Two novel TMEM67 variations in a Chinese family with recurrent pregnancy loss: a case report.

BACKGROUND: Recurrent pregnancy loss (RPL) is a common pregnancy complication that brings great pain to pregnant women and their families. Genetic factors are an important cause reason of RPL. However, clinical research on monogenic diseases with recurrent miscarriage is insufficient. CASE PRESENTATION: Here we reported a Chinese family with RPL and genetic analysis of the abortion and parents. A paternally inherited heterozygous missense variant c.1415T > G (p.V472G) and a maternally inherited heterozygous nonsense variant c.2314del (p.M772*) in TMEM67 gene were identified by trio-exome sequencing. c.2314del (p.M772*) generated a premature stop codon and truncated protein, was classified as "pathogenic". c.1415T > G (p.V472G) located in extra-cellular region, was classified as "likely pathogenic". Biallelic variants in TMEM67 gene cause lethal Meckel syndrome 3, consistent with the proband's prenatal phenotype. CONCLUSION: The current study of the Chinese family expands the pathogenic variant spectrum of TMEM67 and emphasizes the necessity of exome sequencing in RPL condition.

Defects in diffusion barrier function of ciliary transition zone caused by ciliopathy variations of TMEM218.

Primary cilia are antenna-like structures protruding from the surface of various eukaryotic cells, and have distinct protein compositions in their membranes. This distinct protein composition is maintained by the presence of the transition zone (TZ) at the ciliary base, which acts as a diffusion barrier between the ciliary and plasma membranes. Defects in cilia and the TZ are known to cause a group of disorders collectively called the ciliopathies, which demonstrate a broad spectrum of clinical features, such as perinatally lethal Meckel syndrome (MKS), relatively mild Joubert syndrome (JBTS), and nonsyndromic nephronophthisis (NPHP). Proteins constituting the TZ can be grouped into the MKS and NPHP modules. The MKS module is composed of several transmembrane proteins and three soluble proteins. TMEM218 was recently reported to be mutated in individuals diagnosed as MKS and JBTS. However, little is known about how TMEM218 mutations found in MKS and JBTS affect the functions of cilia. In this study, we found that ciliary membrane proteins were not localized to cilia in TMEM218-knockout cells, indicating impaired barrier function of the TZ. Furthermore, the exogenous expression of JBTS-associated TMEM218 variants but not MKS-associated variants in TMEM218-knockout cells restored the localization of ciliary membrane proteins. In particular, when expressed in TMEM218-knockout cells, the TMEM218(R115H) variant found in JBTS was able to restore the barrier function of cells, whereas the MKS variant TMEM218(R115C) could not. Thus, the severity of symptoms of MKS and JBTS individuals appears to correlate with the degree of their ciliary defects at the cellular level.

Novel homozygous mutations in TXNDC15 causing Meckel syndrome.

BACKGROUND: Meckel syndrome (MKS) is the most severe form of an autosomal recessive ciliopathy and is clinically characterized by occipital encephalocele, severely polycystic kidneys, and postaxial polydactyly (toes). The association of TXNDC15-related MKS has been reported. We report the case of a homozygous mutation in the TXNDC15 gene, causing MKS14 in the Chinese population. METHODS: The fetal skin tissue and parental peripheral blood were retained for whole-exome sequencing and Sanger sequencing, which investigated the potential pathogenic variants associated with MKS. RESULTS: The fetus was homozygous for a mutation in the TXNDC15 gene (NM_024715.3), specifically c.560delA (p.Asn187llefsTer4), and both parents were heterozygous for this mutation. CONCLUSION: Our study identified a new mutation that adds to the mutational landscape of MKS, which provide a basis for genetic counseling and the selection of reproductive options.

CEP55-associated lethal fetal syndrome: a case report of a Chinese family.

Background: Research on fetal loss related to germline mutations in single genes remains limited. Disruption of CEP55 has recently been established in association with perinatal deaths characterized by hydranencephaly, renal dysplasia, oligohydramnios, and characteristic dysmorphisms. We herein present a Chinese family with recurrent fetal losses due to compound heterozygous nonsense CEP55 variants. Case presentations: The Chinese couple had a history of five pregnancies, with four of them proceeding abnormally. Two stillbirths (II:3 and II:4) sequentially occurred in the third and fourth pregnancy. Prenatal ultrasound scans revealed phenotypic similarities between fetuses II:3 and II:4, including oligohydramnios, bilateral renal dysplasia and hydrocephalus/hydranencephaly. Clubfoot and syndactyly were also present in both stillborn babies. Fetus II:3 presented with endocardial cushion defects while fetus II:4 did not. With the product of conception in the fourth pregnancy, whole exome sequencing (WES) on fetus II:4 identified compound heterozygous nonsense CEP55 variants comprised of c.190C>T(p.Arg64*) and c.208A>T(p.Lys70*). Both variants were expected to result in lack of the TSG101 and ALIX binding domain. Sanger sequencing confirmed the presence and cosegregation of both variants. Conclusion: This is the fifth reported family wherein biallelic CEP55 variants lead to multiple perinatal deaths. Our findings, taken together with previously described phenotypically similar cases and even those with a milder and viable phenotype, broaden the genotypic and phenotypic spectrum of CEP55-associated lethal fetal syndrome, highlighting the vital biomolecular function of CEP55.

Identification of novel TMEM231 gene splice variants and pathological findings in a fetus with Meckel Syndrome.

Background: Meckel Syndrome (MKS, OMIM #249000) is a rare and fatal autosomal recessive ciliopathy with high clinical and genetic heterogeneity. MKS shows complex allelism with other related ciliopathies such as Joubert Syndrome (JBTS, OMIM #213300). In MKS, the formation and function of the primary cilium is defective, resulting in a multisystem disorder including occipital encephalocele, polycystic kidneys, postaxial polydactyly, liver fibrosis, central nervous system malformations and genital anomalies. This study aimed to analyze the genotype of MKS patients and investigate the correlation between genotype and phenotype. Methods: A nonconsanguineous couple who conceived four times with a fetus affected by multiorgan dysfunction and intrauterine fetal death was studied. Whole exome sequencing (WES) was performed in the proband to identify the potentially pathogenic variant. Sanger sequencing was performed in family members. In silico tools were used to analyse the pathogenicity of the identified variants. cDNA TA-cloning sequencing was performed to validate the effects of intronic variants on mRNA splicing. Quantitative real-time PCR was performed to investigate the effect of the variants on gene expression. Immunofluorescence was performed to observe pathological changes of the primary cilium in kidney tissue from the proband. Results: Two splice site variants of TMEM231 (NM_001077418.2, c.583-1G>C and c.583-2_588delinsTCCTCCC) were identified in the proband, and the two variants have not been previously reported. The parents were confirmed as carriers. The two variants were predicted to be pathogenic by in silico tools and were classified as pathogenic/likely pathogenic variants according to the American College of Medical Genetics and Genomics guideline. cDNA TA cloning analysis showed that both splice site variants caused a deletion of exon 5. RT-PCR revealed that the expression of TMEM231 was significantly decreased and immunofluorescence showed that the primary cilium was almost absent in the proband's kidney tissue. Conclusion: We reported the clinical, genetic, molecular and histochemical characterisation of a family affected by MKS. Our findings not only extended the mutation spectrum of the TMEM231 gene, but also revealed for the first time the pathological aetiology of primary cilia in humans and provide a basis for genetic counselling of the parents to their offspring.

Variable phenotypes and penetrance between and within different zebrafish ciliary transition zone mutants.

Meckel syndrome, nephronophthisis, Joubert syndrome and Bardet-Biedl syndrome are caused by mutations in proteins that localize to the ciliary transition zone (TZ). The phenotypically distinct syndromes suggest that these TZ proteins have differing functions. However, mutations in a single TZ gene can result in multiple syndromes, suggesting that the phenotype is influenced by modifier genes. We performed a comprehensive analysis of ten zebrafish TZ mutants, including mks1, tmem216, tmem67, rpgrip1l, cc2d2a, b9d2, cep290, tctn1, nphp1 and nphp4, as well as mutants in ift88 and ift172. Our data indicate that variations in phenotypes exist between different TZ mutants, supporting different tissue-specific functions of these TZ genes. Further, we observed phenotypic variations within progeny of a single TZ mutant, reminiscent of multiple disease syndromes being associated with mutations in one gene. In some mutants, the dynamics of the phenotype became complex with transitory phenotypes that are corrected over time. We also demonstrated that multiple-guide-derived CRISPR/Cas9 F0 'crispant' embryos recapitulate zygotic null phenotypes, and rapidly identified ciliary phenotypes in 11 cilia-associated gene candidates (ankfn1, ccdc65, cfap57, fhad1, nme7, pacrg, saxo2, c1orf194, ttc26, zmynd12 and cfap52).

Case Report: Preimplantation Genetic Testing for Meckel Syndrome Induced by Novel Compound Heterozygous Mutations of MKS1.

Meckel syndrome (MKS), also known as the Meckel-Gruber syndrome, is a severe pleiotropic autosomal recessive developmental disorder caused by dysfunction of the primary cilia during early embryogenesis. The diagnostic criteria are based on clinical variability and genetic heterogeneity. Mutations in the MKS1 gene constitute approximately 7% of all MKS cases. Herein, we present a non-consanguineous couple with three abnormal pregnancies as the fetuses showed MKS-related phenotypes of the central nervous system malformation and postaxial polydactyly. Whole-exome sequencing identified two novel heterozygous mutations of MKS1: c.350C>A and c.1408-14A>G. The nonsense mutation c.350C>A produced a premature stop codon and induced the truncation of the MKS1 protein (p.S117*). Reverse-transcription polymerase chain reaction (RT-PCR) showed that c.1408-14A>G skipped exon 16 and encoded the mutant MKS1 p.E471Lfs*92. Functional studies showed that these two mutations disrupted the B9-C2 domain of the MKS1 protein and attenuated the interactions with B9D2, the essential component of the ciliary transition zone. The couple finally got a healthy baby through preimplantation genetic testing for monogenic disorder (PGT-M) with haplotype linkage analysis. Thus, this study expanded the mutation spectrum of MKS1 and elucidated the genetic heterogeneity of MKS1 in clinical cases.

Evaluation of novel compound variants of CEP290 in prenatally suspected case of Meckel syndrome through whole exome sequencing.

BACKGROUND: Meckel syndrome (MKS) is a fatal disease characterized by multisystem fibrosis during the prenatal or perinatal period. It has an autosomal recessive genetic pattern and is characterized by meningo occipital encephalocele, polycystic kidney dysplasia, polydactyly, and hepatobiliary ductal plate malformation. Germline variations in CEP290 have been shown to cause MKS4. METHODS: In this study, a 23-year-old Chinese woman who was 18 weeks pregnant was examined. The pregnancy was terminated due to occipital meningocele and enlarged cystic dysplastic kidney revealed by ultrasonography. In addition, the patient had a history of adverse pregnancy whereby the fetus presented with double kidney enlargement. Karyotype analysis and chromosomal microarray examination (CMA) were carried out using amniotic fluid samples. Whole exome sequencing (WES) was performed using tissue specimens of the aborted fetus. RESULTS: Karyotype and CMA analyses showed normal results. However, compound heterozygous mutations of CEP290 c.3175dup and CEP290 c.1201dup were detected through WES. CEP290 c.1201dup is a novel heterozygous mutation of CEP290 that has not been reported previously. CONCLUSIONS: The findings of this study provide information on the correlation between MKS phenotype and genotype in CEP290. In addition, these findings indicate that WES is an effective method for detecting genetic causes of multiple structural defects especially those showing normal karyotype and CMA results.

Identification of Pathogenic Variants in RPGRIP1L with Meckel Syndrome and Preimplantation Genetic Testing in a Chinese Family.

Meckel syndrome (MKS, OMIM:249000) is a severe multiorgan dysplastic lethal ciliopathy with extreme genetic heterogeneity. Defects in RPGRIP1L are the cause of MKS type 5 (MKS5, OMIM:611561). However, only six different variants have been reported in eight MKS5 cases with biallelic variants. Here, we describe the case of a Chinese family with recurrent fetal malformations. The proband was a 14-week gestation fetus with occipital encephalocele, polycystic kidneys, polydactyly, and single ventricular heart. Trio whole-exome sequencing was performed, and two novel compound heterozygous variants of RPGRIP1L (c.427C > T, p.Gln143Ter and c.1351-11A > G) were identified. cDNA studies of the splicing variant demonstrated a reading-frame shift with a subsequent premature stop codon (p.Glu451Serfs*6). After the proband was diagnosed with MKS5, the couple chose preimplantation genetic testing for monogenic disorders (PGT-M) and prenatal genetic diagnosis (PND) to prevent the transmission of pathogenic variants, which led to a successful pregnancy recently. In summary, we have identified two novel variants of RPGRIP1L in a Chinese family, which expand the variant spectrum of MKS5. Furthermore, we have described the successful application of PGT-M and PND in this family. These techniques could assist couples with a genetic predisposition in avoiding the transmission of genetic diseases to their offspring.

Update of genetic variants in CEP120 and CC2D2A-With an emphasis on genotype-phenotype correlations, tissue specific transcripts and exploring mutation specific exon skipping therapies.

BACKGROUND: Mutations in ciliary genes cause a spectrum of both overlapping and distinct clinical syndromes (ciliopathies). CEP120 and CC2D2A are paradigmatic examples for this genetic heterogeneity and pleiotropy as mutations in both cause Joubert syndrome but are also associated with skeletal ciliopathies and Meckel syndrome, respectively. The molecular basis for this phenotypical variability is not understood but basal exon skipping likely contributes to tolerance for deleterious mutations via tissue-specific preservation of the amount of expressed functional protein. METHODS: We systematically reviewed and annotated genetic variants and clinical presentations reported in CEP120- and CC2D2A-associated disease and we combined in silico and ex vivo approaches to study tissue-specific transcripts and identify molecular targets for exon skipping. RESULTS: We confirmed more severe clinical presentations associated with truncating CC2D2A mutations. We identified and confirmed basal exon skipping in the kidney, with possible relevance for organ-specific disease manifestations. Finally, we proposed a multimodal approach to classify exons amenable to exon skipping. By mapping reported variants, 14 truncating mutations in 7 CC2D2A exons were identified as potentially rescuable by targeted exon skipping, an approach that is already in clinical use for other inherited human diseases. CONCLUSION: Genotype-phenotype correlations for CC2D2A support the deleteriousness of null alleles and CC2D2A, but not CEP120, offers potential for therapeutic exon skipping approaches.

DNA Variant in the RPGRIP1L Gene Influences Alternative Splicing.

The retinitis pigmentosa GTPase regulator interacting protein 1-like (RPGRIP1L) gene encodes a ciliary protein that is critical for processes related to brain development, including development of left-right asymmetry, sonic hedgehog signaling, and neural tube formation. RPGRIP1L is a risk factor for retinal degeneration, and rare, deleterious variants in the RPGRIP1L gene cause Joubert syndrome and Meckel syndrome, both autosomal recessive disorders. These syndromes are characterized by dysfunctional primary cilia that result in abnormal development - and even lethality in the case of Meckel syndrome. Genetic studies have also implicated RPGRIP1L in psychiatric disorders by suggestive findings from genome-wide association studies and findings from rare-variant exome analyses for bipolar disorder and de novo mutations in autism. In this study we identify a common variant in RPGRIP1L, rs7203525, that influences alternative splicing, increasing the inclusion of exon 20 of RPGRIP1L. We detected this alternative splicing association in human postmortem brain tissue samples and, using a minigene assay combined with in vitro mutagenesis, confirmed that the alternative splicing is attributable to the alleles of this variant. The predominate RPGRIP1L isoform expressed in adult brains does not contain exon 20; thus, a shift to include this exon may impact brain function.

Whole exome sequencing identified a homozygous novel variant in CEP290 gene causes Meckel syndrome.

Meckel syndrome (MKS) is a pre- or perinatal multisystemic ciliopathic lethal disorder with an autosomal recessive mode of inheritance. Meckel syndrome is usually manifested with meningo-occipital encephalocele, polycystic kidney dysplasia, postaxial polydactyly and hepatobiliary ductal plate malformation. Germline variants in CEP290 cause MKS4. In this study, we investigated a 35-years-old Chinese female who was 17+1 weeks pregnant. She had a history of adverse pregnancy of having foetus with multiple malformations. We performed ultrasonography and identified the foetus with occipital meningoencephalocele and enlarged cystic dysplastic kidneys. So, she decided to terminate her pregnancy and further genetic molecular analysis was performed. We identified the aborted foetus without postaxial polydactyly. Histological examination of foetal kidney showed cysts in kidney and thinning of the renal cortex with glomerular atrophy. Whole exome sequencing identified a novel homozygous variant (c.2144T>G; p.L715* ) in exon 21 of the CEP290 in the foetus. Sanger sequencing confirmed that both the parents of the foetus were carrying this variant in a heterozygous state. This variant was not identified in two elder sisters of the foetus as well as in the 100 healthy individuals. Western blot analysis showed that this variant leads to the formation of truncated CEP290 protein with the molecular weight of 84 KD compared with the wild-type CEP290 protein of 290 KD. Hence, it is a loss-of-function variant. We also found that the mutant cilium appears longer in length than the wild-type cilium. Our present study reported the first variant of CEP290 associated with MKS4 in Chinese population.

The molecular genetics of Joubert syndrome and related ciliopathies: The challenges of genetic and phenotypic heterogeneity.

Joubert syndrome (JS; MIM PS213300) is a rare, typically autosomal recessive disorder characterized by cerebellar vermis hypoplasia and a distinctive malformation of the cerebellum and brainstem identified as the "molar tooth sign" on brain MRI. Other universal features include hypotonia with later ataxia and intellectual disability/developmental delay, with additional features consisting of oculomotor apraxia and abnormal respiratory pattern. Notably, other, more variable features include renal cystic disease, typically nephronophthisis, retinal dystrophy, and congenital hepatic fibrosis; skeletal changes such as polydactyly and findings consistent with short-rib skeletal dysplasias are also seen in many subjects. These pleiotropic features are typical of a number of disorders of the primary cilium, and make the identification of causal genes challenging given the significant overlap between JS and other ciliopathy conditions such as nephronophthisis and Meckel, Bardet-Biedl, and COACH syndromes. This review will describe the features of JS, characterize the 35 known genes associated with the condition, and describe some of the genetic conundrums of JS, such as the heterogeneity of founder effects, lack of genotype-phenotype correlations, and role of genetic modifiers. Finally, aspects of JS and related ciliopathies that may pave the way for development of therapeutic interventions, including gene therapy, will be described.

Meckel syndrome: Clinical and mutation profile in six fetuses.

Meckel syndrome (MKS) is a perinatally lethal, genetically heterogeneous, autosomal recessive condition caused by defective primary cilium formation leading to polydactyly, multiple cysts in kidneys and malformations of nervous system. We performed exome sequencing in six fetuses from six unrelated families with MKS. We identified seven novel variants in B9D2, TNXDC15, CC2D2A, CEP290 and TMEM67. We describe the second family with MKS due to a homozygous variant in B9D2 and fifth family with bi-allelic variant in TXNDC15. Our data validates the causation of MKS by pathogenic variation in B9D2 and TXNDC15 and also adds novel variants in CC2D2A, CEP290 and TMEM67 to the literature.

Co-Occurrence of Leber Congenital Amaurosis and Meckel Syndrome Type 1 in a Fetus: Is There a Lesson to Be Learned?

A patient referred for prenatal diagnostics, after first-trimester ultrasound due to a previous child with Leber congenital amaurosis, was suggestive of a Meckel syndrome-like phenotype. Fetal autopsy confirmed the multiple anomalies, and whole-exome sequencing of the fetal DNA identified a pathogenic variant in the RPGRIP1 gene, previously identified in the elder sibling, and a variant causative of Meckel syndrome 1 in the MKS1 gene. Reporting the MKS1 mutation, which was present in heterozygous state in the elder sibling, as a secondary finding would have enabled the parents to be tested for carrier status of the same variant and appropriate counseling could have been provided prior to the onset of the pregnancy. Although the information may not be of great benefit in cases where the ultrasonographic changes can be recognized early, it would be of definitive help where diagnostic imaging in early pregnancy is not possible.

History and highlights of the teratological collection in the Museum Anatomicum of Leiden University, The Netherlands.

The anatomical collection of the Anatomical Museum of Leiden University Medical Center (historically referred to as Museum Anatomicum Academiae Lugduno-Batavae) houses and maintains more than 13,000 unique anatomical, pathological and zoological specimens, and include the oldest teratological specimens of The Netherlands. Throughout four centuries hundreds of teratological specimens were acquired by more than a dozen collectors. Due to the rich history of this vast collection, teratological specimens can be investigated in a unique retrospective sight going back almost four centuries. The entire 19th century collection was described in full detail by Eduard Sandifort (1742-1814) and his son Gerard Sandifort (1779-1848). Efforts were made to re-describe, re-diagnose and re-categorize all present human teratological specimens, and to match them with historical descriptions. In the extant collection a total of 642 human teratological specimens were identified, including exceptional conditions such as faciocranioschisis and conjoined twins discordant for cyclopia, and sirenomelia. Both father and son Sandifort differed in their opinion regarding the causative explanation of congenital anomalies. Whereas, their contemporaries Wouter Van Doeveren (1730-1783) and Andreas Bonn (1738-1817) both presented an interesting view on how congenital anomalies were perceived and explained during the 18th and 19th centuries; the golden age of descriptive teratology. Although this enormous collection is almost 400 years old, it still impresses scientists, (bio)medical students, and laymen visiting and exploring the collections of the Museum Anatomicum in Leiden, The Netherlands.

Motile and non-motile cilia in human pathology: from function to phenotypes.

Ciliopathies are inherited human disorders caused by both motile and non-motile cilia dysfunction that form an important and rapidly expanding disease category. Ciliopathies are complex conditions to diagnose, being multisystem disorders characterized by extensive genetic heterogeneity and clinical variability with high levels of lethality. There is marked phenotypic overlap among distinct ciliopathy syndromes that presents a major challenge for their recognition, diagnosis, and clinical management, in addition to posing an on-going task to develop the most appropriate family counselling. The impact of next-generation sequencing and high-throughput technologies in the last decade has significantly improved our understanding of the biological basis of ciliopathy disorders, enhancing our ability to determine the possible reasons for the extensive overlap in their symptoms and genetic aetiologies. Here, we review the diverse functions of cilia in human health and disease and discuss a growing shift away from the classical clinical definitions of ciliopathy syndromes to a more functional categorization. This approach arises from our improved understanding of this unique organelle, revealed through new genetic and cell biological insights into the discrete functioning of subcompartments of the cilium (basal body, transition zone, intraflagellar transport, motility). Mutations affecting these distinct ciliary protein modules can confer different genetic diseases and new clinical classifications are possible to define, according to the nature and extent of organ involvement. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

[Meckel Gruber syndrome: about a rare case]. / Syndrome de Meckel Gruber: à propos d'un cas rare.

Meckel Gruber syndrome is a rare autosomal recessive polymalformation syndrome characterized by occipital encephalocele, polydactyly and cystic renal dysplasia. Ultrasound is, at present, the best tool for prenatal screening of this lethal polymalformation and diagnosys is confirmed by karyotyping. We here report a case of Meckel Gruber syndrome detected by ultrasound. Abortion was performed at 25 weeks of amenorrhoea.

Syndromic ciliopathies: From single gene to multi gene analysis by SNP arrays and next generation sequencing.

Joubert syndrome (JS) and related disorders (JSRD), Meckel syndrome (MKS) and Bardet-Biedl syndrome (BBS) are autosomal recessive ciliopathies with a broad clinical and genetic overlap. In our multiethnic cohort of 88 MKS, 61 JS/JSRD and 66 BBS families we performed genetic analyses and were able to determine mutation frequencies and detection rates for the most frequently mutated MKS genes. On the basis of determined mutation frequencies, a next generation gene panel for JS/JSRD and MKS was established. Furthermore 35 patients from 26 unrelated consanguineous families were investigated by SNP array-based homozygosity mapping and subsequent DNA sequencing of known candidate genes according to runs of homozygosity size in descending order. This led to the identification of the causative homozygous mutation in 62% of unrelated index cases. Based on our data we discuss various strategies for diagnostic mutation detection in the syndromic ciliopathies JS/JSRD, MKS and BBS.

Molecular complexes that direct rhodopsin transport to primary cilia.

Rhodopsin is a key molecular constituent of photoreceptor cells, yet understanding of how it regulates photoreceptor membrane trafficking and biogenesis of light-sensing organelles, the rod outer segments (ROS) is only beginning to emerge. Recently identified sequence of well-orchestrated molecular interactions of rhodopsin with the functional networks of Arf and Rab GTPases at multiple stages of intracellular targeting fits well into the complex framework of the biogenesis and maintenance of primary cilia, of which the ROS is one example. This review will discuss the latest progress in dissecting the molecular complexes that coordinate rhodopsin incorporation into ciliary-targeted carriers with the recruitment and activation of membrane tethering complexes and regulators of fusion with the periciliary plasma membrane. In addition to revealing the fundamental principals of ciliary membrane renewal, recent advances also provide molecular insight into the ways by which disruptions of the exquisitely orchestrated interactions lead to cilia dysfunction and result in human retinal dystrophies and syndromic diseases that affect multiple organs, including the eyes.