Townes-Brocks syndrome versus expanded spectrum hemifacial microsomia: review of eight patients and further evidence of a "hot spot" for mutation in the SALL1 gene

Molecular diagnosis, clinical evaluation and phenotypic spectrum of Townes-Brocks syndrome: insights from a large Chinese hearing loss cohort

BACKGROUND

Townes-Brocks syndrome (TBS) is a rare genetic disorder characterised by multiple malformations. Due to its phenotypic heterogeneity and rarity, diagnosis and recognition of TBS can be challenging and there has been a lack of investigation of patients with atypical TBS in large cohorts and delineation of their phenotypic characteristics.

METHODS

We screened SALL1 and DACT1 variants using next-generation sequencing in the China Deafness Genetics Consortium (CDGC) cohort enrolling 20 666 unrelated hearing loss (HL) cases. Comprehensive clinical evaluations were conducted on seven members from a three-generation TBS family. Combining data from previously reported cases, we also provided a landscape of phenotypes and genotypes of patients with TBS.

RESULTS

We identified five novel and two reported pathogenic/likely pathogenic (P/LP) SALL1 variants from seven families. Audiological features in patients differed in severity and binaural asymmetry. Moreover, previously undocumented malformations in the middle and inner ear were detected in one patient. By comprehensive clinical evaluations, we further provide evidence for the causal relationship between SALL1 variation and certain endocrine abnormalities. Penetrance analysis within familial contexts revealed incomplete penetrance among first-generation patients with TBS and a higher disease burden among their affected offspring.

CONCLUSION

This study presents the first insight of genetic screening for patients with TBS in a large HL cohort. We broadened the phenotypic-genotypic spectrum of TBS and our results supported an underestimated prevalence of TBS. Due to the rarity and phenotypic heterogeneity of rare diseases, broader spectrum molecular tests, especially whole genome sequencing, can improve the situation of underdiagnosis and provide effective recommendations for clinical management.

Conductive Hearing Loss in Children

A variety of congenital and acquired disorders result in pediatric conductive hearing loss. Malformations of the external auditory canal are invariably associated with malformations of the middle ear space and ossicles. Isolated ossicular malformations are uncommon. Syndromes associated with external and middle ear malformations are frequently associated with abnormal development of first and second pharyngeal arch derivatives. Chronic inflammatory disorders include cholesteatoma, cholesterol granuloma, and tympanosclerosis.

Chromosomal Microarray Analysis Identifies a Novel SALL1 Deletion, Supporting the Association of Haploinsufficiency with a Mild Phenotype of Townes-Brocks Syndrome

SALL1 heterozygous pathogenic variants cause Townes-Brocks syndrome (TBS), a condition with variable clinical presentation. The main features are a stenotic or imperforate anus, dysplastic ears, and thumb malformations, and other common concerns are hearing impairments, foot malformations, and renal and heart defects. Most of the pathogenic SALL1 variants are nonsense and frameshift, likely escaping nonsense-mediated mRNA decay and causing disease via a dominant-negative mechanism. Haploinsufficiency may result in mild phenotypes, but only four families with distinct SALL1 deletions have been reported to date, with a few more being of larger size and also affecting neighboring genes. We report on a family with autosomal dominant hearing impairment and mild anal and skeletal anomalies, in whom a novel 350 kb SALL1 deletion, spanning exon 1 and the upstream region, was identified by array comparative genomic hybridization. We review the clinical findings of known individuals with SALL1 deletions and point out that the overall phenotype is milder, especially when compared with individuals who carry the recurrent p.Arg276Ter mutation, but with a possible higher risk of developmental delay. Chromosomal microarray analysis is still a valuable tool in the identification of atypical/mild TBS cases, which are likely underestimated.

Novel mutation in the SALL1 gene in a four-generation Chinese family with uraemia: A case report

BACKGROUND

Approximately 10% of adults and nearly all children who receive renal replacement therapy have inherited risk factors or are related to genetic factors. In the past, due to the limitations of detection technology and the nonspecific manifestations of uraemia, the etiological diagnosis is unclear. In addition to common monogenic diseases and complex disorders, advanced testing techniques have led to the recognition of more hereditary renal diseases. Here, we report a four-generation Chinese family in which four individuals had a novel SALL1 mutation and presented with uraemia or abnormal urine tests.

CASE SUMMARY

A 32-year-old man presented with end-stage renal disease with a 4-year history of dialysis. His father and paternal aunt both had a history of unexplained renal failure with haemodialysis, and his 10-year-old daughter presented with proteinuria. The patient had multiple congenital abnormalities, including bilateral overlapping toes, unilateral dysplastic external ears, and sensorineural hearing loss. His family members also presented with similar defects. Genetic testing revealed that the proband carried a novel heterozygous shift mutation in SALL1_exon 2 (c.3437delG), and Sanger sequencing confirmed the same mutation in all affected family members.

CONCLUSION

We report a novel SALL1 exon 2 (c.3437delG) mutation and clinical syndrome with kidney disease, bilateral overlapping toes, unilateral dysplastic external ears, and sensorineural hearing loss in a four-generation Chinese family.

LUZP1: A new player in the actin-microtubule cross-talk

LUZP1 (leucine zipper protein 1) was first described as being important for embryonic development. Luzp1 null mice present defective neural tube closure and cardiovascular problems, which cause perinatal death. Since then, LUZP1 has also been implicated in the etiology of diseases like the 1p36 and the Townes-Brocks syndromes, and the molecular mechanisms involving this protein started being uncovered. Proteomics studies placed LUZP1 in the interactomes of the centrosome-cilium interface, centriolar satellites, and midbody. Concordantly, LUZP1 is an actin and microtubule-associated protein, which localizes to the centrosome, the basal body of primary cilia, the midbody, actin filaments and cellular junctions. LUZP1, like its interactor EPLIN, is an actin-stabilizing protein and a negative regulator of primary cilia formation. Moreover, through the regulation of actin, LUZP1 has been implicated in the regulation of cell cycle progression, cell migration and epithelial cell apical constriction. This review discusses the latest findings concerning LUZP1 molecular functions and implications in disease development.

Adult diagnosis of Townes-Brocks syndrome with renal failure: Two related cases and review of literature

Townes-Brocks syndrome (TBS) is a rare autosomal dominant syndrome, resulting from heterozygous variant in SALL1 gene and initially characterized by the triad of anorectal, thumb, and ear malformations. Essentially described in children, adult case reports are uncommon. Renal involvement has already been reported in adults and children but poorly described. Structural abnormalities such as hypodysplasia, unilateral renal agenesis or multicystic kidneys have been described, as well as functional impairment (with or without structural abnormalities) that may progress to end-stage renal disease (ESRD). We report two adult cases (mother and daughter) which exhibited kidney hypoplasia (focal and segmental glomerulosclerosis for the mother) and ESRD. The mother had unilateral polydactyly. TBS was suggested after physical examination. TBS diagnosis was confirmed by identification of a SALL1 variant. We conducted a literature review to evaluate the renal anomalies in TBS cases diagnosed in adulthood. Among 44 adult cases of TBS with genetic confirmation (including our two cases), 10 had kidney disease. The circumstances of renal failure diagnosis were incidental findings (2/5), gout (2/5), or repeated episodes of pyelonephritis (1/5). The median age of kidney disease diagnosis was 30 years old and of renal transplant 49 years old. The most frequent renal malformation was bilateral kidney hypoplasia. TBS is probably underestimated in adulthood and this report highlights that less obvious elements of morphology such as dysplasic ears can facilitate the diagnosis of TBS. As long-term prognosis of renal involvement in TBS patients remains largely unknown, a regular evaluation is required throughout life for patients.

Haploinsufficiency of BMP4 and OTX2 in the Foetus with an abnormal facial profile detected in the first trimester of pregnancy

Background

Interstitial microdeletion 14q22q23 is a rare chromosomal syndrome associated with variable defects: microphthalmia/anophthalmia, pituitary anomalies, polydactyly/syndactyly of hands and feet, micrognathia/retrognathia. The reports of the microdeletion 14q22q23 detected in the prenatal stages are limited and the range of clinical features reveals a quite high variability.

Case presentation

We report a detection of the microdeletion 14q22.1q23.1 spanning 7,7 Mb and involving the genes BMP4 and OTX2 in the foetus by multiplex ligation-dependent probe amplification (MLPA) and verified by microarray subsequently. The pregnancy was referred to the genetic counselling for abnormal facial profile observed in the first trimester ultrasound scan and micrognathia (suspicion of Pierre Robin sequence), hypoplasia nasal bone and polydactyly in the second trimester ultrasound scan. The pregnancy was terminated on request of the parents.

Conclusion

An abnormal facial profile detected on prenatal scan can provide a clue to the presence of rare chromosomal abnormalities in the first trimester of pregnancy despite the normal result of the first trimester screening test. The patients should be provided with genetic counselling. Usage of quick and sensitive methods (MLPA, microarray) is preferable for discovering a causal aberration because some of the CNVs cannot be detected with conventional karyotyping in these cases. To the best of our knowledge, this is the earliest detection of this microdeletion (occurred de novo), the first case detected by MLPA and confirmed by microarray. Literature review of the genotype-phenotype correlation in similar reports leads us to the conclusion that dosage imbalance of the chromosomal segment 14q22q23 (especially haploinsuffiency of the genes BMP4 and OTX2) contributes significantly to orofacial abnormalities. Association of the region with the Pierre Robin sequence appears to be plausible.

Androgen Regulates Mafb Expression Through its 3'UTR During Mouse Urethral Masculinization

External genitalia are prominent organs showing hormone-dependent sexual differentiation. Androgen is an essential regulator of masculinization of the genital tubercle, which is the anlage of external genitalia. We have previously shown that v-maf avian musculoaponeurotic fibrosarcoma oncogene homolog B (MAFB) is an androgen-inducible regulator of embryonic urethral masculinization in mice. However, it remains unclear how androgen regulates Mafb expression. The current study suggests that the Mafb 3' untranslated region (UTR) is an essential region for its regulation by androgen. We identified 2 functional androgen response elements (AREs) in Mafb 3'UTR. Androgen receptor is bound to such AREs in 3'UTR during urethral masculinization. In addition to 3'UTR, Mafb 5'UTR also showed androgen responsiveness. Moreover, we also demonstrated that β-catenin, one of genital tubercle masculinization factors, may be an additional regulator of Mafb expression during urethral masculinization. This study provides insights to elucidate mechanisms of gene regulation through AREs present in Mafb 3'UTR for a better understanding of the processes of urethral masculinization.

OTX2 duplication is implicated in hemifacial microsomia

Hemifacial microsomia (HFM) is the second most common facial anomaly after cleft lip and palate. The phenotype is highly variable and most cases are sporadic. We investigated the disorder in a large pedigree with five affected individuals spanning eight meioses. Whole-exome sequencing results indicated the absence of a pathogenic coding point mutation. A genome-wide survey of segmental variations identified a 1.3 Mb duplication of chromosome 14q22.3 in all affected individuals that was absent in more than 1000 chromosomes of ethnically matched controls. The duplication was absent in seven additional sporadic HFM cases, which is consistent with the known heterogeneity of the disorder. To find the critical gene in the duplicated region, we analyzed signatures of human craniofacial disease networks, mouse expression data, and predictions of dosage sensitivity. All of these approaches implicated OTX2 as the most likely causal gene. Moreover, OTX2 is a known oncogenic driver in medulloblastoma, a condition that was diagnosed in the proband during the course of the study. Our findings suggest a role for OTX2 dosage sensitivity in human craniofacial development and raise the possibility of a shared etiology between a subtype of hemifacial microsomia and medulloblastoma.

Distinctive spine abnormalities in patients with Goldenhar syndrome: tomographic assessment

PURPOSE

Goldenhar syndrome consists of a combination of unilateral auricular appendages, auricular fistulas, and ocular epibulbar dermoids combined with a unilateral underdevelopment of the craniofacial structures and vertebral abnormalities. We aimed to elicit the underlying spine pathology in a group of patients via tomographic assessment.

MATERIALS AND METHODS

Hemifacial microsomia, cranial asymmetry, multiple ear tags, skin tags around the mouth and microtia were the most prominent facial features encountered in six patients with Goldenhar syndrome. Torticollis and cervico-thoracic scoliosis were the major deformities encountered in all patients. Thoraco-lumbar scoliosis and kyphoscoliosis were of lesser occurrence. Tomographic studies have been applied to all patients to delineate the underlying pathology.

RESULTS

Diverse spectrum of distinctive spine anomalies has been identified. Malsegmentation of the skull base associated with diffuse fusion with the upper cervical vertebrae was the most common spine pathology. Bilateral failure of segmentation, unilateral unsegmented bar and failure of vertebral formation were of lesser occurrence. Strikingly, we observed that the side of the hemifacial microsomia is strongly correlated with that of the craniocervical and the cervical vertebral abnormalities.

CONCLUSION

The importance of this paper is threefold; first, little information is available in the literature regarding the magnitude and the diversity of spine pathology in patients with Goldenhar syndrome. Second, is to alert spine specialists that conventional radiographic assessment of the craniocervical area is an insufficient modality to assess children with syndromic associations. Third, a rotation and flexion deformity of the neck associated with facial asymmetry and/or plagiocephaly should be considered as a syndromic entity rather than a simple physiological deformation.

A comprehensive review of the genetic basis of cleft lip and palate

Cleft lip and palate (CLP) are birth defects that affect the upper lip and the roof of the mouth. CLP has a multifactorial etiology, comprising both genetic and environmental factors. In this review we discuss the recent data on the etiology of cleft lip and palate. We conducted a search of the MEDLINE database (Entrez PubMed) from January 1986 to December 2010 using the key words: ‘cleft lip,’ ‘cleft palate,’ ‘etiology,’ and ‘genetics.’ The etiology of CLP seems complex, with genetics playing a major role. Several genes causing syndromic CLP have been discovered. Three of them—T-box transcription factor-22 (TBX22), poliovirus receptor-like-1 (PVRL1), and interferon regulatory factor-6 (IRF6)—are responsible for causing X-linked cleft palate, cleft lip/palate–ectodermal dysplasia syndrome, and Van der Woude and popliteal pterygium syndromes, respectively; they are also implicated in nonsyndromic CLP. The nature and functions of these genes vary widely, illustrating the high vulnerability within the craniofacial developmental pathways. The etiological complexity of nonsyndromic cleft lip and palate is also exemplified by the large number of candidate genes and loci. To conclude, although the etiology of nonsyndromic CLP is still largely unknown, mutations in candidate genes have been identified in a small proportion of cases. Determining the relative risk of CLP on the basis of genetic background and environmental influence (including smoking, alcohol use, and dietary factors) will be useful for genetic counseling and the development of future preventive measures.

Genome-wide scanning reveals complex etiology of oculo-auriculo-vertebral spectrum

Oculo-auriculo-vertebral spectrum (OAVS) is a common developmental disorder involving first and second pharyngeal arches. Although some family cases and such patients showing chromosomal aberrations suggest that OAVS have a genetic basis, no consistent genetic defects have been recorded at present time. Thus, we conducted genetic studies of a three-generation family with five OAVS patients to identify a causative variant for OAVS. Cytogenetic studies revealed those family members had a normal karyotype and no causative mutations were founded in SALL1 and TCOF1, which known to be responsible for two other syndromes that have clinical overlapping with OAVS. Genotyping with commercially available BeadChips was performed on 13 individuals in the same family, showing no significant difference between the affected and normal members in terms of copy number variations (CNVs) in either number or size and no definitive causative CNV. A total of 8,224 informative autosomal SNPs that are evenly distributed throughout the genome were selected for both parametric and non-parametric linkage analysis. Significant negative LOD scores were obtained for the reported OAVS locus, providing further evidence for genetic heterogeneity of this complex disorder. The highest LOD score of 1.60 was noted on chromosome 15q26.2-q26.3 showing a potential linkage to this locus. The variable phenotypes of the affected members and the failure to identify a causative variant indicate that a complex etiology may be present even in a consanguineous family, which makes it more challenging to ascertain the cause of OAVS in further analysis.

Array-CGH in a series of 30 patients with mental retardation, dysmorphic features, and congenital malformations detected an interstitial 1p22.2-p31.1 deletion in a patient with features overlapping the Goldenhar syndrome

Genosensor Array 300 (Abbott) is a multiplex platform for array-based comparative genomic hybridization that detects unbalanced genomic aberrations including whole chromosome gains/losses, microdeletions, duplications and unbalanced subtelomeric rearrangements. A series of 30 patients with unexplained mental retardation, dysmorphic features, congenital abnormalities and normal high resolution karyotype and FISH subtelomeric studies were analyzed using Genosensor Array 300 array-CGH. We identified a chromosomal aberration in one patient with an interstitial 1p31.1 deletion. FISH analysis with BACs specific probes of the 1p region confirmed the interstitial 1p22.2-p31.1 deletion. The patient was a 20-year-old man with short stature, facial dysmorphism including asymmetry, scoliosis, severe psychomotor delay and an epibulbar dermoid cyst. The phenotype was compatible with Goldenhar syndrome despite the absence of asymmetric ears. This observation is of interest since it could be a clue in the search for the genes responsible for Goldenhar syndrome. This study demonstrates the utility of the array-CGH technology in detecting interstitial deletions.

Oculoauriculovertebral spectrum with radial defects: a new syndrome or an extension of the oculoauriculovertebral spectrum? Report of fourteen Brazilian cases and review of the literature

The first and second branchial arches are embryonic primordium that contributes to craniofacial development. Interferences in normal development of these structures result in variable maxillary, mandibular, and ear abnormalities. These anomalies can be isolated or part of some known and unknown conditions, among them, the oculoauriculovertebral spectrum (OAVS). Malformations of the external ear or microtia are mandatory features of the OAVS and occur as an isolated malformation (population frequency of 0.03%), or in association with other anomalies such as mandible hypoplasia, epibulbar dermoids, and spinal vertebral defects. Extreme variability of phenotypic manifestations is the main feature of the OAVS and, developmental anomalies are not restricted to facial structures. Cardiac, pulmonary, renal, skeletal, and central nervous system involvements have been observed in patients presented with this condition. Radial defects, although rare, have been reported. In this study, we report on the clinical aspects of 14 Brazilian patients with first and second branchial arches abnormalities associated with radial defects and we compared these data with those of 26 cases in the literature. We postulate that radial defects associated with OAVS might represent a subset within this spectrum.

Distinctive collection of fetal anomalies: cleft lip and palate, multicystic dysplastic kidneys, 1-2 syndactyly, heterotopic olivary tissue and thymic hypoplasia

A female fetus with an unusual collection of congenital anomalies was detected prenatally. The pregnancy was terminated at 21 weeks of gestation. Clinical and pathological findings of bilateral cleft lip and palate, micrognathia, thymic hypoplasia, unilateral 1-2 finger syndactyly, bilateral multicystic dysplastic kidneys and heterotopic olivary tissue are presented. Differential diagnoses are discussed.

A family with features overlapping Okihiro syndrome, hemifacial microsomia and isolated Duane anomaly caused by a novelSALL4 mutation

The SALL4 gene encodes a putative zinc finger transcription factor and is located on chromosome 20q13.13-13.2. Mutations in SALL4 have been identified in patients with Okihiro syndrome, which is characterized by radial ray anomalies associated with a Duane anomaly. Here, we report an unusual family in which affected persons show an extremely variable phenotype consistent with either Okihiro syndrome, hemifacial microsomia, or isolated Duane anomaly. A novel nonsense mutation in the SALL4 gene was detected in all affected family members and obligate carriers. This mutation is located in exon 3, only 29 bp 5' of the most 3' intron, and would therefore be expected to escape the nonsense mediated mRNA decay pathway, which might explain the phenotypic variability and mild degree of limb involvement.

Drosophila spalt/spalt-related mutants exhibit Townes-Brocks' syndrome phenotypes

Mutations in SALL1, the human homolog of the Drosophila spalt gene, result in Townes-Brocks' syndrome, which is characterized by hand/foot, anogenital, renal, and ear anomalies, including sensorineural deafness. spalt genes encode zinc finger transcription factors that are found in animals as diverse as worms, insects, and vertebrates. Here, we examine the effect of losing both of the spalt genes, spalt and spalt-related, in the fruit fly Drosophila melanogaster, and report defects similar to those in humans with Townes-Brocks' syndrome. Loss of both spalt and spalt-related function in flies yields morphological defects in the testes, genitalia, and the antenna. Furthermore, spalt/spalt-related mutant antennae show severe reductions in Johnston's organ, the major auditory organ in Drosophila. Electrophysiological analyses confirm that spalt/spalt-related mutant flies are deaf. These commonalities suggest that there is functional conservation for spalt genes between vertebrates and insects.

Goldenhar and cri-du-chat syndromes: a contiguous gene deletion syndrome?

We report a full-term male infant born to nonconsanguinous parents who had clinical features of Goldenhar syndrome and cri du chat syndrome. At birth, the infant was noted to have dysmorphic features with bilateral preauricular tags, rotated ears, bilateral epicanthic folds, a left epibulbar lipodermoid, and an accessory left nipple. After he was assessed for feeding difficulty and tachypnea, he was found to have esophageal atresia with tracheoesophageal fistula. In addition, he had a high-pitched, cat-like cry, characteristic of cri-du-chat syndrome. He also failed a hearing test. Chromosomal analysis and fluorescence in situ hybridisation studies showed an unbalanced karyotype with a terminal deletion of the segment p14 on the short arm of chromosome 5, which is consistent with the cri-du-chat locus. The association of Goldenhar syndrome and cri-du-chat syndrome in this patient suggests that the chromosome 5p14 locus may harbor a gene implicated with Goldenhar syndrome.