Clinical features and a follow-up study in a family with X-linked progressive cone-rod dystrophy

DNA methylation patterns in umbilical cord blood from infants of methadone maintained opioid dependent mothers

Methadone maintenance treatment for opioid dependent mothers is standard of care. Infants of methadone maintained opioid dependent (MMOD) mothers have better outcomes compared to infants of opioid dependent mothers without treatment. However, when compared to non-exposed infants, infants of MMOD mothers are associated with worse outcomes. We conducted a pilot study to examine genome wide differential DNA methylation using cord blood samples from sixteen term and near-term infants of MMOD and opioid naïve mothers, excluding Infants with chorioamnionitis. A total of 152 differentially methylated loci were identified at a difference >  + 2, < - 2 and p-value < 0.05. There were 90 hypermethylated loci (59 annotated genes) and 62 hypomethylated loci (38 annotated genes) observed. The hypermethylated and hypomethylated DNA changes involved multiple genes, pathways and networks that may explain some of the changes seen in infants of MMOD mothers. Top hypermethylated and hypomethylated genes involved areas of cell growth, neurodevelopment, vision and xenobiotic metabolism functions. Our data may explain the role of key pathways and genes relevant to neonatal outcomes seen from methadone exposure in pregnancy. Functional studies on the identified pathways and genes could lead to improved understanding of the mechanisms and identify areas for intervention.

Towards Uncovering the Role of Incomplete Penetrance in Maculopathies through Sequencing of 105 Disease-Associated Genes

Inherited macular dystrophies (iMDs) are a group of genetic disorders, which affect the central region of the retina. To investigate the genetic basis of iMDs, we used single-molecule Molecular Inversion Probes to sequence 105 maculopathy-associated genes in 1352 patients diagnosed with iMDs. Within this cohort, 39.8% of patients were considered genetically explained by 460 different variants in 49 distinct genes of which 73 were novel variants, with some affecting splicing. The top five most frequent causative genes were ABCA4 (37.2%), PRPH2 (6.7%), CDHR1 (6.1%), PROM1 (4.3%) and RP1L1 (3.1%). Interestingly, variants with incomplete penetrance were revealed in almost one-third of patients considered solved (28.1%), and therefore, a proportion of patients may not be explained solely by the variants reported. This includes eight previously reported variants with incomplete penetrance in addition to CDHR1:c.783G>A and CNGB3:c.1208G>A. Notably, segregation analysis was not routinely performed for variant phasing-a limitation, which may also impact the overall diagnostic yield. The relatively high proportion of probands without any putative causal variant (60.2%) highlights the need to explore variants with incomplete penetrance, the potential modifiers of disease and the genetic overlap between iMDs and age-related macular degeneration. Our results provide valuable insights into the genetic landscape of iMDs and warrant future exploration to determine the involvement of other maculopathy genes.

CACNA1F-related synaptic dysfunction: challenges diagnosing congenital stationary night blindness presenting without night blindness

OBJECTIVE

To describe pediatric patients with CACNA1F-associated incomplete X-linked congenital stationary night blindness presenting without nyctalopia, and review the causes leading to diagnosis delay.

DESIGN

Retrospective cohort.

METHODS

This was set in a single institution between 2004 and 2019. There were12 patients. The intervention or observation procedures used were clinical course, visual acuity, refractive error, images, electrophysiology, genetic testing, pedigree. The main outcome measures were cohort description and causes of diagnosis delay.

RESULTS

For these 12 cases, the referring diagnosis was congenital nystagmus (7), reduced best-corrected visual acuity (BCVA, 4), and progressive myopia (1). Nyctalopia was not a presenting symptom and developed in 4 patients during follow-up. Seven patients presented with nystagmus. All patients developed early-onset myopia. Myopia progressed more rapidly before age 6 than after (average 1.14 D vs 0.25 D) (p = 0.0033). The average final BCVA was 20/50 (20/30-20/150). Vision at presentation was correlated with final visual acuity (r2 = 0.87, p = 5.4E-06). The first cycloplegic refraction was correlated to the final refractive error (r2 = 0.49, p = 0.009). Patients with nystagmus had worse BCVA on average. Full-field electroretinogram was abnormal and diagnostic in all cases, as confirmed by genetic testing. The average time to diagnosis was 4.2 years, and the average age at diagnosis was 7.9 years. The delay in diagnosis was due to the absence of nyctalopia, not performing an electroretinogram and/or an alternative diagnosis.

CONCLUSIONS

In children, CACNA1F-associated synaptic dysfunction does not usually present with night blindness. It should be suspected in male patients with early-onset myopia, especially with a history of nystagmus.

Photoreceptor Ion Channels in Signaling and Disease

Photoreceptors (PRs) in the neural retina convert photon capture into an electrical signal that is communicated across a chemical synapse to second-order neurons in the retina and on through the rest of the visual pathway. This information is decoded in the visual cortex to create images. The activity of PRs depends on the concerted action of several voltage-gated ion channels that will be discussed in this chapter.

A New Zebrafish Model for CACNA2D4-Dysfunction

Purpose

Mutations in CACNA2D4, encoding the α2δ4 subunit of retinal voltage-gated calcium channels (Cav), cause a rare type of retinal dysfunction in human, mainly affecting cone vision. Here, we investigate the role of CACNA2D4 in targeting of Cav, its influence on cone-mediated signal transmission, and the cellular and subcellular changes upon loss of α2δ4 by exploiting the advantages of the cone-dominant zebrafish as model system.

Methods

We identified two zebrafish CACNA2D4 paralogs (cacna2d4a and cacna2d4b), analyzed their expression by RNA in situ hybridization and introduced truncating frameshift mutations through CRISPR/Cas9-mediated mutagenesis. We analyzed retinal function and morphology of the single and double mutant lines by electroretinography, immunohistochemistry, light- and electron microscopy.

Results

Knockout of cacna2d4b reduces the expression of Cacna1fa, the pore-forming subunit of retinal Cav1.4, whereas loss of cacna2d4a did not. Only knockout of both paralogs impaired cone-mediated ERG b-wave amplitude. The number of "floating" ribbons is increased in double-KO, while retinal morphology and expression of postsynaptic mGluR6b remain largely unaffected. Both Cacna1fa and Ribeyeb show ectopic punctate expression in cacna2d4b-KO and double-KO photoreceptors.

Conclusions

We find that increasing the expression of Cav at the synaptic membrane is an evolutionarily conserved function of Cacna2d4b. Yet, since both paralogs participate in cone synaptic transmission, we propose partial subfunctionalization in zebrafish. Similar to human patients, our double KO zebrafish model shows mild cone dysfunction, which was not associated with signs of retinal degeneration. Therefore, cacna2d4-KO zebrafish is a suitable model to study the pathophysiological mechanisms underlying CACNA2D4 dysfunction in human.

[Morphological and functional indicators of retinal pigment epithelium and photoreceptor apparatus in inherited retinal diseases]

PURPOSE

To evaluate the relationship between the morphological and functional parameters of retinal pigment epithelium (RPE) and photoreceptors (PR) in inherited retinal diseases (IRD).

MATERIAL AND METHODS

The study included 52 patients (104 eyes), 23 of them with Stargardt Disease (STGD), 19 with cone-rod dystrophy (CRD), 10 with retinitis pigmentosa/pigmentary abiotrophy (RP) of comparable disease durations. All patients underwent standard and additional ophthalmological examination: fundus autofluorescence (AF), spectral optical coherence tomography (OCT), computer perimetry (CP), electro-oculography (EOG), Ganzfeld electroretinography (gERG).

RESULTS

Comparison of the groups of IRD patients and groups according to the degree of RPE damage with the control group revealed an increase in differences in the EOG and gERG indicators as the area and depth of damage to the RPE and PR progressed. The patterns of changes in RPE and PR, the frequency of their occurrence with IRD in this patient sample are described. A moderate correlation was found between the amount of RPE loss and EOG light rise, as well as between the defect of the ellipsoid zone and the amplitude of α- and β-waves, the latency of β-wave of the gERG. Some patients showed a mismatch between a small defect of the ellipsoid zone and RPE with significant damage to the visual field and reduction of the EOG and gERG indicators. The obtained electrophysiological indicators revealed pathological changes in RPE and PR, more significant and widespread in some cases than it was shown with visualization methods. Weak and moderate correlations between visual acuity, and RPE damage and light sensitivity index with loss of ellipsoid zone were calculated.

CONCLUSIONS

Modern methods of retinal examination can help obtain complete and versatile picture of morphological and functional state of the retina in IDR that supplement each other. EOG and gERG have capability to determine the degree of RPE and PR functions impairment including those cases when morphological studies are not sufficiently informative.

Novel truncating mutation in CACNA1F in a young male patient diagnosed with optic atrophy

BACKGROUND

Low vision in children can be accompanied by pallor of the optic disc with little or no characteristic morphologic changes of the retina. A variety of diseases can be the underlying cause, including hereditary optic atrophy, Leber's congenital amaurosis (LCA), achromatopsia, and calcium channel, voltage-dependent, L-type, alpha-1F subunit gene (CACNA1F)-associated retinopathy (most widely known as incomplete congenital stationary night blindness: iCSNB). Differentiation at early age is desirable due to large differences in prognosis, but may be difficult because phenotypes overlap and electrophysiological testing is challenging in young patients. We present the case of a 6-year-old boy with unexplained low vision and pallor of the optic disc who originally had been diagnosed with hereditary optic atrophy in the absence of recordable full-field electroretinography (ERG) due to poor patient cooperation.

MATERIALS AND METHODS

Standard Sanger sequencing excluded mutations in the OPA1 gene (autosomal-dominant optic atrophy). To identify the underlying genetic cause, whole-exome sequencing was performed on patient's DNA. Recording of the full-field ERG was successfully performed 6 months later.

RESULTS

We identified a novel truncating mutation in CACNA1F gene (NM_001256789: c.3895C > T in exon 33) which led to the correct diagnosis of CACNA1F-associated retinopathy in the young boy. ERG recordings showed a negative scotopic mixed response with preserved oscillatory potentials and a flicker ERG with reduced amplitude and biphasic waveform, compatible with a CACNA1F-asssociated phenotype.

CONCLUSIONS

We show that genetic testing may help to differentiate between optic atrophy, LCA, and CACNA1F-associated retinopathy at a much earlier age, in absence of electrophysiological examination and by widely overlapping phenotypes.

Unexpected Genetic Cause in Two Female Siblings with High Myopia and Reduced Visual Acuity

In daily life, myopia is a frequent cause of reduced visual acuity (VA) due to missing or incomplete optical correction. While the genetic cause of high myopia itself is not well understood, a significant number of cases are secondary to hereditary malfunctions or degenerations of the retina. The mechanism by which this occurs remains yet unclear. Two female siblings, 4 y and 2 y, respectively, from a consanguineous Pakistani family were referred to our department for reduced VA and strabismus. Both girls were highly myopic and hence were further examined using standard clinical tests and electroretinography (ERG). The latter confirmed confounded electrical coupling of photoreceptors and bipolar cells. Further inquiry and testing confirmed a similar condition for the father including impaired night vision, reduced VA, photophobia, and an equally characteristic ERG. Findings in the mother were unremarkable. Subsequent genetic analysis of autosomal recessive and X-linked genes for congenital stationary night blindness (CSNB) revealed a novel homozygous splice site mutation in CACNA1F in the two girls transmitted from both the father and the mother. While in males the above clinical constellation is a frequent finding, this report, to the authors' knowledge, is the first demonstrating biallelic mutations at the CACNA1F locus in females.

A novel large in-frame deletion within the CACNA1F gene associates with a cone-rod dystrophy 3-like phenotype

Cone-rod dystrophies (CORDs) represent a heterogeneous group of monogenic diseases leading to early impairment of vision. The majority of CORD entities show autosomal modes of inheritance and X-linked traits are comparably rare. So far, three X-chromosomal entities were reported (CORDX1, -X2 and -X3). In this study, we analysed a large family of German origin with solely affected males over three generations showing a CORDX-like phenotype. Due to the heterogeneity of cone-rod dystrophies, we performed a combined linkage and X-exome sequencing approach and identified a novel large intragenic in-frame deletion encompassing exons 18 to 26 within the CACNA1F gene. CACNA1F is described causative for CORDX3 in a single family originating from Finland and alterations in this gene have not yet been reported in other CORDX pedigrees. Our data independently confirm CACNA1F as the causative gene for CORDX3-like phenotypes and detailed clinical characterization of the family expands the knowledge about the phenotypic spectrum of deleterious CACNA1F alterations.

Tilted disc syndrome and colour vision

PURPOSE

To study colour vision in patients with tilted disc syndrome.

METHODS

Colour vision was examined using Boström-Kugelberg (B-K) plates, Farnsworth-Munsell 100-hue test (FM-100) and Farnsworth panel D-15 and Lanthony desaturated panel tests.

RESULTS

A total of 35 eyes of 21 patients were examined. Seventeen eyes (49%) of 11 patients were found to have a colour vision defect in at least one eye. The severity of the colour vision defect differed between eyes for six of eight patients with bilateral tilted discs. In two of these patients, colour vision was normal in one eye. Seven patients had a unilateral tilted disc and three of these individuals had a colour vision defect in the affected eye. Of all eyes with a colour vision defect, a red-green defect was found in four eyes (24%), a blue defect in one eye (6%), and a mixed defect in 12 eyes (70%). Colour vision defects were not related to visual acuity or to severity of visual field defects.

CONCLUSIONS

This is the first report of colour vision defects in tilted disc syndrome. In the differential diagnosis of tilted disc syndrome, chiasmal lesions and glaucoma, the examination of colour vision may add valuable information. Further, it is recommended that young people with tilted disc syndrome undergo an examination of colour vision so that they can be given appropriate career guidance.

Novel locus for X linked recessive high myopia maps to Xq23-q25 but outside MYP1

BACKGROUND

High myopia is a common genetic variation in most cases, affecting 1-2% of people, and is the fourth most common disorder causing blindness worldwide. Six autosomal dominant loci and one X-linked recessive locus have been reported, but no genes responsible for high myopia have been identified.

OBJECTIVE

To report a Chinese family in which six males presented with high myopia consistent with an X linked recessive trait.

RESULTS

Affected individuals shared three common features: high myopia, reduced visual acuity, and fundal changes of high myopia. Protan and deutan were observed in the family, but they did not co-segregate with the high myopia phenotype. X-chromosome-wide linkage analysis mapped the high myopia locus to a 25 cM (14.9 Mb) region on Xq23-q25 between DXS1210 and DXS8057, with maximum two point lod scores at theta = 0 of 2.75 and 2.29 for DXS1001 and DXS8059, respectively.

CONCLUSIONS

This new myopia locus is outside the linked region of the first high myopia locus (MYP1). Refinement of the linkage region with additional families and screening candidate genes for mutation may lead to the identification of the defect gene.

X linked cone-rod dystrophy, CORDX3, is caused by a mutation in the CACNA1F gene

BACKGROUND

X linked cone-rod dystrophy (CORDX) is a recessive retinal disease characterised by progressive dysfunction of photoreceptors. It is genetically heterogeneous, showing linkage to three X chromosomal loci. CORDX1 is caused by mutations in the RPGR gene (Xp21.1), CORDX2 is located on Xq27.2-28, and we recently localised CORDX3 to Xp11.4-q13.1. We aimed to identify the causative gene behind the CORDX3 phenotype.

METHODS

All 48 exons of the CACNA1F gene were screened for mutations by DNA sequencing. RNA from cultured lymphoblasts and peripheral blood activated T lymphocytes was analysed by RT-PCR and sequencing.

RESULTS

A novel CACNA1F mutation, IVS28-1 GCGTC>TGG, in the splice acceptor site of intron 28 was identified. Messenger RNA studies indicated that the identified mutation leads to altered splicing of the CACNA1F transcript. Aberrant splice variants are predicted to result in premature termination and deletions of the encoded protein, Ca(v)1.4 alpha1 subunit.

CONCLUSION

CACNA1F mutations cause the retinal disorder, incomplete congenital stationary night blindness (CSNB2), although mutations have also been detected in patients with divergent diagnoses. Our results indicate that yet another phenotype, CORDX3, is caused by a mutation in CACNA1F. Clinically, CORDX3 shares some features with CSNB2 but is distinguishable from CSNB2 in that it is progressive, can begin in adulthood, has no nystagmus or hyperopic refraction, has only low grade astigmatism, and in dark adaptation lacks cone threshold and has small or no elevation of rod threshold. Considering all features, CORDX3 is more similar to other X chromosomal cone-rod dystrophies than to CSNB2.

Cone-rod dystrophy and acquired dissociated vertical nystagmus

Although usually a manifestation of vestibular or neurological disease, acquired nystagmus occasionally can be seen in ocular diseases such as ocular albinism and cone dystrophy. The present case of cone-rod dystrophy presenting with acquired dissociated vertical nystagmus probably demonstrates another unusual manifestation of cone-rod dystrophy.

A new genetic locus for X linked progressive cone-rod dystrophy

X linked progressive cone-rod dystrophy (COD) is a retinal disease primarily affecting the cone photoreceptors. The disease is genetically heterogeneous and two loci, COD1 (Xp21.1-11.4) and COD2 (Xq27.2-28), have been previously identified. COD1 was recently shown to be caused by mutations in RPGR exon ORF15 (Xp21.1), the gene that is also responsible for RP3 type retinitis pigmentosa. In this study, we performed a linkage study to map the disease gene in a large Finnish family with X linked cone-rod dystrophy, using a panel of 39 X chromosomal markers. Several recombinations between the disease gene and markers in the Xp21.1-p11.4 region have excluded COD1 as a candidate locus in this family. Consistent with the linkage results, no mutation was detected by direct PCR sequencing of the coding region of RPGR, including exon ORF15. The COD2 locus has been also excluded as the site of the gene on the basis of negative lod score values obtained for COD2 linked markers. The disease causing gene of the studied COD family has been localised between the markers DXS10042 and DXS8060 on Xp11.4-q13.1. Positive pairwise lod scores >3 were obtained for markers DXS993, MAOB, DXS1055, and DXS1194. Since this locus is distinct from the previously identified two loci, COD1 and COD2, our results establish a new third genetic locus for X linked progressive cone-rod dystrophy and further expands our knowledge about the genetic heterogeneity underlying this disease entity.

X-linked recessive atrophic macular degeneration from RPGR mutation

We mapped a new X-linked recessive atrophic macular degeneration locus to Xp21.1-p11.4 and show allelic involvement of the gene RPGR, which normally causes severe peripheral retinal degeneration leading to global blindness. Ten affected males whom we examined had primarily macular atrophy causing progressive loss of visual acuity with minimal peripheral visual impairment. One additional male showed extensive macular degeneration plus peripheral loss of retinal pigment epithelium and choriocapillaries. Full-field electroretinograms (ERGs) showed normal cone and rod responses in some affected males despite advanced macular degeneration, emphasizing the dissociation of atrophic macular degeneration from generalized cone degenerations, including X-linked cone dystrophy (COD1). The RPGR gene nonsense mutation G-->T at open reading frame (ORF)15+1164 cosegregated with the disease and may create a donor splice site. Identification of an RPGR mutation in atrophic maculardegeneration expands the phenotypic range associated with this gene and provides a new tool for the dissection of the relationship between clinically different retinal pathologies.