KCND2 variants associated with global developmental delay differentially impair Kv4.2 channel gating.

Here, we report on six unrelated individuals, all presenting with early-onset global developmental delay, associated with impaired motor, speech and cognitive development, partly with developmental epileptic encephalopathy and physical dysmorphisms. All individuals carry heterozygous missense variants of KCND2, which encodes the voltage-gated potassium (Kv) channel α-subunit Kv4.2. The amino acid substitutions associated with the variants, p.(Glu323Lys) (E323K), p.(Pro403Ala) (P403A), p.(Val404Leu) (V404L) and p.(Val404Met) (V404M), affect sites known to be critical for channel gating. To unravel their likely pathogenicity, recombinant mutant channels were studied in the absence and presence of auxiliary ß-subunits under two-electrode voltage clamp in Xenopus oocytes. All channel mutants exhibited slowed and incomplete macroscopic inactivation, and the P403A variant in addition slowed activation. Co-expression of KChIP2 or DPP6 augmented the functional expression of both wild-type and mutant channels; however, the auxiliary ß-subunit-mediated gating modifications differed from wild type and among mutants. To simulate the putative setting in the affected individuals, heteromeric Kv4.2 channels (wild type + mutant) were studied as ternary complexes (containing both KChIP2 and DPP6). In the heteromeric ternary configuration, the E323K variant exhibited only marginal functional alterations compared to homomeric wild-type ternary, compatible with mild loss-of-function. By contrast, the P403A, V404L and V404M variants displayed strong gating impairment in the heteromeric ternary configuration, compatible with loss-of-function or gain-of-function. Our results support the etiological involvement of Kv4.2 channel gating impairment in early-onset monogenic global developmental delay. In addition, they suggest that gain-of-function mechanisms associated with a substitution of V404 increase epileptic seizure susceptibility.

Expanding the phenotypic spectrum and clinical severity associated with WLS gene.

WLS (Wnt ligand secretion mediator or Wntless) orchestrates the secretion of all Wnt proteins, a family of evolutionary conserved proteins, involved in Wnt signaling pathway that has many essential biological functions including the regulation of development, cell proliferation, migration and apoptosis. Biallelic variants in WLS have recently been described in 10 patients with pleiotropic multiple congenital anomalies (MCA) known as Zaki syndrome. We identified a likely disease-causing variant in WLS (c.1579G>A, p.Gly527Arg) in a boy presented with a broad range of MCA including microcephaly, facial dysmorphism, alopecia, ophthalmologic anomalies, and complete soft tissue syndactyly. These features were reminiscent of Zaki syndrome although variable clinical severity was observed. In a detailed clinical assessment, our patient also displayed microphthalmia, dental anomalies, skeletal dysplasia with spontaneous fractures and Dandy-Walker malformation. As such, we extend the phenotype linked to Zaki syndrome. This study further highlights the importance of a thorough clinical evaluation to delineate the phenotypic spectrum associated with WLS variants and suggests that genotype-phenotype correlations due to variant localization seems likely. However, future work on additional patients and more functional studies may give further insights into genotype-phenotype correlations and the complex function of WLS.

NPHP1 gene-associated nephronophthisis is associated with an occult retinopathy.

Biallelic deletions in the NPHP1 gene are the most frequent molecular defect of nephronophthisis, a kidney ciliopathy and leading cause of hereditary end-stage kidney disease. Nephrocystin 1, the gene product of NPHP1, is also expressed in photoreceptors where it plays an important role in intra-flagellar transport between the inner and outer segments. However, the human retinal phenotype has never been investigated in detail. Here, we characterized retinal features of 16 patients with homozygous deletions of the entire NPHP1 gene. Retinal assessment included multimodal imaging (optical coherence tomography, fundus autofluorescence) and visual function testing (visual acuity, full-field electroretinography, color vision, visual field). Fifteen patients had a mild retinal phenotype that predominantly affected cones, but with relative sparing of the fovea. Despite a predominant cone dysfunction, night vision problems were an early symptom in some cases. The consistent retinal phenotype on optical coherence tomography images included reduced reflectivity and often a granular appearance of the ellipsoid zone, fading or loss of the interdigitation zone, and mild outer retinal thinning. However, there were usually no obvious structural changes visible upon clinical examination and fundus autofluorescence imaging (occult retinopathy). More advanced retinal degeneration might occur with ageing. An identified additional CEP290 variant in one patient with a more severe retinal degeneration may indicate a potential role for genetic modifiers, although this requires further investigation. Thus, diagnostic awareness about this distinct retinal phenotype has implications for the differential diagnosis of nephronophthisis and for individual prognosis of visual function.

Biallelic mutation of human SLC6A6 encoding the taurine transporter TAUT is linked to early retinal degeneration.

We previously reported that inactivation of the transmembrane taurine transporter (TauT or solute carrier 6a6) causes early retinal degeneration in mice. Compatible with taurine's indispensability for cell volume homeostasis, protein stabilization, cytoprotection, antioxidation, and immuno- and neuromodulation, mice develop multisystemic dysfunctions (hearing loss; liver fibrosis; and behavioral, heart, and skeletal muscle abnormalities) later on. Here, by genetic, cell biologic, in vivo1H-magnetic resonance spectroscopy and molecular dynamics simulation studies, we conducted in-depth characterization of a novel disorder: human TAUT deficiency. Loss of TAUT function due to a homozygous missense mutation caused panretinal degeneration in 2 brothers. TAUTp.A78E still localized in the plasma membrane but is predicted to impact structural stabilization. 3H-taurine uptake by peripheral blood mononuclear cells was reduced by 95%, and taurine levels were severely reduced in plasma, skeletal muscle, and brain. Extraocular dysfunctions were not yet detected, but significantly increased urinary excretion of 8-oxo-7,8-dihydroguanosine indicated generally enhanced (yet clinically unapparent) oxidative stress and RNA oxidation, warranting continuous broad surveillance.-Preising, M. N., Görg, B., Friedburg, C., Qvartskhava, N., Budde, B. S., Bonus, M., Toliat, M. R., Pfleger, C., Altmüller, J., Herebian, D., Beyer, M., Zöllner, H. J., Wittsack, H.-J., Schaper, J., Klee, D., Zechner, U., Nürnberg, P., Schipper, J., Schnitzler, A., Gohlke, H., Lorenz, B., Häussinger, D., Bolz, H. J. Biallelic mutation of human SLC6A6 encoding the taurine transporter TAUT is linked to early retinal degeneration.

First confirmatory study on PTPRQ as an autosomal dominant non-syndromic hearing loss gene.

BACKGROUND: Biallelic PTPRQ pathogenic variants have been previously reported as causative for autosomal recessive non-syndromic hearing loss. In 2018 the first heterozygous PTPRQ variant has been implicated in the development of autosomal dominant non-syndromic hearing loss (ADNSHL) in a German family. The study presented the only, so far known, PTPRQ pathogenic variant (c.6881G>A) in ADNSHL. It is located in the last PTPRQ coding exon and introduces a premature stop codon (p.Trp2294*). METHODS: A five-generation Polish family with ADNSHL was recruited for the study (n = 14). Thorough audiological, neurotological and imaging studies were carried out to precisely define the phenotype. Genomic DNA was isolated from peripheral blood samples or buccal swabs of available family members. Clinical exome sequencing was conducted for the proband. Family segregation analysis of the identified variants was performed using Sanger sequencing. Single nucleotide polymorphism array on DNA samples from the Polish and the original German family was used for genome-wide linkage analysis. RESULTS: Combining clinical exome sequencing and family segregation analysis, we have identified the same (NM_001145026.2:c.6881G>A, NP_001138498.1:p.Trp2294*) PTPRQ alteration in the Polish ADNSHL family. Using genome-wide linkage analysis, we found that the studied family and the original German family derive from a common ancestor. Deep phenotyping of the affected individuals showed that in contrast to the recessive form, the PTPRQ-related ADNSHL is not associated with vestibular dysfunction. In both families ADNSHL was progressive, affected mainly high frequencies and had a variable age of onset. CONCLUSION: Our data provide the first confirmation of PTPRQ involvement in ADNSHL. The finding strongly reinforces the inclusion of PTPRQ to the small set of genes leading to both autosomal recessive and dominant hearing loss.

Genetic testing in patients with retinitis pigmentosa: Features of unsolved cases.

IMPORTANCE: Uncommon characteristics in genetically unsolved retinitis pigmentosa (RP) patients may indicate an incorrect clinical diagnosis or as yet unknown genetic causes resulting in specific retinal phenotypes. The diagnostic yield of targeted next-generation sequencing may be increased by a reasonable preselection of RP-patients. BACKGROUND: To systematically evaluate and compare features of genetically solved and unsolved RP-patients. DESIGN: Retrospective, observational study. PARTICIPANTS: One-hundred and twelve consecutive RP-patients who underwent extensive molecular genetic analysis. METHODS: Characterization of patients based on multimodal imaging and medical history. MAIN OUTCOME MEASURES: Differences between genetically solved and unsolved RP-patients. RESULTS: Compared to genetically solved patients (n = 77), genetically unsolved patients (n = 35) more frequently had an age of disease-onset above 30 years (60% vs 8%; P < 0.0001), showed atypical fundus features (49% vs 8%; P < 0. 0001) and indicators for phenocopies (eg, autoimmune diseases) (17% vs 0%; P < 0. 001). Evidence for a particular inheritance pattern was less common (20% vs 49%; P < 0. 01). The diagnostic yield was 84% (71/85) in patients with first symptoms below 30 years-of-age, compared to 69% (77/112) in the overall cohort. The other selection criteria alone or in combination resulted in limited further increase of the diagnostic yield (up to 89%) while excluding considerably more patients (up to 56%) from genetic testing. CONCLUSIONS AND RELEVANCE: The medical history and retinal phenotype differ between genetically solved and a subgroup of unsolved RP-patients, which may reflect undetected genotypes or retinal conditions mimicking RP. Patient stratification may inform on the individual likelihood of identifying disease-causing mutations and may impact patient counselling.

Non-manifesting AHI1 truncations indicate localized loss-of-function tolerance in a severe Mendelian disease gene.

Determination of variant pathogenicity represents a major challenge in the era of high-throughput sequencing. Erroneous categorization may result if variants affect genes that are in fact dispensable. We demonstrate that this also applies to rare, apparently unambiguous truncating mutations of an established disease gene. By whole-exome sequencing (WES) in a consanguineous family with congenital non-syndromic deafness, we unexpectedly identified a homozygous nonsense variant, p.Arg1066*, in AHI1, a gene associated with Joubert syndrome (JBTS), a severe recessive ciliopathy. None of four homozygotes expressed any signs of JBTS, and one of them had normal hearing, which also ruled out p.Arg1066* as the cause of deafness. Homozygosity mapping and WES in the only other reported JBTS family with a homozygous C-terminal truncation (p.Trp1088Leufs*16) confirmed AHI1 as disease gene, but based on a more N-terminal missense mutation impairing WD40-repeat formation. Morpholinos against N-terminal zebrafish Ahi1, orthologous to where human mutations cluster, produced a ciliopathy, but targeting near human p.Arg1066 and p.Trp1088 did not. Most AHI1 mutations in JBTS patients result in truncated protein lacking WD40-repeats and the SH3 domain; disease was hitherto attributed to loss of these protein interaction modules. Our findings indicate that normal development does not require the C-terminal SH3 domain. This has far-reaching implications, considering that variants like p.Glu984* identified by preconception screening ('Kingsmore panel') do not necessarily indicate JBTS carriership. Genomes of individuals with consanguineous background are enriched for homozygous variants that may unmask dispensable regions of disease genes and unrecognized false positives in diagnostic large-scale sequencing and preconception carrier screening.

PEX6 is Expressed in Photoreceptor Cilia and Mutated in Deafblindness with Enamel Dysplasia and Microcephaly.

Deafblindness is part of several genetic disorders. We investigated a consanguineous Egyptian family with two siblings affected by congenital hearing loss and retinal degeneration, initially diagnosed as Usher syndrome type 1. At teenage, severe enamel dysplasia, developmental delay, and microcephaly became apparent. Genome-wide homozygosity mapping and whole-exome sequencing detected a homozygous missense mutation, c.1238G>T (p.Gly413Val), affecting a highly conserved residue of peroxisomal biogenesis factor 6, PEX6. Biochemical profiling of the siblings revealed abnormal and borderline plasma phytanic acid concentration, and cerebral imaging revealed white matter disease in both. We show that Pex6 localizes to the apical extensions of secretory ameloblasts and differentiated odontoblasts at early stages of dentin synthesis in mice, and to cilia of retinal photoreceptor cells. We propose PEX6, and possibly other peroxisomal genes, as candidate for the rare cooccurrence of deafblindness and enamel dysplasia. Our study for the first time links peroxisome biogenesis disorders to retinal ciliopathies.

Mutations in NEK8 link multiple organ dysplasia with altered Hippo signalling and increased c-MYC expression.

Mutations affecting the integrity and function of cilia have been identified in various genes over the last decade accounting for a group of diseases called ciliopathies. Ciliopathies display a broad spectrum of phenotypes ranging from mild manifestations to lethal combinations of multiple severe symptoms and most of them share cystic kidneys as a common feature. Our starting point was a consanguineous pedigree with three affected fetuses showing an early embryonic phenotype with enlarged cystic kidneys, liver and pancreas and developmental heart disease. By genome-wide linkage analysis, we mapped the disease locus to chromosome 17q11 and identified a homozygous nonsense mutation in NEK8/NPHP9 that encodes a kinase involved in ciliary dynamics and cell cycle progression. Missense mutations in NEK8/NPHP9 have been identified in juvenile cystic kidney jck mice and in patients suffering from nephronophthisis (NPH), an autosomal-recessive cystic kidney disease. This work confirmed a complete loss of NEK8 expression in the affected fetuses due to nonsense-mediated decay. In cultured fibroblasts derived from these fetuses, the expression of prominent polycystic kidney disease genes (PKD1 and PKD2) was decreased, whereas the oncogene c-MYC was upregulated, providing potential explanations for the observed renal phenotype. We furthermore linked NEK8 with NPHP3, another NPH protein known to cause a very similar phenotype in case of null mutations. Both proteins interact and activate the Hippo effector TAZ. Taken together, our study demonstrates that NEK8 is essential for organ development and that the complete loss of NEK8 perturbs multiple signalling pathways resulting in a severe early embryonic phenotype.

Reticular Pseudodrusen in Sorsby Fundus Dystrophy.

PURPOSE: To investigate the association of reticular pseudodrusen (RPD) with Sorsby fundus dystrophy (SFD). DESIGN: Prospective, monocenter, cross-sectional case series. SUBJECTS: Sixteen patients of 4 unrelated families with SFD caused by mutations in TIMP3. METHODS: All subjects underwent multimodal imaging including near-infrared (NIR) reflectance and fundus autofluorescence with a confocal scanning laser ophthalmoscope and spectral-domain optical coherence tomography (SD OCT). MAIN OUTCOME MEASURES: Prevalence, topographic distribution, and phenotype of RPD. RESULTS: Mean age of the investigated patients was 56.8 years (range, 23-78 years). Reticular pseudodrusen were identified frequently in SFD patients in the sixth decade of life (5 of 7 [71%]) and were absent in younger (n = 3) or older (n = 6) patients. They were most abundant in the superior quadrant and spared the foveal region. Reticular pseudodrusen appeared as yellowish round to oval (dot subtype; n = 5) or confluent, wriggled (ribbon subtype; n = 3) lesions, sometimes forming irregular networks. Reticular pseudodrusen were hyporeflective on NIR reflectance and hypofluorescent on fundus autofluorescence imaging. They appeared as subretinal deposits on SD OCT imaging. Other lesions, such as peripheral pseudodrusen and soft drusen, were present less frequently. CONCLUSIONS: Reticular pseudodrusen are a frequent finding in patients with SFD. Although SFD patients with RPD are younger, distribution and phenotype of RPD are similar to those observed in patients with age-related macular degeneration. The association of RPD with SFD implicates a role of Bruch's membrane, the Bruch's membrane-retinal pigment epithelium interface, or both in the pathogenesis of RPD.

Targeted and genomewide NGS data disqualify mutations in MYO1A, the "DFNA48 gene", as a cause of deafness.

MYO1A is considered the gene underlying autosomal dominant nonsyndromic hearing loss DFNA48, based on six missense variants, one small in-frame insertion, and one nonsense mutation. Results from NGS targeting 66 deafness genes in 109 patients identified three families challenging this assumption: two novel nonsense (p.Tyr740* and p.Arg262*) and a known missense variant were identified heterozygously not only in index patients, but also in unaffected relatives. Deafness in these families clearly resulted from mutations in other genes (MYO7A, EYA1, and CIB2). Most of the altogether 10 MYO1A mutations are annotated in dbSNP, and population frequencies (dbSNP, 1000 Genomes, Exome Sequencing Project) above 0.1% contradict pathogenicity under a dominant model. One healthy individual was even homozygous for p.Arg262*, compatible with homozygous Myo1a knockout mice lacking any overt pathology. MYO1A seems dispensable for hearing and overall nonessential. MYO1A adds to the list of "erroneous disease genes", which will expand with increasing availability of large-scale sequencing data.

Mutation of POC1B in a severe syndromic retinal ciliopathy.

We describe a consanguineous Iraqi family with Leber congenital amaurosis (LCA), Joubert syndrome (JBTS), and polycystic kidney disease (PKD). Targeted next-generation sequencing for excluding mutations in known LCA and JBTS genes, homozygosity mapping, and whole-exome sequencing identified a homozygous missense variant, c.317G>C (p.Arg106Pro), in POC1B, a gene essential for ciliogenesis, basal body, and centrosome integrity. In silico modeling suggested a requirement of p.Arg106 for the formation of the third WD40 repeat and a protein interaction interface. In human and mouse retina, POC1B localized to the basal body and centriole adjacent to the connecting cilium of photoreceptors and in synapses of the outer plexiform layer. Knockdown of Poc1b in zebrafish caused cystic kidneys and retinal degeneration with shortened and reduced photoreceptor connecting cilia, compatible with the human syndromic ciliopathy. A recent study describes homozygosity for p.Arg106ProPOC1B in a family with nonsyndromic cone-rod dystrophy. The phenotype associated with homozygous p.Arg106ProPOC1B may thus be highly variable, analogous to homozygous p.Leu710Ser in WDR19 causing either isolated retinitis pigmentosa or Jeune syndrome. Our study indicates that POC1B is required for retinal integrity, and we propose POC1B mutations as a probable cause for JBTS with severe PKD.

TMEM237 is mutated in individuals with a Joubert syndrome related disorder and expands the role of the TMEM family at the ciliary transition zone.

Joubert syndrome related disorders (JSRDs) have broad but variable phenotypic overlap with other ciliopathies. The molecular etiology of this overlap is unclear but probably arises from disrupting common functional module components within primary cilia. To identify additional module elements associated with JSRDs, we performed homozygosity mapping followed by next-generation sequencing (NGS) and uncovered mutations in TMEM237 (previously known as ALS2CR4). We show that loss of the mammalian TMEM237, which localizes to the ciliary transition zone (TZ), results in defective ciliogenesis and deregulation of Wnt signaling. Furthermore, disruption of Danio rerio (zebrafish) tmem237 expression produces gastrulation defects consistent with ciliary dysfunction, and Caenorhabditis elegans jbts-14 genetically interacts with nphp-4, encoding another TZ protein, to control basal body-TZ anchoring to the membrane and ciliogenesis. Both mammalian and C. elegans TMEM237/JBTS-14 require RPGRIP1L/MKS5 for proper TZ localization, and we demonstrate additional functional interactions between C. elegans JBTS-14 and MKS-2/TMEM216, MKSR-1/B9D1, and MKSR-2/B9D2. Collectively, our findings integrate TMEM237/JBTS-14 in a complex interaction network of TZ-associated proteins and reveal a growing contribution of a TZ functional module to the spectrum of ciliopathy phenotypes.

Mutations in WDR19 encoding the intraflagellar transport component IFT144 cause a broad spectrum of ciliopathies.

BACKGROUND: An emerging number of clinically and genetically heterogeneous diseases now collectively termed ciliopathies have been connected to the dysfunction of primary cilia. We describe an 8-year-old girl with a complex phenotype that did not clearly match any familiar syndrome. CASE-DIAGNOSIS/TREATMENT: Hypotonia, facial dysmorphism and retardation were noted shortly after birth. Other features included short stature, mild skeletal anomalies, strabism, deafness, subdural hygroma, hepatosplenomegaly and end-stage renal failure. Renal biopsy revealed tubular atrophy, interstitial fibrosis and segmental glomerulosclerosis. After exclusion of a chromosomal abnormality by array-comparative genomic hybridization (CGH), we performed next-generation sequencing (NGS) using a customized panel that targeted 131 genes known or hypothesized to cause ciliopathies. We identified the novel homozygous WDR19 mutation c.1483G > C (p.Gly495Arg) that affects an evolutionarily highly conserved residue in the intraflagellar transport protein IFT144, is absent from databases and is predicted to be pathogenic by all bioinformatic sources used. CONCLUSION: Mutations in WDR19 encoding the intraflagellar transport component IFT144 have recently been described in single families with the clinically overlapping skeletal ciliopathies Jeune and Sensenbrenner syndromes, combined or isolated nephronophthisis (NPHP) and retinitis pigmentosa (RP) (Senior-Loken syndrome). Our patient emphasizes the usefulness and efficiency of a comprehensive NGS panel approach in patients with unclassified ciliopathies. It further suggests that WDR19 mutations can cause a broad spectrum of ciliopathies that extends to Jeune and Sensenbrenner syndromes, RP and renal NPHP-like phenotypes.

Combined NGS approaches identify mutations in the intraflagellar transport gene IFT140 in skeletal ciliopathies with early progressive kidney Disease.

Ciliopathies are genetically heterogeneous disorders characterized by variable expressivity and overlaps between different disease entities. This is exemplified by the short rib-polydactyly syndromes, Jeune, Sensenbrenner, and Mainzer-Saldino chondrodysplasia syndromes. These three syndromes are frequently caused by mutations in intraflagellar transport (IFT) genes affecting the primary cilia, which play a crucial role in skeletal and chondral development. Here, we identified mutations in IFT140, an IFT complex A gene, in five Jeune asphyxiating thoracic dystrophy (JATD) and two Mainzer-Saldino syndrome (MSS) families, by screening a cohort of 66 JATD/MSS patients using whole exome sequencing and targeted resequencing of a customized ciliopathy gene panel. We also found an enrichment of rare IFT140 alleles in JATD compared with nonciliopathy diseases, implying putative modifier effects for certain alleles. IFT140 patients presented with mild chest narrowing, but all had end-stage renal failure under 13 years of age and retinal dystrophy when examined for ocular dysfunction. This is consistent with the severe cystic phenotype of Ift140 conditional knockout mice, and the higher level of Ift140 expression in kidney and retina compared with the skeleton at E15.5 in the mouse. IFT140 is therefore a major cause of cono-renal syndromes (JATD and MSS). The present study strengthens the rationale for IFT140 screening in skeletal ciliopathy spectrum patients that have kidney disease and/or retinal dystrophy.

A de novo GLI3 mutation in a patient with acrocallosal syndrome.

Acrocallosal syndrome is characterized by postaxial polydactyly, macrocephaly, agenesis of the corpus callosum, and severe developmental delay. In a few patients with this disorder, a mutation in the KIF7 gene has been reported, which was associated with impaired GLI3 processing and dysregulaton of GLI3 transcription factors. A single patient with acrocallosal syndrome and a de novo p.Ala934Pro mutation in GLI3 has been reported, whereas diverse and numerous GLI3 mutations have also been described in syndromes with overlapping clinical manifestations, including Greig cephalopolysyndactyly syndrome, Pallister-Hall syndrome, trigonocephaly with craniosynostosis and polydactyly, oral-facial-digital syndrome, and non-syndromic polydactyly. Here, we describe a second patient with acrocallosal syndrome, who has a de novo, novel c.2786T>C mutation in GLI3, which predicts p.Leu929Pro. This mutation is in the same domain as the mutation in the previously reported patient. These data confirm that mutations in GLI3 are a cause of the acrocallosal phenotype.

[Inherited retinal diseases in Germany-Challenges in health care supply structure and diagnostics]. / Erbliche Netzhautdystrophien in Deutschland ­ Versorgungsstrukturelle und diagnostische Herausforderungen.

BACKGROUND: Inherited retinal diseases (IRD) are rare eye diseases and pose high diagnostic challenges. A care structure with few highly specialized centers in Germany, misdiagnosis due to the lack of molecular genetic testing, and a lack of a central registry lead to a lack of reliable information on the prevalence and distribution of IRDs in Germany. METHODS: Based on clinical data from an ophthalmological center and molecular data from a genetic center as well as a nationwide health insurance data query, we estimated the prevalence of IRDs in Germany in addition to collecting information on their phenotypic and genotypic distribution. RESULTS: The median travelling distance to the ophthalmological center was 60 km. The most frequent diagnoses were retinitis pigmentosa, macular dystrophy and general retinal dystrophy. Molecular genetic testing was performed in 87% of patients with clinical suspicion of IRD, with marked differences in frequencies among age cohorts. The molecular genetic detection rate in the genetic center was 51%. The prevalence of inherited retinal dystrophy in Germany determined by health insurance data retrieval was approximately 1:1150. CONCLUSION: Many patients must travel long distances to visit specialized clinics for IRDs with access to genetic testing. To obtain more reliable numbers on the prevalence in Germany, routine molecular genetic testing, and a national registry for IRD detection are needed.

The tectonic complex regulates membrane protein composition in the photoreceptor cilium.

The primary cilium is a signaling organelle with a unique membrane composition maintained by a diffusional barrier residing at the transition zone. Many transition zone proteins, such as the tectonic complex, are linked to preserving ciliary composition but the mechanism remains unknown. To understand tectonic's role, we generate a photoreceptor-specific Tctn1 knockout mouse. Loss of Tctn1 results in the absence of the entire tectonic complex and associated MKS proteins yet has minimal effects on the transition zone structure of rod photoreceptors. We find that the protein composition of the photoreceptor cilium is disrupted as non-resident membrane proteins accumulate in the cilium over time, ultimately resulting in photoreceptor degeneration. We further show that fluorescent rhodopsin moves faster through the transition zone in photoreceptors lacking tectonic, which suggests that the tectonic complex acts as a physical barrier to slow down membrane protein diffusion in the photoreceptor transition zone to ensure proper removal of non-resident membrane proteins.

CEP162 deficiency causes human retinal degeneration and reveals a dual role in ciliogenesis and neurogenesis.

Defects in primary or motile cilia result in a variety of human pathologies, and retinal degeneration is frequently associated with these so-called ciliopathies. We found that homozygosity for a truncating variant in CEP162, a centrosome and microtubule-associated protein required for transition zone assembly during ciliogenesis and neuronal differentiation in the retina, caused late-onset retinitis pigmentosa in 2 unrelated families. The mutant CEP162-E646R*5 protein was expressed and properly localized to the mitotic spindle, but it was missing from the basal body in primary and photoreceptor cilia. This impaired recruitment of transition zone components to the basal body and corresponded to complete loss of CEP162 function at the ciliary compartment, reflected by delayed formation of dysmorphic cilia. In contrast, shRNA knockdown of Cep162 in the developing mouse retina increased cell death, which was rescued by expression of CEP162-E646R*5, indicating that the mutant retains its role for retinal neurogenesis. Human retinal degeneration thus resulted from specific loss of the ciliary function of CEP162.

Biallelic MAD2L1BP (p31comet) mutation is associated with mosaic aneuploidy and juvenile granulosa cell tumors.

MAD2L1BP-encoded p31comet mediates Trip13-dependent disassembly of Mad2- and Rev7-containing complexes and, through this antagonism, promotes timely spindle assembly checkpoint (SAC) silencing, faithful chromosome segregation, insulin signaling, and homology-directed repair (HDR) of DNA double-strand breaks. We identified a homozygous MAD2L1BP nonsense variant, R253*, in 2 siblings with microcephaly, epileptic encephalopathy, and juvenile granulosa cell tumors of ovary and testis. Patient-derived cells exhibited high-grade mosaic variegated aneuploidy, slowed-down proliferation, and instability of truncated p31comet mRNA and protein. Corresponding recombinant p31comet was defective in Trip13, Mad2, and Rev7 binding and unable to support SAC silencing or HDR. Furthermore, C-terminal truncation abrogated an identified interaction of p31comet with tp53. Another homozygous truncation, R227*, detected in an early-deceased patient with low-level aneuploidy, severe epileptic encephalopathy, and frequent blood glucose elevations, likely corresponds to complete loss of function, as in Mad2l1bp-/- mice. Thus, human mutations of p31comet are linked to aneuploidy and tumor predisposition.