Oral-facial-digital syndromes: review and diagnostic guidelines

Thurston syndrome with thalassaemia: a rare case devising a novel molecular and phenotypic variation

A male infant presented with progressive paleness of the body since 3 months of age. On examination, the child had pallor, microcephaly with dysmorphic facies (depressed nasal bridge, low set ears, retrognathia, high arched palate and tongue hamartoma). Postaxial polydactyly in bilateral hands and feet, broad great toes, with syndactyly of left fourth and fifth toes were present. The haemogram showed severe anaemia with a microcytic hypochromic picture. High-performance liquid chromatography (HPLC) was normal. However, the parents' HPLC was suggestive of beta thalassaemia trait. Whole-exome sequencing revealed Thurston syndrome with beta-thalassaemia in homozygous pattern with a novel mutation. It is a rare genetic syndrome exclusively found in the South Asian population. Due to the rarity, identification of this syndrome is often difficult and requires awareness among clinicians. However, it is important to diagnose the disorder accurately in order to provide appropriate genetic counselling and prognostication to the parents.

IK is essentially involved in ciliogenesis as an upstream regulator of oral-facial-digital syndrome ciliopathy gene, ofd1

BACKGROUND

The cilia are microtubule-based organelles that protrude from the cell surface. Abnormalities in cilia result in various ciliopathies, including polycystic kidney disease (PKD), Bardet-Biedl syndrome (BBS), and oral-facial-digital syndrome type I (OFD1), which show genetic defects associated with cilia formation. Although an increasing number of human diseases is attributed to ciliary defects, the functions or regulatory mechanisms of several ciliopathy genes remain unclear. Because multi ciliated cells (MCCs) are especially deep in vivo, studying ciliogenesis is challenging. Here, we demonstrate that ik is essential for ciliogenesis in vivo.

RESULTS

In the absence of ik, zebrafish embryos showed various ciliopathy phenotypes, such as body curvature, abnormal otoliths, and cyst formation in the kidney. RNA sequencing analysis revealed that ik positively regulated ofd1 expression required for cilium assembly. In fact, depletion of ik resulted in the downregulation of ofd1 expression with ciliary defects, and these ciliary defects in ik mutants were rescued by restoring ofd1 expression. Interestingly, ik affected ciliogenesis particularly in the proximal tubule but not in the distal tubule in the kidney.

CONCLUSIONS

This study demonstrates the role of ik in ciliogenesis in vivo for the first time. Loss of ik in zebrafish embryos displays various ciliopathy phenotypes with abnormal ciliary morphology in ciliary tissues. Our findings on the ik-ofd1 axis provide new insights into the biological function of ik in clinical ciliopathy studies in humans.

TOPORS as a novel causal gene for Joubert syndrome

Joubert syndrome (JBTS) is a Mendelian disorder of the primary cilium defined by the clinical triad of hypotonia, developmental delay, and a distinct cerebellar malformation called the molar tooth sign. JBTS is inherited in an autosomal recessive, autosomal dominant, or X-linked recessive manner. Though over 40 genes have been identified as causal for JBTS, molecular diagnosis is not made in 30%-40% of individuals who meet clinical criteria. TOPORS encodes topoisomerase I-binding arginine/serine-rich protein, and homozygosity for a TOPORS missense variant (c.29C > A; p.(Pro10Gln)) was identified in individuals with the ciliopathy oral-facial-digital syndrome in two families of Dominican descent. Here, we report an additional proband of Dominican ancestry with JBTS found by exome sequencing to be homozygous for the identical p.(Pro10Gln) TOPORS missense variant. Query of the Mount Sinai BioMe biobank, which includes 1880 individuals of Dominican ancestry, supports a high carrier frequency of the TOPORS p.(Pro10Gln) variant in individuals of Dominican descent. Our data nominates TOPORS as a novel causal gene for JBTS and suggests that TOPORS variants should be considered in the differential of ciliopathy-spectrum disease in individuals of Dominican ancestry.

Diagnosis of TBC1D32-associated conditions: Expanding the phenotypic spectrum of a complex ciliopathy

Exome sequencing is a powerful tool in prenatal and postnatal genetics and can help identify novel candidate genes critical to human development. We describe seven unpublished probands with rare likely pathogenic variants or variants of uncertain significance that segregate with recessive disease in TBC1D32, including four fetal probands in three unrelated pedigrees and three pediatric probands in unrelated pedigrees. We also report clinical comparisons with seven previously published patients. Index probands were identified through an ongoing prenatal exome sequencing study and through an online data sharing platform (Gene Matcher™). A literature review was also completed. TBC1D32 is involved in the development and function of cilia and is expressed in the developing hypothalamus and pituitary gland. We provide additional data to expand the phenotype correlated with TBC1D32 variants, including a severe prenatal phenotype associated with life-limiting congenital anomalies.

Exploring the Genetic Causality of Discordant Phenotypes in Familial Apparently Balanced Translocation Cases Using Whole Exome Sequencing

Familial apparently balanced translocations (ABTs) are usually not associated with a phenotype; however, rarely, ABTs segregate with discordant phenotypes in family members carrying identical rearrangements. The current study was a follow-up investigation of four familial ABTs, where whole exome sequencing (WES) was implemented as a diagnostic tool to identify the underlying genetic aetiology of the patients' phenotypes. Data were analysed using an in-house bioinformatics pipeline alongside VarSome Clinical. WES findings were validated with Sanger sequencing, while the impact of splicing and missense variants was assessed by reverse-transcription PCR and in silico tools, respectively. Novel candidate variants were identified in three families. In family 1, it was shown that the de novo pathogenic STXBP1 variant (NM_003165.6:c.1110+2T>G) affected splicing and segregated with the patient's phenotype. In family 2, a likely pathogenic TUBA1A variant (NM_006009.4:c.875C>T, NP_006000.2:p.(Thr292Ile)) could explain the patient's symptoms. In family 3, an SCN1A variant of uncertain significance (NM_006920.6:c.5060A>G, NP_008851.3:p.(Glu1687Gly)) required additional evidence to sufficiently support causality. This first report of WES application in familial ABT carriers with discordant phenotypes supported our previous findings describing such rearrangements as coincidental. Thus, WES can be recommended as a complementary test to find the monogenic cause of aberrant phenotypes in familial ABT carriers.

Cystic Kidney Diseases That Require a Differential Diagnosis from Autosomal Dominant Polycystic Kidney Disease (ADPKD)

Autosomal dominant polycystic kidney disease (ADPKD) is the most common hereditary cystic kidney disease, with patients often having a positive family history that is characterized by a similar phenotype. However, in atypical cases, particularly those in which family history is unclear, a differential diagnosis between ADPKD and other cystic kidney diseases is important. When diagnosing ADPKD, cystic kidney diseases that can easily be excluded using clinical information include: multiple simple renal cysts, acquired cystic kidney disease (ACKD), multilocular renal cyst/multilocular cystic nephroma/polycystic nephroma, multicystic kidney/multicystic dysplastic kidney (MCDK), and unilateral renal cystic disease (URCD). However, there are other cystic kidney diseases that usually require genetic testing, or another means of supplementing clinical information to enable a differential diagnosis of ADPKD. These include autosomal recessive polycystic kidney disease (ARPKD), autosomal dominant tubulointerstitial kidney disease (ADTKD), nephronophthisis (NPH), oral-facial-digital (OFD) syndrome type 1, and neoplastic cystic kidney disease, such as tuberous sclerosis (TSC) and Von Hippel-Lindau (VHL) syndrome. To help physicians evaluate cystic kidney diseases, this article provides a review of cystic kidney diseases for which a differential diagnosis is required for ADPKD.

INTS13 variants causing a recessive developmental ciliopathy disrupt assembly of the Integrator complex

Oral-facial-digital (OFD) syndromes are a heterogeneous group of congenital disorders characterized by malformations of the face and oral cavity, and digit anomalies. Mutations within 12 cilia-related genes have been identified that cause several types of OFD, suggesting that OFDs constitute a subgroup of developmental ciliopathies. Through homozygosity mapping and exome sequencing of two families with variable OFD type 2, we identified distinct germline variants in INTS13, a subunit of the Integrator complex. This multiprotein complex associates with RNA Polymerase II and cleaves nascent RNA to modulate gene expression. We determined that INTS13 utilizes its C-terminus to bind the Integrator cleavage module, which is disrupted by the identified germline variants p.S652L and p.K668Nfs*9. Depletion of INTS13 disrupts ciliogenesis in human cultured cells and causes dysregulation of a broad collection of ciliary genes. Accordingly, its knockdown in Xenopus embryos leads to motile cilia anomalies. Altogether, we show that mutations in INTS13 cause an autosomal recessive ciliopathy, which reveals key interactions between components of the Integrator complex.

Mutations in SCNM1 cause orofaciodigital syndrome due to minor intron splicing defects affecting primary cilia

Orofaciodigital syndrome (OFD) is a genetically heterogeneous ciliopathy characterized by anomalies of the oral cavity, face, and digits. We describe individuals with OFD from three unrelated families having bi-allelic loss-of-function variants in SCNM1 as the cause of their condition. SCNM1 encodes a protein recently shown to be a component of the human minor spliceosome. However, so far the effect of loss of SCNM1 function on human cells had not been assessed. Using a comparative transcriptome analysis between fibroblasts derived from an OFD-affected individual harboring SCNM1 mutations and control fibroblasts, we identified a set of genes with defective minor intron (U12) processing in the fibroblasts of the affected subject. These results were reproduced in SCNM1 knockout hTERT RPE-1 (RPE-1) cells engineered by CRISPR-Cas9-mediated editing and in SCNM1 siRNA-treated RPE-1 cultures. Notably, expression of TMEM107 and FAM92A encoding primary cilia and basal body proteins, respectively, and that of DERL2, ZC3H8, and C17orf75, were severely reduced in SCNM1-deficient cells. Primary fibroblasts containing SCNM1 mutations, as well as SCNM1 knockout and SCNM1 knockdown RPE-1 cells, were also found with abnormally elongated cilia. Conversely, cilia length and expression of SCNM1-regulated genes were restored in SCNM1-deficient fibroblasts following reintroduction of SCNM1 via retroviral delivery. Additionally, functional analysis in SCNM1-retrotransduced fibroblasts showed that SCNM1 is a positive mediator of Hedgehog (Hh) signaling. Our findings demonstrate that defective U12 intron splicing can lead to a typical ciliopathy such as OFD and reveal that primary cilia length and Hh signaling are regulated by the minor spliceosome through SCNM1 activity.

Additional findings of tibial dysplasia in a male with orofaciodigital syndrome type XVI

We describe the case of a male patient with orofaciodigital (OFD) syndrome type XVI with a homozygous variant of TMEM107 (p.Phe106del) and the additional findings of tibial dysplasia, which is a pivotal finding of OFD syndrome type IV. His family history included two fetuses with anencephaly with or without cleft lip/palate and polydactyly with no genetic information. Careful attention should be given to the interpretation of this rare pattern.

Oral-Facial-Digital Syndrome Type 1: A Case Report and Review

Oral-facial-digital syndrome type 1 (OFD1), first described by Papillon-Léage in 1954, is transmitted as an X-linked dominant condition and is characterized by a combination of malformations in the face, oral cavity, and digits. Malformations of the brain and polycystic kidney disease are also commonly associated with OFD1. An 11-month-old female presented with multiple tiny whitish papules on her face that had been present since birth. The histopathologic examination was consistent with milium. She also had congenital anomalies, including incomplete cleft palate, bifid tongue, short frenulum, anomalous deformities of both toes, and clino-brachy-syndactyly. Based on the characteristic dysmorphic features of her face, mouth, and hands, a clinical diagnosis of OFD1 was made. Herein, we report a rare case of OFD1 featuring congenital milia, which has not been previously reported in the Korean literature.

Novel Surgical Technique for Correction of Incomplete Median Cleft Lip Deformity in Oral-Facial-Digital Syndrome Type II

ABSTRACT

Oral-facial-digital syndromes (OFDSs) represent a heterogenous group of embryonic development disorders characterized by malformations of the face, oral cavity, and extremities. Oral-facial-digital syndrome type II is an autosomal recessive disease characterized by median cleft lip, gingival frenula, cleft lobulated tongue, and polydactyly. There are few reports on surgical techniques for correction of incomplete median cleft lip. Here we describe a novel surgical method that we used to correct an incomplete median cleft lip in a 5-year-old girl with oral-facial-digital syndrome type II. She had previously undergone surgery for congenital heart disease, oral anomalies, and polydactyly. Cheiloplasty was performed at 5 years and 8 months using a surgical approach that focused on repair of the median tubercle using lateral labial elements. A reasonably good Cupid's bow and median tubercle were achieved. Our technique for surgical correction of moderate incomplete median cleft lip provides adequate philtral height, vermillion fullness, and a good-shaped Cupid's bow.

Expanding the genetic landscape of oral-facial-digital syndrome with two novel genes

Oral‐facial‐digital syndromes (OFDS) are a heterogeneous and rare group of Mendelian disorders characterized by developmental abnormalities of the oral cavity, face, and digits caused by dysfunction of the primary cilium, a mechanosensory organelle that exists atop most cell types that facilitates organ patterning and growth. OFDS is inherited both in an X‐linked dominant, X‐linked recessive, and autosomal recessive manner. Importantly, though many of the causal genes for OFDS have been identified, up to 40% of OFD syndromes are of unknown genetic basis. Here we describe three children with classical presentations of OFDS including lingual hamartomas, polydactyly, and characteristic facial features found by exome sequencing to harbor variants in causal genes not previously associated with OFDS. We describe a female with hypothalamic hamartoma, urogenital sinus, polysyndactyly, and multiple lingual hamartomas consistent with OFDVI with biallelic pathogenic variants in CEP164, a gene associated with ciliopathy‐spectrum disease, but never before with OFDS. We additionally describe two unrelated probands with postaxial polydactyly, multiple lingual hamartomas, and dysmorphic features both found to be homozygous for an identical TOPORS missense variant, c.29 C>A; (p.Pro10Gln). Heterozygous TOPORS pathogenic gene variants are associated with autosomal dominant retinitis pigmentosa, but never before with syndromic ciliopathy. Of note, both probands are of Dominican ancestry, suggesting a possible founder allele.

Orofaciodigital syndrome type II (Mohr syndrome): a case report

Background

Orofacial digital syndrome is a rare genetic disorder with oral cavity, facial and digits anomalies. Orofacial digital syndrome type II, also called the “Mohr syndrome” is a very rare subtype that has been reported scarcely in Asia especially in Japanese patients.

Case presentation

The case is an Iranian 5-year old girl who had been admitted for orthopedic surgery. She surprisingly had pre and postaxial polydactyly of all the four limbs concurrent with syndromic face and most of the features of Orofaciodigital syndrome type II.

Conclusion

Mohr syndrome, anesthesia and surgical considerations are discussed in this case report. It is recommended to consider these considerations and the possibility of OFDS in every child with pre and postaxial polydactyly of the four limbs and to try to distinguish type II from other types of ODFS.

Functional Characterization of a Novel IRF6 Frameshift Mutation From a Van Der Woude Syndrome Family

Background

Loss-of-function mutations in interferon regulatory factor-6 (IRF6) are responsible for about 70% of cases of Van Der Woude Syndrome (VWS), an autosomal dominant developmental disorder characterized by pits and/or sinuses of the lower lip and cleft lip, cleft palate, or both.

Methods

We collected a Chinese Han VWS pedigree, performed sequencing and screening for the causal gene mutant. Initially, species conservation analysis and homology protein modeling were used to predict the potential pathogenicity of mutations. To test whether a VWS family-derived mutant variant of IRF6 retained function, we carried out rescue assays in irf6 maternal-null mutant zebrafish embryos. To assess protein stability, we overexpressed reference and family-variants of IRF6 in vitro.

Results

We focused on a VWS family that includes a son with bilateral lip pits, uvula fissa and his father with bilateral cleft lip and palate. After sequencing and screening, a frameshift mutation of IRF6 was identified as the potential causal variant (NM.006147.3, c.1088-1091delTCTA; p.Ile363ArgfsTer33). The residues in this position are strongly conserved among species and homology modeling suggests the variant alters the protein structure. In irf6 maternal-null mutant zebrafish embryos the periderm differentiates abnormally and the embryos rupture and die during gastrulation. Injection of mRNA encoding the reference variant of human IRF6, but not of the frame-shift variant, rescued such embryos through gastrulation. Upon overexpression in HEK293FT cells, the IRF6 frame-shift mutant was relatively unstable and was preferentially targeted to the proteasome in comparison to the reference variant.

Conclusion

In this VWS pedigree, a novel frameshift of IRF6 was identified as the likely causative gene variant. It is a lost function mutation which could not rescue abnormal periderm phenotype in irf6 maternal-null zebrafish and which causes the protein be unstable through proteasome-dependent degradation.

Genetics of atrioventricular canal defects

Atrioventricular canal defect (AVCD) represents a quite common congenital heart defect (CHD) accounting for 7.4% of all cardiac malformations. AVCD is a very heterogeneous malformation that can occur as a phenotypical cardiac aspect in the context of different genetic syndromes but also as an isolated, non-syndromic cardiac defect. AVCD has also been described in several pedigrees suggesting a pattern of familiar recurrence. Targeted Next Generation Sequencing (NGS) techniques are proved to be a powerful tool to establish the molecular heterogeneity of AVCD.

Given the complexity of cardiac embryology, it is not surprising that multiple genes deeply implicated in cardiogenesis have been described mutated in patients with AVCD. This review attempts to examine the recent advances in understanding the molecular basis of this complex CHD in the setting of genetic syndromes or in non-syndromic patients.

Oral-Facial-Digital Syndrome Type 1: Further Clinical and Molecular Delineation in 2 New Families

OBJECTIVE

Oral-facial-digital syndrome type 1 (OFD1) [OMIM 311200] is a rare genetic disorder associated with congenital anomalies of the oral cavity, face, and digits. This condition is associated with mutations in the OFD1 gene. Our objective was to recruit patients with the OFD1 clinical phenotype without genetic confirmation, aiming to identify genetic variants in the OFD1 gene.

DESIGN

Three patients from 2 unrelated families were recruited into our study. We employed a variety of genomic techniques on these patients, including candidate gene analysis, array comparative genomic hybridization, whole-exome sequencing, and whole-genome sequencing.

RESULTS

We investigated 3 affected patients from 2 unrelated families with a clinical diagnosis of OFD1. We discovered a novel pathogenic dominant missense mutation c.635G>C (p.Arg212Pro) in the OFD1 gene in one family. A novel frameshift, loss-of-function mutation c.306delA (p.Glu103LysfsTer42) was detected in the affected patient in the second family.

CONCLUSIONS

These new genetic variants will add to the spectrum of known OFD1 mutations associated with the OFD1 disorder. Our study also confirms the variable phenotypic presentation of OFD1 and its well-recognized association with central nervous system malformations and renal anomalies. Molecular diagnostic confirmation achieved in these families will have positive implications for their medical management.

Genetic and developmental disorders of the oral mucosa: Epidemiology; molecular mechanisms; diagnostic criteria; management

A large number of disorders may affect the oral cavity, including genetic diseases, infections, cancers, blood diseases, skin diseases, endocrine and metabolic disorders, autoimmune and rheumatologic diseases, local lesions, to name a few. Oral mucosa shows a considerable variation in its normal structure and a wide range of conditions may affect it. Such conditions are often harmless or minor and could be primary or secondary to systemic disease. Several of them are quite rare and, hence, the diagnosis is not easy. Clinically, lesions may appear as ulcers, discoloration of the oral mucosa and alterations in size and configuration of oral anatomy. Genetic disorders have specific manifestations and can be caused by a derangement of one or more components of the tissue. Many of them follow the skin or systemic signs of the underlying genetic disease, but in a few cases oral signs could be the first manifestation of the disorder. Among them genodermatoses are prominent. They are inherited disorders characterized by a multisystem involvement. This review describes chondro-ectodermal dysplasia, dyskeratosis congenita, Ehlers-Danlos syndrome, hereditary benign intraepithelial dyskeratosis, keratosis follicularis, lipoid proteinosis, multiple hamartoma syndrome, pachyonychia congenita, Peutz-Jeghers syndrome, tuberous sclerosis and white sponge nevus. Other genetic disorders not included in the genodermatosis group and reported in the present review are: acanthosis nigricans, angio-osteo-hypertrophic syndrome, encephalotrigeminal angiomatosis, familial adenomatous polyposis, focal dermal hypoplasia, focal palmoplantar and oral mucosa hyperkeratosis syndrome, gingival fibromatosis, Maffucci's syndrome, neurofibromatosis (type 1) and oro-facial-digital syndrome (type 1). Disorders during embryonic development might lead to a wide range of abnormalities in the oral cavity; some of them are quite common but of negligible concern, whereas others are rare but serious, affecting not only the oral mucosa, but also other structures of the oral cavity (ie palate, tongue and gingiva). Fordyce's granules, leukoedema, cysts of the oral mucosa in newborns, retrocuspid papilla, geographic tongue, fissured tongue, median rhomboid glossitis, hairy tongue, lingual varices and lingual thyroid nodule are described. This review may help dentists, dental hygienists, but also general internists and pediatricians to diagnose different disorders of the oral mucosa, to understand the pathogenesis and to schedule a treatment plan.

Midline Cleft of Lip With Preaxial Polydactyly in One Hand: A Possible New Variation of Thurston Syndrome?

Oral-facial-digital syndromes are a group of disorders with various subtypes. Type V, also known as the Thurston syndrome, is an autosomal recessive condition characterized by median cleft of the upper lip, postaxial polydactyly of hands and feet, and oral manifestations. Majority of the cases reported in the literature have been of Indian ethnic origin. We report a case of a possible variation of this syndrome in a 5-month-old Indian girl who presented with severe midline clefting, cleft palate, and atypically, preaxial polydactyly of the right hand.

A novel pathogenic variant in OFD1 results in X-linked Joubert syndrome with orofaciodigital features and pituitary aplasia

Orofaciodigital syndrome type I and X-linked recessive Joubert syndrome are known ciliopathic disorders that are caused by pathogenic variants in OFD1 gene. Endocrine system involvement with these conditions is not well described. We present the first report of a newborn male with a novel hemizygous variant in OFD1 gene c.515T>C, (p.Leu172Pro) resulting in X-linked Joubert syndrome and orofaciodigital features with complete pituitary gland aplasia and subsequent severe hypoplasia of peripheral endocrine glands. This clinical report expands the phenotypic spectrum of endocrine system involvement in OFD1-related disorders and suggests that OFD1 gene may be related to pituitary gland development.

Opportunities and Challenges for Molecular Understanding of Ciliopathies-The 100,000 Genomes Project

Cilia are highly specialized cellular organelles that serve multiple functions in human development and health. Their central importance in the body is demonstrated by the occurrence of a diverse range of developmental disorders that arise from defects of cilia structure and function, caused by a range of different inherited mutations found in more than 150 different genes. Genetic analysis has rapidly advanced our understanding of the cell biological basis of ciliopathies over the past two decades, with more recent technological advances in genomics rapidly accelerating this progress. The 100,000 Genomes Project was launched in 2012 in the UK to improve diagnosis and future care for individuals affected by rare diseases like ciliopathies, through whole genome sequencing (WGS). In this review we discuss the potential promise and medical impact of WGS for ciliopathies and report on current progress of the 100,000 Genomes Project, reviewing the medical, technical and ethical challenges and opportunities that new, large scale initiatives such as this can offer.

Salivary hamartoma with a bifid tongue in an adult patient

Congenital anomalies of tongue are rare disorders usually associated with syndromes. In present article we describe a case of a non-syndromic adult patient with bifid tongue with salivary hamartoma on the dorsum of the tongue. We described the clinical features, problems faced by the patient and management. As etiology is uncertain we should have proper understanding of embryology.

Atrioventricular canal defect and genetic syndromes: The unifying role of sonic hedgehog

The atrioventricular canal defect (AVCD) is a congenital heart defect (CHD) frequently associated with extracardiac anomalies (75%). Previous observations from a personal series of patients with AVCD and "polydactyly syndromes" showed that the distinct morphology and combination of AVCD features in some of these syndromes is reminiscent of the cardiac phenotype found in heterotaxy, a malformation complex previously associated with functional cilia abnormalities and aberrant Hedgehog (Hh) signaling. Hh signaling coordinates multiple aspects of left-right lateralization and cardiovascular growth. Being active at the venous pole the secondary heart field (SHF) is essential for normal development of dorsal mesenchymal protrusion and AVCD formation and septation. Experimental data show that perturbations of different components of the Hh pathway can lead to developmental errors presenting with partially overlapping manifestations and AVCD as a common denominator. We review the potential role of Hh signaling in the pathogenesis of AVCD in different genetic disorders. AVCD can be viewed as part of a "developmental field," according to the concept that malformations can be due to defects in signal transduction cascades or pathways, as morphogenetic units which may be altered by Mendelian mutations, aneuploidies, and environmental causes.

Novel mutations in the ciliopathy-associated gene CPLANE1 (C5orf42) cause OFD syndrome type VI rather than Joubert syndrome

Mutations in CPLANE1 (previously known as C5orf42) cause Oral-Facial-Digital Syndrome type VI (OFD6) as well as milder Joubert syndrome (JS) phenotypes. Seven new cases from five unrelated families diagnosed with pure OFD6 were systematically examined. Based on the clinical manifestations of these patients and those described in the literature, we revised the diagnostic features of OFD6 and include the seven most common characteristics: 1) molar tooth sign, 2) tongue hamartoma and/or lobulated tongue, 3) additional frenula, 4) mesoaxial polydactyly of hands, 5) preaxial polydactyly of feet, 6) syndactyly and/or bifid toe, and 7) hypothalamic hamartoma. By whole or targeted exome sequencing, we identified seven novel germline recessive mutations in CPLANE1, including missense, nonsense, frameshift and canonical splice site variants, all causing OFD6 in these patients. Since CPLANE1 is also mutated in JS patients, we examined whether a genotype-phenotype correlation could be established. We gathered and compared 46 biallelic CPLANE1 mutations reported in 32 JS and 26 OFD6 patients. Since no clear correlation between paired genotypes and clinical outcomes could be determined, we concluded that patient's genetic background and gene modifiers may modify the penetrance and expressivity of CPLANE1 causal alleles. To conclude, our study provides a comprehensive view of the phenotypic range, the genetic basis and genotype-phenotype association in OFD6 and JS. The updated phenotype scoring system together with the identification of new CPLANE1 mutations will help clinicians and geneticists reach a more accurate diagnosis for JS-related disorders.

Novel STIL Compound Heterozygous Mutations Cause Severe Fetal Microcephaly and Centriolar Lengthening

STIL (SCL/TAL1 interrupting locus) is a core component of the centriole duplication process. STIL mutations have been associated with both autosomal recessive primary microcephaly (MCPH) and holoprosencephaly. In this report, we describe a family with multiple miscarriages and 2 terminations of pregnancy due to marked fetal microcephaly, delayed cortical gyrification, and dysgenesis of the corpus callosum. Whole exome sequencing allowed us to identify novel compound heterozygous mutations in STIL. The mutations lie, respectively, in the CPAP/CENPJ and the hsSAS6 interacting domains of STIL. M-phase synchronized amniocytes from both affected fetuses did not display an aberrant number of centrioles, as shown previously for either STIL-depleted or overexpressing cells. However, we observed an elongation of at least 1 centriole for each duplicated centrosome. These preliminary results may point to a novel mechanism causing MCPH and embryonic lethality in humans.

Micrognathia in mouse models of ciliopathies

Defects in the development of the mandible can lead to micrognathia, or small jaw, which manifests in ciliopathic conditions, such as orofaciodigital syndrome, Meckel-Gruber syndrome, and Bardet-Biedl syndrome. Although micrognathia occurs frequently in human and mouse ciliopathies, it has been difficult to pinpoint the underlying cellular causes. In this mini-review, we shed light on the tissue-specific contributions to ciliary dysfunction in the development of the mandible. First, we outline the steps involved in setting up the jaw primordium and subsequent steps in the outgrowth of the mandibular skeleton. We then determine the critical tissue interactions using mice carrying a conditional mutation in the cilia gene Ofd1 Our studies highlight the usefulness of the Ofd1 mouse model and illustrate long-term possibilities for understanding the cellular and biochemical events underlying micrognathia.

Acromelia-oligodontia syndrome

This case report describes a patient with ankyloglossia, oligodontia, unilateral hypoplasia of the zygoma and mandible, along with bilateral distal reduction anomalies of his limbs without long bone abnormalities. This may represent a mild variant of oromandibular limb hypogenesis syndrome, expanding the phenotypic spectrum, or a previously unrecognized malformation syndrome.

Fifteen years of research on oral-facial-digital syndromes: from 1 to 16 causal genes

Oral-facial-digital syndromes (OFDS) gather rare genetic disorders characterised by facial, oral and digital abnormalities associated with a wide range of additional features (polycystic kidney disease, cerebral malformations and several others) to delineate a growing list of OFDS subtypes. The most frequent, OFD type I, is caused by a heterozygous mutation in the OFD1 gene encoding a centrosomal protein. The wide clinical heterogeneity of OFDS suggests the involvement of other ciliary genes. For 15 years, we have aimed to identify the molecular bases of OFDS. This effort has been greatly helped by the recent development of whole-exome sequencing (WES). Here, we present all our published and unpublished results for WES in 24 cases with OFDS. We identified causal variants in five new genes (C2CD3, TMEM107, INTU, KIAA0753 and IFT57) and related the clinical spectrum of four genes in other ciliopathies (C5orf42, TMEM138, TMEM231 and WDPCP) to OFDS. Mutations were also detected in two genes previously implicated in OFDS. Functional studies revealed the involvement of centriole elongation, transition zone and intraflagellar transport defects in OFDS, thus characterising three ciliary protein modules: the complex KIAA0753-FOPNL-OFD1, a regulator of centriole elongation; the Meckel-Gruber syndrome module, a major component of the transition zone; and the CPLANE complex necessary for IFT-A assembly. OFDS now appear to be a distinct subgroup of ciliopathies with wide heterogeneity, which makes the initial classification obsolete. A clinical classification restricted to the three frequent/well-delineated subtypes could be proposed, and for patients who do not fit one of these three main subtypes, a further classification could be based on the genotype.

Oral-facial-digital syndrome type I cells exhibit impaired DNA repair; unanticipated consequences of defective OFD1 outside of the cilia network

Defects in OFD1 underlie the clinically complex ciliopathy, Oral-Facial-Digital syndrome Type I (OFD Type I). Our understanding of the molecular, cellular and clinical consequences of impaired OFD1 originates from its characterised roles at the centrosome/basal body/cilia network. Nonetheless, the first described OFD1 interactors were components of the TIP60 histone acetyltransferase complex. We find that OFD1 can also localise to chromatin and its reduced expression is associated with mis-localization of TIP60 in patient-derived cell lines. TIP60 plays important roles in controlling DNA repair. OFD Type I cells exhibit reduced histone acetylation and altered chromatin dynamics in response to DNA double strand breaks (DSBs). Furthermore, reduced OFD1 impaired DSB repair via homologous recombination repair (HRR). OFD1 loss also adversely impacted upon the DSB-induced G2-M checkpoint, inducing a hypersensitive and prolonged arrest. Our findings show that OFD Type I patient cells have pronounced defects in the DSB-induced histone modification, chromatin remodelling and DSB-repair via HRR; effectively phenocopying loss of TIP60. These data extend our knowledge of the molecular and cellular consequences of impaired OFD1, demonstrating that loss of OFD1 can negatively impact upon important nuclear events; chromatin plasticity and DNA repair.

Autosomal recessive IFT57 hypomorphic mutation cause ciliary transport defect in unclassified oral-facial-digital syndrome with short stature and brachymesophalangia

The 13 subtypes of oral-facial-digital syndrome (OFDS) belong to the heterogeneous group of ciliopathies. Disease-causing genes encode for centrosomal proteins, components of the transition zone or proteins implicated in ciliary signaling. A unique consanguineous family presenting with an unclassified OFDS with skeletal dysplasia and brachymesophalangia was explored. Homozygosity mapping and exome sequencing led to the identification of a homozygous mutation in IFT57, which encodes a protein implicated in ciliary transport. The mutation caused splicing anomalies with reduced expression of the wild-type transcript and protein. Both anterograde ciliary transport and sonic hedgehog signaling were significantly decreased in subjects' fibroblasts compared with controls. Sanger sequencing of IFT57 in 13 OFDS subjects and 12 subjects with Ellis-Van Creveld syndrome was negative. This report identifies the implication of IFT57 in human pathology and highlights the first description of a ciliary transport defect in OFDS, extending the genetic heterogeneity of this subgroup of ciliopathies.

Compound heterozygous NEK1 variants in two siblings with oral-facial-digital syndrome type II (Mohr syndrome)

The oral-facial-digital (OFD) syndromes comprise a group of related disorders with a combination of oral, facial and digital anomalies. Variants in several ciliary genes have been associated with subtypes of OFD syndrome, yet in most OFD patients the underlying cause remains unknown. We investigated the molecular basis of disease in two brothers with OFD type II, Mohr syndrome, by performing single-nucleotide polymorphism (SNP)-array analysis on the brothers and their healthy parents to identify homozygous regions and candidate genes. Subsequently, we performed whole-exome sequencing (WES) on the family. Using WES, we identified compound heterozygous variants c.[464G>C];[1226G>A] in NIMA (Never in Mitosis Gene A)-Related Kinase 1 (NEK1). The novel variant c.464G>C disturbs normal splicing in an essential region of the kinase domain. The nonsense variant c.1226G>A, p.(Trp409*), results in nonsense-associated alternative splicing, removing the first coiled-coil domain of NEK1. Candidate variants were confirmed with Sanger sequencing and alternative splicing assessed with cDNA analysis. Immunocytochemistry was used to assess cilia number and length. Patient-derived fibroblasts showed severely reduced ciliation compared with control fibroblasts (18.0 vs 48.9%, P<0.0001), but showed no significant difference in cilia length. In conclusion, we identified compound heterozygous deleterious variants in NEK1 in two brothers with Mohr syndrome. Ciliation in patient fibroblasts is drastically reduced, consistent with a ciliary defect pathogenesis. Our results establish NEK1 variants involved in the etiology of a subset of patients with OFD syndrome type II and support the consideration of including (routine) NEK1 analysis in patients suspected of OFD.

The ciliopathy-associated CPLANE proteins direct basal body recruitment of intraflagellar transport machinery

Cilia use microtubule-based intraflagellar transport (IFT) to organize intercellular signaling. Ciliopathies are a spectrum of human diseases resulting from defects in cilia structure or function. The mechanisms regulating the assembly of ciliary multiprotein complexes and the transport of these complexes to the base of cilia remain largely unknown. Combining proteomics, in vivo imaging and genetic analysis of proteins linked to planar cell polarity (Inturned, Fuzzy and Wdpcp), we identified and characterized a new genetic module, which we term CPLANE (ciliogenesis and planar polarity effector), and an extensive associated protein network. CPLANE proteins physically and functionally interact with the poorly understood ciliopathy-associated protein Jbts17 at basal bodies, where they act to recruit a specific subset of IFT-A proteins. In the absence of CPLANE, defective IFT-A particles enter the axoneme and IFT-B trafficking is severely perturbed. Accordingly, mutation of CPLANE genes elicits specific ciliopathy phenotypes in mouse models and is associated with ciliopathies in human patients.

Update on oral-facial-digital syndromes (OFDS)

Oral-facial-digital syndromes (OFDS) represent a heterogeneous group of rare developmental disorders affecting the mouth, the face and the digits. Additional signs may involve brain, kidneys and other organs thus better defining the different clinical subtypes. With the exception of OFD types I and VIII, which are X-linked, the majority of OFDS is transmitted as an autosomal recessive syndrome. A number of genes have already found to be mutated in OFDS and most of the encoded proteins are predicted or proven to be involved in primary cilia/basal body function. Preliminary data indicate a physical interaction among some of those proteins and future studies will clarify whether all OFDS proteins are part of a network functionally connected to cilia. Mutations in some of the genes can also lead to other types of ciliopathies with partially overlapping phenotypes, such as Joubert syndrome (JS) and Meckel syndrome (MKS), supporting the concept that cilia-related diseases might be a continuous spectrum of the same phenotype with different degrees of severity. To date, seven of the described OFDS still await a molecular definition and two unclassified forms need further clinical and molecular validation. Next-generation sequencing (NGS) approaches are expected to shed light on how many OFDS geneticists should consider while evaluating oral-facial-digital cases. Functional studies will establish whether the non-ciliary functions of the transcripts mutated in OFDS might contribute to any of the phenotypic abnormalities observed in OFDS.

OFIP/KIAA0753 forms a complex with OFD1 and FOR20 at pericentriolar satellites and centrosomes and is mutated in one individual with oral-facial-digital syndrome

Oral-facial-digital (OFD) syndromes are rare heterogeneous disorders characterized by the association of abnormalities of the face, the oral cavity and the extremities, some due to mutations in proteins of the transition zone of the primary cilia or the closely associated distal end of centrioles. These two structures are essential for the formation of functional cilia, and for signaling events during development. We report here causal compound heterozygous mutations of KIAA0753/OFIP in a patient with an OFD VI syndrome. We show that the KIAA0753/OFIP protein, whose sequence is conserved in ciliated species, associates with centrosome/centriole and pericentriolar satellites in human cells and forms a complex with FOR20 and OFD1. The decreased expression of any component of this ternary complex in RPE1 cells causes a defective recruitment onto centrosomes and satellites. The OFD KIAA0753/OFIP mutant loses its capacity to interact with FOR20 and OFD1, which may be the molecular basis of the defect. We also show that KIAA0753/OFIP has microtubule-stabilizing activity. OFD1 and FOR20 are known to regulate the integrity of the centriole distal end, confirming that this structural element is a target of importance for pathogenic mutations in ciliopathies.

TMEM107 Is a Critical Regulator of Ciliary Protein Composition and Is Mutated in Orofaciodigital Syndrome

The proximate causes of multiple human genetic syndromes (ciliopathies) are disruptions in the formation or function of the cilium, an organelle required for a multitude of developmental processes. We previously identified Tmem107 as a critical regulator of cilia formation and embryonic organ development in the mouse. Here, we describe a patient with a mutation in TMEM107 that developed atypical Orofaciodigital syndrome (OFD), and show that the OFD patient shares several morphological features with the Tmem107 mutant mouse including polydactyly and reduced numbers of ciliated cells. We show that TMEM107 appears to function within cilia to regulate protein content, as key ciliary proteins do not localize normally in cilia derived from the Tmem107 mouse mutant and the human patient. These data indicate that TMEM107 plays a key, conserved role in regulating ciliary protein composition, and is a novel candidate for ciliopathies of unknown etiology.

Joubert Syndrome in French Canadians and Identification of Mutations in CEP104

Joubert syndrome (JBTS) is a primarily autosomal-recessive disorder characterized by a distinctive mid-hindbrain and cerebellar malformation, oculomotor apraxia, irregular breathing, developmental delay, and ataxia. JBTS is a genetically heterogeneous ciliopathy. We sought to characterize the genetic landscape associated with JBTS in the French Canadian (FC) population. We studied 43 FC JBTS subjects from 35 families by combining targeted and exome sequencing. We identified pathogenic (n = 32 families) or possibly pathogenic (n = 2 families) variants in genes previously associated with JBTS in all of these subjects, except for one. In the latter case, we found a homozygous splice-site mutation (c.735+2T>C) in CEP104. Interestingly, we identified two additional non-FC JBTS subjects with mutations in CEP104; one of these subjects harbors a maternally inherited nonsense mutation (c.496C>T [p.Arg166*]) and a de novo splice-site mutation (c.2572-2A>G), whereas the other bears a homozygous frameshift mutation (c.1328_1329insT [p.Tyr444fs*3]) in CEP104. Previous studies have shown that CEP104 moves from the mother centriole to the tip of the primary cilium during ciliogenesis. Knockdown of CEP104 in retinal pigment epithelial (RPE1) cells resulted in severe defects in ciliogenesis. These observations suggest that CEP104 acts early during cilia formation by regulating the conversion of the mother centriole into the cilia basal body. We conclude that disruption of CEP104 causes JBTS. Our study also reveals that the cause of JBTS has been elucidated in the great majority of our FC subjects (33/35 [94%] families), even though JBTS shows substantial locus and allelic heterogeneity in this population.

Congenital Tongue Mass With Concomitant Cleft Palate and Bifid Tongue: A Case Report and Review of the Literature

A case report of a congenital, lingual, salivary gland choristoma with bifid tongue and cleft palate is presented. The patient was born with airway obstruction in supine positioning. Laryngoscopy revealed a midline tongue mass that extended into the hypopharyx and pathological examination showed a congenital ectopic salivary gland. The bifid tongue was repaired at the time of surgical excision. Literature review revealed nine additional cases of congenital lingual mass, bifid tongue, and cleft palate. The most common tongue mass reported was hamartoma (40%), but the differential diagnoses include hamartoma, teratoma, and salivary choristoma.

Unmasking the ciliopathies: craniofacial defects and the primary cilium

Over the past decade, the primary cilium has emerged as a pivotal sensory organelle that acts as a major signaling hub for a number of developmental signaling pathways. In that time, a vast number of proteins involved in trafficking and signaling have been linked to ciliary assembly and/or function, demonstrating the importance of this organelle during embryonic development. Given the central role of the primary cilium in regulating developmental signaling, it is not surprising that its dysfunction results in widespread defects in the embryo, leading to an expanding class of human congenital disorders known as ciliopathies. These disorders are individually rare and phenotypically variable, but together they affect virtually every vertebrate organ system. Features of ciliopathies that are often overlooked, but which are being reported with increasing frequency, are craniofacial abnormalities, ranging from subtle midline defects to full-blown orofacial clefting. The challenge moving forward is to understand the primary mechanism of disease given the link between the primary cilium and a number of developmental signaling pathways (such as hedgehog, platelet-derived growth factor, and WNT signaling) that are essential for craniofacial development. Here, we provide an overview of the diversity of craniofacial abnormalities present in the ciliopathy spectrum, and reveal those defects in common across multiple disorders. Further, we discuss the molecular defects and potential signaling perturbations underlying these anomalies. This provides insight into the mechanisms leading to ciliopathy phenotypes more generally and highlights the prevalence of widespread dysmorphologies resulting from cilia dysfunction.

Association of oral-facial-digital syndrome type VI (Varadi-Papp syndrome) with optochiasmatic pilocytic astrocytoma

INTRODUCTION

Varadi-Papp syndrome (VPS) or oral-facial-digital syndrome type VI (OFDS-VI) is a rare autosomal recessive disorder distinguished from other OFDSs by metacarpal abnormalities with central polydactyly and by cerebellar abnormalities. It can be associated with central nervous system tumors, which most commonly has been a hypothalamic hamartoma.

CLINICAL CASE REPORT

The boy had unusual facial features, developmental delay, limb malformations, and other phenotypic anomalies suggestive of VPS. X-ray of the hand and feet showed right hand polydactyly. He also had a deep wider peduncular fossa, thickened superior cerebellar peduncle, and inferior vermian hypoplasia along with optochiasmatic tumor. The patient underwent a right pterional craniotomy and tumor decompression. Histopathology was suggestive of a pilocytic astrocytoma.

CONCLUSION

This is the first case in available literature in which the OFDS-VI has been associated with an optochiasmatic pilocytic astrocytoma. We suggest an expansion of the disease spectrum of OFDS-VI to include the association of optochiasmatic pilocytic astrocytoma.