients with mutations in LIM2.

Methods

A total of four Chinese families with CCs were recruited for this study, including three families inheriting in an autosomal dominant (AD) pattern and one sporadic case. Genomic DNA was extracted from the leukocytes of peripheral blood collected from all available patients. Whole-exome sequencing (WES) was performed on all probands and at least one of their parents. Bioinformatics analysis was performed to evaluate the pathogenicity of the candidate variants. Exon 4 of LIM2 was amplified by polymerase chain reaction and directly sequenced. All patients underwent full ocular examinations. This was an observational study to explore the genotype-phenotype relationships in the four families with a common candidate variant.

Results

Various ocular phenotypes were detected in these families, mainly including CCs, elongated axial length, and myopia-related fundus changes. The LIM2 gene mutation, p.Arg130Cys, was detected in all patients. This was further confirmed by Sanger sequencing. The proportion of probands with this mutation in our CCs database was 3.1% (4/130), which indicated that this mutation appears to be a frequent cause of cataracts in the Han Chinese population. This variation has been reported by other investigators before and was correlated with isolated cataracts.

Conclusions

This is the first study that reports various ocular phenotypes associated with the p.Arg130Cys mutation in the LIM2 gene, which indicated the phenotypic heterogeneity of this gene. LIM2 might not only function as an integral membrane protein in lens fiber cells but also be associated with the axial development of the eyeball. Functional studies of the LIM2 gene are important and should receive more attention.

Screening for galactosemia: is there a place for it?

Galactose is a hexose essential for production of energy, which has a prebiotic role and is essential for galactosylation of endogenous and exogenous proteins, ceramides, myelin sheath metabolism and others. The inability to metabolize galactose results in galactosemia. Galactosemia is an autosomal recessive disorder that affects newborns who are born asymptomatic, apparently well and healthy, then develop serious morbidity and mortality upon consuming milk that contains galactose. Those with galactosemia have a deficiency of an enzyme: classic galactosemia (type 1) results from severe deficiency of galactose-1-uridylyltransferase, while galactosemia type II results from galactokinase deficiency and type III results from galactose epimerase deficiency. Many countries include neonatal screening for galactosemia in their national newborn screening program; however, others do not, as the condition is rather rare, with an incidence of 1:30,000-1:100,000, and screening may be seen as not cost-effective and logistically demanding. Early detection and intervention by restricting galactose is not curative but is very rewarding, as it prevents deaths, mental retardation, liver cell failure, renal tubular acidosis and neurological sequelae, and may lead to resolution of cataract formation. Hence, national newborn screening for galactosemia prevents serious potential life-long suffering, morbidity and mortality. Recent advances in communication and biotechnology promise facilitation of logistics of neonatal screening, including improved cost-effectiveness.

Status of Newborn Screening and Inborn Errors of Metabolism in India

Inborn errors of metabolism (IEM) are a heterogeneous group of genetic disorders that cause significant neonatal and infant mortality. Expanded newborn screening which detects these disorders at birth is the standard preventive strategy in most countries. Prospective studies to evaluate the impact of these in the Indian population are lacking. The imminent need to address this lacuna warrants a review of available pan India data, as well as efforts for a carefully conducted prospective assessment of the burden of IEM. Published data on IEM in the Indian population comprising universal prospective screening and screening in selected subgroups (patients admitted to pediatric/neonatal ICUs, patients with developmental delay/mental retardation) was collected through a systematic search. The primary focus was to get an estimate of the disease burden in the Indian population. A true prevalence of IEM in India is not available. The systematic review identifies and stratifies the various situations where IEM are found. Data collected by universal screening of the low risk population is essential to identify the true prevalence of IEM in India.

Association of alpha A-crystallin polymorphisms with susceptibility to nuclear age-related cataract in a Han Chinese population

Background

Alpha A-crystallin (CRYAA) is considered critical for the maintenance of lens transparency and is related to the pathogenesis of age-related cataracts (ARCs), especially the nuclear subtype. As the 5′ untranslated region (5′ UTR) modulates gene expression, the purpose of current study was to investigate whether single nucleotide polymorphisms (SNPs) in the 5′ UTR of CRYAA were associated with susceptibility to ARC in a Han Chinese population and to clarify the mechanism of this association.

Methods

SNPs in the 5′ UTR (−1 to −1000) of CRYAA were identified in 243 nuclear ARC patients and 263 controls using polymerase chain reaction and DNA sequencing. Allele and genotype frequencies were calculated and compared between two groups. Haploview 4.2 was used to calculate the linkage disequilibrium index, and the SHEsis analysis platform was used to infer haplotype construction. A dual-luciferase reporter gene assay was used for transcription of CRYAA in the presence of a protective haplotype with individual SNP alteration, Chromatin immunoprecipitation (ChIP) was employed to determine whether SNPs regulated CRYAA expression by altering the binding affinity of transcription factors.

Results

Three polymorphisms were identified in the 5′ UTR of CRYAA: rs3761381 (P = 0.000357, odds ratio [OR] = 1.837), rs13053109 (P = 0.788, OR = 1.086), and rs7278468 (P = 0.00136, OR = 0.652). The haplotype C-G-T (P = 0.0014, OR = 1.536) increased the risk of nuclear ARC, whereas the haplotype T-G-G (P = 0.00029, OR = 0.535) decreased the risk. The haplotype C-G-T decreased CRYAA transcription through rs7278468, which is located in the binding site of specificity protein 1 (Sp1). Furthermore, the G allele of rs7278468 increased CRYAA transcription by enhancing the binding affinity of Sp1.

Conclusions

These data indicate that the CRYAA polymorphism is a genetic marker of inter-individual differences in the risk of nuclear ARC.

Electronic supplementary material

The online version of this article (doi:10.1186/s12886-017-0529-9) contains supplementary material, which is available to authorized users.

Inherited Congenital Cataract: A Guide to Suspect the Genetic Etiology in the Cataract Genesis

Cataracts are the principal cause of treatable blindness worldwide. Inherited congenital cataract (CC) shows all types of inheritance patterns in a syndromic and nonsyndromic form. There are more than 100 genes associated with cataract with a predominance of autosomal dominant inheritance. A cataract is defined as an opacity of the lens producing a variation of the refractive index of the lens. This variation derives from modifications in the lens structure resulting in light scattering, frequently a consequence of a significant concentration of high-molecular-weight protein aggregates. The aim of this review is to introduce a guide to identify the gene involved in inherited CC. Due to the manifold clinical and genetic heterogeneity, we discarded the cataract phenotype as a cardinal sign; a 4-group classification with the genes implicated in inherited CC is proposed. We consider that this classification will assist in identifying the probable gene involved in inherited CC.

Cataract surgery in infants with microphthalmos

PURPOSE

To report the postoperative outcomes of cataract surgery in microphthalmic eyes of infants.

METHODS

This prospective observational study was carried out on 20 infants with microphthalmos with visually significant cataract. Microphthalmos was defined as axial length of the globe 16.50 mm or less. We excluded eyes with ocular trauma, inflammation, posterior hyperplastic primary vitreous or a tractional retinal detachment, aniridia, or chorioretinal coloboma. All the infants enrolled in this study underwent phacoaspiration with primary posterior capsulotomy, anterior vitrectomy, and peripheral iridectomy. Intraocular lens was not implanted in these children. Post-operative evaluation included refractive errors, irregularity of pupil, posterior synechiae, visual axis obscuration, and intraocular pressure. These children were followed up for a minimum of 12 months.

RESULTS

We evaluated 37 eyes of 20 infants, of whom 17 infants had bilateral and three infants had unilateral cataract. The mean age of the children and the mean axial length at the time of surgery were 3.78 ± 2.25 months and 15.76 ± 0.56 mm respectively. The complications observed were irregularity of pupil in seven eyes (18.9 %), glaucoma in five eyes (13.5 %), posterior synechiae in two eyes (5.2 %), visual axis obscuration due to posterior capsule opacification (PCO) in two eyes (5.2 %) and phthisis in one eye (2.7 %).

CONCLUSION

Infants achieved a favorable outcome after phacoaspiration with primary posterior capsulotomy with anterior vitrectomy. However, these children must be followed up to detect and treat postoperative complications such as visual axis obscuration, posterior synechiae, and glaucoma to achieve optimal outcome.