A Novel Heterozygous Intragenic Sequence Variant in DLX6 Probably Underlies First Case of Autosomal Dominant Split-Hand/Foot Malformation Type 1

Orthologs at the Base of the Olfactores Clade

Tunicate orthologs in the human genome comprise just 84 genes of the 19,872 protein-coding genes and 23 of the 16,528 non-coding genes, yet they stand at the base of the Olfactores clade, which radiated to generate thousands of tunicate and vertebrate species. What were the powerful drivers among these genes that enabled this process? Many of these orthologs are present in gene families. We discuss the biological role of each family and the orthologs' quantitative contribution to the family. Most important was the evolution of a second type of cadherin. This, a Type II cadherin, had the property of detaching the cell containing that cadherin from cells that expressed the Type I class. The set of such Type II cadherins could now detach and move away from their Type I neighbours, a process which would eventually evolve into the formation of the neural crest, "the fourth germ layer", providing a wide range of possibilities for further evolutionary invention. A second important contribution were key additions to the broad development of the muscle and nerve protein and visual perception toolkits. These developments in mobility and vision provided the basis for the development of the efficient predatory capabilities of the Vertebrata.

Gollop-Wolfgang Complex Is Associated with a Monoallelic Variation in WNT11

Gollop-Wolfgang complex (GWC) is a rare congenital limb anomaly characterized by tibial aplasia with femur bifurcation, ipsilateral bifurcation of the thigh bone, and split hand and monodactyly of the feet, resulting in severe and complex limb deformities. The genetic basis of GWC, however, has remained elusive. We studied a three-generation family with four GWC-affected family members. An analysis of whole-genome sequencing results using a custom pipeline identified the WNT11 c.1015G>A missense variant associated with the phenotype. In silico modelling and an in vitro reporter assay further supported the link between the variant and GWC. This finding further contributes to mapping the genetic heterogeneity underlying split hand/foot malformations in general and in GWC specifically.

Variable clinical presentation of split hand/foot malformation syndrome in a family with microduplication of 10q24.32: a case report

SHFM (Split Hand/Foot Malformation) is a heterogeneous group of disorders characterized by the presence of clefts in the hands and feet, along with syndactyly of the digits. In this article, we describe a family in which two members exhibit characteristic developmental abnormalities associated with SHFM, presenting with variable clinical features. Using whole-genome sequencing, we identified a microduplication of a chromosomal segment on locus 10q24.32, specifically spanning positions 102934495 to 103496555, encompassing genes BTRC, POLL, FBXW4 and LBX1 in the proband. Genomic duplications, including these genes, were previously described in patients diagnosed with the third type of SHFM. We validated the presence of this structural rearrangement in 7 family members, including the proband and the proband's father. Remarkably, further investigation demonstrated that the detected duplication exhibits a mosaic state in the phenotypically normal paternal grandmother of the proband, thereby providing a plausible explanation for the absence of a pathological phenotype in her.

Sequence Variants in the WNT10B Underlying Non-Syndromic Split-Hand/Foot Malformation

Introduction

Split hand and foot malformation (SHFM) or ectrodactyly is a rare limb deformity characterized by median cleft of the hand and foot with impaired or missing central rays. It can occur as an isolated anomaly or in association with abnormalities of other body parts.

Methods

After delineating the clinical features of two families (A-B), with non-syndromic SHFM, exome and Sanger sequencing were employed to search for the disease-causing variants.

Results

Analysis of exome and Sanger sequencing data revealed two causative variants in the WNT10B gene in affected members of the two families. This included a novel missense change [c.338G>C; p.(Gly113Ala)] in family A and a previously reported frameshift variant [c.884-896delTCCAGCCCCGTCT; p.(Phe295Cysfs*87)] in family B.

Conclusion

Our findings add a novel variant in WNT10B gene as the underlying cause of SHFM. The finding adds to the growing body of knowledge about the genetic basis of developmental disorders and provides valuable insights into the molecular mechanisms that regulate limb development.

A genotype-phenotype correlation in split-hand/foot malformation type 1: further refinement of the phenotypic subregions within the 7q21.3 locus

Background: Split-hand/foot malformation type 1 (SHFM1) refers to the group of rare congenital limb disorders defined by the absence or hypoplasia of the central rays of the autopods with or without accompanying anomalies, such as hearing loss, craniofacial malformation, and ectodermal dysplasia. Consequently, the condition is characterized by clinical variability that hinders diagnostic and counseling procedures. SHFM1 is caused by pathogenic variants affecting the DLX5/6 genes and/or their tissue-specific enhancers at the 7q21.3 locus. Herein, we report on seven patients from five unrelated Polish families affected by variable symptoms of the SHFM1 spectrum, all harboring 7q21.3 or 7q21.2-q21.3 rearrangements, and provide a genotype-phenotype correlation in the studied cohort. Methods: We applied GTG banding, array-based comparative genomic hybridization (aCGH), and whole-genome sequencing (WGS) in order to identify the causative aberrations in all affected patients. Results: The identified pathogenic structural variants included deletions and/or translocations involving the 7q21.3 locus, i.e., t(7;10)(q21.3;q22.2) and t(7;12)(q21.3;q21.2) in all affected individuals. Interestingly, a sporadic carrier of the latter aberration presented the SHFM1 phenotype with additional features overlapping with Baker-Gordon syndrome (BAGOS), which resulted from the translocation breakpoint at chromosome 12 within the SYT1 gene. Conclusion: Clinical variability of the studied cohort reflects the composition of the DLX5/6 regulatory elements that were dislocated from their target genes by chromosomal rearrangements. The correlation of our data with the previously published observations enabled us to update the phenotypic subregions and regulatory units within the SHFM1 locus. In addition, we present the first case of SHFM1 and BAGOS-like phenotype that resulted from translocation breakpoints at chromosomes 7 and 12, both of which were pathogenic, and consequently, we show the first evidence that BAGOS can also result from the regulatory loss-of-function SYT1 mutations. In this paper, we emphasize the utility of sequence-based approaches in molecular diagnostics of disorders caused by regulatory structural variants.

A novel homozygous nonsense mutation in NECTIN4 gene in a Pakistani family with ectodermal dysplasia syndactyly syndrome 1

BACKGROUND

Ectodermal dysplasia syndactyly syndrome 1 (EDSS1) is a rare hereditary disorder characterized by defects in teeth, hair, and nails in association with a fusion of the digits. Genetically, the disease phenotypes are caused by homozygous and compound heterozygous variants in NECTIN4 gene.

OBJECTIVE

The main objective of the study was to identify the pathogenic sequence variant(s) for family screening and identification of carriers.

METHODS

In the present study, the authors have investigated a large consanguineous family of Pakistani origin segregating autosomal recessive EDSS1. All the coding exons of the NECTIN4 gene were directly sequenced using gene-specific primers.

RESULTS

The affected individuals presented the classical EDSS1 clinical features including sparse hair, hypoplastic nails with thick flat discolored nail plates, peg-shaped, conical, and widely spaced teeth with enamel hypoplasia, proximal cutaneous syndactyly of fingers and toes. Sequence analysis of the coding region of the NECTIN4 identified a novel nonsense variant [c.163C>T; p.(Arg55*)] in exon-2 of the gene. Computational analysis of protein structure revealed that the variant induced premature termination at Arg55 located in Ig-like V-loop region leading to loss of Ig-C2 type domains and transmembrane region, and most likely Nectin-4 function will be lost.

STUDY LIMITATION

Gene expression studies are absent that would have strengthened the findings of computational analysis.

CONCLUSION

The present study expanded the phenotypic and mutation spectrum of the NECTIN4 gene. Further, the study would assist in carrier testing and prenatal diagnosis of the affected families.

Split Hand-Foot and Deafness in a Patient with 7q21.13-q21.3 Deletion Not Including the DLX5/6 Genes

Split Hand-Foot Malformation (SHFM) is a congenital limb defect characterized by a median cleft of the hands and/or feet due to the absence/hypoplasia of the central rays. It may occur as part of a syndromic condition or as an isolated malformation. The most common of the six genetic loci identified for this condition is correlated to SHFM1 and maps in the 7q21q22 region. SHFM1 is characterized by autosomal dominant transmission, incomplete penetrance and variable expressivity. Associated features often include hearing loss, intellectual disability/developmental delay and craniofacial abnormalities. Disruption of the DLX5/DLX6 genes, mapping within the SHFM1 locus, is now known to be responsible for the phenotype. Through SNP array, we analyzed a patient affected by SHFM1 associated with deafness and an abnormality of the inner ear (incomplete partition type I); we identified a deletion in 7q21, not involving the DLX5/6 genes, but including exons 15 and 17 of DYNC1I1, known to act as exonic enhancers (eExons) of the DLX5/6 genes. We further demonstrated the role of DYNC1I1 eExons in regulating DLX5/6 expression by means of showing a reduced expression of the DLX5/6 genes through RT-PCR in a patient-derived lymphoblastoid cell line. Furthermore, our data and a review of published cases do not support the hypothesis that DLX5/6 are imprinted in humans. This work is an example of how the disruption of regulatory elements can be responsible for congenital malformations.

PRDM1 DNA-binding zinc finger domain is required for normal limb development and is disrupted in split hand/foot malformation

Split hand/foot malformation (SHFM) is a rare limb abnormality with clefting of the fingers and/or toes. For many individuals, the genetic etiology is unknown. Through whole-exome and targeted sequencing, we detected three novel variants in a gene encoding a transcription factor, PRDM1, that arose de novo in families with SHFM or segregated with the phenotype. PRDM1 is required for limb development; however, its role is not well understood and it is unclear how the PRDM1 variants affect protein function. Using transient and stable overexpression rescue experiments in zebrafish, we show that the variants disrupt the proline/serine-rich and DNA-binding zinc finger domains, resulting in a dominant-negative effect. Through gene expression assays, RNA sequencing, and CUT&RUN in isolated pectoral fin cells, we demonstrate that Prdm1a directly binds to and regulates genes required for fin induction, outgrowth and anterior/posterior patterning, such as fgfr1a, dlx5a, dlx6a and smo. Taken together, these results improve our understanding of the role of PRDM1 in the limb gene regulatory network and identified novel PRDM1 variants that link to SHFM in humans.

Oculo-dento-digital dysplasia: a systematic analysis of published dental literature

INTRODUCTION

Oculo-dento-digital dysplasia (ODDD, OMIM# 164200) is a rare genetic disorder caused by mutation in Gap junction alpha gene that encodes connexin 43 (Cx43) protein. In this paper, the case of a 16-year-old boy is reported who presented with the complaint of toothache. Examination revealed unusual facial features, i.e., long narrow nose, hypertelorism, prominent epicanthal folds along with syndactyly and camptodactyly. We have also compiled available dental literature on ODDD that will help clinicians in early diagnosis and management of this condition.

MATERIALS AND METHODS

A literature search was performed in PubMed NLM, EBSCO Dentistry & Oral Sciences Source, and EBSCO CINAHL Plus.

RESULTS

A total of 309 articles were identified in the literature search. Only 17 articles were included based on the predetermined inclusion and exclusion criteria in the review synthesis. The included articles were case reports (n = 15), a case report and review (n = 1), and an original article (n = 1). Enamel hypoplasia, hypomineralization, microdontia, pulp stones, curved roots, and taurodontism were common dental findings in ODDD.

CONCLUSIONS

After establishing definitive diagnosis, a multidisciplinary team should work in cohesion to improve the quality of life of patients. Immediate treatment should be focused on the correction of current oral condition and symptomatic treatment. In the long term, attention should be diverted to prevent tooth wear and maintaining the occlusal vertical dimension to establish adequate function.

Genetic overview of postaxial polydactyly: Updated classification

Polydactyly or polydactylism, also known as a hyperdactyly, is a congenital limb defect with various morphologic phenotypes. Apart from physical and functional impairments, the presence of polydactyly is an indication of an underlying syndrome in the newborn. Usually, it follows as an autosomal dominant/recessive inheritance pattern with defects in the limb development's anteroposterior patterning. Although mutations in several genes have been associated with polydactyly; however, the exact underlying cause, pathways, and disease mechanisms are still unexplored, thus making it of multi-factorial origin. Polydactyly is divided into three subtypes; radial, ulnar, and central polydactyly. So far, 11 loci (PAPA1-PAPA11) and seven human genes have been reported to cause non-syndromic postaxial polydactyly in humans, including the ZNF141, GLI3, IQCE, GLI1, FAM92A1, KIAA0825, and DACH1. In this review, we discuss emerging evidences of clinical and molecular characterization of polydactyly types in term of the involvement of newly associated genes and loci for non-syndromic postaxial polydactyly, and how these might impact our understanding of the genetic mechanisms and molecular etiology involved in the cause of polydactyly.

The molecular genetics of human appendicular skeleton

Disorders that result from de-arrangement of growth, development and/or differentiation of the appendages (limbs and digit) are collectively called as inherited abnormalities of human appendicular skeleton. The bones of appendicular skeleton have central role in locomotion and movement. The different types of appendicular skeletal abnormalities are well described in the report of "Nosology and Classification of Genetic skeletal disorders: 2019 Revision". In the current article, we intend to present the embryology, developmental pathways, disorders and the molecular genetics of the appendicular skeletal malformations. We mainly focused on the polydactyly, syndactyly, brachydactyly, split-hand-foot malformation and clubfoot disorders. To our knowledge, only nine genes of polydactyly, five genes of split-hand-foot malformation, nine genes for syndactyly, eight genes for brachydactyly and only single gene for clubfoot have been identified to be involved in disease pathophysiology. The current molecular genetic data will help life sciences researchers working on the rare skeletal disorders. Moreover, the aim of present systematic review is to gather the published knowledge on molecular genetics of appendicular skeleton, which would help in genetic counseling and molecular diagnosis.

Clinical and genetic characterization of congenital lipoid adrenal hyperplasia

Disorders of steroid synthesis are a group of anomalies caused by defects in any step of conversion of cholesterol into steroid hormones. The disorders are characterized by defects leading to abnormalities of salt-water balance and/or sexual differentiation. Congenital lipoid adrenal hyperplasia (CLAH) is the most severe form of steroid synthesis disorder caused by the accumulation of cholesterol in the outer mitochondrial membrane due to steroidogenic acute regulatory protein (StAR) deficiency. Pathogenic sequence variants in the gene STAR encoding StAR protein leads to CLAH. In the present study, a Pakistani family was clinically diagnosed with the LAH phenotype. Sanger sequencing of STAR in the family revealed a novel homozygous nonsense mutation [c.295G>T, p.(Glu99*)] in the living affected individual. The study was designed to assist in carrier testing and prenatal diagnosis within the affected family. In addition, searching for common variants in the STAR gene would help in designing low-cost targeted variation testing in other patients.

Sequence Variants in the WNT10B and TP63 Genes Underlying Isolated Split-Hand/Split-Foot Malformation

Aims: Split-hand/split-foot malformation (SHFM) is a developmental and congenital limb malformation characterized by variable degrees of medial clefting or absence of one or more digits in hands and/or feet. The aim of this study was to identify the underlying cause of three consanguineous Pakistani families showing various types of SHFM-related features. Materials and Methods: Standard molecular methods, including whole-genome sequencing (WGS), whole-exome sequencing (WES), microsatellite markers-based genotyping, and Sanger sequencing were performed to search for the likely causative variants. Results: In family A, WES revealed a novel homozygous missense variant [c.338G>A, p.(Gly113Asp)] in the WNT10B gene. In family B, microsatellite-based genotyping followed by Sanger sequencing revealed a novel homozygous 13 base pairs deletion [c.884-896delTCCAGCCCCGTCT, p.(Phe295Cysfs*87)] in the same gene. In family C, WGS divulged a previously reported heterozygous missense variant [c.956G>A, p.(Arg319His)] in the TP63 gene. Conclusions: Mapping and sequencing genes and variants for severe skeletal disorders, such as SHRM, will facilitate establishing specific genotype-phenotype correlations and providing genetic counseling for the families suffering from such conditions.

Sequence variants in three genes underlying leukodystrophy in Pakistani families

Leukodystrophies (LDs) are a heterogeneous group of rare and progressive genetic diseases that affect brain, spinal cord, and often the peripheral nerves. They are characterized by abnormal development or destruction of the myelin sheath of the brain. This study was aimed to search for the causative variants in three unrelated consanguineous families presented with LD. Detailed clinical investigations were carried out on probands in three unrelated consanguineous families of Pakistani origin. Targeted gene sequencing and Whole Exome Sequencing (WES) were performed for variant identification. Candidate variants were checked for co-segregation with the phenotype using Sanger sequencing. Public databases including ExAC, gnomAD, dbSNP, and the 1,000 Genome Project were searched to determine frequencies of the alleles. Conservation of the missense variants was ensured by aligning orthologous protein sequences from diverse vertebrate species. Targeted gene sequencing identified a novel homozygous missense mutation [c.2135G > A, p.(Arg712His) in the ATP Binding Cassette Subfamily D Member 1 (ABCD1; OMIM# 300371) in three affected siblings in family A.WES followed by validation by Sanger sequencing revealed previously reported homozygous missense variants [c.162C > A; p.(Asn54Lys)] in ASPA (OMIM# 608034) in family B and [c.361G > C,p.(Gly121Arg)] in ARSA (OMIM# 607574) in family C. Investigation of three families underlies importance of WES as an amazing diagnostic tool for conclusive determination of a specific type of LD. Further, the study would assist in carrier testing and prenatal diagnosis of the affected families. In addition, searching for common variants in the genes causing LD would help in designing low-cost targeted variation testing in patients.

Nonsyndromic Split-Hand/Foot Malformation: Recent Classification

Split-hand/foot malformation (SHFM) is a genetic limb anomaly disturbing the central rays of the autopod. SHFM is a genetically heterogeneous disorder with variable expressivity inherited as syndromic and nonsyndromic forms. We provide an update of the clinical and molecular aspects of nonsyndromic SHFM. This rare condition is highly complex due to the clinical variability and irregular genetic inheritance observed in the affected individuals. Nonsyndromic SHFM types have been reviewed in terms of major molecular genetic alterations reported to date. This updated overview will assist researchers, scientists, and clinicians in making an appropriate molecular diagnosis, providing an accurate recurrence risk assessment, and developing a management plan.

Genetic regulatory pathways of split-hand/foot malformation

Split-hand/foot malformation (SHFM) is caused by mutations in TP63, DLX5, DLX6, FGF8, FGFR1, WNT10B, and BHLHA9. The clinical features of SHFM caused by mutations of these genes are not distinguishable. This implies that in normal situations these SHFM-associated genes share an underlying regulatory pathway that is involved in the development of the central parts of the hands and feet. The mutations in SHFM-related genes lead to dysregulation of Fgf8 in the central portion of the apical ectodermal ridge (AER) and subsequently lead to misexpression of a number of downstream target genes, failure of stratification of the AER, and thus SHFM. Syndactyly of the remaining digits is most likely the effects of dysregulation of Fgf-Bmp-Msx signaling on apoptotic cell death. Loss of digit identity in SHFM is hypothesized to be the effects of misexpression of HOX genes, abnormal SHH gradient, or the loss of balance between GLI3A and GLI3R. Disruption of canonical and non-canonical Wnt signaling is involved in the pathogenesis of SHFM. Whatever the causative genes of SHFM are, the mutations seem to lead to dysregulation of Fgf8 in AER cells of the central parts of the hands and feet and disruption of Wnt-Bmp-Fgf signaling pathways in AER.

Split hand-foot malformation and a novel WNT10B mutation

We report an Indian girl with split-hand/foot malformation (SHFM), sparse hair, and interrupted eyebrows, who carries a novel homozygous deletion c.695_697delACA in WNT10B. The variant is deduced to cause an in-frame deletion of Asn residue 232 (p.Asn232del). According to the protein model, this single amino acid deletion at the critical position in the protein structure is likely to severely affect the protein structure and function. This deletion is likely to lead decreased lifetime and make it unable to bind to its receptors and other ligands. The patient and all family members had normal bone density and they were not obese like some of the patients with WNT10B variants. Here we report a patient with SHFM6 who carried a novel WNT10B mutation. Sparse hair and interrupted eyebrows may be associated findings of SHFM6.

Homozygous sequence variants in the WNT10B gene underlie split hand/foot malformation

Split-hand/split-foot malformation (SHFM), also known as ectrodactyly is a rare genetic disorder. It is a clinically and genetically heterogeneous group of limb malformations characterized by absence/hypoplasia and/or median cleft of hands and/or feet. To date, seven genes underlying SHFM have been identified. This study described four consanguineous families (A-D) segregating SHFM in an autosomal recessive manner. Linkage in the families was established to chromosome 12p11.1-q13.13 harboring WNT10B gene. Sequence analysis identified a novel homozygous nonsense variant (p.Gln154*) in exon 4 of the WNT10B gene in two families (A and B). In the other two families (C and D), a previously reported variant (c.300_306dupAGGGCGG; p.Leu103Argfs*53) was detected. This study further expands the spectrum of the sequence variants reported in the WNT10B gene, which result in the split hand/foot malformation.