CHM gene molecular analysis and X-chromosome inactivation pattern determination in two families with choroideremia

Female carriers of X-linked inherited retinal diseases - Genetics, diagnosis, and potential therapies

Inherited retinal diseases (IRDs) are a group of heterogeneous conditions that cause progressive vision loss, typically due to monogenic mutations. Female carriers of X-linked IRDs have a single copy of the disease-causing gene, and therefore, may exhibit variable clinical signs that vary from near normal retina to severe disease and vision loss. The relationships between individual genetic mutations and disease severity in X-linked carriers requires further study. This review summarises the current literature surrounding the spectrum of disease seen in female carriers of choroideremia and X-linked retinitis pigmentosa. Various classification systems are contrasted to accurately grade retinal disease. Furthermore, genetic mechanisms at the early embryonic stage are explored to potentially explain the variability of disease seen in female carriers. Future research in this area will provide insight into the association between genotype and retinal phenotypes of female carriers, which will guide in the management of these patients. This review acknowledges the importance of identifying which patients may be at high risk of developing severe symptoms, and therefore should be considered for emerging treatments, such as retinal gene therapy.

Choroideremia: Toward Regulatory Approval of Retinal Gene Therapy

Choroideremia is an X-linked inherited retinal degeneration characterized by primary centripetal degeneration of the retinal pigment epithelium (RPE), with secondary degeneration of the choroid and retina. Affected individuals experience reduced night vision in early adulthood with blindness in late middle age. The underlying CHM gene encodes REP1, a protein involved in the prenylation of Rab GTPases essential for intracellular vesicle trafficking. Adeno-associated viral gene therapy has demonstrated some benefit in clinical trials for choroideremia. However, challenges remain in gaining regulatory approval. Choroideremia is slowly progressive, which presents difficulties in demonstrating benefit over short pivotal clinical trials that usually run for 1-2 years. Improvements in visual acuity are particularly challenging due to the initial negative effects of surgical detachment of the fovea. Despite these challenges, great progress toward a treatment has been made since choroideremia was first described in 1872.

A Novel Hypothesis on Choroideremia-Manifesting Female Carriers: Could CHM In-Frame Variants Exert a Dominant Negative Effect? A Case Report

Choroideremia is an X-linked recessive condition presenting in males, with progressive degeneration of retinal and choroidal tissues leading to progressive visual loss. Its pathological mechanism is due to alterations in the CHM gene that encodes for REP1, a protein required for prenylation of Rab by the Rab geranylgeranyl transferase (RGGT). Even though female carriers are predicted to be not affected by the disease, a wide phenotypic spectrum ranging from mild to severe cases has been reported in women. The reason why Choroideremia manifests in female carriers remains elusive. While X chromosome inactivation (XCI) skewing has been proposed as a leading putative mechanism, emerging evidence has shown that CHM could variably escape from XCI. We described a family with an initial clinical suspicion of Retinitis Pigmentosa in which a novel CHM pathogenic splicing variant was found by exome sequencing. The variant, initially found in the 63-year-old female presenting with impaired visual acuity and severe retinal degeneration, segregated in the 31-year-old daughter and the 37-year-old son, both presenting with fundus anomalies. mRNA studies revealed a shorter in-frame CHM isoform lacking exon 10. Molecular modeling of the ternary REP1/Rab/RGGT protein complex predicted significant impairing of REP1/Rab binding without alteration of REP1/RGGT interaction. We suggest that, in our female cases, the biallelic expression of CHM may have led to the production of both the mutant and wild type REP1. The mutant isoform, sequestrating RGGT, could reduce its available amount for Rab prenylation, thus exerting a dominant-negative effect. If confirmed with further studies and in large cohorts of female carriers, the here proposed molecular mechanism could help to explain the complexity of manifestation of Choroideremia in females.

Long-read technologies identify a hidden inverted duplication in a family with choroideremia

The lack of molecular diagnoses in rare genetic diseases can be explained by limitations of current standard genomic technologies. Upcoming long-read techniques have complementary strengths to overcome these limitations, with a particular strength in identifying structural variants. By using optical genome mapping and long-read sequencing, we aimed to identify the pathogenic variant in a large family with X-linked choroideremia. In this family, aberrant splicing of exon 12 of the choroideremia gene CHM was detected in 2003, but the underlying genomic defect remained elusive. Optical genome mapping and long-read sequencing approaches now revealed an intragenic 1,752 bp inverted duplication including exon 12 and surrounding regions, located downstream of the wild-type copy of exon 12. Both breakpoint junctions were confirmed with Sanger sequencing and segregate with the X-linked inheritance in the family. The breakpoint junctions displayed sequence microhomology suggestive for an erroneous replication mechanism as the origin of the structural variant. The inverted duplication is predicted to result in a hairpin formation of the pre-mRNA with the wild-type exon 12, leading to exon skipping in the mature mRNA. The identified inverted duplication is deemed the hidden pathogenic cause of disease in this family. Our study shows that optical genome mapping and long-read sequencing have significant potential for the identification of (hidden) structural variants in rare genetic diseases.

Molecular Characterization of Choroideremia-Associated Deletions Reveals an Unexpected Regulation of CHM Gene Transcription

Choroideremia (CHM) is a X-linked recessive chorioretinal dystrophy due to deficiency of the CHM gene product, i.e., Rab escort protein isoform 1 (REP1). To date, gene therapy for CHM has shown variable effectiveness, likely because the underlying pathogenic mechanisms as well as genotype-phenotype correlation are not yet fully known. Small nucleotide variants leading to premature termination codons (PTCs) are a major cause of CHM, but about 20% of patients has CHM gene deletions. To improve understanding of the disease mechanisms, we analyzed molecular features of seven deletions involving the CHM gene sequence. We mapped the deletion breakpoints by using polymerase chain reaction, sequencing and array comparative genomic hybridization; to identify rearrangement-promoting DNA sequences, we analyzed genomic architecture surrounding the breakpoint regions. Moreover, in some CHM patients with different mutation types, we measured transcript level of CHM and of CHML, encoding the REP2 isoform. Scattered along the whole CHM gene and in close proximity to the deletion breakpoints we found numerous repeat elements that generate a locus-specific rearrangement hot spot. Unexpectedly, patients with non-PTC variants had increased expression of the aberrant CHM mRNA; CHML expression was higher than normal in a patient lacking CHM and its putative regulatory sequences. This latest evidence suggests that mechanisms regulating CHM and CHML gene expression are worthy of further study, because their full knowledge could be also useful for developing effective therapies for this hitherto untreatable inherited retinal degeneration.

Choriocapillaris: Fundamentals and advancements

The choriocapillaris is the innermost structure of the choroid that directly nourishes the retinal pigment epithelium and photoreceptors. This article provides an overview of its hemovasculogenesis development to achieve its final architecture as a lobular vasculature, and also summarizes the current histological and molecular knowledge about choriocapillaris and its dysfunction. After describing the existing state-of-the-art tools to image the choriocapillaris, we report the findings in the choriocapillaris encountered in the most frequent retinochoroidal diseases including vascular diseases, inflammatory diseases, myopia, pachychoroid disease spectrum disorders, and glaucoma. The final section focuses on the development of imaging technology to optimize visualization of the choriocapillaris as well as current treatments of retinochoroidal disorders that specifically target the choriocapillaris. We conclude the article with pertinent unanswered questions and future directions in research for the choriocapillaris.

CHM mutation spectrum and disease: An update at the time of human therapeutic trials

Choroideremia is an X-linked inherited retinal disorder (IRD) characterized by the degeneration of retinal pigment epithelium, photoreceptors, choriocapillaris and choroid affecting males with variable phenotypes in female carriers. Unlike other IRD, characterized by a large clinical and genetic heterogeneity, choroideremia shows a specific phenotype with causative mutations in only one gene, CHM. Ongoing gene replacement trials raise further interests in this disorder. We describe here the clinical and genetic data from a French cohort of 45 families, 25 of which carry novel variants, in the context of 822 previously reported choroideremia families. Most of the variants represent loss-of-function mutations with eleven families having large (i.e. ≥6 kb) genomic deletions, 18 small insertions, deletions or insertion deletions, six showing nonsense variants, eight splice site variants and two missense variants likely to affect splicing. Similarly, 822 previously published families carry mostly loss-of-function variants. Recurrent variants are observed worldwide, some of which linked to a common ancestor, others arisen independently in specific CHM regions prone to mutations. Since all exons of CHM may harbor variants, Sanger sequencing combined with quantitative polymerase chain reaction or multiplex ligation-dependent probe amplification experiments are efficient to achieve the molecular diagnosis in patients with typical choroideremia features.

CHOROIDEREMIA: Retinal Degeneration With an Unmet Need

PURPOSE

Choroideremia is an incurable, X-linked, recessive retinal dystrophy caused by loss of function mutations in the CHM gene. It is estimated to affect approximately 1 in 50,000 male patients. It is characterized by progressive degeneration of the retinal pigment epithelium, choroid, and photoreceptors, resulting in visual impairment and blindness. There is an unmet need in choroideremia, because currently, there are no approved treatments available for patients with the disease.

METHODS

We review the patient journey, societal impact, and emerging treatments for patients with choroideremia.

RESULTS

Its relative rarity and similarities with other retinal diseases in early years mean that diagnosis of choroideremia can often be delayed. Furthermore, its impact on affected individuals, and wider society, is also likely underestimated. AAV2-mediated gene therapy is an investigational treatment that aims to replace the faulty CHM gene. Early-phase studies reported potentially important visual acuity gains and maintenance of vision in some patients, and a large Phase 3 program is now underway.

CONCLUSION

Choroideremia is a disease with a significant unmet need. Interventions that can treat progression of the disease and improve visual and functional outcomes have the potential to reduce health care costs and enhance patient quality of life.

Autofluorescence in female carriers with choroideremia: A familial case with a novel mutation in the CHM gene

BACKGROUND

Choroideremia is an X-linked chorioretinal dystrophy caused by mutations in the CHM gene. The main differential diagnosis is X-linked retinitis pigmentosa. Clinically, male patients that are affected by these two diseases have similar symptoms. This work aims to report a familial case of choroideremia initially diagnosed as X-linked retinitis pigmentosa with a novel mutation in the CHM gene, and the relevance of fundus autofluorescence (FAF) in female carriers.

MATERIALS AND METHODS

A complete ophthalmological evaluation was done in a 37-year-old woman and her 53-year-old maternal uncle; the uncle had been diagnosed previously with X-linked retinitis pigmentosa. A visual field test, FAF imaging, full-field electroretinography, and a genetic test were performed.

RESULTS

In the proband, the fundoscopy revealed diffuse changes in the retinal pigment epithelium in both eyes, and the FAF showed a speckled pattern of low- and high-density. The maternal uncle's ophthalmological evaluation showed choroidal and retinal atrophy consistent with choroideremia. The molecular analysis revealed a pathogenic variant in the CHM gene, c.190-1 G > T.

CONCLUSIONS

In female carriers of choroideremia and X-linked retinitis pigmentosa, differential diagnosis may be challenging. A speckled pattern of low- and high-density in autofluorescence is commonly found in female carriers of choroideremia. FAF is a powerful tool for making a correct clinical diagnosis because the pattern in FAF is much more apparent than the visible retinal changes obtained by fundoscopy. Although it is crucial to perform molecular analysis to confirm the diagnosis, FAF is useful when genetic testing may not be readily available.

Next-generation sequencing-based clinical diagnosis of choroideremia and comprehensive mutational and clinical analyses

Background

To report the clinical and genetic findings from seven Chinese patients with choroideremia.

Methods

Five hundred seventy-eight patients with a clinically suspected diagnosis of retinitis pigmentosa (RP) underwent comprehensive ophthalmic examinations. Next-generation sequencing (NGS) was performed on samples from all patients. Detailed clinical characteristics of the patients with choroideremia identified in this study were assessed using multimodal imaging.

Results

Seven patients with choroideremia were identified, and six novel variants in CHM (c.1960 T > C p.Ter654Gln, c.1257del p.Ile420*fs1, c.1103_1121delATGGCAACACTCCATTTTT p.Tyr368Cysfs35, c.1414-2A > T, and c.1213C > T p.Gln405Ter, c.117-1G > A) were revealed. All variants were deleterious mutations: two were frameshifts, two were nonsense mutations, two were splicing mutations, and one was a readthrough mutation. The clinical phenotypes of these patients were markedly heterogeneous, and they shared many common clinical features with RP, including night blindness, constriction of the visual field and gradually reduced visual acuity. However, patients with choroideremia showed pigment hypertrophy and clumping, and chorioretinal atrophy, and a majority of patients with choroideremia presented with retinal tubulations in the outer layer of the retina.

Conclusions

We provide a detailed description of the genotypes and phenotypes of seven patients with choroideremia who were accurately diagnosed using NGS. These findings provide a better understanding of the genetics and phenotypes of choroideremia.

Spectrum of Disease Severity and Phenotype in Choroideremia Carriers

PURPOSE

To characterize and bring awareness to the disease spectrum of female choroideremia patients, as severity can vary from mild to severe disease, comparable to that observed in male patients.

DESIGN

Retrospective cohort study.

METHODS

Twelve female carriers of disease-causing variants in the CHM gene confirmed by molecular genetic sequencing were characterized clinically and imaged with short-wave fundus autofluorescence (SW-FAF), spectral-domain optical coherence tomography (OCT), and color fundus imaging.

RESULTS

Twelve unrelated female patients with a clinical and genetic diagnosis of choroideremia carriers were included in this study. Disease severity among these phenotypes ranged from mild to severe, resembling the typical presentation of choroideremia in male patients. Mild disease presented with retinal pigment epithelium mottling, a patchy pattern of hypoautofluorescent speckles on SW-FAF, and intact retinal layers on spectral-domain OCT. Severe disease presented with widespread chorioretinal atrophy as shown by SW-FAF and spectral-domain OCT. Each of the identified genetic variants in CHM was predicted to be disease-causing according to in silico prediction software. Disease progression analysis of 4 patients with follow-up showed a decline in visual acuity for 2 patients, with progression observed on spectral-domain OCT in 1 of the patients. No significant disease progression on SW-FAF was observed for any of the patients.

CONCLUSIONS

Female carriers of choroideremia can present with a wide range of clinical phenotypes and disease severity, from mild to severe disease, similar to male subjects. Symptomatic female subjects should be considered for current and upcoming gene replacement therapy clinical trials.

Insights into Retinal Development Using Live Imaging in Female Carriers of Choroideremia

Lineage tracing can provide key insights into the development of tissues, such as the retina. Yet it is not possible to manipulate human cells during embryogenesis. The authors observed a distinct phenotype in female carriers of X-linked disorders, in particular, carriers of choroideremia caused by mutations in CHM, encoding Rab escort protein-1. The authors found that X chromosome inactivation provides a method for retinal lineage tracing in human patients. Live imaging of female carriers displays a developmental pattern that is different within the peripheral retina compared with the posterior retina and provides important insights into the development and migration of retinal cells. [Ophthalmic Surg Lasers Imaging Retina. 2019;50:e158-e162.].

Toward the Mutational Landscape of Autosomal Dominant Retinitis Pigmentosa: A Comprehensive Analysis of 258 Spanish Families

Purpose

To provide a comprehensive overview of the molecular basis of autosomal dominant retinitis pigmentosa (adRP) in Spanish families. Thus, we established the molecular characterization rate, gene prevalence, and mutational spectrum in the largest European cohort reported to date.

Methods

A total of 258 unrelated Spanish families with a clinical diagnosis of RP and suspected autosomal dominant inheritance were included. Clinical diagnosis was based on complete ophthalmologic examination and family history. Retrospective and prospective analysis of Spanish adRP families was carried out using a combined strategy consisting of classic genetic techniques and next-generation sequencing (NGS) for single-nucleotide variants and copy number variation (CNV) screening.

Results

Overall, 60% of our families were genetically solved. Interestingly, 3.1% of the cohort carried pathogenic CNVs. Disease-causing variants were found in an autosomal dominant gene in 55% of the families; however, X-linked and autosomal recessive forms were also identified in 3% and 2%, respectively. Four genes (RHO, PRPF31, RP1, and PRPH2) explained up to 62% of the solved families. Missense changes were most frequently found in adRP-associated genes; however, CNVs represented a relevant disease cause in PRPF31- and CRX-associated forms.

Conclusions

Implementation of NGS technologies in the adRP study clearly increased the diagnostic yield compared with classic approaches. Our study outcome expands the spectrum of disease-causing variants, provides accurate data on mutation gene prevalence, and highlights the implication of CNVs as important contributors to adRP etiology.

High-Resolution Retinal Imaging Reveals Preserved Cone Photoreceptor Density and Choroidal Thickness in Female Carriers of Choroideremia

BACKGROUND AND OBJECTIVE

To characterize the photoreceptors and choroidal morphology of heterozygous female carriers of choroideremia who typically do not have any visual defects but can have severe funduscopic changes.

PATIENTS AND METHODS

This was a clinical case series study. Detailed ophthalmic examinations were performed on six female carriers from four families with choroideremia. The subfoveal choroidal thickness (SFCT) was determined by spectral-domain optical coherence tomography (SD-OCT) and the cone photoreceptor density by adaptive optics (AO) retinal imaging. SFCT and cone densities of the carriers were compared to that of normal eyes of healthy subjects.

RESULTS

The mean age of the carriers was 42.5 years. Fundus photographs showed diffuse, patchy depigmentation; however, the SFCT was within the normal limits. AO retinal imaging revealed preserved cone densities at temporal eccentricities from 2 to 8 angular degrees.

CONCLUSIONS

The findings indicate that despite the presence of distinctive depigmentation of the retinal pigment epithelium in female carriers of choroideremia, their cone photoreceptor densities and SFCT are well-preserved. These observations may account for the good visual acuity and lack of an awareness of visual disturbances. [Ophthalmic Surg Lasers Imaging Retina. 2019;50:76-85.].

Novel CHM mutations in Polish patients with choroideremia - an orphan disease with close perspective of treatment

Background

Choroideremia (CHM) is a rare X-linked recessive retinal dystrophy characterized by progressive chorioretinal degeneration in the males affected. The symptoms include night blindness in childhood, progressive peripheral vision loss and total blindness in the late stages. The disease is caused by mutations in the CHM gene encoding Rab Escort Protein 1 (REP-1). The aim of the study was to identify the molecular basis of choroideremia in five families of Polish origin.

Methods

Six male patients from five unrelated families of Polish ethnicity, who were clinically diagnosed with choroideremia, were examined in this study. An ophthalmologic examination performed in all the probands included: best-corrected visual acuity, slit-lamp examination, funduscopy, fluorescein angiography and perimetry. The entire coding region encompassing 15 exons and the flanking intronic sequences of the CHM gene were amplified with PCR and directly sequenced in all the patients.

Results

Five variants in the CHM gene were identified in the five families examined. Two of the variants were new: c.1175dupT and c.83C > G, while three had been previously reported.

Conclusions

This study provides the first molecular genetic characteristics of patients with choroideremia from the previously unexplored Polish population.

A frameshift mutation in the CHM gene causes choroideremia with acute angle‑closure glaucoma

Choroideremia is an X‑linked recessive chorioretinal degenerative disease that is characterized by progressive centripetal loss of the photoreceptor, retinal pigment epithelium (RPE), and choriocapillaris layers. The CHM gene [choroideremia (Rab escort protein 1)] has been identified as the pathogenic gene in choroideremia. The aim of the present study was to describe the clinical and genetic characteristics of a family with choroideremia family. In the present study, a family with choroideremia presenting with serious chorioretinal atrophy and pigment proliferation, shallow anterior chambers, angle closure and high intraocular pressure (IOP) were recruited. The affected family members underwent a complete ophthalmologic examination. DNA samples obtained from the proband II:1 and the patient II:2 were used for targeted exome sequencing of the CHM gene. PCR amplification and Sanger sequencing were used to validate the variations exhibited in family members and controls. A novel frameshift mutation c.280delA (p.Thr94LeufsTer32), in CHM was identified in the male proband, the normal carrier I:2 and the phenotyped carrier II:2, which was absent in the normal individual II:3 as well as in 200 normal controls. Comparing the amino acid sequences of CHM between multiple species through Clustal Omega indicated conserved amino acids in these mutant sites. Additionally, an X‑chromosome inactivation (XCI) assay was performed in the female carriers in the family, in which DNA of the abnormal carrier II:2 and normal carrier I:2 showed a random XCI pattern. To conclude, the present findings strongly indicate that the c.280delA mutation is a disease‑causing mutation in our choroideremia pedigree with acute angle‑closure glaucoma.

Clinical applications of retinal gene therapies

Retinal degenerative diseases are a major cause of blindness. Retinal gene therapy is a trail-blazer in the human gene therapy field, leading to the first FDA approved gene therapy product for a human genetic disease. The application of Clustered Regularly Interspaced Short Palindromic Repeat/Cas9 (CRISPR/Cas9)-mediated gene editing technology is transforming the delivery of gene therapy. We review the history, present, and future prospects of retinal gene therapy.

Identification of the genetic determinants responsible for retinal degeneration in families of Mexican descent

PURPOSE

To investigate the clinical characteristics and genetic basis of inherited retinal degeneration (IRD) in six unrelated pedigrees from Mexico.

METHODS

A complete ophthalmic evaluation including measurement of visual acuities, Goldman kinetic or Humphrey dynamic perimetry, Amsler test, fundus photography, and color vision testing was performed. Family history and blood samples were collected from available family members. DNA from members of two pedigrees was examined for known mutations using the APEX ARRP genotyping microarray and one pedigree using the APEX LCA genotyping microarray. The remaining three pedigrees were analyzed using a custom-designed targeted capture array covering the exons of 233 known retinal degeneration genes. Sequencing was performed on Illumina HiSeq. Reads were mapped against hg19, and variants were annotated using GATK and filtered by exomeSuite. Segregation and ethnicity-matched control sample analyses were performed by dideoxy sequencing.

RESULTS

Six pedigrees with IRD were analyzed. Nine rare or novel, potentially pathogenic variants segregating with the phenotype were detected in IMPDH1, USH2A, RPE65, ABCA4, and FAM161A genes. Among these, six were known mutations while the remaining three changes in USH2A, RPE65, and FAM161A genes have not been previously reported to be associated with IRD. Analysis of 100 ethnicity-matched controls did not detect the presence of these three novel variants indicating, these are rare variants in the Mexican population.

CONCLUSIONS

Screening patients diagnosed with IRD from Mexico identified six known mutations and three rare or novel potentially damaging variants in IMPDH1, USH2A, RPE65, ABCA4, and FAM161A genes that segregated with disease.

The Role of X-Chromosome Inactivation in Retinal Development and Disease

The expression of X-linked genes is equalized between males and females in mammalian species through X-Chromosome inactivation (XCI). Every cell in a female mammalian embryo randomly chooses one X Chromosome for epigenetic silencing at the 8-16 cell stage, resulting in a Gaussian distribution of XCI ratios with a peak at 50:50. At the tail extremes of this distribution, X-linked recessive mutations can manifest in disease in female carriers if the mutant allele is disproportionately active. The role of XCI skewing, if any, in X-linked retinal disease is still unknown, although many have speculated that such skewing accounts for phenotypic variation in female carriers of X-linked retinitis pigmentosa (XlRP). Some investigators have used clinical findings such as tapetal-like reflex, pigmentary changes, and multifocal ERG parameters to approximate XCI patches in the retina. These studies are limited by small cohorts and the relative inaccessibility of retinal tissue for genetic and epigenetic analysis. Although blood has been used as a proxy for other tissues in determining XCI ratios, blood XCI skews with age out of proportion to other tissues and may not accurately reflect retinal XCI ratios. Future investigations in determining retinal XCI ratios and the contribution of XCI to phenotype could potentially impact prognosis for female carriers of X-linked retinal disease.

Pathogenic mechanisms and the prospect of gene therapy for choroideremia

INTRODUCTION

Choroideremia is a rare, X-linked disorder recognized by its specific ocular phenotype as a progressive degenerative retinopathy resulting in blindness. New therapeutic approaches, primarily based on genetic mechanisms, have emerged that aim to prevent the progressive vision loss.

AREAS COVERED

This article will review the research that has progressed incrementally over the past two decades from mapping to gene discovery, uncovering the presumed mechanisms triggering the retinopathy to preclinical testing of potential therapies.

EXPERT OPINION

While still in an evaluative phase, the introduction of gene replacement as a potential therapy has been greeted with great enthusiasm by patients, advocacy groups and the medical community.

AAV-mediated gene therapy for choroideremia: preclinical studies in personalized models

Choroideremia (CHM) is an X- linked retinal degeneration that is symptomatic in the 1^st or 2^nd decade of life causing nyctalopia and loss of peripheral vision. The disease progresses through mid-life, when most patients become blind. CHM is a favorable target for gene augmentation therapy, as the disease is due to loss of function of a protein necessary for retinal cell health, Rab Escort Protein 1 (REP1).The CHM cDNA can be packaged in recombinant adeno-associated virus (rAAV), which has an established track record in human gene therapy studies, and, in addition, there are sensitive and quantitative assays to document REP1 activity. An animal model that accurately reflects the human condition is not available. In this study, we tested the ability to restore REP1 function in personalized in vitro models of CHM: lymphoblasts and induced pluripotent stems cells (iPSCs) from human patients. The initial step of evaluating safety of the treatment was carried out by evaluating for acute retinal histopathologic effects in normal-sighted mice and no obvious toxicity was identified. Delivery of the CHM cDNA to affected cells restores REP1 enzymatic activity and also restores proper protein trafficking. The gene transfer is efficient and the preliminary safety data are encouraging. These studies pave the way for a human clinical trial of gene therapy for CHM.

Clinical characteristics of a large choroideremia pedigree carrying a novel CHM mutation

OBJECTIVE

To describe a large family with a novel mutation in CHM.

METHODS

Family members were characterized using clinical examination, wide-field fundus photography, wide-field autofluorescence, and spectral domain optical coherence tomography. The CHM mutation was identified with the National Institutes of Health-sponsored eyeGene program.

RESULTS

A novel nonsense CHM mutation (T1194G), resulting in a premature stop (Y398X) and loss of the final one-third C-terminal portion of the protein, was identified. A large pedigree was generated from information provided by the twice-married proband. Seven men (aged 27-39 years) and 7 women (aged 22-89 years) were evaluated. Affected men showed characteristic peripheral chorioretinal atrophy with islands of macular sparing. Female carriers exhibited a wide range of variability, from mild pigmentary alterations to significant chorioretinal atrophy with severe vision loss. Older women tended to have a more severe phenotype. Autofluorescence demonstrating subfoveal loss or absence of retinal pigment epithelium correlated with vision loss in both sexes. Spectral domain optical coherence tomography demonstrated dynamic changes and remodeling of the outer retina over time, including focal thickening, drusenlike deposits, and disruption to photoreceptor inner segment and outer segment junctions in young female carriers.

CONCLUSIONS

CHM (T1194G) is a novel mutation that manifests a wide range of phenotypic variability in a single family with a trend toward more severe phenotypes in older female carriers. Our findings emphasize the importance of considering X-linked diseases by carefully evaluating pedigrees in women with severe manifestations of disease.

CLINICAL RELEVANCE

These findings demonstrate a novel CHM mutation that emphasizes severe posterior pole carrier phenotypes, age-related changes, and early choroideremia disease.