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

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.

Optic nerve involvement in CACNA1F-related disease: observations from a multicentric case series

BACKGROUND

Congenital Stationary Night Blindness (CSNB) constitutes a group of non-progressive retinal disorders characterized by disturbances in scotopic vision and/or by a delay in adaptation to darkness, as well as by low visual acuity, myopia, nystagmus, and strabismus. Color vision and fundus appearance tend to be normal. To date, several CACNA1F gene variants have been linked to a CSNB phenotype but only few reports have focused on the optic nerve in this disease.

MATERIALS AND METHODS

Twelve patients underwent standard ophthalmological and genetic evaluation including spectral domain optical coherence tomography (SD-OCT), full-field electroretinography (ffERG), kinetic perimetry, fundus photography, magnetic resonance imaging (MRI), and next-generation sequencing (NGS). Bilateral thinning of the peripapillary nerve fiber layer (pRNFL) and the ganglion cell complex (GCC) supported involvement of the optic nerves. MRI, when available, was assessed for gross intracranial optic pathway abnormalities.

RESULTS

All patients were shown to carry pathogenic variants in the CACNA1F gene, and all showed signs of optic nerve involvement. All patients showed a certain degree of myopic refractive error. Low average pRNFL thickness was evident in all patients. In three of them, pRNFL thickness was evaluated longitudinally and was proven to be stable over time. MRI imaging was unremarkable in all cases.

CONCLUSION

Our data support the hypothesis that CACNA1F could be related to early-onset or congenital optic nerve involvement without any signs of a progressive optic neuropathy. Even though additional data from larger cohorts and longer follow-up periods are needed to further support and confirm our findings, there is a clear significance to our findings in the preparation for future CACNA1F gene therapy trials.

Concomitant Calcium Channelopathies Involving CACNA1A and CACNA1F: A Case Report and Review of the Literature

Calcium channels are an integral component in maintaining cellular function. Alterations may lead to channelopathies, primarily manifested in the central nervous system. This study describes the clinical and genetic features of a unique 12-year-old boy harboring two congenital calcium channelopathies, involving the CACNA1A and CACNA1F genes, and provides an unadulterated view of the natural history of sporadic hemiplegic migraine type 1 (SHM1) due to the patient's inability to tolerate any preventative medication. The patient presents with episodes of vomiting, hemiplegia, cerebral edema, seizure, fever, transient blindness, and encephalopathy. He is nonverbal, nonambulatory, and forced to have a very limited diet due to abnormal immune responses. The SHM1 manifestations apparent in the subject are consistent with the phenotype described in the 48 patients identified as part of a systematic literature review. The ocular symptoms of CACNA1F align with the family history of the subject. The presence of multiple pathogenic variants make it difficult to identify a clear phenotype-genotype correlation in the present case. Moreover, the detailed case description and natural history along with the comprehensive review of the literature contribute to the understanding of this complex disorder and point to the need for comprehensive clinical assessments of SHM1.

Identification of a novel CACNA1F mutation in a Chinese family with CORDX3

BACKGROUND

X-linked cone-rod dystrophy (CORDX) is one form of inherited retinal disorders (IRDs) characterized by progressive dysfunction of photoreceptor. Three types of CORDX were reported and CACNA1F gene defect can cause CORDX3. The aim of this study was to investigate the pathogenic variant in a Chinese family with IRD.

METHODS

The two affected subjects including the proband and his elder sister underwent ophthalmic examinations. Whole exome sequencing (WES) was performed in the proband at first, then co-segregation analysis was performed in the family by Sanger sequencing. Minigene approach was used to verify the effect of the mutation on the splicing of CACNA1F. X-chromosomal inactivation assay was performed to evaluate the inactivation patterns of the female carriers.

RESULTS

The ophthalmic examination results of the proband fit the clinical description of CORDX3, and the female patient presented with only mild symptoms due to mildly skewed X-chromosomal inactivation (ratio 67: 33). Molecular genetic testing identified a novel splice-site mutation c.3847-2A > G in CACNA1F (NM_005183.4) gene in the patients, which inherited from their asymptomatic mother. Minigene approach confirmed that c.3847-2A > G could affect the splicing of CACNA1F.

CONCLUSION

Our study identified a novel splice-site mutation in the CACNA1F gene, which expanded the mutational spectrum of CACNA1F-releated diseases and demonstrated the importance of combining clinical and genetic testing in the diagnosis of IRDs.

Cav1.4 dysfunction and congenital stationary night blindness type 2

Cav1.4 L-type Ca2+ channels are predominantly expressed in retinal neurons, particularly at the photoreceptor terminals where they mediate sustained Ca2+ entry needed for continuous neurotransmitter release at their ribbon synapses. Cav1.4 channel gating properties are controlled by accessory subunits, associated regulatory proteins, and also alternative splicing. In humans, mutations in the CACNA1F gene encoding for Cav1.4 channels are associated with X-linked retinal disorders such as congenital stationary night blindness type 2. Mutations in the Cav1.4 protein result in a spectrum of altered functional channel activity. Several mouse models broadened our understanding of the role of Cav1.4 channels not only as Ca2+ source at retinal synapses but also as synaptic organizers. In this review, we highlight different structural and functional phenotypes of Cav1.4 mutations that might also occur in patients with congenital stationary night blindness type 2. A further important yet mostly neglected aspect that we discuss is the influence of alternative splicing on channel dysfunction. We conclude that currently available functional phenotyping strategies should be refined and summarize potential specific therapeutic options for patients carrying Cav1.4 mutations. Importantly, the development of new therapeutic approaches will permit a deeper understanding of not only the disease pathophysiology but also the physiological function of Cav1.4 channels in the retina.

Optic Atrophy and Inner Retinal Thinning in CACNA1F-related Congenital Stationary Night Blindness

Hemizygous pathogenic variants in CACNA1F lead to defective signal transmission from retinal photoreceptors to bipolar cells and cause incomplete congenital stationary night blindness in humans. Although the primary defect is at the terminal end of first-order neurons (photoreceptors), there is limited knowledge of higher-order neuronal changes (inner retinal) in this disorder. This study aimed to investigate inner retinal changes in CACNA1F-retinopathy by analyzing macular ganglion cell layer-inner plexiform layer (GCL-IPL) thickness and optic disc pallor in 22 subjects with molecularly confirmed CACNA1F-retinopathy. Detailed ocular phenotypic data including distance and color vision, refraction and electroretinogram (ERG) were collected. Distance vision was universally reduced (mean: 0.42 LogMAR), six had abnormal color vision and myopia was common (n = 15; mean: −6.32 diopters). Mean GCL-IPL thickness was significantly lower in patients (55.00 µm) compared to age-matched controls (n = 87; 84.57 µm; p << 0.001). The GCL-IPL thickness correlated with scotopic standard (p = 0.04) and bright-flash (p = 0.014) ERG b/a ratios and photopic b-wave amplitudes (p = 0.05). Twenty-one patients had some degree of disc pallor (bilateral in 19). Fifteen putative disease-causing, including five novel variants were identified. This study establishes macular inner retinal thinning and optic atrophy as characteristic features of CACNA1F-retinopathy, which are independent of myopia and could impact potential future treatment strategies.