Leber's congenital amaurosis with anterior keratoconus in Pakistani families is caused by the Trp278X mutation in the AIPL1 gene on 17p

Pediatric keratoconus

Keratoconus is a common pediatric corneal disease, leading to vision impairment and amblyopia. Compared to its adult counterpart, pediatric keratoconus has an advanced presentation, rapid progression, higher incidence of complications such as corneal hydrops, and greater potential impact on the quality of life. It typically manifests during puberty and can evolve rapidly to more severe stages if left untreated. This rapid progression underscores the importance of early diagnosis through regular screening in pediatric populations and vigilant monitoring of pediatric keratoconus suspects. Concomitant ocular allergies, ocular anomalies, systemic diseases (e.g. syndromes), and poor compliance with contact lenses might impede prompt intervention and frequently postpone rehabilitation. Corneal collagen crosslinking is a crucial intervention in the management of pediatric keratoconus because it strengthens the corneal microstructure and halts the disease progression. When conservative measures fail, keratoplasty remains a viable option with generally favorable outcomes, though with unique challenges in post-operative care, including concerns related to sutures, long-term graft survival and need for repeated examinations under anesthesia. A multidisciplinary approach involving ophthalmologists, optometrists, pediatricians, and other healthcare professionals, focusing on early diagnosis and timely intervention, is essential for the comprehensive management of pediatric keratoconus and to mitigate its impact on children's lives.

Clinical and Molecular Characterization of AIPL1-Associated Leber Congenital Amaurosis/Early-Onset Severe Retinal Dystrophy

PURPOSE

This study aimed to characterize the clinical features, genetic findings, and genotype-phenotype correlations of patients with Leber congenital amaurosis (LCA) or early-onset severe retinal dystrophy (EOSRD) harboring biallelic AIPL1 pathogenic variants.

DESIGN

Retrospective case series.

METHODS

This study consecutively enrolled 51 patients from 47 families with a clinical diagnosis of LCA/EOSRD harboring disease-causing variants in the AIPL1 gene, from October 2021 to September 2023. Molecular genetic findings, medical history, and ophthalmic evaluation including visual acuity (VA), multimodal retinal imaging, and electrophysiologic assessment were reviewed.

RESULTS

Of the 51 patients (32 with LCA and 19 with EOSRD), 27 (53%) were females, and age at last review ranged from 0.5 to 58.4 years. We identified 28 disease-causing AIPL1 variants, with 18 being novel. In patients with EOSRD, the mean (range) VA was 1.3 (0.7-2.7) logMAR and 1.3 (0.5-2.3) logMAR for right and left eyes respectively, with an average annual decline of 0.03 logMAR (R2 = 0.7547, P < .01). For patients with LCA, the VA ranged from light perception to counting fingers. Optical coherence tomography imaging demonstrated preservation of foveal ellipsoid zone in the 5 youngest EOSRD patients and 9 LCA children. Electroretinography showed severe cone-rod patterns in 78.6% (11/14) of patients with EOSRD, while classical extinguished pattern was documented in all patients with LCA available for the examination. The most common mutation was the nonsense variants of c.421C>T, with an allele frequency of 53.9%. All patients with EOSRD carried at least one missense mutation, of whom 13 identified with c.152A>G and 5 with c.572T>C. Twenty-six patients with LCA harbored two null AIPL1 variants, while 18 were homozygous for c.421C>T and 6 were heterozygous for c.421C>T with another loss-of-function variant.

CONCLUSIONS

This study reveals distinct clinical features and variation spectrum between AIPL1-associated LCA and EOSRD. Patients harboring at least one nonnull mutation, especially c.152A>G and c.572T>C, were significantly more likely to have a milder EOSRD phenotype than those with two null mutations. Residual foveal outer retinal structure observed in the youngest proportion of patients suggests an early window for gene augmentation therapy.

Genotypic and phenotypic characterisation of RP2- and RPGR-associated X-linked inherited retinal dystrophy, including female manifestations

BACKGROUND

With the promise of gene replacement therapy, eligible males and females with X-linked inherited retinal dystrophy (XL-IRD) should be identified.

METHODS

Retrospective observational cohort study to establish the phenotypic and genotypic spectrum of XL-IRD within New Zealand (NZ). Thirty-two probands, including 9 females, with molecularly proven XL-IRD due to RP2 or RPGR mutations, and 72 family members, of which 43 were affected, were identified from the NZ IRD Database. Comprehensive ophthalmic phenotyping, familial cosegregation, genotyping, and bioinformatics were undertaken. Main outcome measures were: RP2 and RPGR pathogenic variant spectrum, phenotype in males and females (symptoms, age of onset, visual acuity, refraction, electrophysiology, autofluorescence, retinal appearance), and genotype-phenotype correlation.

RESULTS

For 32 families, 26 unique pathogenic variants were identified; in RP2 (n = 6, 21.9% of all families), RPGR exons 1-14 (n = 10, 43.75%), and RPGR-ORF15 (n = 10, 34.3%). Three RP2 and 8 RPGR exons 1-14 variants are novel, rare, and cosegregate. Thirty-one percent of carrier females were significantly affected, with 18.5% of families initially classified as autosomal dominant. Of five Polynesian families, 80% had novel disease-causing variants. One Māori family showed keratoconus segregating with an ORF15 variant.

CONCLUSIONS

Significant disease was present in 31% of genetically proven female carriers, often leading to an erroneous presumption of the inheritance pattern. Pathogenic variants in 44% of the families were in exon 1-14 of RPGR, more frequent than usually described, which may inform the gene testing algorithm. Proving cosegregation in families for novel variants and identifying affected females and males translates to optimised clinical care and potential for gene therapy.

Keratoconus: An updated review

Keratoconus is a bilateral and asymmetric disease which results in progressive thinning and steeping of the cornea leading to irregular astigmatism and decreased visual acuity. Traditionally, the condition has been described as a noninflammatory disease; however, more recently it has been associated with ocular inflammation. Keratoconus normally develops in the second and third decades of life and progresses until the fourth decade. The condition affects all ethnicities and both sexes. The prevalence and incidence rates of keratoconus have been estimated to be between 0.2 and 4,790 per 100,000 persons and 1.5 and 25 cases per 100,000 persons/year, respectively, with highest rates typically occurring in 20- to 30-year-olds and Middle Eastern and Asian ethnicities. Progressive stromal thinning, rupture of the anterior limiting membrane, and subsequent ectasia of the central/paracentral cornea are the most commonly observed histopathological findings. A family history of keratoconus, eye rubbing, eczema, asthma, and allergy are risk factors for developing keratoconus. Detecting keratoconus in its earliest stages remains a challenge. Corneal topography is the primary diagnostic tool for keratoconus detection. In incipient cases, however, the use of a single parameter to diagnose keratoconus is insufficient, and in addition to corneal topography, corneal pachymetry and higher order aberration data are now commonly used. Keratoconus severity and progression may be classified based on morphological features and disease evolution, ocular signs, and index-based systems. Keratoconus treatment varies depending on disease severity and progression. Mild cases are typically treated with spectacles, moderate cases with contact lenses, while severe cases that cannot be managed with scleral contact lenses may require corneal surgery. Mild to moderate cases of progressive keratoconus may also be treated surgically, most commonly with corneal cross-linking. This article provides an updated review on the definition, epidemiology, histopathology, aetiology and pathogenesis, clinical features, detection, classification, and management and treatment strategies for keratoconus.

Inferior Spear-like Lens Opacity as a Sign of Keratoconus

Purpose

To report 21 cases of typical inferior feather-shape lens opacity associated with keratoconus.

Methods

In this cross-sectional study, we evaluated the association of keratoconus with inferior feather-shape lens opacity in refractive surgery candidates. Visual acuity, demographic, refractive, and topographic characteristics of 26 eyes of 21 patients with inferior feather-shape lens opacity were evaluated in detail. Pedigree analysis was also performed to assess possible inheritance.

Results

Overall, 2122 out of 33,368 cases (6.4%) without lens opacity had keratoconus, while 20 out of 21 patients (95.2%) with peculiar lens opacity had definite keratoconus (P < 0.001). Lens opacity was bilateral in 5 cases (24%), and keratoconus was bilateral in all 20 patients with lens opacity. Nine eyes out of thirty-six with a complete data record (25%) had a severe keratoconus and underwent deep lamellar keratoplasty, while 11 (31%) had forme fruste keratoconus. Pedigrees were drawn for eight patients, most families of whom suggested an X-linked recessive inheritance.

Conclusion

The present study was the first to investigate patients with a peculiar inferior feather-shape lens opacity accompanied by bilateral keratoconus, which was observed in 95% of the patients. This finding should raise awareness as to the possibility of diagnosing keratoconus in the eyes of the patients with these characteristics.

Novel mutations in PDE6A and CDHR1 cause retinitis pigmentosa in Pakistani families

AIM

To investigate the genetic basis of autosomal recessive retinitis pigmentosa (arRP) in two consanguineous/ endogamous Pakistani families.

METHODS

Whole exome sequencing (WES) was performed on genomic DNA samples of patients with arRP to identify disease causing mutations. Sanger sequencing was performed to confirm familial segregation of identified mutations, and potential pathogenicity was determined by predictions of the mutations' functions.

RESULTS

A novel homozygous frameshift mutation [NM_000440.2:c.1054delG, p. (Gln352Argfs*4); Chr5:g.149286886del (GRCh37)] in the PDE6A gene in an endogamous family and a novel homozygous splice site mutation [NM_033100.3:c.1168-1G>A, Chr10:g.85968484G>A (GRCh37)] in the CDHR1 gene in a consanguineous family were identified. The PDE6A variant p. (Gln352Argfs*4) was predicted to be deleterious or pathogenic, whilst the CDHR1 variant c.1168-1G>A was predicted to result in potential alteration of splicing.

CONCLUSION

This study expands the spectrum of genetic variants for arRP in Pakistani families.

PPIP5K2 and PCSK1 are Candidate Genetic Contributors to Familial Keratoconus

Keratoconus (KC) is the most common corneal ectatic disorder affecting >300,000 people in the US. KC normally has its onset in adolescence, progressively worsening through the third to fourth decades of life. KC patients report significant impaired vision-related quality of life. Genetic factors play an important role in KC pathogenesis. To identify novel genes in familial KC patients, we performed whole exome and genome sequencing in a four-generation family. We identified potential variants in the PPIP5K2 and PCSK1 genes. Using in vitro cellular model and in vivo gene-trap mouse model, we found critical evidence to support the role of PPIP5K2 in normal corneal function and KC pathogenesis. The gene-trap mouse showed irregular corneal surfaces and pathological corneal thinning resembling KC. For the first time, we have integrated corneal tomography and pachymetry mapping into characterization of mouse corneal phenotypes which could be widely implemented in basic and translational research for KC diagnosis and therapy in the future.

Molecular and Histopathological Changes Associated with Keratoconus

Keratoconus (KC) is a corneal thinning disorder that leads to loss of visual acuity through ectasia, opacity, and irregular astigmatism. It is one of the leading indicators for corneal transplantation in the Western countries. KC usually starts at puberty and progresses until the third or fourth decade; however its progression differs among patients. In the keratoconic cornea, all layers except the endothelium have been shown to have histopathological structural changes. Despite numerous studies in the last several decades, the mechanisms of KC development and progression remain unclear. Both genetic and environmental factors may contribute to the pathogenesis of KC. Many previous articles have reviewed the genetic aspects of KC, but in this review we summarize the histopathological features of different layers of cornea and discuss the differentially expressed proteins in the KC-affected cornea. This summary will help emphasize the major molecular defects in KC and identify additional research areas related to KC, potentially opening up possibilities for novel methods of KC prevention and therapeutic intervention.

Homozygosity mapping and targeted sanger sequencing reveal genetic defects underlying inherited retinal disease in families from pakistan

Background

Homozygosity mapping has facilitated the identification of the genetic causes underlying inherited diseases, particularly in consanguineous families with multiple affected individuals. This knowledge has also resulted in a mutation dataset that can be used in a cost and time effective manner to screen frequent population-specific genetic variations associated with diseases such as inherited retinal disease (IRD).

Methods

We genetically screened 13 families from a cohort of 81 Pakistani IRD families diagnosed with Leber congenital amaurosis (LCA), retinitis pigmentosa (RP), congenital stationary night blindness (CSNB), or cone dystrophy (CD). We employed genome-wide single nucleotide polymorphism (SNP) array analysis to identify homozygous regions shared by affected individuals and performed Sanger sequencing of IRD-associated genes located in the sizeable homozygous regions. In addition, based on population specific mutation data we performed targeted Sanger sequencing (TSS) of frequent variants in AIPL1, CEP290, CRB1, GUCY2D, LCA5, RPGRIP1 and TULP1, in probands from 28 LCA families.

Results

Homozygosity mapping and Sanger sequencing of IRD-associated genes revealed the underlying mutations in 10 families. TSS revealed causative variants in three families. In these 13 families four novel mutations were identified in CNGA1, CNGB1, GUCY2D, and RPGRIP1.

Conclusions

Homozygosity mapping and TSS revealed the underlying genetic cause in 13 IRD families, which is useful for genetic counseling as well as therapeutic interventions that are likely to become available in the near future.

The genetics of keratoconus

Keratoconus is a bilateral, non-inflammatory corneal ectasia characterized by progressive conical thinning and protrusion of the cornea. Its etiology has long been believed to be multifactorial, with environmental, behavioral, and genetic factors all contributing to the disease process. This review focuses specifically on examining the evidence that supports a genetic basis for keratoconus.

The molecular basis of retinal dystrophies in pakistan

The customary consanguineous nuptials in Pakistan underlie the frequent occurrence of autosomal recessive inherited disorders, including retinal dystrophy (RD). In many studies, homozygosity mapping has been shown to be successful in mapping susceptibility loci for autosomal recessive inherited disease. RDs are the most frequent cause of inherited blindness worldwide. To date there is no comprehensive genetic overview of different RDs in Pakistan. In this review, genetic data of syndromic and non-syndromic RD families from Pakistan has been collected. Out of the 132 genes known to be involved in non-syndromic RD, 35 different genes have been reported to be mutated in families of Pakistani origin. In the Pakistani RD families 90% of the mutations causing non-syndromic RD and all mutations causing syndromic forms of the disease have not been reported in other populations. Based on the current inventory of all Pakistani RD-associated gene defects, a cost-efficient allele-specific analysis of 11 RD-associated variants is proposed, which may capture up to 35% of the genetic causes of retinal dystrophy in Pakistan.

Spontaneous activity promotes synapse formation in a cell-type-dependent manner in the developing retina

Spontaneous activity is thought to regulate synaptogenesis in many parts of the developing nervous system. In vivo evidence for this regulation, however, is scarce and comes almost exclusively from experiments in which normal activity was reduced or blocked completely. Thus, whether spontaneous activity itself promotes synaptogenesis or plays a purely permissive role remains uncertain. In addition, how activity influences synapse dynamics to shape connectivity and whether its effects among neurons are uniform or cell-type-dependent is unclear. In mice lacking the cone-rod homeobox gene (Crx), photoreceptors fail to establish normal connections with bipolar cells (BCs). Here, we find that retinal ganglion cells (RGCs) in Crx⁻/⁻ mice become rhythmically hyperactive around the time of eye opening as a result of increased spontaneous glutamate release from BCs. This elevated neurotransmission enhances synaptogenesis between BCs and RGCs, without altering the overall circuit architecture. Using live imaging, we discover that spontaneous activity selectively regulates the rate of synapse formation, not elimination, in this circuit. Reconstructions of the connectivity patterns of three BC types with a shared RGC target further revealed that neurotransmission specifically promotes the formation of multisynaptic appositions from one BC type without affecting the maintenance or elimination of connections from the other two. Although hyperactivity in Crx⁻/⁻ mice persists, synapse numbers do not increase beyond 4 weeks of age, suggesting closure of a critical period for synaptic refinement in the inner retina. Interestingly, despite their hyperactivity, RGC axons maintain normal eye-specific territories and cell-type-specific layers in the dorsal lateral geniculate nucleus.

The Genetics of Keratoconus: A Review

Keratoconus is the most common ectatic disorder of the corneal. Genetic and environmental factors may contribute to its pathogenesis. The focus of this article is to summarize current research into the complex genetics of keratoconus. We discuss the evidence of genetic etiology including family-based linkage studies, twin studies, genetic mutations, and genome-wide association studies. The genes implicated potentially include VSX1, miR-184, DOCK9, SOD1, RAB3GAP1, and HGF. Besides the coding mutations, we also highlight the potential contribution of DNA copy number variants in the pathogenesis of keratoconus. Finally, we present future directions for genetic research in the understanding of the complex genetics of keratoconus and its clinical significance. As new functional, candidate genes for keratoconus are being discovered at a rapid pace, the molecular genetic mechanisms underlying keratoconus pathogenesis will advance our understanding of keratoconus and promote the development of a novel therapy.

Keratoconus: a review

Keratoconus is the most common primary ectasia. It usually occurs in the second decade of life and affects both genders and all ethnicities. The estimated prevalence in the general population is 54 per 100,000. Ocular signs and symptoms vary depending on disease severity. Early forms normally go unnoticed unless corneal topography is performed. Disease progression is manifested with a loss of visual acuity which cannot be compensated for with spectacles. Corneal thinning frequently precedes ectasia. In moderate and advance cases, a hemosiderin arc or circle line, known as Fleischer's ring, is frequently seen around the cone base. Vogt's striaes, which are fine vertical lines produced by Descemet's membrane compression, is another characteristic sign. Most patients eventually develop corneal scarring. Munson's sign, a V-shape deformation of the lower eyelid in downward position; Rizzuti's sign, a bright reflection from the nasal area of the limbus when light is directed to the limbus temporal area; and breakages in Descemet's membrane causing acute stromal oedema, known as hydrops, are observed in advanced stages. Classifications based on morphology, disease evolution, ocular signs and index-based systems of keratoconus have been proposed. Theories into the genetic, biomechanical and biochemical causes of keratoconus have been suggested. Management varies depending on disease severity. Incipient cases are managed with spectacles, mild to moderate cases with contact lenses and severe cases can be treated with keratoplasty. This article provides a review on the definition, epidemiology, clinical features, classification, histopathology, aetiology and pathogenesis, and management and treatment strategies for keratoconus.

Management of acute hydrops with perforation in a patient with keratoconus and cone dystrophy: case report and literature review

PURPOSE

To describe a patient with cone dystrophy who presented with acute hydrops and perforation, leading to the diagnosis of keratoconus.

METHODS

Case report and literature review.

RESULTS

A 21 -year-old male patient with a history of cone dystrophy presented with a flat anterior chamber, diffuse corneal stromal edema with an intrastromal cleft, and ruptured Descemet membrane, findings consistent with acute hydrops with corneal perforation. After bandage contact lens placement and instillation of a cycloplegic agent, the anterior chamber reformed within 24 hours. Over the next week, conservative management with a bandage lens, pressure patching, topical fluoroquinolone antibiotic, and topical cycloplegic led to the reformation and maintenance of anterior chamber stability. Corneal topography of the unaffected eye showed global corneal thinning and steep sim K readings suspicious for early keratoconus.

CONCLUSIONS

Although the association between keratoconus and cone dystrophy is extremely rare, our patient's vision-threatening complication of acute hydrops with corneal perforation highlights the importance of corneal evaluation including topography in cone dystrophy. Conservative management was successful in the restoration of anatomic integrity in this situation.

Leber congenital amaurosis: disease, genetics and therapy

Leber congenital amaurosis (LCA) is a congenital retinal dystrophy that was first described almost 150 years ago. LCA still remains an important cause of blindness with about 20% of children in schools for the blind being affected by it. LCA has genetic heterogeneity and the study of this disease is elucidating the genetics and molecular interactions involved in the development of the retina. This paper reviews the clinical history of the disease since it was first described. We further discuss the differential diagnosis of the disease and the difficulties encountered in making the diagnosis. We also review the genetics of the disease and the role of future therapies.

Exclusion of LCA5 locus in a consanguineous Turkish family with macular coloboma-type LCA

BACKGROUND

Leber's congenital amaurosis (LCA) is an inherited retinal dystrophy, which causes severe visual impairment in early childhood. Recent molecular genetic studies have linked 11 loci (AIPL1, CRB1, CRX, GUCY2D, RPE65, RDH12, RPGRIP1, TULP1, LCA3, LCA5, and LCA9) to LCA. LCA5 is a new locus, which maps to the 6q11-q16 chromosomal region and was found to be associated with macular coloboma-type LCA in a Pakistani family. Herein, we describe the molecular genetic features of a consanguineous Turkish family in which four children have macular coloboma-type LCA.

METHODS

Haplotype analysis was performed on the DNA of the family members using microsatellite markers against GUCY2D, RPE65, and LCA5. Genomic DNA was screened for mutations by means of single-strand conformational polymorphism (SSCP) analysis in exons of the RPE65 and CRX genes.

RESULTS

In haplotype analysis, no linkage to LCA5 or GUCY2D loci was detected. None of the tested markers showed homozygosity or segregation between affected siblings. PCR-SSCP mutation analysis revealed no mutations in the screened RPE65 and CRX genes.

CONCLUSION

We excluded LCA5 as the genetic cause of macular coloboma-type LCA in this Turkish family. Macular coloboma-type LCA shows genetic heterogeneity and it is not possible to establish a phenotype-genotype correlation with LCA5 and macular coloboma.

Purification, characterisation and intracellular localisation of aryl hydrocarbon interacting protein-like 1 (AIPL1) and effects of mutations associated with inherited retinal dystrophies

Mutations in AIPL1 are associated with Leber Congenital Amaurosis (LCA), a major cause of childhood blindness, yet the cellular function of the encoded protein has yet to be fully elucidated. In order to investigate the biochemistry of AIPL1, we have developed a system for the expression of the recombinant protein in bacteria and its subsequent purification. The secondary structure and thermostability of wild-type and mutant proteins have been examined by circular dichroism (CD) spectroscopy. Some of the variants, notably W278X and P376S, had markedly different secondary structure compositions, indicating that the proteins had not folded properly, whilst W278X and T114I were particularly thermolabile. When eukaryotic cells were transfected with the AIPL1 expression constructs, we show by immunofluorescence microscopy that wild-type protein is distributed throughout the nucleus and cytoplasm. Several of the mutants give similar results. With two of the disease-associated variants (W278X and A336Delta2), however, the protein remains in the cytoplasm in aggresome-like particles. These particles were shown to be ubiquitinated, indicating that the mutant protein had been tagged for proteosomal degradation. On this basis, we can conclude that wild-type protein is expressed in a soluble and folded manner, and that some of the disease-associated mutant proteins are nonfunctional because they are insoluble and are degraded by the cell. Other mutations appear to have a more localised effect on secondary structure, which does not result in insolubility or affect protein targeting, but reduces the stability of the protein at human body temperature.

An overview of Leber congenital amaurosis: a model to understand human retinal development

Leber congenital amaurosis is a congenital retinal dystrophy described almost 150 years ago. Today, Leber congenital amaurosis is proving instrumental in our understanding of the molecular events that determine normal and aberrant retinal development. Six genes have been shown to be mutated in Leber congenital amaurosis, and they participate in a wide variety of retinal pathways: retinoid metabolism (RPE65), phototransduction (GUCY2D), photoreceptor outer segment development (CRX), disk morphogenesis (RPGRIP1), zonula adherens formation (CRB1), and cell-cycle progression (AIPL1). Longitudinal studies of visual performance show that most Leber congenital amaurosis patients remain stable, some deteriorate, and rare cases exhibit improvements. Histopathological analyses reveal that most cases have extensive degenerative retinal changes, some have an entirely normal retinal architecture, whereas others have primitive, poorly developed retinas. Animal models of Leber congenital amaurosis have greatly added to understanding the impact of the genetic defects on retinal cell death, and response to rescue. Gene therapy for RPE65 deficient dogs partially restored sight, and provides the first real hope of treatment for this devastating blinding condition.

Inner retinal abnormalities in a mouse model of Leber's congenital amaurosis

Leber's congenital amaurosis (LCA) is the earliest and most severe form in the world of genetic retinal dystrophy causing blindness. An animal model of LCA was recently created in which the cone-rod homeobox (crx) gene was disrupted using homologous recombination. Crx-/- mice display abnormal development of photoreceptors followed by their degeneration. We analyzed the morphology of inner retinal cells in crx-/- mice in order to evaluate the effects of abnormal photoreceptor development and death upon other retinal neurons. The identification of a time window during which inner retinal cells are still viable could be very important in view of the possibilities that photoreceptor transplantation or gene therapy might be used to restore vision in LCA. We used a combination of immunocytochemical and confocal microscopy techniques to screen the crx-/- inner retina and verify its morphological integrity after photoreceptor degeneration. We found significant morphological alterations in second-order neurons in crx-/- animals. The appearance of mutant retinas after photoreceptor death is indistinguishable from that of the retinal degeneration (rd/rd) mouse, a different genetic model of a retinal disease characterized by photoreceptor degeneration. However, at early stages of photoreceptor degeneration the morphology of retinal cells in the crx-/- mutant is considerably well preserved. It is likely that different genetic mechanisms that cause abnormal photoreceptor development and/or degeneration lead to a common pathway that determines second-order neuron modifications. The severity of modifications is linked to the timing of onset of the degeneration and appears to increase with time.

AIPL1, a protein implicated in Leber's congenital amaurosis, interacts with and aids in processing of farnesylated proteins

The most common form of blindness at birth, Leber's congenital amaurosis (LCA), is inherited in an autosomal recessive fashion. Mutations in six different retina-specific genes, including a recently discovered gene, AIPL1, have been linked to LCA in humans. To understand the molecular basis of LCA caused by aryl hydrocarbon receptor-interacting protein-like 1 (AIPL1) mutations, and to elucidate the normal function of AIPL1, we performed a yeast two-hybrid screen using AIPL1 as bait. The screen demonstrated that AIPL1 interacts specifically with farnesylated proteins. Mutations in AIPL1 linked to LCA compromise this activity. These findings suggest that the essential function of AIPL1 within photoreceptors requires interactions with farnesylated proteins. Analysis of isoprenylation in cultured human cells shows that AIPL1 enhances the processing of farnesylated proteins. Based on these findings, we propose that AIPL1 interacts with farnesylated proteins and plays an essential role in processing of farnesylated proteins in retina.

Mutation screening of Pakistani families with congenital eye disorders

To map the disease loci several Pakistani families suffering from autosomal recessive retinitis pigmentosa with preserved para-arteriolar retinal pigment epithelium and Leber congenital amaurosis (LCA) were analyzed. Analysis revealed close genetic linkage between the disease phenotype of some of the families (3330RP, 111RP and 010LCA) and the microsatellite markers on chromosome 1q31. Mutation screening of the candidate gene CRB1 revealed a G to A transversion in exon 7 in arRP family 330RP and a T to C substitution in another arRP family, 111RP. In exon 9 of the CRB1 gene a T to C transversion was found in the family suffering from LCA (010LCA). The LCA phenotype of another family (011LCA) in which the CRB1 locus was excluded, showed linkage with microsatellite markers D17S1294 and D17S796 on chromosome 17p13.1. The association of the candidate gene GUCY2D (17p13.1) with the disease phenotype was excluded as no disease-associated mutation was found in any of its exons. Mutation screening of another candidate gene, AIPL1 located in the same region, showed a novel homozygous C to A substitution in exon 2. These sequence changes are unique for the Pakistani families and some of these have not been reported previously.

Clinicopathologic effects of mutant GUCY2D in Leber congenital amaurosis

PURPOSE

To study the retinal degeneration in an 11 -year-old patient with Leber congenital amaurosis (LCA) caused by mutation in GUCY2D.

STUDY DESIGN

Comparative human tissue study.

PARTICIPANTS

Two subjects with LCA; postmortem eye from one LCA patient and three normal donors.

METHODS

Clinical and visual function studies were performed between the ages of 6 and 10 years in the LCA eye donor and at age 6 in an affected sibling. Genomic DNA was screened for mutations in known LCA genes. The retina of the 11 -year-old subject with LCA was compared with normal retinas from donors age 3 days, 18 years, and 53 years. The tissues were processed for histopathologic studies and immunofluorescence with retinal cell-specific antibodies.

RESULTS

Vision in both siblings at the ages examined was limited to severely impaired cone function. Mutation in the GUCY2D gene was identified in both siblings. Histopathologic study revealed rods and cones without outer segments in the macula and far periphery. The cones formed a monolayer of cell bodies, but the rods were clustered and had sprouted neurites in the periphery. Rods and cones were not identified in the midperipheral retina. The inner nuclear layer appeared normal in thickness throughout the retina, but ganglion cells were reduced in number.

CONCLUSIONS

An 11-year-old subject with LCA caused by mutant GUCY2D had only light perception but retained substantial numbers of cones and rods in the macula and far periphery. The finding of numerous photoreceptors at this age may portend well for therapies designed to restore vision at the photoreceptor level.