Polydactyly: how many disorders and how many genes? 2010 update

Cancer risk in individuals with polydactyly: a Swedish population-based cohort study

BACKGROUND

Polydactyly is a feature of several cancer predisposition syndromes (CPS), however, cancer risk in individuals with polydactyly is largely unknown.

METHODS

We performed a matched cohort study using data from Swedish national registers. We included 6694 individuals with polydactyly, born in Sweden between 1970-2017. Polydactyly was categorised as thumb polydactyly, finger polydactyly, polydactyly+ (additional birth defects and/or intellectual disability) or isolated polydactyly. Each exposed individual was matched to 50 comparisons by sex, birth year and birth county. Associations were estimated through Cox proportional hazard models.

FINDINGS

An increased childhood cancer risk was found in males (HR 4.24, 95% CI 2.03-8.84) and females (HR 3.32, 95% CI 1.44-7.63) with polydactyly+. Isolated polydactyly was associated with cancer in childhood (HR 1.87, 95% CI 1.05-3.33) and young adulthood (HR 2.30, 95% CI 1.17-4.50) in males but not in females. The increased cancer risk remained after exclusion of two known CPS: Down syndrome and neurofibromatosis. The highest site-specific cancer risk was observed for kidney cancer and leukaemia.

CONCLUSIONS

An increased cancer risk was found in individuals with polydactyly, especially in males and in individuals with polydactyly+. We encourage future research about polydactyly and cancer associations and emphasise the importance of clinical phenotyping.

Congenital three generation wide familial non-syndromic polydactyly

Polydactyly is typically observed as isolated and sporadic occurrences, although familial cases do exist, albeit with lower frequency, manifesting in various inheritance patterns. In around 30% of polydactyly cases, there exists a familial history, suggesting the probable involvement of a single gene. Given its potential for hereditary transmission, thorough investigation of the patients' parents, first-degree relatives, grandparents, and even great-grandparents for similar disorders becomes imperative. In our clinic, we conducted an analysis focusing on patients presenting with foot polydactyly, along with occurrences of polydactyly among their first- and second-degree relatives spanning two to three generations of family history. The study encompassed three patients and their respective families, including a pair of siblings. We speculate that the inheritance type in our cases was autosomal dominant. Among our patients, one presented with central polydactyly, while the remaining patients and all familial cases displayed postaxial polydactyly. In terms of morphologic classification, one patient had a Y-shaped metatarsal, another had a T-shaped metatarsal, and the third patient exhibited a duplicated ray-shaped anomaly. In our review of the literature, we haven't come across a case spanning three generations like the ones we encountered. Additionally, the presence of a transverse accessory extensor tendon between both extensor tendons in cases with T- and Y-shaped metatarsals intrigued us from an anatomical perspective. Our goal is to present these rare cases of congenital familial polydactyly spanning three generations, highlighting the anatomical variations observed and aiming to contribute to the existing body of literature on the subject.

A novel homozygous FAM92A gene (CIBAR1) variant further confirms its association with non-syndromic postaxial polydactyly type A9 (PAPA9)

Polydactyly is a very common digit anomaly, having extra digits in hands and/or toes. Non-syndromic polydactyly in both autosomal dominant and autosomal recessive forms are caused by disease-causing variants in several genes, including GLI1, GLI3, ZNF141, FAM92A, IQCE, KIAA0825, MIPOL1, STKLD1, PITX1, and DACH1. Whole exome sequencing (WES) followed by bi-directional Sanger sequencing was performed for the single affected individual (II-1) of the family to reveal the disease causative variant/gene. 3D protein modeling and structural molecular docking was performed to determine the effect of the identified mutation on the overall protein structure. WES revealed a novel biallelic missense variant (c.472G>C; p.Ala158Pro) in exon 6 of the FAM92A gene. The identified variant segregated perfectly with the disease phenotype using Sanger sequencing. Furthermore, Insilco analysis revealed that the variant significantly changes the protein secondary structure, and substantially impact the stability of FAM92A. We report the second FAM92A disease-causing mutation associated with recessive non-syndromic postaxial polydactyly. The data further confirms the contribution of FAM92A in limb development and patterning.

A novel missense variant located within the zinc finger domain of the GLI3 gene was identified in a Vietnamese pedigree with index finger polydactyly

BACKGROUND

Polydactyly, particularly of the index finger, remains an intriguing anomaly for which no specific gene or locus has been definitively linked to this phenotype. In this study, we conducted an investigation of a three-generation family displaying index finger polydactyly.

METHODS

Exome sequencing was conducted on the patient, with a filtration to identify potential causal variation. Validation of the obtained variant was conducted by Sanger sequencing, encompassing all family members.

RESULTS

Exome analysis uncovered a novel heterozygous missense variant (c.1482A>T; p.Gln494His) at the zinc finger DNA-binding domain of the GLI3 protein within the proband and all affected family members. Remarkably, the variant was absent in unaffected individuals within the pedigree, underscoring its association with the polydactyly phenotype. Computational analyses revealed that GLI3 p.Gln494His impacts a residue that is highly conserved across species.

CONCLUSION

The GLI3 zinc finger DNA-binding region is an essential part of the Sonic hedgehog signaling pathway, orchestrating crucial aspects of embryonic development through the regulation of target gene expression. This novel finding not only contributes valuable insights into the molecular pathways governing polydactyly during embryonic development but also has the potential to enhance diagnostic and screening capabilities for this condition in clinical settings.

Whole-Genome Sequencing for Identifying Candidate Genes Related to the Special Phenotypes of the Taihu Dianzi Pigeon

The Taihu Dianzi pigeon is a breed native to China, and its special piebalding, crest, and polydactyly phenotypes are the result of artificial and natural selection. Here, we analyzed the genetic differences among three kinds of pigeons with different phenotypes at the genomic level. A selective sweep was conducted based on the fixation index (FST) and nucleotide diversity (π) ratio, and the results revealed that MC1R was related to the formation of the distinctive piebalding of the Taihu Dianzi pigeon. Combined with the results of genome-wide association studies, we identified candidate genes associated with the crest (SMYD and STOX2) and polydactyly (SLC52A3 and ANGPT4). The candidate genes identified in this study and their variants may be useful for understanding the genetic mechanism underlying the special phenotypes of the Taihu Dianzi pigeon. This study provides new insights into the genetic factors that may influence the formation of the special piebalding, crest, and polydactyly characteristics in pigeons.

Heavy metals and trace elements in maternal blood and prevalence of congenital limb abnormalities among newborns: the Japan Environment and Children's Study

BACKGROUND

Heavy metals such as lead (Pb) and cadmium (Cd) have been associated with adverse pregnancy and developmental outcomes, including congenital abnormalities. This study investigated the association between exposure to heavy metals and trace elements during fetal life and congenital limb abnormalities in infants.

METHODS

This study is based on a prospective ongoing nationwide birth cohort from the Japan Environment and Children's Study (JECS). The concentrations of Cd, Pb, mercury (Hg), selenium (Se), and manganese (Mn) were measured in maternal blood collected during the mid-late trimesters. Inclusion criteria were available from questionnaires filled in during pregnancy, including information about congenital limb abnormalities at birth or at one month. To examine the associations with limb anomalies and individual chemicals, logistic regression models were applied following log-transformation or division into quartiles of Cd, Pb, Hg, Se, and Mn concentrations. To assess the associations with the heavy metals and trace elements mixture, quantile g-computation was employed. All models were adjusted for age, maternal smoking history, maternal alcohol intake, history of smoking, and infant sex.

RESULTS

Data from 90,163 participants were included in the analysis, of whom 369 had congenital limb abnormalities in any of the collected information, and 89,794 had none. Among the 369 cases of congenital limb abnormalities, there were 185 and 142 cases of polydactyly and syndactyly, respectively. The median concentrations of Pb, Cd, Hg, Se, and Mn were 5.85, 0.66, 3.64, 168, and 15.3 ng/g, respectively. There were no associations between maternal blood concentrations of Pb [adjusted odd ratio = 0.83; 95% confidence interval = 0.61, 1.11], Cd [0.87; 0.68, 1.10], Hg [0.88; 0.73, 1.07], Se [1.07; 0.44, 2.59], and Mn [0.91; 0.64, 1.30] with congenital limb abnormalities. No significant association was observed between the mixture of heavy metals and trace elements [0.85; 0.72, 1.02] and any congenital limb abnormalities. Moreover, there was no association with all polydactylies and all syndactylies, or any type of abnormality as a subdivision.

CONCLUSION

At the maternal exposure levels of Cd, Pb, Hg, Se, and Mn assessed in the present study, no association was identified with the risk of developing congenital limb abnormalities in children.

Paternal age and risk for selected birth defects in a large South American sample

BACKGROUND

The relationship between maternal age (MA) and birth defects (BD) has been extensively studied while much less research, mostly with discordant results, has focused on the risk of paternal age (PA) for BD. Furthermore, no consensus has been reached on the best way to control the association of PA with MA.

OBJECTIVES

The aim of the study was to evaluate the risk of PA increase, at 1-year intervals, for selected BD, especially controlling for the confounding effect of MA.

METHODS

The sample comprised of 27,944 liveborns presenting 1 of 18 selected isolated BD. Conditional logistic regressions were applied to evaluate the risk of advanced PA and its yearly increase, adjusting by MA and other variables.

RESULTS

Of the 18 analyzed BD, only the risk for preaxial polydactyly (PreP) showed a significant association with increasing PA, while advanced MA was of low risk. For esophageal and anal atresia, associations with both PA and MA increases were observed.

CONCLUSIONS

Results support the hypothesis of advanced PA as a risk factor for PreP and helps clarify the so far unexplained nonrandom association between this defect and Down syndrome.

Identification of GLI1 and KIAA0825 Variants in Two Families with Postaxial Polydactyly

Polydactyly is a rare autosomal dominant or recessive appendicular patterning defect of the hands and feet, phenotypically characterized by the duplication of digits. Postaxial polydactyly (PAP) is the most common form and includes two main types: PAP type A (PAPA) and PAP type B (PAPB). Type A involves a well-established extra digit articulated with the fifth or sixth metacarpal, while type B presents a rudimentary or poorly developed superfluous digit. Pathogenic variants in several genes have been identified in isolated and syndromic forms of polydactyly. The current study presents two Pakistani families with autosomal recessive PAPA with intra- and inter-familial phenotype variability. Whole-exome sequencing and Sanger analysis revealed a novel missense variant in KIAA0825 (c.3572C>T: p.Pro1191Leu) in family A and a known nonsense variant in GLI1 (c.337C>T: p.Arg113*) in family B. In silico studies of mutant KIAA0825 and GLI1 proteins revealed considerable structural and interactional modifications that suggest an abnormal function of the proteins leading to the disease phenotype. The present study broadens the mutational spectrum of KIAA0825 and demonstrates the second case of a previously identified GLI1 variant with variable phenotypes. These findings facilitate genetic counseling in Pakistani families with a polydactyly-related phenotype.

Retinal determination gene networks: from biological functions to therapeutic strategies

The retinal determinant gene network (RDGN), originally discovered as a critical determinator in Drosophila eye specification, has become an important regulatory network in tumorigenesis and progression, as well as organogenesis. This network is not only associated with malignant biological behaviors of tumors, such as proliferation, and invasion, but also regulates the development of multiple mammalian organs. Three members of this conservative network have been extensively investigated, including DACH, SIX, and EYA. Dysregulated RDGN signaling is associated with the initiation and progression of tumors. In recent years, it has been found that the members of this network can be used as prognostic markers for cancer patients. Moreover, they are considered to be potential therapeutic targets for cancer. Here, we summarize the research progress of RDGN members from biological functions to signaling transduction, especially emphasizing their effects on tumors. Additionally, we discuss the roles of RDGN members in the development of organs and tissue as well as their correlations with the pathogenesis of chronic kidney disease and coronary heart disease. By summarizing the roles of RDGN members in human diseases, we hope to promote future investigations into RDGN and provide potential therapeutic strategies for patients.

A review of polydactyly and its inheritance: Connecting the dots

OBJECTIVE

This study collects what is known about the inheritance underpinnings of syndromic and non-syndromic polydactylies and highlights dactyly presentations with unknown genetic roots. This review summarizes the current information and genetics-enhanced understanding of polydactyly.

BACKGROUND

There is a frequency of 0.37 to 1.2 per 1000 live births for polydactyly, which is also known as hyperdactyly. It is characterized by the presence of extra fingers. Polydactyly is caused by a failure in limb development, specifically the patterning of the developing limb bud. The phenotypic and genetic variability of polydactyly makes its etiology difficult to understand. Pre-axial polydactyly, central polydactyly (axial), and postaxial polydactyly are all examples of non-syndromic polydactyly (ulnar). An autosomal dominant disorder with varying penetrance that is mostly passed down via limb development patterning abnormalities.

METHOD

A comprehensive search of MEDLINE/PubMed and other databases was followed by an evaluation of the relevant papers, with a particular focus on those published between 2000 and 2022.

RESULTS

Of 747 published article related to Polydactyly from MEDLINE/PubMed search, 43 were from the last 10 years and were the focus of this review.

CONCLUSION

Polydactyly is one of the most frequent congenital hand malformations. PAP is more common than PPD, whereas central polydactyly is very uncommon.

Prenatal Detection of Novel Compound Heterozygous Splice Site Variants of the KIAA0825 Gene in a Fetus with Postaxial Polydactyly Type A

Postaxial polydactyly (PAP) is a common abnormality characterized by extra digits on hands and/or feet. To date, sequence variants in seven genes have been identified in non-syndromic PAP. In the present study, a fetus manifesting non-syndromic postaxial polydactyly type A (PAPA) was found by fetal ultrasonography. To better evaluate fetal prognosis, SNP array analysis and trio whole-exome sequencing (trio-WES) were performed to identify the underlying etiology. Although SNP array analysis revealed no abnormality, trio-WES identified compound heterozygous splice site variants in KIAA0825, c.-1-2A>T and c.2247-2A>G in intron 2 and intron 12, respectively. These two splice site variants were absent in control databases and were predicted to influence splicing by in silico analysis. To confirm the potential pathogenicity of the variants, in vitro splicing assays using minigene and RNA from peripheral leukocytes of the heterozygous parents were conducted. Minigene and RT-PCR assays demonstrated that the c.-1-2A>T variant led to the loss of the initiation codon, and the c.2247-2A>G variant mainly resulted in exon 13 skipping. Prenatal WES and subsequent functional studies are important approaches for defining the genetic etiology of fetuses with PAPA and are also essential for accurate genetic counseling and decision making. Taken together, this study expands the spectrum of KIAA0825 variations in PAPA patients and increases the knowledge of the molecular consequences of KIAA0825 splice site variants.

When Is Primary Metacarpal Corrective Osteotomy Recommended in Patients with Flatt Type IV Radial Polydactyly?

BACKGROUND

The aim of this study was to determine when primary metacarpal corrective osteotomy is recommended in patients with Flatt type IV radial polydactyly.

METHODS

A total of 78 patients with Flatt type IV radial polydactyly were included. The authors performed metacarpal osteotomy if the angulation of the metacarpophalangeal joint was not correctable by the intraoperative radial stress test. The authors measured the metacarpal deviation angle of the thumb in simple posteroanterior radiographs. The clinical outcomes were assessed using Japanese Society for Surgery of the Hand evaluation total score and the metacarpal deviation angle correction angle. These outcomes were compared between the patients who underwent metacarpal osteotomy and those who did not. Of the patients who did not undergo metacarpal osteotomy, the relationships between preoperative metacarpal deviation angle and the metacarpal deviation angle correction angle were formulated using segmented linear regression analysis.

RESULTS

There were no significant differences in the demographic features and the value of preoperative metacarpal deviation angle between the two groups. However, the metacarpal deviation angle correction angle and Japanese Society for Surgery of the Hand evaluation total score were significantly higher in the patients who underwent metacarpal osteotomy. The segmented linear regression analysis demonstrated a breakpoint, indicating that the soft-tissue procedure alone does not sufficiently correct the metacarpal deviation angle. For the postoperative metacarpal deviation angle to be 5 degrees, the preoperative metacarpal deviation angle was calculated as 10.8 degrees.

CONCLUSION

If the preoperative metacarpal deviation angle is greater than 10.8 degrees, metacarpal osteotomy can be considered even in patients with correctable metacarpophalangeal joint by intraoperative radial stress test.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, III.

Megalencephaly Polymicrogyria Polydactyly Hydrocephalus (MPPH): A Case Report and Review of Literature

Megacephaly polymicrogyria, polydactyly, hydrocephalus (MPPH) is an extremely rare condition caused by a defect in the AKT3, CCND2, or PIKR2 genes. Although the prevalence of the syndrome is very low, there is a significant clinical and radiological variation in the syndrome. We present a case with MPPH admitted to the hospital due to an increase in seizure frequency. The patient had a history of cerebral palsy, global developmental delay, spasticity, and hypoglycemic episodes. MRI findings revealed ventriculomegaly, polymicrogyria, abnormal encephalon, and pachygyria. The addition of clobazam and alprazolam diminished the seizures' frequency and the patient's spasticity, respectively. To highlight the clinical and radiological variation of the syndrome, we review cases of MPPH with clinical and radiological variants. Pachygyria and cerebral palsy are new associations not previously described before in MPPH. Pachygyria and cerebral palsy could be worsening the seizures and the global delay in this patient. Hypoglycemic episodes are probably related to the AKT3 gene, promoting more glucose consumption. Spasticity is most probably related to an upper motor sign due to the patient's cerebral palsy. This case highlights the clinical and radiological variation of the syndrome. More cases of MPPH need to be described to consolidate the knowledge and have a better understanding of the clinical and radiological variation of the syndrome.

Biallelic variant in DACH1, encoding Dachshund Homolog 1, defines a novel candidate locus for recessive postaxial polydactyly type A

Polydactyly or hexadactyly is characterized by an extra digit/toe with or without a bone. Currently, variants in ten genes have been implicated in the non-syndromic form of polydactyly. DNA from a single affected individual having bilateral postaxial polydactyly was subjected to whole exome sequencing (WES), followed by Sanger sequencing. Homology modeling was performed for the identified variant and advance microscopy imaging approaches were used to reveal the localization of the DACH1 protein at the base of primary cilia. A disease-causing biallelic missense variant (c.563G > A; p.Cys188Tyr; NM_080760.5) was identified in the DACH1 gene segregating perfectly within the family. Structural analysis using homology modeling of the DACH1 protein revealed secondary structure change that might result in loss of function or influence downstream interactions. Moreover, siRNA-mediated depletion of DACH1 showed a key role of DACH1 in ciliogenesis and cilia function. This study provides the first evidence of involvement of the DACH1 gene in digits development in humans and its role in primary cilia. This signifies the importance and yet unexplored role of DACH1.

A Frameshift Variant in KIAA0825 Causes Postaxial Polydactyly

Postaxial polydactyly (PAP) is characterized by counterproductive 5th digit (pinky finger) duplication on hands and/or feet which often leads to functional complications. To date, at least 11 genes involved in causing various types of nonsyndromic polydactylies have been reported. In the present study, a consanguineous family of Sindhi origin with a segregating nonsyndromic form of PAP in an autosomal recessive manner was clinically and genetically evaluated. Genotyping, using polymorphic microsatellite markers, established linkage in the family on chromosome 5q15 harboring the KIAA0825 gene (MIM 617266). Sequence analysis of the gene revealed a novel frameshift variant leading to a premature stop codon [c.143delG, p.(Cys48Serfs*28)]. This is only the 4th novel variant in the KIAA0825 gene that leads to PAP type A10 (PAPA10) (MIM 618498). Identification of variants in the PAP causative gene will support the diagnosis of patients with limb malformations in the Pakistani population.

Maternal occupational exposure to chemicals in the textile factory during pregnancy is associated with a higher risk of polydactyly in the offspring

Background: The number of children with polydactyly seen in our clinic is increasing. In addition to genetic factors, an influence of environmental effects during pregnancy is becoming increasingly apparent; however, epidemiological data on these effects are lacking.Methods: This hospital-based, case-control study enrolled 143 patients with polydactyly and 286 control patients with no genetic diseases, to evaluate the association between maternal exposure to a textile factory environment during pregnancy and the likelihood of giving birth to a child with polydactyly.Results: Maternal exposure to a textile factory environment during pregnancy was associated with an increased risk of giving birth to a child with polydactyly (exposure to textile factory environment: unadjusted odds ratio (OR) = 3.31, 95% confidence interval (CI) = 1.75-6.27, p = .0002; work seniority of exposed occupation: unadjusted OR 1.28, 95% CI = 1.13-1.47, p = .0002). Covariate screening indicated that certain risk factors (family monthly income per capita, mother's emotional state during pregnancy, colporrhagia, passive smoking, smoking, and history of consanguineous marriage) were potential confounding factors. After adjusting for these variables, the OR of exposure to a textile factory environment remained significant (exposure to textile factory environment: adjusted OR = 3.08, 95% CI = 1.32-7.19, p = .0094; work seniority of exposed occupation: adjusted OR = 1.58, 95% CI = 1.20-2.08, p = .0010). The risk of polydactyly increased with the number of years of employment.Conclusions: Maternal exposure to a textile factory environment appears to be a risk factor for polydactyly in newborns.

Clinical Characteristics and Distribution of Thumb Polydactyly in South China: A Retrospective Analysis of 483 Hands

PURPOSE

This study was intended to characterize the epidemiological features of thumb polydactyly (TP) in South China.

METHODS

Clinical records were retrieved from 1 central hospital in South China to identify the patients with a definite diagnosis of TP from January 2004 to January 2017. The cases were classified by their x-ray appearance. The data collected included sex, age at first operation, reoperation, family history, unilateral/bilateral polydactyly, right/left hand involvement in unilateral cases, classification of polydactyly, and the presence of associated congenital anomalies.

RESULTS

A total of 428 patients with a definite diagnosis of TP were identified (278 males and 150 females) involving 483 cases, 373 unilateral and 55 bilateral. A syndrome or associated congenital anomaly was found in 26 (18 unilateral and 8 bilateral cases). A dominant thumb, larger and more developed, was observed in 448 hands (93%), and was the ulnar thumb in 433. Owing to postoperative complications, 31 thumbs (6.4%) underwent reoperation. The average interval from initial surgery to reoperation was 4.8 years.

CONCLUSIONS

Thumb polydactyly had a male predominance in this Chinese cohort, mostly occurring on the right hand with an ulnar dominant thumb. Bilateral cases had a higher incidence of associated anomaly and positive family history than unilateral cases. The need for additional surgery for TP might occur as late as 4.8 years after primary surgery.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic IV.

Identification of a novel biallelic missense variant in the KIAA0825 underlies postaxial polydactyly type A

Postaxial polydactyly (PAP) is characterized by development of extra digits, which mostly segregates in autosomal recessive pattern. The underlying genetic cause of recessive non-syndromic PAP type A has been associated with sequence variants in five different genes (ZNF141, IQCE, GLI1, FAM92A, KIAA0825). The present study was aimed to investigate clinical and genetic causes of PAPA in a consanguineous family of Pakistani origin. Microsatellite-based linkage analysis was used to search for the disease-causing gene. Linkage in the family was established at chromosome 5q15 harbouring a candidate gene KIAA0825. Subsequently, Sanger sequencing revealed a novel homozygous missense variant [c.50T>C; p. (Leu17Ser)] in the gene, which co-segregated with the disease within the family. Protein structural analysis predicted a substantial change in the secondary structure of the mutant protein affecting its function. This is the third disease causing variant identified in the KIAA0825. This has not only expanded spectrum of the mutations in the gene but also further substantiated its role in the limb development in human.

Thumb Hypoplasia Occurring in Patients With Preaxial Polydactyly

PURPOSE

Thumb polydactyly and thumb hypoplasia are generally regarded as separate clinical entities. However, several case reports indicate that hypoplasia of both the thumb and the radius can occur in patients with thumb polydactyly and improved understanding of the genetics of the developing upper limb may give an embryologic explanation for this occurrence. Our hypothesis was that patients with preaxial polydactyly can have ipsilateral thumb hypoplasia that may not be recognized until after surgical reconstruction of the extra digit.

METHODS

We searched our surgical database for all procedures performed on patients with a diagnosis of preaxial polydactyly between 2002 and 2014. We reviewed the medical record for demographic data, surgical procedures, and follow-up information. In addition, all available radiographs were reviewed. Through this, we identified patients with a diagnosis of ipsilateral thumb hypoplasia, including when in the course of treatment the diagnosis was made, and any related subsequent procedures.

RESULTS

We reviewed 132 patients who underwent reconstruction of thumb polydactyly, 10 of whom were identified as having evidence of ipsilateral thumb hypoplasia, an incidence of 8.2%. The diagnosis of thumb hypoplasia was made before surgery in 3 of the 10 patients. One additional patient was noted to have a duplicate thumb on one side and a hypoplastic thumb on the contralateral side.

CONCLUSIONS

This study supports the hypothesis that children with preaxial polydactyly can have ipsilateral thumb hypoplasia that may not be noted before surgery. In this study group, 8% of patients with preaxial polydactyly had ipsilateral hypoplasia.

TYPE OF STUDY/LEVEL OF EVIDENCE

Prognostic IV.

A novel missense in GLI3 possibly affecting one of the zinc finger domains may lead to postaxial synpolydactyly: case report

Background

Polydactyly is one of the most common congenital hand/foot malformations in humans. Mutations in GLI3 have been reported to cause syndromic and non-syndromic forms of preaxial and postaxial polydactylies.

Case presentation

The patient was a 2-year-old boy who underwent surgery in our hospital. The right hand and left foot of the patient were labelled as postaxial polydactyly type B, and there was cutaneous webbing between the 3rd and 4th fingers of the left hand. We identified a novel c. 1622C > T variant in GLI3 leading to an isolated postaxial synpolydactyly.

Conclusions

The patient carries a novel autosomal dominant heterozygous missense mutation. This mutation c.1622C > T;p.(Thr541Met) in the GLI3 gene may affect the normal function of the zinc finger domain (ZFD) in a different way. However, it seems that more research is needed to determine the exact effects of this mutation.

A rare TTC30B variant is identified as a candidate for synpolydactyly in a Chinese pedigree

BACKGROUND

Syndactyly type II (synpolydactyly, SPD) is a rare autosomal dominant inherited disease with higher incomplete penetrance. Currently, several variants in HOXD13 and one deletion in FBLN1 have been associated with SPD. However, the causative variants in several SPD families and their etiological mechanism are still largely unknown.

METHODS

Whole exome and PCR-sanger sequencing followed by two-point linkage analysis were performed to identify the pathogenic variant in a six-generation Chinese pedigree. Homology modeling in combination with the RNAi and qRT-PCR experiments was used for revealing the pathogenic mechanism of the TTC30B variant.

RESULTS

A six-generation SPD family was reported. The affected subjects in this family had no other clinical malformation beyond SPD. A rare missense variant c.1157C>T [p.Ala375Val] (chr2:178416368, hg19) in TTC30B was demonstrated to be responsible for this SPD family. The modeling structure indicated that the Ala375 was evolutionarily and structurally conserved. The variant p.Ala375Val was predicted to be deleterious for protein structure and/or stability. Two-point linkage analysis resulted in a maximum LOD score of 3.1444 (P = 0.000071). Furthermore, we found that TTC30B was regulated by the Shh signaling pathway and the abnormal expression of TTC30B will affect the activation of the Shh signaling pathway in human retinal pigment epithelial cells.

CONCLUSIONS

This study demonstrates for the first time that an IFT (intraflagellar transport) - related gene TTC30B is implicated with SPD.

A novel ZRS variant causes preaxial polydactyly type I by increased sonic hedgehog expression in the developing limb bud

Purpose

Preaxial polydactyly (PPD) is a common congenital hand malformation classified into four subtypes (PPD I–IV). Variants in the zone of polarizing activity regulatory sequence (ZRS) within intron 5 of the LMBR1 gene are linked to most PPD types. However, the genes responsible for PPD I and the underlying mechanisms are unknown.

Methods

A rare large four-generation family with isolated PPD I was subjected to genome-wide genotyping and sequence analysis. In vitro and in vivo functional studies were performed in Caco-2 cells, 293T cells, and a knockin transgenic mouse model.

Results

A novel g.101779T>A (reference sequence: NG_009240.2; position 446 of the ZRS) variant segregates with all PPD I–affected individuals. The knockin mouse with this ZRS variant exhibited PPD I phenotype accompanying ectopic and excess expression of Shh. We confirmed that HnRNP K can bind the ZRS and SHH promoters. The ZRS mutant enhanced the binding affinity for HnRNP K and upregulated SHH expression.

Conclusion

Our results identify the first PPD I disease-causing variant. The variant leading to PPD I may be associated with enhancing SHH expression mediated by HnRNP K. This study adds to the ZRS-associated syndromes classification system for PPD and clarifies the underlying molecular mechanisms.

Identification of novel mutations in preaxial polydactyly patients through whole-exome sequencing

BACKGROUND

Polydactyly is one of the most common hereditary limb malformation characterized by additional digits in hands and/or feet. With extra fingers/toes, which could be very problematic, polydactyly patients are usually treated in early childhood by removing of extra digits with surgery. Genetically, polydactyly is caused by mutations of genes that involve in digit formation.

METHODS

In the current report, we performed genetic analysis for polydactyly using DNA samples from a cohort of 20 Chinese patients. All patients show preaxial polydactyly in one of their hands.

RESULTS

With whole-exome sequencing (WES), we have identified two novel heterozygous mutations c.G2844A in GLI3 gene (OMIM 165240) and c.1409_1410del in EVC gene (OMIM 604831). Compound heterozygous mutations that affect KIAA0586 gene (OMIM 610178) are also detected. Proteins encoded by the genes have important roles in primary cilia and regulate sonic hedgehog signaling pathway.

CONCLUSION

Our study highlights the important roles of primary cilia in limb development, and helps to further understand the molecular mechanisms for polydactyly formation.

A single-cell transcriptomic atlas of the developing chicken limb

BACKGROUND

Through precise implementation of distinct cell type specification programs, differentially regulated in both space and time, complex patterns emerge during organogenesis. Thanks to its easy experimental accessibility, the developing chicken limb has long served as a paradigm to study vertebrate pattern formation. Through decades' worth of research, we now have a firm grasp on the molecular mechanisms driving limb formation at the tissue-level. However, to elucidate the dynamic interplay between transcriptional cell type specification programs and pattern formation at its relevant cellular scale, we lack appropriately resolved molecular data at the genome-wide level. Here, making use of droplet-based single-cell RNA-sequencing, we catalogue the developmental emergence of distinct tissue types and their transcriptome dynamics in the distal chicken limb, the so-called autopod, at cellular resolution.

RESULTS

Using single-cell RNA-sequencing technology, we sequenced a total of 17,628 cells coming from three key developmental stages of chicken autopod patterning. Overall, we identified 23 cell populations with distinct transcriptional profiles. Amongst them were small, albeit essential populations like the apical ectodermal ridge, demonstrating the ability to detect even rare cell types. Moreover, we uncovered the existence of molecularly distinct sub-populations within previously defined compartments of the developing limb, some of which have important signaling functions during autopod pattern formation. Finally, we inferred gene co-expression modules that coincide with distinct tissue types across developmental time, and used them to track patterning-relevant cell populations of the forming digits.

CONCLUSIONS

We provide a comprehensive functional genomics resource to study the molecular effectors of chicken limb patterning at cellular resolution. Our single-cell transcriptomic atlas captures all major cell populations of the developing autopod, and highlights the transcriptional complexity in many of its components. Finally, integrating our data-set with other single-cell transcriptomics resources will enable researchers to assess molecular similarities in orthologous cell types across the major tetrapod clades, and provide an extensive candidate gene list to functionally test cell-type-specific drivers of limb morphological diversification.

Isolated postaxial polydactyly: Epidemiologic characteristics from a multicenter birth defects study

Isolated postaxial polydactyly (I-PAP), as a single defect, is a frequent malformation, characterized by an extra digit placed on the ulnar or fibular side of the limbs. Worldwide prevalence varies from as high as 225/10,000 in Nigerians to so low as 6.08/10,000 in Argentinians. Genetic-ethnic background significantly affects worldwide prevalence and type of I-PAP. Herein we describe the epidemiological characteristics of I-PAP in 697 newborns, 383 males and 314 females identified in 1,178,993 examined live births from a multicenter case-control hospital-based population study, the Mexican program of Registry and Epidemiological Surveillance of Congenital Malformations (RYVEMCE). The main characteristics analyzed included total I-PAP, stratified in Types A and B, defined as complete or incomplete extra-digit formation, respectively, sex prevalence, affected limb, laterality, parity, prematurity, delivery-type, twinning, consanguinity, and parental age. Males (6.35/10,000) are significantly more frequently affected than females (5.45/10,000), hands more than feet, left more than right limbs, and Type B (74.50%) more than A (25.50%). Prematurity and forceps use were significantly more frequent in cases than controls. An evident decreasing time-trend prevalence was present. Similar findings with other studies were males, upper and left limbs more frequently affected. Findings that were not previously reported include prematurity, forceps use, a significant decreasing time trend and an inverse ethnic prevalence for Types A (75%) and B (25%) in the Mayan population in contrast to other worldwide ethnic groups.

Variants in KIAA0825 underlie autosomal recessive postaxial polydactyly

Postaxial polydactyly (PAP) is a common limb malformation that often leads to cosmetic and functional complications. Molecular evaluation of polydactyly can serve as a tool to elucidate genetic and signaling pathways that regulate limb development, specifically, the anterior-posterior specification of the limb. To date, only five genes have been identified for nonsyndromic PAP: FAM92A, GLI1, GLI3, IQCE and ZNF141. In this study, two Pakistani multiplex consanguineous families with autosomal recessive nonsyndromic PAP were clinically and molecularly evaluated. From both pedigrees, a DNA sample from an affected member underwent exome sequencing. In each family, we identified a segregating frameshift (c.591dupA [p.(Q198Tfs*21)]) and nonsense variant (c.2173A > T [p.(K725*)]) in KIAA0825 (also known as C5orf36). Although KIAA0825 encodes a protein of unknown function, it has been demonstrated that its murine ortholog is expressed during limb development. Our data contribute to the establishment of a catalog of genes important in limb patterning, which can aid in diagnosis and obtaining a better understanding of the biology of polydactyly.

FAM92A Underlies Nonsyndromic Postaxial Polydactyly in Humans and an Abnormal Limb and Digit Skeletal Phenotype in Mice

Polydactyly is a common congenital anomaly of the hand and foot. Postaxial polydactyly (PAP) is characterized by one or more posterior or postaxial digits. In a Pakistani family with autosomal recessive nonsyndromic postaxial polydactyly type A (PAPA), we performed genomewide genotyping, linkage analysis, and exome and Sanger sequencing. Exome sequencing revealed a homozygous nonsense variant (c.478C>T, p.[Arg160*]) in the FAM92A gene within the mapped region on 8q21.13-q24.12 that segregated with the PAPA phenotype. We found that FAM92A is expressed in the developing mouse limb and E11.5 limb bud including the progress zone and the apical ectodermal ridge, where it strongly localizes at the cilia level, suggesting an important role in limb patterning. The identified variant leads to a loss of the FAM92A/Chibby1 complex that is crucial for ciliogenesis and impairs the recruitment and the colocalization of FAM92A with Chibby1 at the base of the cilia. In addition, we show that Fam92a^-/- homozygous mice also exhibit an abnormal digit morphology, including metatarsal osteomas and polysyndactyly, in addition to distinct abnormalities on the deltoid tuberosity of their humeri. In conclusion, we present a new nonsyndromic PAPA ciliopathy due to a loss-of-function variant in FAM92A. © 2018 American Society for Bone and Mineral Research.

Mutational Screening of GLI3, SHH, and SHH ZRS in 78 Chinese Children with Nonsyndromic Polydactyly

BACKGROUND

Polydactyly is one of the most common congenital limb abnormalities. Our objective was to identify the genetic causes of non-syndromic polydactyly in 78 Chinese children.

MATERIALS AND METHODS

Genomic DNA was isolated from 78 independent nonsyndromic polydactyly patients, of whom 71 had preaxial polydactyly (PPD), six had postaxial polydactyly (PAP), and one showed combined PPD1 and PAP-A/B. The coding areas and exon/intron boundaries of the GLI3 and SHH genes and the genomic region of SHH ZRS were amplified by polymerase chain reaction and sequenced.

RESULTS

The patient with combined PPD1 and PAP-A/B (subject DUO36) exhibited a heterozygous nonsense mutation in chr7: 42004164G>A (ENST00000395925, c.4507C>T, p.Gln1503Stop ) of the GLI3 gene that has not been previously recorded. We did not detect any mutations in GLI3, SHH, or SHH ZRS in the other 77 nonsyndromic polydactyly patients.

CONCLUSION

The novel mutation in GLI3 c.4507C>T is likely one of the causes of the PAP and PPD1 of subject DUO36. This important finding should facilitate the optimization of genetic testing for nonsyndromic polydactyly.

Mesenchymal stromal cells from infants with simple polydactyly modulate immune responses more efficiently than adult mesenchymal stromal cells

Bone marrow-derived stromal cells or mesenchymal stromal cells (BMSCs or MSCs, as we will call them in this work) are multipotent progenitor cells that can differentiate into osteoblasts, adipocytes and chondrocytes. In addition, MSCs have been shown to modulate the function of a variety of immune cells. Donor age has been shown to affect the regenerative potential, differentiation, proliferation and anti-inflammatory potency of MSCs; however, the impact of donor age on their immunosuppressive activity is unknown. In this study, we evaluated the ability of MSCs derived from very young children and adults on T-cell suppression and cytokine secretion by monocytes/macrophages. MSCs were obtained from extra digits of children between 10 and 21 months and adults between 28 and 64 years of age. We studied cell surface marker expression, doubling time, lineage differentiation potential and immunosuppressive function of the MSCs. Young MSCs double more quickly and differentiate into bone and fat cells more efficiently than those from older donors. They also form more and dense colonies of fibroblasts (colony forming unit-fibroblast [CFU-F]). MSCs from both young and adult subjects suppressed T-cell proliferation in a mitogen-induced assay at 1:3 and 1:30 ratios. At a 1:30 ratio, however, MSCs from adults did not, but MSCs from infants did suppress T-cell proliferation. In the mixed lymphocyte reaction assay, MSCs from infants produced similar levels of suppression at all three MSC/T-cell ratios, but adult MSCs only inhibited T-cell proliferation at a 1:3 ratio. Cytokine analyses of co-cultures of MSCs and macrophages showed that both adult and young MSCs suppress tumor necrosis factor alpha (TNF-α) and induce interleukin-10 (IL-10) production in macrophage co-culture assay in a similar manner. Overall, this work shows that developing MSCs display a higher level of immunosuppression than mature MSCs.

Pallister-Hall syndrome with orofacial narrowing and tethered cord: a case report

Background

Pallister–Hall syndrome is a rare, autosomal dominant, genetic disorder characterized by different congenital abnormalities: hypothalamic hamartoblastoma, bifid or shortened epiglottis, polydactyly, renal anomalies, and imperforate anus.

Case presentation

In this case report, we describe the case of a 13-year-old Lebanese-Armenian boy born with Pallister–Hall syndrome showing newly associated manifestations (orofacial narrowing and tethered cord), and currently showing a spontaneous puberty with normal growth pattern following management with growth hormones.

Conclusions

This case report shows a practical approach to this very rare syndrome, mainly with testosterone and growth hormones, and its follow-up in the long term. Being familiar with such cases may allow improvement of our knowledge for better management in the future.

Development and Evolutionary Constraints in Animals

We review the evolutionary importance of developmental mechanisms in constraining evolutionary changes in animals—in other words, developmental constraints. We focus on hard constraints that can act on macroevolutionary timescales. In particular, we discuss the causes and evolutionary consequences of the ancient metazoan constraint that differentiated cells cannot divide and constraints against changes of phylotypic stages in vertebrates and other higher taxa. We conclude that in all cases these constraints are caused by complex and highly controlled global interactivity of development, the disturbance of which has grave consequences. Mutations that affect such global interactivity almost unavoidably have many deleterious pleiotropic effects, which will be strongly selected against and will lead to long-term evolutionary stasis. The discussed developmental constraints have pervasive consequences for evolution and critically restrict regeneration capacity and body plan evolution.

Synchronous Chiari III Malformation and Polydactyly

BACKGROUND

Chiari III malformation is an extremely rare congenital anomaly. At present, its primary and associated pathognomonic factors remain poorly understood. The authors report a case of a male neonate born with an occipital encephalocoele with herniation of posterior fossa contents associated with bilateral postaxial polydactyly.

CASE DESCRIPTION

The patient is a dichorionic, diamniotic twin conceived via assisted reproductive methods; his twin sister has no congenital anomaly. Neurosurgical management included successful repair of the encephalocoele and subsequent cerebrospinal fluid diversion via a ventriculoperitoneal shunt.

CONCLUSIONS

Owing to the uniqueness of this patient's presentation, the concurrent diagnoses of Chiari III malformation and polydactyly are discussed in concordance with updated literature.

Molecular testing in holoprosencephaly

Holoprosencephaly (HPE) is a structural brain anomaly characterized by failure of the forebrain to separate during early embryogenesis. Both genetic and environmental etiologies of HPE have been discovered over the last three decades. Traditionally, the genetic workup for HPE has been a karyotype, chromosomal microarray, and/or Sanger sequencing of select genes. The recent increased availability of next-generation sequencing has changed the molecular diagnostic landscape for HPE, associating new genes with this disorder such as FGFR1. We conducted a systematic review of the medical literature for the molecular testing of HPE for studies published in the last 20 years. We also queried known commercial diagnostic laboratories and used information on their websites to construct a list of available commercial testing. Our group released its first recommendations in 2010 and this update incorporates the technology shifts and gene discoveries over the last decade. These recommendations provide a guide for genetic diagnosis of HPE, which is paramount for patients and their families for prognosis, treatment, and genetic counseling.

GLI1 inactivation is associated with developmental phenotypes overlapping with Ellis-van Creveld syndrome

GLI1, GLI2 and GLI3 form a family of transcription factors which regulate development by mediating the action of Hedgehog (Hh) morphogens. Accordingly, inactivating variants in GLI2 and GLI3 are found in several developmental disorders. In contrast, loss-of-function mutations in GLI1 have remained elusive, maintaining enigmatic the role of this gene in the human embryo. We describe eight patients from three independent families having biallelic truncating variants in GLI1 and developmental defects overlapping with Ellis-van Creveld syndrome (EvC), a disease caused by diminished Hh signaling. Two families had mutations in the last exon of the gene and a third family was identified with an N-terminal stop gain variant predicted to be degraded by the NMD-pathway. Analysis of fibroblasts from one of the patients with homozygous C-terminal truncation of GLI1 demonstrated that the corresponding mutant GLI1 protein is fabricated by patient cells and becomes upregulated in response to Hh signaling. However, the transcriptional activity of the truncated GLI1 factor was found to be severely impaired by cell culture and in vivo assays, indicating that the balance between GLI repressors and activators is altered in affected subjects. Consistent with this, reduced expression of the GLI target PTCH1 was observed in patient fibroblasts after chemical induction of the Hh pathway. We conclude that GLI1 inactivation is associated with a phenotypic spectrum extending from isolated postaxial polydactyly to an EvC-like condition.

Preaxial polydactyly of the foot

Background and purpose - Preaxial polydactyly of the foot is a rare malformation and clinicians are often unfamiliar with the associated malformations and syndromes. In order to give guidelines for diagnostics and referral to a clinical geneticist, we provide an overview of the presentation using a literature review and our own patient population. Patients and methods - The literature review was based on the Human Phenotype Ontology (HPO) project. From the HPO dataset, all phenotypes describing preaxial polydactyly were obtained and related diseases were identified and selected. An overview was generated in a heatmap, in which the phenotypic contribution of 12 anatomical groups to each disease is displayed. Clinical cases were obtained from our hospital database and were reviewed in terms of phenotype, genotype, heredity, and diagnosed syndromes. Results - From the HPO dataset, 21 diseases were related to preaxial polydactyly of the foot. The anatomical groups with the highest phenotypic contribution were lower limb, upper limb, and craniofacial. From our clinical database, we included 76 patients with 9 different diseases, of which 27 had a GLI3 mutation. Lower limb malformations (n = 55), upper limb malformations (n = 59), and craniofacial malformations (n = 32) were most frequently observed. Malformations in other anatomical groups were observed in 27 patients. Interpretation - Preaxial polydactyly of the foot often presents with other upper and lower limb malformations. In patients with isolated preaxial polydactyly of the foot, referral to a clinical geneticist is not mandatory. In patients with additional malformations, consultation with a clinical geneticist is recommended. When additional limb malformations are present, analysis of GLI3 is most feasible.

A Novel Role for CSRP1 in a Lebanese Family with Congenital Cardiac Defects

Despite an obvious role for consanguinity in congenital heart disease (CHD), most studies fail to document a monogenic model of inheritance except for few cases. We hereby describe a first-degree cousins consanguineous Lebanese family with 7 conceived children: 2 died in utero of unknown causes, 3 have CHD, and 4 have polydactyly. The aim of the study is to unveil the genetic variant(s) causing these phenotypes using next generation sequencing (NGS) technology. Targeted exome sequencing identified a heterozygous duplication in CSRP1 which leads to a potential frameshift mutation at position 154 of the protein. This mutation is inherited from the father, and segregates only with the CHD phenotype. The in vitro characterization demonstrates that the mutation dramatically abrogates its transcriptional activity over cardiac promoters like NPPA. In addition, it differentially inhibits the physical association of CSRP1 with SRF, GATA4, and with the newly described partner herein TBX5. Whole exome sequencing failed to show any potential variant linked to polydactyly, but revealed a novel missense mutation in TRPS1. This mutation is inherited from the healthy mother, and segregating only with the cardiac phenotype. Both TRPS1 and CSRP1 physically interact, and the mutations in each abrogate their partnership. Our findings add fundamental knowledge into the molecular basis of CHD, and propose the di-genic model of inheritance as responsible for such malformations.

Genetic Overview of Syndactyly and Polydactyly

Syndactyly and polydactyly-respectively characterized by fused and supernumerary digits-are among the most common congenital limb malformations, with syndactyly presenting at an estimated incidence of 1 in 2,000-3,000 live births and polydactyly at a frequency of 1 in approximately 700-1,000 live births. Despite their relatively regular manifestation in the clinic, the etiologies of syndactyly and polydactyly remain poorly understood because of their phenotypic and genetic diversity. Further, even though concrete knowledge of genotypic links has been established for some variants of syndactyly and polydactyly, there appears to be no single comprehensive published summary of all syndromic and nonsyndromic syndactyly and polydactyly presentations, and there is decidedly no resource that maps all syndromic and nonsyndromic syndactylies and polydactylies to their genetic bases. This gap in the literature problematizes comprehensive carrier screening and prenatal diagnosis and complicates novel diagnostic attempts. This review thus attempts to collect all that is known about the genetic bases of syndromic and nonsyndromic syndactylies and polydactylies, as well as to highlight the dactyly manifestations for which no genetic bases are as yet known. Then, having established a summation of existing and missing knowledge, this work briefly outlines the diagnostic techniques that a genetics-reinforced understanding of syndactyly and polydactyly could inform.

Disentangling Timing of Admixture, Patterns of Introgression, and Phenotypic Indicators in a Hybridizing Wolf Population

Hybridization is a natural or anthropogenic process that can deeply affect the genetic make-up of populations, possibly decreasing individual fitness but sometimes favoring local adaptations. The population of Italian wolves (Canis lupus), after protracted demographic declines and isolation, is currently expanding in anthropic areas, with documented cases of hybridization with stray domestic dogs. However, identifying admixture patterns in deeply introgressed populations is far from trivial. In this study, we used a panel of 170,000 SNPs analyzed with multivariate, Bayesian and local ancestry reconstruction methods to identify hybrids, estimate their ancestry proportions and timing since admixture. Moreover, we carried out preliminary genotype-phenotype association analyses to identify the genetic bases of three phenotypic traits (black coat, white claws, and spur on the hind legs) putative indicators of hybridization. Results showed no sharp subdivisions between nonadmixed wolves and hybrids, indicating that recurrent hybridization and deep introgression might have started mostly at the beginning of the population reexpansion. In hybrids, we identified a number of genomic regions with excess of ancestry in one of the parental populations, and regions with excess or resistance to introgression compared with neutral expectations. The three morphological traits showed significant genotype-phenotype associations, with a single genomic region for black coats and white claws, and with multiple genomic regions for the spur. In all cases the associated haplotypes were likely derived from dogs. In conclusion, we show that the use of multiple genome-wide ancestry reconstructions allows clarifying the admixture dynamics even in highly introgressed populations, and supports their conservation management.

Exome sequencing revealed a splice site variant in the IQCE gene underlying post-axial polydactyly type A restricted to lower limb

Polydactyly is characterized by an extra supernumerary digit/toe with or without bony element. To date variants in four genes GLI3, ZNF141, MIPOL1 and PITX1 have been implicated in developing non-syndromic form of polydactyly. The present study involved characterization of large consanguineous family of Pakistani origin segregating post-axial polydactyly type A, restricted to lower limb, in autosomal recessive pattern. DNA of two affected members in the family was subjected to exome sequencing. Sanger sequencing was then followed to validate segregation of the variants in the family members. A homozygous splice acceptor site variant (c.395-1G>A) was identified in the IQCE gene, which completely co-segregated with post-axial polydactyly phenotype within the family. The homozygous variant was absent in different public variant databases, 7000 in-house exomes, 130 exomes from unrelated Pakistani individuals and 215 ethnically matched controls. Mini-gene splicing assay was used to test effect of the variant on function of the gene. The assay revealed loss of first nucleotide of exon 6, producing a -1 frameshift and a premature stop codon 22 bases downstream of the variant (p.Gly132Valfs*22). The study provided the first evidence of involvement of the IQCE gene in limbs development in humans.

Achondroplasia with Polydactyly: A Case Report

An eight-year-old girl child reported to the Department of Oral Medicine and Radiology with the chief complaint of unerupted permanent teeth for past two years. The child presented features like disproportionately short stature, rhizomelic shortening of arms and legs, long face, frontal bossing and saddle nose. Based on the findings of chest and spine radiographs and ultrasound the case was diagnosed as a rare bone disorder "Achondroplasia". This case also presents a unique feature of polydactyly. Polydactyly is a manifestation in clinical medicine because it can serve as an indicator for a plethora of congenital anamolies. This case gained dental interest because of its characteristic craniofacial features. This article highlights the peculiar manifestations of this anamoly.

Sonic Hedgehog Signaling in Limb Development

The gene encoding the secreted protein Sonic hedgehog (Shh) is expressed in the polarizing region (or zone of polarizing activity), a small group of mesenchyme cells at the posterior margin of the vertebrate limb bud. Detailed analyses have revealed that Shh has the properties of the long sought after polarizing region morphogen that specifies positional values across the antero-posterior axis (e.g., thumb to little finger axis) of the limb. Shh has also been shown to control the width of the limb bud by stimulating mesenchyme cell proliferation and by regulating the antero-posterior length of the apical ectodermal ridge, the signaling region required for limb bud outgrowth and the laying down of structures along the proximo-distal axis (e.g., shoulder to digits axis) of the limb. It has been shown that Shh signaling can specify antero-posterior positional values in limb buds in both a concentration- (paracrine) and time-dependent (autocrine) fashion. Currently there are several models for how Shh specifies positional values over time in the limb buds of chick and mouse embryos and how this is integrated with growth. Extensive work has elucidated downstream transcriptional targets of Shh signaling. Nevertheless, it remains unclear how antero-posterior positional values are encoded and then interpreted to give the particular structure appropriate to that position, for example, the type of digit. A distant cis-regulatory enhancer controls limb-bud-specific expression of Shh and the discovery of increasing numbers of interacting transcription factors indicate complex spatiotemporal regulation. Altered Shh signaling is implicated in clinical conditions with congenital limb defects and in the evolution of the morphological diversity of vertebrate limbs.

Polydactyly: A Review

Polydactyly, also known as hyperdactyly, is a common congenital limb defect, which can present with various morphologic phenotypes. Apart from cosmetic and functional impairments, it can be the first indication of an underlying syndrome in the newborn. Usually, it follows an autosomal dominant pattern of inheritance with defects occurring in the anteroposterior patterning of limb development. Although many mutations have been discovered, teratogens have also been implicated in leading to this anomaly, thus making it of multifactorial origin. There are three polydactyly subtypes (radial, ulnar, and central), and treatment options depend on the underlying feature.

Congenital Anomalies of the Hand--Principles of Management

Physicians who specialize in pediatric orthopedics and hand surgery frequently encounter congenital hand abnormalities, despite their relative rarity. The treating physician should be aware of the associated syndromes and malformations that may, in some cases, be fatal if not recognized and treated appropriately. Although these congenital disorders have a wide variability, their treatment principles are similar in that the physician should promote functional use and cosmesis for the hand. This article discusses syndactyly, preaxial polydactyly and post-axial polydactyly, and the hypoplastic thumb.

Two cases of polydactyly in wild brown howler monkeys (Alouatta guariba clamitans)

We report the first two cases of polydactyly in an atelid species: (i) a wild ca. 16-week-old infant female presenting seven digits in both feet and other bone malformations and (ii) a wild newborn male presenting six digits in both feet with the extra digit fused to the hallux.

Advances in the molecular genetics of non-syndromic polydactyly

Polydactyly is one of the most common inherited limb abnormalities, characterised by supernumerary fingers or toes. It results from disturbances in the normal programme of the anterior-posterior axis of the developing limb, with diverse aetiology and variable inter- and intra-familial clinical features. Polydactyly can occur as an isolated disorder (non-syndromic polydactyly) or as a part of an anomaly syndrome (syndromic polydactyly). On the basis of the anatomic location of the duplicated digits, non-syndromic polydactyly is divided into three kinds, including preaxial polydactyly, axial polydactyly and postaxial polydactyly. Non-syndromic polydactyly frequently exhibits an autosomal dominant inheritance with variable penetrance. To date, in human, at least ten loci and four disease-causing genes, including the GLI3 gene, the ZNF141 gene, the MIPOL1 gene and the PITX1 gene, have been identified. In this paper, we review clinical features of non-syndromic polydactyly and summarise the recent progress in the molecular genetics, including loci and genes that are responsible for the disorder, the signalling pathways that these genetic factors are involved in, as well as animal models of the disorder. These progresses will improve our understanding of the complex disorder and have implications on genetic counselling such as prenatal diagnosis.

Evidence for an amphibian sixth digit

INTRODUCTION

Despite the great diversity in digit morphology reflecting the adaptation of tetrapods to their lifestyle, the number of digits in extant tetrapod species is conservatively stabilized at five or less, which is known as the pentadactyl constraint.

RESULTS

We found that an anuran amphibian species, Xenopus tropicalis (western clawed frog), has a clawed protrusion anteroventral to digit I on the foot. To identify the nature of the anterior-most clawed protrusion, we examined its morphology, tissue composition, development, and gene expression. We demonstrated that the protrusion in the X. tropicalis hindlimb is the sixth digit, as is evident from anatomical features, development, and molecular marker expression.

CONCLUSION

Identification of the sixth digit in the X. tropicalis hindlimb strongly suggests that the prehallux in other Xenopus species with similar morphology and at the same position as the sixth digit is also a vestigial digit. We propose here that the prehallux seen in various species of amphibians generally represents a rudimentary sixth digit.