Whole exome sequencing is an efficient, sensitive and specific method for determining the genetic cause of short-rib thoracic dystrophies

Clinical report and genetic analysis of rare premature infant nephronophthisis caused by biallelic TTC21B variants

BACKGROUND

Nephronophthisis (NPHP) is a genetically heterogeneous disease that can lead to end-stage renal disease (ESRD) in children. The TTC21B variant is associated with NPHP12 and mainly characterized by cystic kidney disease, skeletal malformation, liver fibrosis, and retinopathy. Affected patients range from children to adults. Some patients experience ESRD in infancy or early childhood, but clinical reports on neonatal patients are rare. We report a case of NPHP12 in a premature infant and analyze its genetic etiology.

METHODS

Trio-whole exome sequencing analysis was performed on the patient and her parents; bioinformatics software was used to predict and analyze the hazards of the variants. Sanger sequencing was performed to verify variants. We calculated the free energy between mutant IFT139 and the IFT121-IFT122-IFT43 complex structure using molecular dynamics (MD). Finally, the clinical and genetic characteristics of patients with hotspot variant Cys518Arg were reviewed.

RESULTS

Genetic analysis revealed compound-heterozyous TTC21B variants in the patient, c.497delA (p.Lys166fs*36) and c.1552T>C (p.Cys518Arg). Her father and mother had heterozygous c.497delA (p.Lys166fs*36) and heterozygous c.1552T>C (p.Cys518Arg), respectively. Cys518Arg represents a hotspot variant, and the MD calculation results show that this can reduce the structural stability of the IFT121-IFT122-IFT139-IFT43 complex structure. A literature review showed that Cys518Arg might lead to the early occurrence of ESRD.

CONCLUSIONS

Compound-heterozygous TTC21B variants underlie the phenotype in this patient. Thus, Cys518Arg may be a hotspot variant in the Chinese population. Genetic testing should be recommended for NPHP in neonates and early infants.

[Cost of high-throughput sequencing (NGS) technologies: Literature review and insights]

Although high-throughput sequencing technologies (Next-Generation Sequencing [NGS]) are revolutionizing medicine, the estimation of their production cost for pricing/tariffication by health systems raises methodological questions. The objective of this review of cost studies of high-throughput sequencing techniques is to draw lessons for producing robust cost estimates of these techniques. We analyzed, using an eleven item analysis framework, micro-costing studies of high-throughput sequencing technologies (n=17), including two studies conducted in the French context. The factors of variability between the studies that we identified were temporality (early evaluation of the innovation vs. evaluation of a mature technology), the choice of cost evaluation method (scope, micro- vs. gross-costing technique), the choice of production steps observed and the transposability of these studies. The lessons we have learned are that it is necessary to have a comprehensive vision of the sequencing production process by integrating all the steps from the collection of the biological sample to the delivery of the result to the clinician. It is also important to distinguish between what refers to the local context and what refers to the general context, by favouring the use of mixed methods to calculate costs. Finally, sensitivity analyses and periodic re-estimation of the costs of the techniques must be carried out in order to be able to revise the tariffs according to changes linked to the diffusion of the technology and to competition between reagent suppliers.

Primary cilia in skeletal development and disease

Primary cilia are non-motile, microtubule-based sensory organelle present in most vertebrate cells with a fundamental role in the modulation of organismal development, morphogenesis, and repair. Here we focus on the role of primary cilia in embryonic and postnatal skeletal development. We examine evidence supporting its involvement in physiochemical and developmental signaling that regulates proliferation, patterning, differentiation and homeostasis of osteoblasts, chondrocytes, and their progenitor cells in the skeleton. We discuss how signaling effectors in mechanotransduction and bone development, such as Hedgehog, Wnt, Fibroblast growth factor and second messenger pathways operate at least in part at the primary cilium. The relevance of primary cilia in bone formation and maintenance is underscored by a growing list of rare genetic skeletal ciliopathies. We collate these findings and summarize the current understanding of molecular factors and mechanisms governing primary ciliogenesis and ciliary function in skeletal development and disease.

Dynein-2-driven intraciliary retrograde trafficking indirectly requires multiple interactions of IFT54 in the IFT-B complex with the dynein-2 complex

Within cilia, the dynein-2 complex needs to be transported as an anterograde cargo to achieve its role as a motor to drive retrograde trafficking of the intraflagellar transport (IFT) machinery containing IFT-A and IFT-B complexes. We previously showed that interactions of WDR60 and the DYNC2H1-DYNC2LI1 dimer of dynein-2 with multiple IFT-B subunits, including IFT54, are required for the trafficking of dynein-2 as an IFT cargo. However, specific deletion of the IFT54-binding site from WDR60 demonstrated only a minor effect on dynein-2 trafficking and function. We here show that the C-terminal coiled-coil region of IFT54, which participates in its interaction with the DYNC2H1-DYNC2LI1 dimer of dynein-2 and with IFT20 of the IFT-B complex, is essential for IFT-B function, and suggest that the IFT54 middle linker region between the N-terminal WDR60-binding region and the C-terminal coiled-coil is required for ciliary retrograde trafficking, probably by mediating the effective binding of IFT-B to the dynein-2 complex, and thereby ensuring dynein-2 loading onto the anterograde IFT trains. The results presented here agree with the notion predicted from the previous structural models that the dynein-2 loading onto the anterograde IFT train relies on intricate, multivalent interactions between the dynein-2 and IFT-B complexes.

Functional characterization of C21ORF2 association with the NEK1 kinase mutated in human in diseases

The NEK1 kinase controls ciliogenesis, mitosis, and DNA repair, and NEK1 mutations cause human diseases including axial spondylometaphyseal dysplasia and amyotrophic lateral sclerosis. C21ORF2 mutations cause a similar pattern of human diseases, suggesting close functional links with NEK1 Here, we report that endogenous NEK1 and C21ORF2 form a tight complex in human cells. A C21ORF2 interaction domain "CID" at the C-terminus of NEK1 is necessary for its association with C21ORF2 in cells, and pathogenic mutations in this region disrupt the complex. AlphaFold modelling predicts an extended binding interface between a leucine-rich repeat domain in C21ORF2 and the NEK1-CID, and our model may explain why pathogenic mutations perturb the complex. We show that NEK1 mutations that inhibit kinase activity or weaken its association with C21ORF2 severely compromise ciliogenesis, and that C21ORF2, like NEK1 is required for homologous recombination. These data enhance our understanding of how the NEK1 kinase is regulated, and they shed light on NEK1-C21ORF2-associated diseases.

Multiple interactions of the dynein-2 complex with the IFT-B complex are required for effective intraflagellar transport

The dynein-2 complex must be transported anterogradely within cilia to then drive retrograde trafficking of the intraflagellar transport (IFT) machinery containing IFT-A and IFT-B complexes. Here, we screened for potential interactions between the dynein-2 and IFT-B complexes and found multiple interactions among the dynein-2 and IFT-B subunits. In particular, WDR60 (also known as DYNC2I1) and the DYNC2H1-DYNC2LI1 dimer from dynein-2, and IFT54 (also known as TRAF3IP1) and IFT57 from IFT-B contribute to the dynein-2-IFT-B interactions. WDR60 interacts with IFT54 via a conserved region N-terminal to its light chain-binding regions. Expression of the WDR60 constructs in WDR60-knockout (KO) cells revealed that N-terminal truncation mutants lacking the IFT54-binding site fail to rescue abnormal phenotypes of WDR60-KO cells, such as aberrant accumulation of the IFT machinery around the ciliary tip and on the distal side of the transition zone. However, a WDR60 construct specifically lacking just the IFT54-binding site substantially restored the ciliary defects. In line with the current docking model of dynein-2 with the anterograde IFT trains, these results indicate that extensive interactions involving multiple subunits from the dynein-2 and IFT-B complexes participate in their connection.

Genetic variations in the DYNC2H1 gene causing SRTD3 (short-rib thoracic dysplasia 3 with or without polydactyly)

Background and aims: Short-rib thoracic dysplasia 3 with or without polydactyly (SRTD3) represents a type of severe fetal skeletal dysplasia (SD) characterized by shortened limbs, narrow thorax with or without polydactyly, which is caused by the homozygous or compound heterozygous mutations in the DYNC2H1 gene. SRTD3 is a recessive disorder, identification of the responsible genetic variation would be beneficial to an accurate prenatal diagnosis and well-grounded counseling for the affected families. Material and methods: Two families having experienced recurrent fetal SDs were recruited and submitted to a multiplatform genetic investigation. Whole-exome sequencing (WES) was performed with samples collected from the probands. Sanger sequencing and fluorescent quantitative PCR (qPCR) were conducted as validation assays for suspected variations. Results: WES identified two compound heterozygous variations in the DYNC2H1(NM_001080463.2) gene, namely c.2386C>T (p.Arg796Trp) and c.7289T>C (p.Ile2430Thr) for one; and exon (64-83)del and c.8190G>T (p.Leu2730Phe) for the other, respectively. One variant in them, exon (64-83)del, was novelly identified. Conclusion: The study detected two compound heterozygous variation in DYNC2H1 including one novel deletion: exon (64-83) del. Our findings clarified the cause of fetal skeletal dysplasia in the subject families, provided guidance for their future pregnancies, and highlighted the value of WES in diagnosis of skeletal dysplasia with unclear prenatal indications.

Clinical genetics of spondylocostal dysostosis: A mini review

Spondylocostal dysostosis is a genetic defect associated with severe rib and vertebrae malformations. In recent years, extensive clinical and molecular diagnosis advancements enabled us to identify disease-causing variants in different genes for such severe conditions. The identification of novel candidate genes enabled us to understand the developmental biology and molecular and cellular mechanisms involved in the etiology of these rare diseases. Here, we discuss the clinical and molecular targets associated with spondylocostal dysostosis, including clinical evaluation, genes, and pathways involved. This review might help us understand the basics of such a severe disorder, which might help in proper clinical characterization and help in future therapeutic strategies.

A novel WDR60 variant contributes to a late diagnosis of Jeune asphyxiating thoracic dystrophy in a Chinese patient: A case report

We report a Chinese patient with JATD presenting a mild skeletal phenotype and with renal insufficiency as the initial symptom of the disease. A novel homozygous c.2789C>T (p.S930L) variant in the WDR60 gene was identified. Our report will help to improve awareness and diagnosability for this disease.

A late diagnosis of Jeune asphyxiating thoracic dystrophy in a Chinese patient. The patient presented mild skeletal phenotype, and with renal insufficiency as the initial symptom of the disease.

Molecular basis underlying the ciliary defects caused by IFT52 variations found in skeletal ciliopathies

Bidirectional protein trafficking within cilia is mediated by the intraflagellar transport (IFT) machinery, which contains the IFT-A and IFT-B complexes powered by the kinesin-2 and dynein-2 motors. Mutations in genes encoding subunits of the IFT-A and dynein-2 complexes cause skeletal ciliopathies. Some subunits of the IFT-B complex, including IFT52, IFT80, and IFT172, are also mutated in skeletal ciliopathies. We here show that IFT52 variants found in individuals with short-rib polydactyly syndrome (SRPS) are compromised in terms of formation of the IFT-B holocomplex from two subcomplexes and its interaction with heterotrimeric kinesin-II. IFT52-knockout (KO) cells expressing IFT52 variants that mimic the cellular conditions of individuals with SRPS demonstrated mild ciliogenesis defects and a decrease in ciliary IFT-B level. Furthermore, in IFT52-KO cells expressing an SRPS variant of IFT52, ciliary tip localization of ICK/CILK1 and KIF17, both of which are likely to be transported to the tip via binding to the IFT-B complex, was significantly impaired. Altogether these results indicate that impaired anterograde trafficking caused by a decrease in the ciliary level of IFT-B or in its binding to kinesin-II underlies the ciliary defects found in skeletal ciliopathies caused by IFT52 variations.

Biallelic variants in TTC21B as a rare cause of early-onset arterial hypertension and tubuloglomerular kidney disease

Monogenic disorders of the kidney typically affect either the glomerular or tubulointerstitial compartment producing a distinct set of clinical phenotypes. Primary focal segmental glomerulosclerosis (FSGS), for instance, is characterized by glomerular scarring with proteinuria and hypertension while nephronophthisis (NPHP) is associated with interstitial fibrosis and tubular atrophy, salt wasting, and low- to normal blood pressure. For both diseases, an expanding number of non-overlapping genes with roles in glomerular filtration or primary cilium homeostasis, respectively, have been identified. TTC21B, encoding IFT139, however has been associated with disorders of both the glomerular and tubulointerstitial compartment, and linked with defective podocyte cytoskeleton and ciliary transport, respectively. Starting from a case report of extreme early-onset hypertension, proteinuria, and progressive kidney disease, as well as data from the Genomics England 100,000 Genomes Project, we illustrate here the difficulties in assigning this mixed phenotype to the correct genetic diagnosis. Careful literature review supports the notion that biallelic, often hypomorph, missense variants in TTC21B are commonly associated with early-onset hypertension and histological features of both FSGS and NPHP. Increased clinical recognition of this mixed glomerular and tubulointerstitial disease with often mild or absent features of a typical ciliopathy as well as inclusion of TTC21B on gene panels for early-onset arterial hypertension might shorten the diagnostic odyssey for patients affected by this rare tubuloglomerular kidney disease.

Combinations of deletion and missense variations of the dynein-2 DYNC2LI1 subunit found in skeletal ciliopathies cause ciliary defects

Cilia play crucial roles in sensing and transducing extracellular signals. Bidirectional protein trafficking within cilia is mediated by the intraflagellar transport (IFT) machinery containing IFT-A and IFT-B complexes, with the aid of kinesin-2 and dynein-2 motors. The dynein-2 complex drives retrograde trafficking of the IFT machinery after its transportation to the ciliary tip as an IFT cargo. Mutations in genes encoding the dynein-2-specific subunits (DYNC2H1, WDR60, WDR34, DYNC2LI1, and TCTEX1D2) are known to cause skeletal ciliopathies. We here demonstrate that several pathogenic variants of DYNC2LI1 are compromised regarding their ability to interact with DYNC2H1 and WDR60. When expressed in DYNC2LI1-knockout cells, deletion variants of DYNC2LI1 were unable to rescue the ciliary defects of these cells, whereas missense variants, as well as wild-type DYNC2LI1, restored the normal phenotype. DYNC2LI1-knockout cells coexpressing one pathogenic deletion variant together with wild-type DYNC2LI1 demonstrated a normal phenotype. In striking contrast, DYNC2LI1-knockout cells coexpressing the deletion variant in combination with a missense variant, which mimics the situation of cells of compound heterozygous ciliopathy individuals, demonstrated ciliary defects. Thus, DYNC2LI1 deletion variants found in individuals with skeletal ciliopathies cause ciliary defects when combined with a missense variant, which expressed on its own does not cause substantial defects.

Tubuloglomerular Disease With Cone-Shaped Epiphyses Associated With Hypomorphic Variant and a Novel p.Cys14Arg in the TTC21B Gene: A Case Report

Monogenic nephrotic syndrome (NS) is associated with a resistance to initial glucocorticoid therapy and causative variants, which may be found in several genes influencing podocyte stability and kidney development. The TTC21B gene, which encodes the retrograde intraflagellar transport protein IFT139, is found mostly in association with ciliopathies in humans. The role of this protein in podocyte cytoskeleton stability was confirmed later and the mutated TTC21B also may be associated with proteinuric diseases, such as nephrotic syndrome. Our patient manifested as an infant with brachydactyly, nephrotic-range proteinuria, and renal tubular acidosis, and a kidney biopsy revealed focal segmental glomerulosclerosis (FSGS). Multiple phalangeal cone-shaped epiphyses of the hand were seen on X-ray. Next-generation sequencing revealed the well-described p.Pro209Leu heterozygous variant and a novel heterozygous p.Cys14Arg variant in the TTC21B gene. Our finding confirmed that the causative variants in the TTC21B gene may contribute to a spectrum of clinical features, such as glomerular proteinuric disease with tubulointerstitial involvement and skeletal abnormalities.

Cilia kinases in skeletal development and homeostasis

Primary cilia are dynamic compartments that regulate multiple aspects of cellular signaling. The production, maintenance, and function of cilia involve more than 1000 genes in mammals, and their mutations disrupt the ciliary signaling which manifests in a plethora of pathological conditions-the ciliopathies. Skeletal ciliopathies are genetic disorders affecting the development and homeostasis of the skeleton, and encompass a broad spectrum of pathologies ranging from isolated polydactyly to lethal syndromic dysplasias. The recent advances in forward genetics allowed for the identification of novel regulators of skeletogenesis, and revealed a growing list of ciliary proteins that are critical for signaling pathways implicated in bone physiology. Among these, a group of protein kinases involved in cilia assembly, maintenance, signaling, and disassembly has emerged. In this review, we summarize the functions of cilia kinases in skeletal development and disease, and discuss the available and upcoming treatment options.

High diagnostic yield in skeletal ciliopathies using massively parallel genome sequencing, structural variant screening and RNA analyses

Skeletal ciliopathies are a heterogenous group of disorders with overlapping clinical and radiographic features including bone dysplasia and internal abnormalities. To date, pathogenic variants in at least 30 genes, coding for different structural cilia proteins, are reported to cause skeletal ciliopathies. Here, we summarize genetic and phenotypic features of 34 affected individuals from 29 families with skeletal ciliopathies. Molecular diagnostic testing was performed using massively parallel sequencing (MPS) in combination with copy number variant (CNV) analyses and in silico filtering for variants in known skeletal ciliopathy genes. We identified biallelic disease-causing variants in seven genes: DYNC2H1, KIAA0753, WDR19, C2CD3, TTC21B, EVC, and EVC2. Four variants located in non-canonical splice sites of DYNC2H1, EVC, and KIAA0753 led to aberrant splicing that was shown by sequencing of cDNA. Furthermore, CNV analyses showed an intragenic deletion of DYNC2H1 in one individual and a 6.7 Mb de novo deletion on chromosome 1q24q25 in another. In five unsolved cases, MPS was performed in family setting. In one proband we identified a de novo variant in PRKACA and in another we found a homozygous intragenic deletion of IFT74, removing the first coding exon and leading to expression of a shorter message predicted to result in loss of 40 amino acids at the N-terminus. These findings establish IFT74 as a new skeletal ciliopathy gene. In conclusion, combined single nucleotide variant, CNV and cDNA analyses lead to a high yield of genetic diagnoses (90%) in a cohort of patients with skeletal ciliopathies.

Retinal dystrophy as part of TTC21B-associated ciliopathy

Background: TCC21B is a ciliary protein. The most common phenotypic features associated with TCC21B biallelic mutations are nephronophthisis and skeletal abnormalities. To date, retinal dystrophy has been reported in only one patient.Materials and Methods: Clinical evaluation included best-corrected visual acuity, cycloplegic refraction, fundus examination, fundus photography, retinal imaging by optical coherence tomography, full-field electroretinography, multifocal electroretinography, and visual evoked potentials. Genetic analysis included Whole Exome Sequencing and confirmation of the identified mutations in the patient and his parents by PCR amplification and direct sequencing.Results: A ten-year-old Caucasian male presented with nephronophthisis, high myopia and nycatalopia. Best-corrected visual acuity was preserved to 20/20 in each eye with significant myopic correction. Visual fields were constricted. Optical coherence tomography confirmed the lack of outer retinal layers in the perifoveal area on both eyes. Electroretinography confirmed significant retinal dystrophy. Whole Exome Sequencing revealed compound heterozygous mutations in the TTC21B gene.Conclusions: TTC21B is associated with ciliopathy, but retinal dystrophy is a rare finding in these patients. We report retinal dystrophy secondary to TTC21B mutations, and provide for the first time detailed clinical information of the ophthalmic phenotype.

Molecular basis of ciliary defects caused by compound heterozygous IFT144/WDR19 mutations found in cranioectodermal dysplasia

Primary cilia contain specific proteins to achieve their functions as cellular antennae. Ciliary protein trafficking is mediated by the intraflagellar transport (IFT) machinery containing the IFT-A and IFT-B complexes. Mutations in genes encoding the IFT-A subunits (IFT43, IFT121/WDR35, IFT122, IFT139/TTC21B, IFT140 and IFT144/WDR19) often result in skeletal ciliopathies, including cranioectodermal dysplasia (CED). We here characterized the molecular and cellular defects of CED caused by compound heterozygous mutations in IFT144 [the missense variant IFT144(L710S) and the nonsense variant IFT144(R1103*)]. These two variants were distinct with regard to their interactions with other IFT-A subunits and with the IFT-B complex. When exogenously expressed in IFT144-knockout (KO) cells, IFT144(L710S) as well as IFT144(WT) rescued both moderately compromised ciliogenesis and the abnormal localization of ciliary proteins. As the homozygous IFT144(L710S) mutation was found to cause autosomal recessive retinitis pigmentosa, IFT144(L710S) is likely to be hypomorphic at the cellular level. In striking contrast, the exogenous expression of IFT144(R1103*) in IFT144-KO cells exacerbated the ciliogenesis defects. The expression of IFT144(R1103*) together with IFT144(WT) restored the abnormal phenotypes of IFT144-KO cells. However, the coexpression of IFT144(R1103*) with the hypomorphic IFT144(L710S) variant in IFT144-KO cells, which mimics the genotype of compound heterozygous CED patients, resulted in severe ciliogenesis defects. Taken together, these observations demonstrate that compound heterozygous mutations in IFT144 cause severe ciliary defects via a complicated mechanism, where one allele can cause severe ciliary defects when combined with a hypomorphic allele.

Phenotype and genotype spectra of a Chinese cohort with nephronophthisis-related ciliopathy

BACKGROUND

Nephronophthisis-related ciliopathies (NPHP-RC) account for the majority of cases of monogenetically caused end-stage renal disease (ESRD) in children. Exploring the correlation between the phenotype and genotype of NPHP-RC is helpful for early diagnosis and management. We investigated the phenotype and genotype spectra of NPHP-RC in a Chinese multicentre cohort.

METHODS

Crosss-ectional and longitudinal data of 60 patients from 57 families with pathogenic NPHP-RC gene mutations distributed in 22 regions of China were collected into a unified, anonymous database. The mean observation time of this cohort was 3.5±3.1 years.

RESULTS

Mutations in NPHP1 and NPHP3 were the most common genetic defects. Overall, 45% of patients presented with isolated nephronophthisis (NPH), and 55% exhibited the extrarenal phenotype, which frequently involved the liver (41.7%, n=25), central nervous system (26.7%, n=16), eyes (26.7%, n=16) and skeletal system (11.7%, n=7). Accidental detection of elevated serum creatinine and non-specific symptoms caused by chronic kidney disease occurred in 65% of patients. Patients carrying NPHP1 mutations mainly presented with isolated NPH (90%, 18/20) and progressed to ESRD at a mean age of 12.9±0.5 years. The mean age of ESRD onset in the non-NPHP1 group was lower than that in the NPHP1 group (6.2±1.4 years, p<0.001), especially for patients carrying NPHP3 mutations (3.1±1.2 years), showing a heterogeneous phenotype characterised by Bardet-Biedl syndrome (12.5%, n=5), Joubert syndrome (7.5%, n=3), COACH syndrome (2.5%, n=1), Mainzer-Saldino syndrome (2.5%, n=1), short-rib thoracic dysplasia (2.5%, n=1) and unclassified symptoms (32.5%, n=13).

CONCLUSIONS

The Chinese Children Genetic Kidney Disease Database registry characterised the spectrum of the phenotype and genotype of NPHP-RC in the Chinese population. NPHP1 and NPHP3 were the most common pathogenic genes. Rapid progression to ESRD and liver involvement were noted in patients with NPHP3 mutations.

Anterograde trafficking of ciliary MAP kinase-like ICK/CILK1 by the intraflagellar transport machinery is required for intraciliary retrograde protein trafficking

ICK (also known as CILK1) is a mitogen-activated protein kinase-like kinase localized at the ciliary tip. Its deficiency is known to result in the elongation of cilia and causes ciliopathies in humans. However, little is known about how ICK is transported to the ciliary tip. We here show that the C-terminal noncatalytic region of ICK interacts with the intraflagellar transport (IFT)-B complex of the IFT machinery and participates in its transport to the ciliary tip. Furthermore, total internal reflection fluorescence microscopy demonstrated that ICK undergoes bidirectional movement within cilia, similarly to IFT particles. Analysis of ICK knockout cells demonstrated that ICK deficiency severely impairs the retrograde trafficking of IFT particles and ciliary G protein-coupled receptors. In addition, we found that in ICK knockout cells, ciliary proteins are accumulated at the bulged ciliary tip, which appeared to be torn off and released into the environment as an extracellular vesicle. The exogenous expression of various ICK constructs in ICK knockout cells indicated that the IFT-dependent transport of ICK, as well as its kinase activity and phosphorylation at the canonical TDY motif, is essential for ICK function. Thus, we unequivocally show that ICK transported to the ciliary tip is required for retrograde ciliary protein trafficking and consequently for normal ciliary function.

Medullary Cystic Kidney Disease and Focal Segmental Glomerulosclerosis Caused by a Compound Heterozygous Mutation in TTC21B

Mutations in the TTC21B gene have been identified in patients with nephronophthisis and were recently found in some patients with focal segmental glomerulosclerosis. We herein report a Japanese boy with end-stage renal disease due to medullary polycystic kidney disease and primary focal segmental glomerulosclerosis. Next-generation sequencing detected a new compound heterozygous missense mutation in the TTC21B gene. His renal pathological findings and gene mutations have not been previously reported in patients with ciliopathy. For children with severe renal dysfunction, mutations in the TTC21B gene cause both ciliopathy characterized by bilateral polycystic kidney disease and primary focal segmental glomerulosclerosis.

Identification of novel compound heterozygous mutations of the DYNC2H1 gene in a fetus with short-rib thoracic dysplasia 3 with or without polydactyly

A prenatal sonograph revealed a 26-week-old fetus with short limbs and a narrow chest in a 23-year-old woman with a history of fetal skeletal dysplasia. A single nucleotide polymorphism-based chromosomal microarray (CMA) indicated a normal karyotype, and no chromosomal segments with abnormal copy numbers were noted in the fetus. Whole exome sequencing identified compound heterozygous mutations in the DYNC2H1 gene responsible for a lethal type of bone growth disorder, short-rib thoracic dysplasia 3 with or without polydactyly (SRTD3), and revealed a missense mutation c.515C>A (p. Pro172Gln) of paternal origin and a missense mutation c.5983G>A (p. Ala1995Thr) of maternal origin. These variants were further confirmed by Sanger sequencing. To the extent known, the c.515C>A (p. Pro172Gln) mutation is novel for SRTD3, and the site is conserved across species. This study found a novel mutation of the DYNC2H1 gene for SRTD3 and it has increased the number of reported cases and expanded the spectrum of mutations causing this rare disease.

Checking NEKs: Overcoming a Bottleneck in Human Diseases

In previous years, several kinases, such as phosphoinositide 3-kinase (PI3K), mammalian target of rapamycin (mTOR), and extracellular-signal-regulated kinase (ERK), have been linked to important human diseases, although some kinase families remain neglected in terms of research, hiding their relevance to therapeutic approaches. Here, a review regarding the NEK family is presented, shedding light on important information related to NEKs and human diseases. NEKs are a large group of homologous kinases with related functions and structures that participate in several cellular processes such as the cell cycle, cell division, cilia formation, and the DNA damage response. The review of the literature points to the pivotal participation of NEKs in important human diseases, like different types of cancer, diabetes, ciliopathies and central nervous system related and inflammatory-related diseases. The different known regulatory molecular mechanisms specific to each NEK are also presented, relating to their involvement in different diseases. In addition, important information about NEKs remains to be elucidated and is highlighted in this review, showing the need for other studies and research regarding this kinase family. Therefore, the NEK family represents an important group of kinases with potential applications in the therapy of human diseases.

WDR34 Activates Wnt/Beta-Catenin Signaling in Hepatocellular Carcinoma

BACKGROUND

Wnt ligand binding initiates the interaction between Frizzled and Dvl proteins. However, the regulation of Frizzled-Dvl proteins interaction remains largely unknown.

AIMS

The present study aims to elucidate the regulation of Frizzled-Dvl interaction by WDR34.

METHODS

The protein levels of WDR34 in hepatocellular carcinoma (HCC) tissues were examined by western blot and immunohistochemistry. The effects of WDR34 on the growth and migration of HCC cells were examined using MTT assay and Boyden chamber assay. The interaction between Frizzled and Dvl was evaluated by immunoprecipitation and GST pull-down assay.

RESULTS

In this study, we have shown that WDR34, the binding protein of Frizzled (Fz) activated beta-catenin/TCF signaling by enhancing the interaction between Fz and Dvl2. WDR34 was found to up-regulate in HCC tissues, and its expression was negatively correlated with the survival of HCC patients. WDR34 promoted the growth, colony formation and migration of HCC cells. However, knocking down the expression of WDR34 inhibited the growth, colony formation and migration of HCC cells.

CONCLUSION

Taken together, this study demonstrated the oncogenic roles of WDR34 in the progression of HCC and suggested that WDR34 might be a therapeutic target for HCC.

[Clinical features and TTC21B genotype of a child with nephronophthisis type 12]

Nephronophthisis (NPHP) is a group of autosomal recessive tubulointerstitial cystic kidney disorders. This article reports a case of NPHP type 12 caused by TTC21B mutations. The girl had an insidious onset, with moderate proteinuria, renal dysfunction, stage 2 hypertension, situs inversus, and short phalanges when she visited the hospital for the first time at the age of 3 years and 6 months. The renal lesions progressed to end-stage renal disease (ESRD) before she was 4 years old. Urine protein electrophoresis showed glomerular proteinuria. There were significant increases in urinary β2-microglobulin and α1-microglobulin. Gene detection revealed two compound heterozygous mutations, c.1552T>C (p.C518R) and c.752T>G (p.M251R), in the TTC21B gene, which came from her father and mother respectively. The c.752T>G mutation was a novel mutation. It is concluded that besides typical tubular changes of NPHP, marked glomerular damage is also observed in patients with TTC21B gene mutations.

The Role of IFT140 in Osteogenesis of Adult Mice Long Bone

Primary cilia have a pivotal role in bone development and the dysfunctions of primary cilia cause skeletal ciliopathies. Intraflagellar transport (IFT) proteins are conserved mediators of cilium signaling. IFT sub-complex A is known to regulate retrograde IFT in the cilium. As a core protein of IFT complex A, IFT140 has been shown to have a relationship with serious skeletal ciliopathies caused in humans. However, the effects and mechanisms of IFT140 in bone formation have not been systematically disclosed. To further investigate the potential role of IFT140 in osteogenesis, we established a mouse model by conditional deletion of IFT140 in pre-osteoblasts. The adult knock-out mice exhibited dwarf phenotypes, such as short bone length, less bone mass, and decreased bone mineral apposition rate. In addition, by IFT140 deletion, the expressions of several osteoblastic markers were decreased and loss of bone became severe with aging. These results suggest that cilia gene Ift140 is essential in bone development.

Dynll1 is essential for development and promotes endochondral bone formation by regulating intraflagellar dynein function in primary cilia

Mutations in subunits of the cilia-specific cytoplasmic dynein-2 (CD2) complex cause short-rib thoracic dystrophy syndromes (SRTDs), characterized by impaired bone growth and life-threatening perinatal respiratory complications. Different SRTD mutations result in varying disease severities. It remains unresolved whether this reflects the extent of retained hypomorphic protein functions or relative importance of the affected subunits for the activity of the CD2 holoenzyme. To define the contribution of the LC8-type dynein light chain subunit to the CD2 complex, we have generated Dynll1-deficient mouse strains, including the first-ever conditional knockout (KO) mutant for any CD2 subunit. Germline Dynll1 KO mice exhibit a severe ciliopathy-like phenotype similar to mice lacking another CD2 subunit, Dync2li1. Limb mesoderm-specific loss of Dynll1 results in severe bone shortening similar to human SRTD patients. Mechanistically, loss of Dynll1 leads to a partial depletion of other SRTD-related CD2 subunits, severely impaired retrograde intra-flagellar transport, significant thickening of primary cilia and cilia signaling defects. Interestingly, phenotypes of Dynll1-deficient mice are very similar to entirely cilia-deficient Kif3a/Ift88-null mice, except that they never present with polydactyly and retain relatively higher signaling outputs in parts of the hedgehog pathway. Compared to complete loss of Dynll1, maintaining very low DYNLL1 levels in mice lacking the Dynll1-transcription factor ASCIZ (ATMIN) results in significantly attenuated phenotypes and improved CD2 protein levels. The results suggest that primary cilia can maintain some functionality in the absence of intact CD2 complexes and provide a viable animal model for the analysis of the underlying bone development defects of SRTDs.

Interactions of the dynein-2 intermediate chain WDR34 with the light chains are required for ciliary retrograde protein trafficking

The dynein-2 complex drives retrograde ciliary protein trafficking by associating with the intraflagellar transport (IFT) machinery, containing IFT-A and IFT-B complexes. We recently showed that the dynein-2 complex, which comprises 11 subunits, can be divided into three subcomplexes: DYNC2H1-DYNC2LI1, WDR34-DYNLL1/DYNLL2-DYNLRB1/DYNLRB2, and WDR60-TCTEX1D2-DYNLT1/DYNLT3. In this study, we demonstrated that the WDR34 intermediate chain interacts with the two light chains, DYNLL1/DYNLL2 and DYNLRB1/DYNLRB2, via its distinct sites. Phenotypic analyses of WDR34-knockout cells exogenously expressing various WDR34 constructs showed that the interactions of the WDR34 intermediate chain with the light chains are crucial for ciliary retrograde protein trafficking. Furthermore, we found that expression of the WDR34 N-terminal construct encompassing the light chain-binding sites but lacking the WD40 repeat domain inhibits ciliary biogenesis and retrograde trafficking in a dominant-negative manner, probably by sequestering WDR60 or the light chains. Taken together with phenotypic differences of several WDR34-knockout cell lines, these results indicate that incorporation of DYNLL1/DYNLL2 and DYNLRB1/DYNLRB2 into the dynein-2 complex via interactions with the WDR34 intermediate chain is crucial for dynein-2 function in retrograde ciliary protein trafficking.

Prenatal diagnosis of short-rib polydactyly syndrome type III or short-rib thoracic dysplasia 3 with or without polydactyly (SRTD3) associated with compound heterozygous mutations in DYNC2H1 in a fetus

OBJECTIVE

We present the perinatal imaging findings and molecular genetic analysis in a fetus with short-rib polydactyly syndrome (SRPS) type III or short-rib thoracic dysplasia 3 with or without polydactyly (SRTD3).

CASE REPORT

A 29-year-old, primigravid woman was referred for genetic counseling at 15 weeks of gestation because of abnormal ultrasound findings of short limbs, a narrow chest and bilateral polydactyly of the hands and feet, consistent with a diagnosis of SRPS type III. Chorionic villus sampling was performed, and targeted next-generation sequencing (NGS) was applied to analyze a panel of 25 genes including CEP120, DYNC2H1, DYNC2LI1, EVC, EVC2, FGFR2, FGFR3, HOXD10, IFT122, IFT140, IFT172, IFT52, IFT80, KIAA0586, NEK1, PAPSS2, SLC26A2, SOX9, TCTEX1D2, TCTN3, TTC21B, WDR19, WDR34, WDR35 and WDR60. The NGS analysis identified novel mutations in the DYNC2H1 gene. The fetus was compound heterozygous for a missense mutation c.8077G > T (p.Asp2693Tyr) of paternal origin in DYNC2H1 and a frameshift mutation c.11741_11742delTT (p.Phe3914X) of maternal origin in DYNC2H1. The fetus had a karyotype of 46,XY, and postnatally manifested characteristic SRPS type III phenotype.

CONCLUSION

Targeted NGS is useful in genetic diagnosis of fetal skeletal dysplasia and SRPS, and the information acquired is helpful in genetic counseling.

Mutations in TTC21B cause different phenotypes in two childhood cases in China

AIM

The TTC21B gene is now known as causative of nephronophthisis-related ciliopathies (NPHP-RC). We reported two Chinese paediatric cases with end-stage renal disease and other phenotypes caused by the TTC21B gene mutations.

METHODS

The clinical features of Chinese paediatric cases with NPHP-RC were summarized. Mutation analysis of the TTC21B gene was performed using next-generation sequencing.

RESULTS

The two cases both had nephrotic proteinuria, renal failure, hypertension and abnormal liver function (or hepatic fibrosis). One case also presented situs inversus and short phalanges. They developed end-stage renal disease (ESRD) at 1 year old and 8 years old, respectively, when renal pathology both showed focal segmental glomerular sclerosis (FSGS) with tubulointerstitial lesions including interstitial fibrosis and atrophic tubules. Three novel disease-causing TTC21B mutations were identified. One case carried homozygous mutation c.2211 + 3A > G, while the other case carried compound heterozygous mutations c.1552 T > C (p.C518R) and c.1456dupA (p.R486KfsX22).

CONCLUSION

Mutations in TTC21B cause a range of ciliopathy phenotypes in humans. We identified 3 novel TTC21B mutations in two Chinese paediatric cases that both presented end-stage renal disease and other different features. This is the first TTC21B mutations ever reported in China.

Identification of a c.544C>T mutation in WDR34 as a deleterious recessive allele of short rib-polydactyly syndrome

OBJECTIVE

Single-nucleotide polymorphism (SNP) microarrays and whole-exome sequencing (WES) are tools to precisely diagnose rare autosomal recessive (AR) diseases. In this study, SNP chip and WES were used to identify a mutated location in WDR34 in a baby born to consanguineous parents.

CASE REPORT

The baby, born at 36 gestational weeks had a small thoracic cage, symmetric short proximal bones, and polydactyly. Radiography showed short ribs with reduced lung volume and pulmonary opacities, compatible with asphyxiating thoracic dystrophy or short rib-polydactyly syndrome (SRPS). At 4 months of age, she died of pulmonary hypoplasia and sepsis. SNP microarray and evaluation tool confirmed WDR34 as the candidate gene. WES detected an AR mutation at c.554C > T [p.Arg182Trp] in WDR34.

CONCLUSION

This study was the first to identify c.544C > T [p.Arg182Trp] mutation in WDR34 in a patient with SRPS. According to the database, the homozygous mutation of c.544C > T in WDR34 was deleterious and the prevalence of heterozygous mutation was relatively higher in Asian population. More studies of this mutation in patients with SRPS are required.

Interaction of WDR60 intermediate chain with TCTEX1D2 light chain of the dynein-2 complex is crucial for ciliary protein trafficking

The dynein-2 complex mediates trafficking of ciliary proteins by powering the intraflagellar transport (IFT) machinery containing IFT-A and IFT-B complexes. Although 11 subunits are known to constitute the dynein-2 complex, with several light-chain subunits shared by the dynein-1 complex, the overall architecture of the dynein-2 complex has not been fully clarified. Utilizing the visible immunoprecipitation assay, we demonstrated the interaction modes among the dynein-2 subunits, including previously undefined interactions, such as that between WDR60 and the TCTEX1D2-DYNLT1/DYNLT3 dimer. The dynein-2 complex can be divided into three subcomplexes, namely DYNC2H1-DYNC2LI1, WDR34-DYNLL1/DYNLL2-DYNLRB1/DYNLRB2, and WDR60-TCTEX1D2-DYNLT1/DYNLT3. We established cell lines lacking WDR60 or TCTEX1D2, both of which are dynein-2-specific subunits encoded by ciliopathy-causing genes, and found that both WDR60-knockout (KO) and TCTEX1D2-KO cells show defects in retrograde ciliary protein trafficking, with WDR60-KO cells demonstrating more severe defects probably due to failed assembly of the dynein-2 complex. The exogenous expression of a WDR60 mutant lacking TCTEX1D2 binding partially restored retrograde trafficking to a level comparable to that of TCTEX1D2-KO cells. Thus, our results demonstrated that WDR60 plays a major role and TCTEX1D2 plays an auxiliary role in the dynein-2 complex to mediate retrograde ciliary protein trafficking.

Are whole-exome and whole-genome sequencing approaches cost-effective? A systematic review of the literature

PURPOSE

We conducted a systematic literature review to summarize the current health economic evidence for whole-exome sequencing (WES) and whole-genome sequencing (WGS).

METHODS

Relevant studies were identified in the EMBASE, MEDLINE, Cochrane Library, EconLit and University of York Centre for Reviews and Dissemination databases from January 2005 to July 2016. Publications were included in the review if they were economic evaluations, cost studies, or outcome studies.

RESULTS

Thirty-six studies met our inclusion criteria. These publications investigated the use of WES and WGS in a variety of genetic conditions in clinical practice, the most common being neurological or neurodevelopmental disorders. Study sample size varied from a single child to 2,000 patients. Cost estimates for a single test ranged from $555 to $5,169 for WES and from $1,906 to $24,810 for WGS. Few cost analyses presented data transparently and many publications did not state which components were included in cost estimates.

CONCLUSION

The current health economic evidence base to support the more widespread use of WES and WGS in clinical practice is very limited. Studies that carefully evaluate the costs, effectiveness, and cost-effectiveness of these tests are urgently needed to support their translation into clinical practice.

Expanding the phenotype associated with biallelic WDR60 mutations: Siblings with retinal degeneration and polydactyly lacking other features of short rib thoracic dystrophies

Ciliopathies are disorders of the primary cilium that can affect almost all organs and that are characterized by pleiotropy and extensive intra- and interfamilial phenotypic variability. Accordingly, mutations in the same gene can cause different ciliopathy phenotypes of varying severity. WDR60 encodes a protein thought to play a role in the primary cilium's intraflagellar transport machinery. Mutations in this gene are a rare cause of Jeune asphyxiating thoracic dystrophy (JATD) and short-rib polydactyly syndrome (SRPS). Here we report on a milder and distinct phenotype in a consanguineous Pakistani pedigree with two adolescent sisters affected by retinal degeneration and postaxial polydactyly, but lack of any further skeletal or chondrodysplasia features. By targeted high-throughput sequencing of genes known or suspected to be involved in ciliogenesis, we detected a novel homozygous N-terminal truncating WDR60 mutation (c.44delC/p.Ala15Glufs*90) that co-segregated with the disease in the family. Our finding broadens the spectrum of WDR60-related phenotypes and shows the utility of broad multigene panels during the genetic work-up of patients with ciliopathies.

Homozygous variant in C21orf2 in a case of Jeune syndrome with severe thoracic involvement: Extending the phenotypic spectrum

We previously reported exome sequencing in a short-rib thoracic dystrophy (SRTD) cohort, in whom recessive mutations were identified in SRTD-associated genes in 10 of 11 cases. A heterozygous stop mutation in the known SRTD gene WDR60 was identified in the remaining case; no novel candidate gene/s were suggested by homozygous/compound heterozygous analysis. This case was thus considered unsolved. Re-analysis following an analysis pipeline update identified a homozygous mutation in C21orf2 (c.218G > C; p.Arg73Pro). This homozygous variant was previously removed at the quality control stage by the default GATK parameter "in-breeding co-efficient." C21orf2 was recently associated with both Jeune asphyxiating thoracic dystrophy (JATD) and axial spondylometaphyseal dysplasia (axial SMD); this particular mutation was reported in homozygous and compound heterozygous state in both conditions. Our case has phenotypic features of both JATD and axial SMD; and the extent of thoracic involvement appears more severe than in other C21orf2-positive cases. Identification of a homozygous C21orf2 mutation in this case emphasizes the value of exome sequencing for simultaneously screening known genes and identifying novel genes. Additionally, it highlights the importance of re-interrogating data both as novel gene associations are identified and as analysis pipelines are refined. Finally, the severity of thoracic restriction in this case adds to the phenotypic spectrum attributable to C21orf2 mutations.

Mutations in DYNC2H1, the cytoplasmic dynein 2, heavy chain 1 motor protein gene, cause short-rib polydactyly type I, Saldino-Noonan type

The short-rib polydactyly syndromes (SRPS) are autosomal recessively inherited, genetically heterogeneous skeletal ciliopathies. SRPS phenotypes were historically categorized as types I-IV, with type I first delineated by Saldino and Noonan in 1972. Characteristic findings among all forms of SRP include short horizontal ribs, short limbs and polydactyly. The SRP type I phenotype is characterized by a very small thorax, extreme micromelia, very short, poorly mineralized long bones, and multiple organ system anomalies. To date, the molecular basis of this most severe type of SRP, also known as Saldino-Noonan syndrome, has not been determined. We identified three SRP cases that fit the original phenotypic description of SRP type I. In all three cases, exome sequence analysis revealed compound heterozygosity for mutations in DYNC2H1, which encodes the main component of the retrograde IFT A motor, cytoplasmic dynein 2 heavy chain 1. Thus SRP type I, II, III and asphyxiating thoracic dystrophy (ATD), which also result from DYNC2H1 mutations. Herein we describe the phenotypic features, radiographic findings, and molecular basis of SRP type I.

Compound heterozygous mutations in the IFT140 gene cause Opitz trigonocephaly C syndrome in a patient with typical features of a ciliopathy

〈 We report on an infant with Opitz trigonocephaly C syndrome (OTCS), who also had manifestations of ciliopathy, including short ribs (non-asphyxiating), trident acetabular roofs, postaxial polydactyly cone-shaped epiphyses, and dysplasia of the renal, hepatic and pancreatic tissues. To investigate the molecular cause, we used an exome sequencing strategy followed by Sanger sequencing. Two rare variants, both predicted to result in loss of functional protein, were identified in the IFT140 gene; a substitution at the splice donor site of exon 24 (c.723 + 1 G > T) and a 17 bp deletion, impacting the first coding exon (c.-11_6del). The variants were confirmed as being biallelic using Sanger sequencing, showing that the splice variant was inherited from the propositus mother and the deletion from the father. To date, Mainzer-Saldino syndrome, Jeune syndrome, and a form of nonsyndromic retinal dystrophy, have been identified as ciliopathies caused by IFT140 mutations. We provide the first description of an OTCS phenotype that appears to result from IFT140 mutations. The presentation of this patient is consistent with previous reports showing that OTCS already exhibited skeleletal and nonskeletal features of a ciliopathy.

Axial spondylometaphyseal dysplasia is also caused by NEK1 mutations

Axial spondylometaphyseal dysplasia (axial SMD) is a unique form of SMD characterized by dysplasia of axial skeleton and retinal dystrophy. Recently, C21orf2 has been identified as the first disease gene for axial SMD; however, the presence of genetic heterogeneity is known. In this study, we identified NEK1 as the second disease gene for axial SMD. By whole-exome sequencing in a patient with axial SMD, we identified compound heterozygous mutations of NEK1, c.3107C>G (p.S1036*) and c.3830A>C (p.D1277A), which co-segregated in the family. NEK1 mutations have previously been found in three types of short rib thoracic dystrophy, which have no retinal dystrophy. The skeletal phenotype of our patient was milder than those of previously reported cases with NEK1 mutations and those with axial SMD harboring C21orf2 mutations. Phenotypes associated with NEK1 mutations are variable and the phenotype-genotype corelation in skeletal ciliopathies is challenging.

New mutations in DYNC2H1 and WDR60 genes revealed by whole-exome sequencing in two unrelated Sardinian families with Jeune asphyxiating thoracic dystrophy

Jeune asphyxiating thoracic dystrophy (JATD; Jeune syndrome, MIM 208500) is a rare autosomal recessive chondrodysplasia, phenotypically overlapping with short-rib polydactyly syndromes (SRPS). JATD typical hallmarks include skeletal abnormalities such as narrow chest, shortened ribs, limbs shortened bones, extra fingers and toes (polydactyly), as well as extraskeletal manifestations (renal, liver and retinal disease). To date, disease-causing mutations have been found in several genes, highlighting a marked genetic heterogeneity that prevents a molecular diagnosis of the disease in most families. Here, we report the results of whole-exome sequencing (WES) carried out in four JATD cases, belonging to three unrelated families of Sardinian origin. The exome analysis allowed to identify mutations not previously reported in the DYNC2H1 (MIM 603297) and WDR60 (MIM 615462) genes, both codifying for ciliary intraflagellar transport components whose mutations are known to cause Jeune syndrome.