Duplications involving the long range HMX1 enhancer are associated with human isolated bilateral concha-type microtia

Whole genome sequencing of a family with autosomal dominant features within the oculoauriculovertebral spectrum

Background

Oculoauriculovertebral Spectrum (OAVS) encompasses abnormalities on derivatives from the first and second pharyngeal arches including macrostomia, hemifacial microsomia, micrognathia, preauricular tags, ocular and vertebral anomalies. We present genetic findings on a three-generation family affected with macrostomia, preauricular tags and uni- or bilateral ptosis following an autosomal dominant pattern.

Methods

We generated whole genome sequencing data for the proband, affected parent and unaffected paternal grandparent followed by Sanger sequencing on 23 family members for the top 10 candidate genes: KCND2, PDGFRA, CASP9, NCOA3, WNT10A, SIX1, MTF1, KDR/VEGFR2, LRRK1, and TRIM2 We performed parent and sibling-based transmission disequilibrium tests and burden analysis via a penalized linear mixed model, for segregation and mutation burden respectively. Next, via bioinformatic tools we predicted protein function, mutation pathogenicity and pathway enrichment to investigate the biological relevance of mutations identified.

Results

Rare missense mutations in SIX1, KDR/VEGFR2, and PDGFRA showed the best segregation with the OAV phenotypes in this family. When considering any of the 3 OAVS phenotypes as an outcome, SIX1 had the strongest associations in parent-TDTs and sib-TDTs (p=0.025, p=0.052) (unadjusted p-values). Burden analysis identified SIX1 (RC=0.87) and PDGFRA (RC=0.98) strongly associated with OAVS severity. Using phenotype-specific outcomes, sib-TDTs identified SIX1 with uni- or bilateral ptosis (p=0.049) and ear tags (p=0.01), and PDGFRA and KDR/VEGFR2 with ear tags (both p<0.01).

Conclusion

SIX1, PDGFRA, and KDR/VEGFR2 are strongly associated to OAVS phenotypes. SIX1 has been previously associated with OAVS ear malformations and is co-expressed with EYA1 during ear development. Efforts to strengthen the genotype-phenotype co-relation underlying the OAVS are key to discover etiology, family counseling and prevention.

A 76-base pair duplication within the enhancer region of the HMX1 gene causes sheep microtia

Sheep congenital microtia is characterized by underdeveloped ears and provides an ideal basis for studying human microtia. This study identified the causal mutation and regulatory mechanisms underlying this disorder. Whole-genome association analysis was conducted using 23 ear tissue samples from sheep with microtia and 28 samples from normal-eared sheep. A significant correlation was found between microtia and a 76-base pair duplication in the enhancer region of the HMX1 gene. Further analysis of offspring phenotypes confirmed an autosomal dominant inheritance pattern. Genotypic analysis showed that individuals that are homozygous for this duplication were earless, heterozygous individuals exhibited shortened ears, and wild-type individuals had normal ears. Moreover, luciferase assays confirmed that this duplication increased HMX1 gene expression, and duplication knock-in mice also exhibited shorter and narrower external ears compared to wild-type mice. Transcriptomic analysis further demonstrated that this duplication enhanced HMX1 gene expression in animal models. This study characterized the causal regulatory mutation underlying sheep microtia.

Role of HOXA1-4 in the development of genetic and malignant diseases

The HOXA genes, belonging to the HOX family, encompass 11 members (HOXA1-11) and exert critical functions in early embryonic development, as well as various adult processes. Furthermore, dysregulation of HOXA genes is implicated in genetic diseases, heart disease, and various cancers. In this comprehensive overview, we primarily focused on the HOXA1-4 genes and their associated functions and diseases. Emphasis was placed on elucidating the impact of abnormal expression of these genes and highlighting their significance in maintaining optimal health and their involvement in the development of genetic and malignant diseases. Furthermore, we delved into their regulatory mechanisms, functional roles, and underlying biology and explored the therapeutic potential of targeting HOXA1-4 genes for the treatment of malignancies. Additionally, we explored the utility of HOXA1-4 genes as biomarkers for monitoring cancer recurrence and metastasis.

Genetic basis of ear length in sheep breeds sampled across the region from the Middle East to the Alps

Ear length in sheep (Ovis aries) shows a wide range of natural variation, from the absence of an outer ear structure (anotia), to small outer ears (microtia), to regular ear length. Up until now, the underlying genetics of this phenotype has been studied in four sheep breeds from China, Jordan and Italy. These studies revealed a broad range of genes significantly associated with ear length, potentially indicating genetic heterogeneity across breeds or geographic regions. In the current study, we performed genome-wide SNP genotyping and haplotype-based mapping, in a population of 340 individuals, to identify loci influencing ear length variation in additional sheep breeds from Slovenia, Croatia, Cyprus and Greece. Additionally, two previously described candidate variants were also genotyped in our mapping population. The mapping model without candidate variant genotypes revealed only one genome-wide significant signal, which was located next to HMX1 on OAR6. This region was previously described as being associated with ear length variation in the Altay and Awassi sheep breeds. The mapping model including the candidate duplication genotype near HMX1 as a fixed effect explained the phenotypic variance on OAR6 and revealed an additional genome-wide significant locus on OAR13 associated with ear length. Our results, combined with published evidence, suggest that a duplication in the evolutionarily conserved region near HMX1 is the major regulator of ear length in sheep breeds descended from a larger region from Central Asia, to the Middle East, Cyprus, Greece and to the Alps. This distribution suggests an ancient origin of the derived allele.

Subtractive thinking: A novel combined application of antihelix reconstruction and outer helix reconstruction to treat mild cases of type I to II conchal microtia

BACKGROUND

The management of mild cases of type Ⅰ to Ⅱ conchal microtia involves grafting cartilage to the affected ear to increase the cartilaginous area and transfer more skin to cover the larger cartilage. Herein, we performed a novel combined surgical procedure based on "subtractive thinking" that included antihelix reconstruction and outer helix reconstruction that was successful in patients with mild type I to II conchal microtia.

METHODS

From January 2018 to September 2022, 65 patients with mild, unilateral, type I to II conchal microtia were enrolled in this study. All patients were treated with a novel method at the Plastic Surgery Hospital of Peking Union Medical College. The perimeters, widths, and lengths of the healthy and affected ears were measured both preoperatively and postoperatively. Patients' levels of satisfaction were determined based on postoperative results.

RESULTS

The mean postoperative follow-up duration was 14.9 ± 2.65 months. All patients experienced no complications. Analysis revealed that our surgical method could effectively treat mild type I to II concha microtia irrespective of the auricular perimeter, width, and length (p < 0.0001). Furthermore, the patient satisfaction rate was 100%.

CONCLUSION

The combined surgical procedure, which includes antihelix and outer helix reconstructions, is a viable method of reconstructing type I to II auricular concha microtia.

Whole genome sequencing analysis of four patients: Are de novo copy number variations in non-coding region responsible for microtia with lung hypoplasia?

BACKGROUND

Microtia is a congenital malformation of the out ear, occurring either as an isolated defect or part of a specific pattern of multiple congenital anomalies. The etiology of microtia is poorly understood. Four patients with microtia and lung hypoplasia were reported by our team in a previous article. The purpose of this study was to identify the underlying genetic basis, mainly focusing on de novo copy number variations (CNVs) embedded in the noncoding region, in the four subjects.

METHODS

DNA samples from all four patients and their unaffected parents were extracted for whole-genome sequencing on the Illumina platform. All variants were obtained through data quality control, variant calling and bioinformatics analysis. De novo strategy was used to prioritize the variants, and candidate variants were verified by PCR amplification combined with Sanger sequencing and visual inspection of bam file.

RESULTS

Whole gene sequencing following bioinformatics analysis showed no potential de novo pathogenic variants in the coding region. Nonetheless, four de novo CNVs in the non-coding region, intronic or intergenic, were identified in each subject, ranging in size from 10 Kb to 12.5 Kb, and all are deletions. Case 1 had a de novo deletion of 10 Kb on chromosome10q22.3, located in the intronic region of the LRMDA gene. The other three cases all had a de novo deletion in intergenic regions, located on chromosome 20q11.21, 7q31.1 and 13q12.13, respectively.

CONCLUSIONS

This study reported multiple long-lived cases of microtia with pulmonary hypoplasia and provided genome-wide genetic analysis focusing on de novo mutations. Whether the de novo CNVs identified are responsible for the rare phenotypes remains an open question. However, the results of our study provided a new perspective that the unsolved etiology of microtia might involve in non-coding sequences, which have long been ignored.

Developmentally regulated expression of integrin alpha-6 distinguishes neural crest derivatives in the skin

Neural crest-derived cells play essential roles in skin function and homeostasis. However, how they interact with environmental cues and differentiate into functional skin cells remains unclear. Using a combination of single-cell data analysis, neural crest lineage tracing, and flow cytometry, we found that the expression of integrin α6 (ITGA6) in neural crest and its derivatives was developmentally regulated and that ITGA6 could serve as a functional surface marker for distinguishing neural crest derivatives in the skin. Based on the expression of ITGA6, Wnt1-Cre lineage neural crest derivatives in the skin could be categorized into three subpopulations, namely, ITGA6^bright, ITGA6^dim, and ITGA6^neg, which were found to be Schwann cells, melanocytes, and fibroblasts, respectively. We further analyzed the signature genes and transcription factors that specifically enriched in each cell subpopulation, as well as the ligand or receptor molecules, mediating the potential interaction with other cells of the skin. Additionally, we found that Hmx1 and Lhx8 are specifically expressed in neural crest-derived fibroblasts, while Zic1 and homeobox family genes are expressed in mesoderm-derived fibroblasts, indicating the distinct development pathways of fibroblasts of different origins. Our study provides insights into the regulatory landscape of neural crest cell development and identifies potential markers that facilitate the isolation of different neural crest derivatives in the skin.

OTX2 duplications: a recurrent cause of oculo-auriculo-vertebral spectrum

Background

Oculo-auriculo-vertebral spectrum (OAVS) is the second most common cause of head and neck malformations in children after orofacial clefts. OAVS is clinically heterogeneous and characterised by a broad range of clinical features including ear anomalies with or without hearing loss, hemifacial microsomia, orofacial clefts, ocular defects and vertebral abnormalities. Various genetic causes were associated with OAVS and copy number variations represent a recurrent cause of OAVS, but the responsible gene often remains elusive.

Methods

We described an international cohort of 17 patients, including 10 probands and 7 affected relatives, presenting with OAVS and carrying a 14q22.3 microduplication detected using chromosomal microarray analysis. For each patient, clinical data were collected using a detailed questionnaire addressed to the referring clinicians. We subsequently studied the effects ofOTX2overexpression in a zebrafish model.

Results

We defined a 272 kb minimal common region that only overlaps with theOTX2gene. Head and face defects with a predominance of ear malformations were present in 100% of patients. The variability in expressivity was significant, ranging from simple chondromas to severe microtia, even between intrafamilial cases. Heterologous overexpression ofOTX2in zebrafish embryos showed significant effects on early development with alterations in craniofacial development.

Conclusions

Our results indicate that properOTX2dosage seems to be critical for the normal development of the first and second branchial arches. Overall, we demonstrated thatOTX2genomic duplications are a recurrent cause of OAVS marked by auricular malformations of variable severity.

Oculo-auriculo-vertebral spectrum: new genes and literature review on a complex disease

Oculo-auriculo-vertebral spectrum (OAVS) or Goldenhar syndrome is due to an abnormal development of first and second branchial arches derivatives during embryogenesis and is characterised by hemifacial microsomia associated with auricular, ocular and vertebral malformations. The clinical and genetic heterogeneity of this spectrum with incomplete penetrance and variable expressivity, render its molecular diagnosis difficult. Only a few recurrent CNVs and genes have been identified as causatives in this complex disorder so far. Prenatal environmental causal factors have also been hypothesised. However, most of the patients remain without aetiology. In this review, we aim at updating clinical diagnostic criteria and describing genetic and non-genetic aetiologies, animal models as well as novel diagnostic tools and surgical management, in order to help and improve clinical care and genetic counselling of these patients and their families.

De novo 22q11.2 deletions and auricular findings in two Chinese patients with microtia

BACKGROUND

Congenital microtia is a common craniofacial malformation resulting from both environmental and genetic factors. Recurrent chromosomal imbalances were observed in patients with microtia. The 22q11.2 deletion is one of the most common microdeletions in human beings. The cell division cycle 45 gene (CDC45) embedded in the proximal 22q11.2 deleted region is involved in craniofacial development. However, only a few studies have focused on the 22q11.2 deletion as genetic etiology in microtia patients and studied its associated external ear deformity characteristics in detail.

METHODS

In this research, a total of 65 patients from north China with sporadic microtia were studied. Copy number variations of CDC45 were screened using AccuCopy assay. The 22q11.2 deletion harboring CDC45 was identified by whole-genome sequencing and targeted next-generation sequencing. A parental test was carried out to determine the origin of the deletion.

RESULTS

CDC45 copy number loss was identified in two patients with microtia. A set of qPCR assays demonstrated two patients carried a typical proximal 22q11.2 deletion between the low-copy repeats on chromosome 22q11.2 (LCR22A and LCR22D), encompassing CDC45. The 22q11.2 deletions were de novo in each patient. In-depth auricular phenotype assessment showed these two patients have a distinct concha-type ear malformation while other microtia patients have lobule-type microtia among the 65 microtia patient cohort in this study.

CONCLUSION

Here we present two additional Chinese microtia patients with de novo 22q11.2 proximal deletion harboring CDC45 and further report these patients' distinct ear malformation.

Generation of an induced pluripotent stem cell line from a congenital microtia patient with 4p16.1 microduplication involving the long-range enhancer of HMX1

Congenital microtia is a malformation of the middle and external ear. Duplications involving the ECR, an ear-specific long-range enhancer of HMX1, lead to ear malformation in different species. Use of electroporation of episomal plasmids encodes OCT4, SOX2, NANOG, LIN28, KLF4, and LMYC into peripheral blood mononuclear cells (PBMCs), we generated an induced pluripotent stem cell (iPSCs) line of a microtia patient carrying the duplication involving ECR. The iPSCs express pluripotency markers, have the potential to differentiate into three germ layers, and show the normal karyotype. This patient-specific iPSC will be used for modeling the pathophysiology of ear malformation.