Nager acrofacial dysostosis: male-to-male transmission in 2 families

Molecular mechanisms of hearing loss in Nager syndrome

Nager syndrome is a rare human developmental disorder characterized by hypoplastic neural crest-derived craniofacial bones and limb defects. Mutations in SF3B4 gene, which encodes a component of the spliceosome, are a major cause for Nager. A review of the literature indicates that 45% of confirmed cases are also affected by conductive, sensorineural or mixed hearing loss. Conductive hearing loss is due to defective middle ear ossicles, which are neural crest derived, while sensorineural hearing loss typically results from defective inner ear or vestibulocochlear nerve, which are both derived from the otic placode. Animal model of Nager syndrome indicates that upon Sf3b4 knockdown cranial neural crest progenitors are depleted, which may account for the conductive hearing loss in these patients. To determine whether Sf3b4 plays a role in otic placode formation we analyzed the impact of Sf3b4 knockdown on otic development. Sf3b4-depleted Xenopus embryos exhibited reduced expression of several pan-placodal genes six1, dmrta1 and foxi4.1. We confirmed the dependence of placode genes expression on Sf3b4 function in animal cap explants expressing noggin, a BMP antagonist critical to induce placode fate in the ectoderm. Later in development, Sf3b4 morphant embryos had reduced expression of pax8, tbx2, otx2, bmp4 and wnt3a at the otic vesicle stage, and altered otic vesicle development. We propose that in addition to the neural crest, Sf3b4 is required for otic development, which may account for sensorineural hearing loss in Nager syndrome.

Rare syndromes of the head and face: mandibulofacial and acrofacial dysostoses

Craniofacial anomalies account for approximately one-third of all congenital birth defects reflecting the complexity of head and facial development. Craniofacial development is dependent upon a multipotent, migratory population of neural crest cells, which generate most of the bone and cartilage of the head and face. In this review, we discuss advances in our understanding of the pathogenesis of a specific array of craniofacial anomalies, termed facial dysostoses, which can be subdivided into mandibulofacial dysostosis, which present with craniofacial defects only, and acrofacial dysostosis, which encompasses both craniofacial and limb anomalies. In particular, we focus on Treacher Collins syndrome, Acrofacial Dysostosis-Cincinnati Type as well as Nager and Miller syndromes, and animal models that provide new insights into the molecular and cellular basis of these congenital syndromes. We emphasize the etiologic and pathogenetic similarities between these birth defects, specifically their unique deficiencies in global processes including ribosome biogenesis, DNA damage repair, and pre-mRNA splicing, all of which affect neural crest cell development and result in similar tissue-specific defects. WIREs Dev Biol 2017, 6:e263. doi: 10.1002/wdev.263 For further resources related to this article, please visit the WIREs website.

A synonymous splicing mutation in the SF3B4 gene segregates in a family with highly variable Nager syndrome

Nager syndrome is a rare preaxial acrofacial dysostosis that is caused by heterozygous loss-of-function variants in SF3B4. This gene encodes for a protein required for the assembly of spliceosomal complexes, being a master gene for splicing regulation. The main clinical features of Nager syndrome include facial-mandibular and preaxial limb malformations, with normal cognitive functioning. Most Nager patients are sporadic, but few familial cases with a highly variable phenotype have been reported. In this work, we report a novel synonymous variant within exon 3 of the SF3B4 gene in a family with three members affected by Nager syndrome. No pathogenic variants have been detected in other 24 genes associated with syndromes characterized by mandibulo-facial anomalies. The pathogenicity of the mutation was demonstrated through a hybrid minigene assay, which confirmed an aberrant splicing with the creation of a cryptic splice site, and showed that this allele is hypomorphic. Our findings emphasize the importance to perform functional analyses to assess the possible consequences of synonymous variants and confirmed that hybrid minigenes represent an effective tool to evaluate the effects of variants on splicing, particularly when RNA is not available.

Sf3b4-depleted Xenopus embryos: A model to study the pathogenesis of craniofacial defects in Nager syndrome

Mandibulofacial dysostosis (MFD) is a human developmental disorder characterized by defects of the facial bones. It is the second most frequent craniofacial malformation after cleft lip and palate. Nager syndrome combines many features of MFD with a variety of limb defects. Mutations in SF3B4 (splicing factor 3b, subunit 4) gene, which encodes a component of the pre-mRNA spliceosomal complex, were recently identified as a cause of Nager syndrome, accounting for 60% of affected individuals. Nothing is known about the cellular pathogenesis underlying Nager type MFD. Here we describe the first animal model for Nager syndrome, generated by knocking down Sf3b4 function in Xenopus laevis embryos, using morpholino antisense oligonucleotides. Our results indicate that Sf3b4-depleted embryos show reduced expression of the neural crest genes sox10, snail2 and twist at the neural plate border, associated with a broadening of the neural plate. This phenotype can be rescued by injection of wild-type human SF3B4 mRNA but not by mRNAs carrying mutations that cause Nager syndrome. At the tailbud stage, morphant embryos had decreased sox10 and tfap2a expression in the pharyngeal arches, indicative of a reduced number of neural crest cells. Later in development, Sf3b4-depleted tadpoles exhibited hypoplasia of neural crest-derived craniofacial cartilages, phenocopying aspects of the craniofacial skeletal defects seen in Nager syndrome patients. With this animal model we are now poised to gain important insights into the etiology and pathogenesis of Nager type MFD, and to identify the molecular targets of Sf3b4.

A 22-Week-Old Fetus with Nager Syndrome and Congenital Diaphragmatic Hernia due to a Novel SF3B4 Mutation

Nager syndrome, or acrofacial dysostosis type 1 (AFD1), is a rare multiple malformation syndrome characterized by hypoplasia of first and second branchial arches derivatives and appendicular anomalies with variable involvement of the radial/axial ray. In 2012, AFD1 has been associated with dominant mutations in SF3B4. We report a 22-week-old fetus with AFD1 associated with diaphragmatic hernia due to a previously unreported SF3B4 mutation (c.35-2A>G). Defective diaphragmatic development is a rare manifestation in AFD1 as it is described in only 2 previous cases, with molecular confirmation in 1 of them. Our molecular finding adds a novel pathogenic splicing variant to the SF3B4 mutational spectrum and contributes to defining its prenatal/fetal phenotype.

Facial dysostoses: Etiology, pathogenesis and management

Approximately 1% of all live births exhibit a minor or major congenital anomaly. Of these approximately one-third display craniofacial abnormalities which are a significant cause of infant mortality and dramatically affect national health care budgets. To date, more than 700 distinct craniofacial syndromes have been described and in this review, we discuss the etiology, pathogenesis and management of facial dysostoses with a particular emphasis on Treacher Collins, Nager and Miller syndromes. As we continue to develop and improve medical and surgical care for the management of individual conditions, it is essential at the same time to better characterize their etiology and pathogenesis. Here we describe recent advances in our understanding of the development of facial dysostosis with a view towards early in utero identification and intervention which could minimize the manifestation of anomalies prior to birth. The ultimate management for any craniofacial anomaly however, would be prevention and we discuss this possibility in relation to facial dysostosis.

Possible autosomal recessive inheritance in an infant with acrofacial dysostosis similar to Nager syndrome

The acrofacial dysostosis syndromes, which are characterized by malformations of the craniofacial region and limbs, are a clinically heterogeneous group of disorders. Based primarily on the of the pattern of limb defects two major groups have emerged: Nager syndrome with predominantly preaxial malformations plus mandibulofacial dysostosis (severe micrognathia and malar hypoplasia) and Miller syndrome with postaxial malformations plus mandibulofacial dysostosis. Among these syndromes, Nager syndrome is a rare condition but the most common form of acrofacial dysostosis. Most cases are sporadic, while autosomal dominant and autosomal recessive inheritance patterns have been reported. Recently, heterozygous mutations in the SF3B4 gene on chromosome 1q12-q21 were found to be responsible for a subset of sporadic and autosomal dominant cases. We present a female infant born to consanguineous parents with craniofacial features resembling Nager syndrome and a unilateral preaxial limb malformation. Mutation analysis of coding exons of SF3B4 did not identify any mutations. This couple also had a deceased child who had similar clinical features. We conclude that, the presence of consanguinity and absence of mutation in SF3B4, provides evidence in support of a recessive form of Nager syndrome.

Haploinsufficiency of SF3B4, a component of the pre-mRNA spliceosomal complex, causes Nager syndrome

Nager syndrome, first described more than 60 years ago, is the archetype of a class of disorders called the acrofacial dysostoses, which are characterized by craniofacial and limb malformations. Despite intensive efforts, no gene for Nager syndrome has yet been identified. In an international collaboration, FORGE Canada and the National Institutes of Health Centers for Mendelian Genomics used exome sequencing as a discovery tool and found that mutations in SF3B4, a component of the U2 pre-mRNA spliceosomal complex, cause Nager syndrome. After Sanger sequencing of SF3B4 in a validation cohort, 20 of 35 (57%) families affected by Nager syndrome had 1 of 18 different mutations, nearly all of which were frameshifts. These results suggest that most cases of Nager syndrome are caused by haploinsufficiency of SF3B4. Our findings add Nager syndrome to a growing list of disorders caused by mutations in genes that encode major components of the spliceosome and also highlight the synergistic potential of international collaboration when exome sequencing is applied in the search for genes responsible for rare Mendelian phenotypes.

Nager syndrome: a case report

Nager syndrome (preaxial acrofacial dysostosis) is rare and mostly sporadic. We present a case of Nager syndrome in Taiwan. Craniofacial findings included micrognathia, malar hypoplasia, downslanting palpebral fissures, cleft palate, and ear anomalies. Radial defects consisted of hypoplastic thumb, short forearm, and proximal radioulnar synostosis. Patent ductus arteriosus, atrial septal defect, lower limb deformities, and uncommon flat nasal bridge were noted. Nasal endotube passing through a narrowing oropharynx region or oral airway is life-saving before tracheostomy is performed on patients with Nager syndrome and restricted jaw opening and glossoptosis.

Acrofacial dysostosis syndromes: A relevant prenatal dilemma. A case report and brief literature review

The acrofacial dysostosis (AFD) syndromes are an heterogeneous group of disorders with undefined classification and inheritance. We report the sonographic and clinical features of an AFD fetus with predominantly pre-axial forms. We made a prenatal diagnosis of Nager syndrome but postnatal examination showed post-axial defects previously undetectable by ultrasound.

Holoprosencephaly and limb reduction defects: a consideration of Steinfeld syndrome and related conditions

Individuals with holoprosencephaly (HPE) and limb reduction defects have been ascribed historically to a variety of syndromes with overlapping phenotypic features. As such, these patients are challenges for clinicians and researchers alike. In an effort to better understand this association, we reviewed our autopsy records and identified five cases of HPE with reduction defects of the limbs and other anomalies. One case appears to be the third reported instance of Steinfeld syndrome, while others represent microgastria-limb reduction sequence, VATER/VACTERL association, and an additional unique condition characterized by HPE, rhombencephalosynapsis, absent left radius, first metacarpal, and thumb, and congenital heart disease. The phenotypic heterogeneity inherent in these patients continues to complicate diagnosis, which will hopefully be simplified by continuing delineation at morphologic and especially genetic levels.

Genitourinary anomalies in Mowat-Wilson syndrome with deletion/mutation in the zinc finger homeo box 1B gene (ZFHX1B). Report of three Italian cases with hypospadias and review

Hypospadias, when the urethra opens on the ventral side of the penis, is a common malformation seen in about 3 per 1,000 male births. It is a complex disorder associated with genetic and environmental factors and can be part of genetic syndromes. Mowat-Wilson syndrome (MWS) is a multiple congenital anomaly syndrome characterized by a distinct facial phenotype, Hirschsprung disease, microcephaly and mental retardation. It is caused by mutations in the zinc finger homeo box 1B gene, ZFHX1B (SIP1). To date, 68 deletion/mutation-positive cases have been reported. Genitourinary anomalies are common in MWS. Here we report that hypospadias is common in males with this syndrome. In 39 patients where this information was available, hypospadias was present in 46% of patients (18/39). In the 3 Italian male cases reported here, hypospadias was always present. MWS should be considered by endocrinologists in patients with hypospadias associated with developmental delays/mental retardation, in particular in the presence of a distinct facial phenotype.

Newly recognized autosomal recessive acrofacial dysostosis syndrome resembling Nager syndrome

We report on two patients with a unique constellation of anomalies resembling the Nager acrofacial dysostosis syndrome. Clinical manifestations which differentiate their condition from Nager syndrome include: microcephaly, cleft lip and palate, a peculiar beaked nose, blepharophimosis, microtia, symmetrical involvement of the thumbs, and great toes and developmental delay. We postulate that the inheritance is autosomal recessive on the basis of similarly affected male and female sibs.

Acrofacial dysostosis (AFD) with preaxial limb hypoplasia (Nager AFD) and club foot diagnosed in a fetus from 1812 in the anatomical collections at the University of Halle, Germany

The Anatomical Collections of the Department of Anatomy and Cell Biology at the University of Halle, Germany, comprise more than 8,000 specimens, about 600 of them congenital anomalies. The collection of abnormal human and animal specimens began with the private collections of Johann Friedrich Meckel the Elder (1724-1774), his son Philipp Friedrich Theodor Meckel (1755-1803), and his grandson Johann Friedrich Meckel the Younger (1781-1833). Meckel the Younger founded the science of developmental pathology in Germany. Radiographical techniques, computer tomographic methods (CT), magnetic resonance imaging (MRI), and molecular cytogenetic techniques, for example, comparative genomic hybridization (CGH) were used to diagnose abnormal human fetuses in the Meckel Collection. On examination of one of the human fetuses, originally described by JF Meckel the Younger in 1812 or earlier, we found striking clinical manifestations including mandibulofacial defects and preaxially malformed limbs. With respect to external findings, we propose that the condition is acrofacial dysostosis (AFD) with preaxial limb hypoplasia (Nager AFD) in combination with club foot, tibial torsion, and single umbilical artery. We used genetic analyses to test whether the observed limb malformations could be caused by aneuploidy. CGH-ratio profiles of all chromosomes were apparently normal. It is likely that Meckel's specimen is the earliest known fetus with Nager AFD.

Nager syndrome (preaxial acrofacial dysostosis): a case report

The Nager syndrome is a rare condition associated with craniofacial malformations such as micrognathia, zygomatic hypoplasia, cleft palate, and preaxial limb deformities. This report features a case of the Nager syndrome occurring in a 4-year-old boy showing microdontia, thumb duplication and radioulnar synostosis, and ventricular septum defect, characteristics not usually encountered in the published cases.

Trigonomicrocephaly, severe micrognathia, large ears, atrioventricular septal defect, symmetrical cutaneous syndactyly of hands and feet, and multiple café-au-lait spots: new acrocraniofacial dysostosis syndrome?

We report on a patient with a unique constellation of anomalies comprising trigonomicrocephaly, asymmetric severe micrognathia, large ears, atrioventricular septal defect, vertebral anomalies, bilateral cutaneous syndactyly of fingers and toes, unilateral cryptorchidism and multiple café-au-lait spots. The mother of the propositus has multiple café-au-lait spots. Search of POSSUM and the London Dysmorphology Database (LDDB) uncovered no similar case. We think that this patient represents a new acrocraniofacial dysostosis syndrome.

Mandibulofacial dysostosis, microcephaly and thorax deformities in two brothers: a new recessive syndrome?

We report two brothers who presented with mandibulofacial dysostosis, growth retardation, microcephaly, thoracic deformities and conductive hearing loss along with asplenia in one case and aplasia of the gallbladder in the other. The pattern of malformations differs significantly from established syndromes with mandibulofacial dysostosis such as Nager syndrome or Genée-Wiedemann syndrome and also from cerebro-costo-mandibular syndrome. As chromosome analysis revealed normal male karyotypes, we consider this to be a distinct heritable syndrome that may be either autosomal recessive or X-chromosomal recessive.

A nager acrofacial dysostosis syndrome patient with severe respiratory distress syndrome (RDS)

Nager acrofacial dysostosis is characterized by radial defect and the facial manifestations like Treacher-Collins syndrome. There are few reports about this syndrome in Japan. We report a typical Japanese Nager syndrome patient. He was complicated with respiratory distress syndrome.

Acrofacial dysostoses: review and report of a previously undescribed condition: the autosomal or X-linked dominant Catania form of acrofacial dysostosis

The acrofacial dysostoses (AFDs) are a heterogeneous group of disorders combining defects of craniofacial and limb development. The predominantly preaxial form is called Nager AFD, the predominantly postaxial form of AFD (POADS) is also known as the Genée-Wiedemann or Miller syndrome. The former appears to be about twice as common as the latter with well-documented autosomal dominant and recessive occurrences in both conditions. Only 1 AD occurrence of POADS is known, but 5 sets of sibs are suggestive of AR inheritance. Heterogeneity of apparently nonsyndromal AFD of both types is powerful support for the hypothesis that the AFDs are polytopic field defects arising during blastogenesis. Six other previously described forms of AFD include the AFD syndrome of Kelly et al. (AR), the Rodríguez or Madrid form of AFD (AR or XLR), the Reynolds or Idaho form of AFD (AD), the Arens or Tel Aviv type of AFD (AF?), the presumed AR AFD syndrome of Richieri-Costa et al., and the AD Patterson-Stevenson-Fontaine syndrome. Here we review the AFDs and report on a previously apparently undescribed autosomal or X-linked dominant form of AFD with mental retardation in a Sicilian mother and her 4 sons.

Nager acrofacial dysostosis

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Nager acrofacial dysostosis: minor familial manifestations supporting dominant inheritance

We report on a girl with Nager acrofacial dysostosis, three of whose relatives had variable mild anomalies of the thumb. The possible relationship of such minor features to the radial limb anomalies in the proposita provides further evidence that the Nager syndrome can be the manifestation of a dominantly inherited disorder with very variable expressivity.