Clinical Genetics of Polydactyly: An Updated Review

The Prenatal Ultrasound Diagnosis and Perinatal Outcome of Polydactyly: A Retrospective Cohort Study, 2016-2023

OBJECTIVE

To determine the significance of polydactyly identified on prenatal ultrasonography and provide a detailed analysis of characteristics and perinatal outcomes of fetal polydactyly.

METHODS

This is a retrospective cohort study of pregnancies with a postnatal diagnosis of fetal polydactyly between January 2016 and December 2023. The population was divided into 2 groups at postnatal diagnosis: the isolated polydactyly group and the nonisolated polydactyly group. Clinical data, prenatal ultrasonography, related genetic results, and postnatal outcomes were obtained.

RESULTS

Our study cohort comprised 328 fetuses with polydactyly. The overall detection rate of polydactyly by prenatal ultrasound was 19.2%, and the first detection rate in the first-, second-, and third-trimester were 0.9%, 14.6%, and 3.7%, respectively. Preaxial polydactyly (PPD) of hand was the most common type and the most common type of foot polydactyly was postaxial polydactyly (PAP) both in the isolated group and in the nonisolated group; the central polydactyly is rare. Syndactyly was the most common abnormality complicated with polydactyly. Between the nonpolydactyly group, the isolatedpolydactyly group and the nonisolated polydactyly group, there was a significant difference in perinatal outcome (P < .001).

CONCLUSION

The second trimester is the best gestational age for prenatal ultrasound detection of polydactyly. Polydactyly of hand was more likely PPD, while polydactyly of foot was more likely PAP. When polydactyly is detected by routine prenatal ultrasound, detailed ultrasound examination and prenatal counseling should be performed to determine the possibility of an underlying genetic syndrome.

Unraveling the Genetic Basis of Congenital Limb Anomalies in Eight Families

Limb abnormalities are the second most frequent birth defects seen in infants, after congenital heart disease. Over the past 150 years, more than 50 classifications for limb malformations based on morphology and osseous anatomy have been presented. The goal of the current study is to investigate the genetic basis of congenital limb abnormalities in the Pakistani population. Eight families, presenting different forms of limb anomalies, including syndactyly, polydactyly, synpolydactyly, and ectrodactyly in an autosomal dominant manner, were genetically and clinically investigated. Whole exome sequencing followed by Sanger sequencing was used to search for the disease-causing variants. Sequence analysis revealed five novel variants in LMBR1, GJA1, HOXD13, and TP63 and three previously reported variants in GJA1 and HOXD13. This study expanded the mutation spectrum in the identified genes and will also help in improved diagnosis of the limb anomalies in the local population.

Genetic analysis of preaxial polydactyly: identification of novel variants and the role of ZRS duplications in a Chinese cohort of 102 cases

Preaxial polydactyly (PPD) is a congenital limb malformation, previously reported to be caused primarily by variants in the ZRS and upstream preZRS regions. This study investigated genetic variations associated with PPD, focusing on point variants and copy number variations (CNVs) in the ZRS and preZRS regions. Comprehensive genetic analyses were conducted on 102 patients with PPD, including detailed clinical examinations and Sanger sequencing of the ZRS and preZRS regions. Additionally, real-time quantitative PCR (qPCR) was used to detect CNVs in the ZRS region. The evolutionary conservation and population frequencies of identified variants were also evaluated. Six point variants were identified, among which four are likely pathogenic novel variants: 93G > T (g.156584477G > T), 106G > A (g.156584464G > A), 278G > A (g.156584292G > A), and 409A > C (g.156585378A > C). Additionally, qPCR analysis revealed that 66.67% of patients exhibited ZRS duplications. Notably, these duplications were also present in cases with newly identified potential pathogenic point variants. These findings suggest the possible interaction of point variants in ZRS and preZRS through a common pathogenic mechanism, leading jointly to PPD. The findings expand the variant spectrum associated with non-syndromic polydactyly and highlight that, despite different classifications, anterior polydactyly caused by variants in ZRS and nearby regions may share common pathogenic mechanisms. The incorporation of various variant types in genetic screening can effectively enhance the rate of pathogenic variant detection and contribute to the cost-effectiveness of genetic testing for limb developmental defects, thereby promoting healthy births.

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.

Postaxial polydactyly: A case report highlighting genetic context, epidemiological trends, and management options

This case report examines a newborn with bilateral postaxial polydactyly type B, delivered by a 42-year-old mother with a history of third-degree consanguinity. The mother, having had no prior live births and one abortion, presented at 39 weeks gestation. The absence of prenatal care is noted, with its potential impact on prenatal diagnosis not assessed. The newborn, a healthy girl, weighed 3400 g with an Apgar score of 9/10. Radiographic and physical examination revealed vestigial sixth digits with rudimentary phalanges, influencing the surgical approach. This report underscores the importance of genetic counseling in cases of consanguinity and illustrates the multidisciplinary strategy necessary for managing polydactyly, from surgical considerations to genetic evaluation.

Surgical management of bilateral preaxial and postaxial polydactyly with syndactyly: A case report

INTRODUCTION AND IMPORTANCE

Polydactyly is the most common congenital malformation in the limbs. However, it is rare for a patient to exhibit concomitant preaxial and postaxial polydactyly alongside syndactyly in both limbs, and there are limited recommendations for such conditions. This report presents a case of bilateral preaxial and postaxial polydactyly with syndactyly of the feet.

PRESENTATION OF CASE

A 2-year-old girl was presented with an excess number of toes on both feet and an abnormal connection between the second and third toes. After a physical examination and plain radiography, the patient was diagnosed with bilateral preaxial and postaxial polydactyly with syndactyly. We performed a one-stage surgical correction consisting of ablation at the extra digit of bilateral great and little toes, followed by syndactyly release using z-plasty. The surgery was uneventful, and the parents were satisfied with the result.

DISCUSSION

A plain radiograph is necessary for pre-operative planning. We discarded the excess digits for cosmetics and soft and hard tissue for optimal function. It is necessary to preserve the soft tissues, remove the auxiliary digit, realign the digit, and restore the ligaments to preserve digit stability.

CONCLUSION

The complexity of this case required a meticulous surgical approach to address the structural abnormalities, restore functionality, and improve cosmetic appearance. In this case, the surgery can be performed in one procedure to minimize patient morbidity.

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.

Comparison of Surgical Wait Times and Procedure Length in the Management of Postaxial Polydactyly Using Local or General Anesthesia

Introduction: For infants with ulnar polydactyly, surgical removal of the supernumerary digit can be performed under general or local anesthetic. This study evaluated the wait times, surgical duration, and sedation times associated with performing the procedure under local versus general anesthetic in infants with ulnar polydactyly. Methods: The databases of three surgeons at our institution were reviewed for children less than 2 years of age who underwent surgery for non-syndromic ulnar polydactyly. Data collection included patient demographics, wait times, duration of surgery and sedation and complications. Results: The study included children (n  =  55) who received treatment under local (n  =  22) or general (n  =  33) anesthesia. The wait times for the local anesthetic group were significantly shorter than the general anesthetic group (p < 0.05) for: referral to first consultation appointment; referral to surgery date, and decision date to surgery date. The duration of surgery (17.9  ±  6.9 vs 36.6  ±  20.2 min) and sedation time (26.3  ±  11.1 vs 74.8  ±  29.1 min) were significantly shorter in the local anaesthetic group (p < 0.05). There were no differences in complication rates between the groups. Conclusion: In this single-institution retrospective analysis, treatment of non-syndromic ulnar polydactyly with local anesthetic and bottle sedation was associated with shorter wait times, and duration of surgery and sedation. Level of Evidence: III, retrospective chart review and quality improvement initiative.

Central Tetrapolydactyly With Atrial Septal Defect and Facial Nerve Palsy in a 15-Month-Old Female Child

Polydactyly, which is the presence of an extra appendage on the hand or the foot, is a common congenital anomaly encountered in children. It may be an isolated finding or found in conjunction with other congenital anomalies and syndromes. Polydactyly can occur in the hands or the feet. In the hand, it may occur as radial polydactyly (pre-axial polydactyly) or ulnar polydactyly (post-axial polydactyly (PAP)). Depending upon the side of occurrence, it may be medial, that is, toward the little finger (called ulnar polydactyly) or lateral, that is, toward the thumb (called radial polydactyly). On the feet, the extra digit can either be present on the side of the great toe (called tibial polydactyly) or on the side of the little toe (called fibular polydactyly). In both the upper and the lower limbs, affection of the central three digits is called central polydactyly. Central tetrapolydactyly, which is the presence of an extra appendage on all four limbs, is much more rarely encountered. This case report describes a 15-month-old female child who presented with findings of six digits on all four limbs and deviation of the left angle of mouth since birth. Her echocardiography showed a large atrial septal defect measuring 7 mm, with a left-to-right shunt. This is the first such case reported from all over the world from a tertiary care hospital with the aforementioned findings. Polydactyly, a very common congenital anomaly, should not be ignored in pediatric settings. It is important to diagnose associated features such as congenital heart diseases (CHDs), genitourinary abnormalities, and orofacial abnormalities to facilitate timely surgical correction and help improve the quality of life of those affected.

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.

Postaxial polydactyly of the bilateral hand in toddler: Case report and literature review

Polydactyly is a common congenital malformation of the hand and foot characterized by an extra digit or duplication of digits. Polydactyly can present as preaxial, complex, or postaxial types. It has various presentations, and it can be an isolated anomaly or part of other diseases or syndromic conditions. Incidences are more common in European and Asian descent. The first line of treatment commonly practiced is surgery to create an aesthetically normal functioning hand. In this report, we present a case of bilateral hand polydactyly in a 2-year 6-month-old boy of Asian descent. No other abnormalities or malformations were observed elsewhere in his body. He is otherwise a healthy boy with no family history of malformations. The pattern is not consistent with any syndromic disease. He subsequently underwent surgical resection of the extra digits and a follow-up review showed normal function of the hands without contracture and other complications of the surgical site.

A Rare Case of Unilateral Fetal Cataract and Coincidental Polydactyly in Congenital Toxoplasmosis

Congenital toxoplasmosis is caused by transplacental infection of Toxoplasma gondii during pregnancy. We present a case of a congenital toxoplasma with intracranial calcifications, microcephaly, growth restriction, a unilateral cataract that developed in the third trimester, and a coincidental post-axial-polydactyly. Antenatal imaging findings are important to guide further testing and confirmation of diagnosis, it is important to know all possible associations and prognoses for timely counseling, testing, and intervention. To our knowledge, no case has been published with findings of unilateral cataract in congenital toxoplasmosis and associated coincidental polydactyly. Therefore, we wish to add this case to the current scientific literature.

A novel GLI3 frameshift mutation in a Chinese pedigree with polydactyly: A case report

Background

GLI3 gene mutations can result in various forms of polysyndactyly, such as Greig cephalopolysyndactyly syndrome (GCPS, MIM: #175700), Pallister-Hall syndrome (PHS, MIM: #146510), and isolated polydactyly (IPD, MIM: #174200, #174700). Reports on IPD-associated GLI3 mutations are rare. In this study, a novel GLI3 mutation was identified in a Chinese family with IPD.

Results

We report a family with six members affected by IPD. The family members demonstrated several special phenotypes, including sex differences, abnormal finger joint development, and different polydactyly types. We identified a novel frameshift variant in the GLI3 gene (NM_000168.6: c.1820_1821del, NP_000159.3: p.Tyr607Cysfs*9) by whole-exome sequencing. Further analysis suggested that this mutation was the cause of polydactyly in this family.

Conclusions

The discovery of this novel frameshift variant in our study further solidifies the relationship between IPD and GLI3 and expands the previously established spectrum of GLI3 mutations and associated phenotypes.

Novel Finding of an Excess Bone in Postaxial Polydactyly of the Foot

Background

Postaxial polydactyly is a common congenital foot anomaly. However, the severity of the anomaly varies from simple cases with only soft tissue duplication to complex cases with bone and joint disorders. In our clinical practice, we found a new morphological anomaly of postaxial polydactyly. We encountered several cases of postaxial polydactyly with bone fragments located between the fourth and fifth toes. The bone fragments were independent of the joint cavity. The mechanisms underlying its development remain unknown because it is a novel disorder. In the present study, we investigated the characteristics of the excess bone to formulate an embryological hypothesis.

Methods

We examined the frequency and trends in the occurrence of excess bone using data from photographs and radiographs of these cases. An example of a disorder similar to excess bone is mosaic-like alignment, as reported by Iba et al. We also compared the characteristics of the mosaic-like alignment with those of the excess bone. Based on these data and existing embryological knowledge, we hypothesized the origin of the excess bone.

Results

Excess bone and mosaic-like alignments showed different characteristics. Therefore, both were considered completely different disorders. We hypothesized that excess bone was caused by damage to the interdigital ectoderm immediately before interdigital programmed cell death.

Conclusions

We encountered a new form of postaxial polydactyly. This can be a factor influencing the treatment strategy because it can affect alignment and stability.

Polydactyly-Myopia Syndrome: Genetic and Ophthalmologic Perspectives

Polydactyly-myopia syndrome is a rare genetic condition characterized by the co-occurrence of polydactyly and myopia. Herein, we present the case of a 28-year-old Muslim male, born of consanguineous parents, who presented with complaints of diminished vision since childhood. Ophthalmologic examination revealed severe myopia with characteristic fundus changes indicative of high myopia. Additionally, the patient exhibited polydactyly in all limbs, with a positive family history of both polydactyly and myopia. This case underscores the importance of recognizing and managing rare syndromes to provide appropriate genetic counseling and clinical care. Further research is warranted to elucidate the underlying genetic mechanisms and optimize therapeutic strategies for polydactyly-myopia syndrome. Awareness of this syndrome among healthcare providers is essential to facilitate early diagnosis and intervention for affected individuals and their families.

Epidemiology of congenital polydactyly and syndactyly in Hunan Province, China

OBJECTIVE

To describe the prevalence and epidemiology of congenital polydactyly and syndactyly in Hunan Province, China, 2016-2020.

METHODS

Data were obtained from the Birth Defects Surveillance System in Hunan Province, China, 2016-2020. Prevalence of birth defects (polydactyly or syndactyly) is the number of cases per 1000 births (unit: ‰). Prevalence and 95% confidence intervals (CI) were calculated by the log-binomial method. Chi-square trend tests (χ2trend) were used to determine trends in prevalence by year. Crude odds ratios (ORs) were calculated to examine the association of each demographic characteristic with polydactyly and syndactyly.

RESULTS

Our study included 847,755 births, and 14,459 birth defects were identified, including 1,888 polydactyly and 626 syndactyly cases, accounting for 13.06% and 4.33% of birth defects, respectively. The prevalences of total birth defects, polydactyly, and syndactyly were 17.06‰ (95%CI: 16.78-17.33), 2.23‰ (95%CI: 2.13-2.33), and 0.74‰ (95%CI: 0.68-0.80), respectively. Most polydactyly (96.77%) and syndactyly (95.69%) were diagnosed postnatally (within 7 days). From 2016 to 2020, the prevalences of polydactyly were 1.94‰, 2.07‰, 2.20‰, 2.54‰, and 2.48‰, respectively, showing an upward trend (χ2trend = 19.48, P < 0.01); The prevalences of syndactyly were 0.62‰, 0.66‰, 0.77‰, 0.81‰, and 0.89‰, respectively, showing an upward trend (χ2trend = 10.81, P = 0.03). Hand polydactyly (2.26‰ vs. 1.33‰, OR = 1.69, 95%CI: 1.52-1.87) and hand syndactyly (0.43‰ vs. 0.28‰, OR = 1.42, 95%CI: 1.14-1.76) were more common in males than females. Polydactyly (2.67‰ vs. 1.93‰, OR = 1.38, 95%CI: 1.26-1.51) and syndactyly (0.91‰ vs. 0.62‰, OR = 1.47, 95%CI: 1.26-1.72) were more common in urban areas than in rural areas. Compared to maternal age 25-29, hand polydactyly was more common in maternal age < 20 (2.48‰ vs. 1.74‰, OR = 1.43, 95%CI: 1.01-2.02) or ≥ 35 (2.25‰ vs. 1.74‰, OR = 1.30, 95%CI: 1.12-1.50).

CONCLUSION

In summary, we have described the prevalence and epidemiology of polydactyly and syndactyly from hospital-based surveillance in Hunan Province, China, 2016-2020. Our findings make some original contributions to the field, which may be valuable for future research.

Medical findings and congenital anomalies in Vermeer's paintings

The 17th century was a time of scientific discovery in Europe. Leading academic centers provided the general population with an opportunity to view anatomic dissections of human bodies. Rather than portray idealized versions of individuals, Dutch painters were committed to accurately representing their models. This was true for Johannes Vermeer. The 2023 exhibition of Vermeer's paintings at the Rijksmuseum in Amsterdam provided an unprecedented opportunity to observe 28 of his 37 existing paintings simultaneously in person. Here the authors suggest that in at least eight paintings a visibly pregnant woman is present. Vermeer's wife was pregnant or lactating most of the time during their 22-year marriage. Further, evidence of specific medical findings and congenital anomalies such as polydactyly, ectrodactyly, alopecia, kyphosis, and hyperthyroidism were observed in the paintings. These have not been previously reported in the medical or art history literature.

Retinoblastoma and polydactyly in a child with 46, XY, 15pstk+ karyotype-A case report and literature review

BACKGROUND

Retinoblastoma (Rb) is the most common intraocular malignancy in childhood, originating from primitive retinal stem cells or cone precursor cells. It can be triggered by mutations of the RB1 gene or amplification of the MYCN gene. Rb may rarely present with polydactyly.

METHODS

We conducted karyotype analysis, copy number variation sequencing, and whole-genome sequencing on the infant proband and his family. The clinical course and laboratory results of the proband's infant were documented and collected. We also reviewed the relevant literature.

RESULTS

A 68-day-old boy presented with preaxial polydactyly and corneal edema. His intraocular pressure (IOP) was 40/19 mmHg, and color Doppler imaging revealed vitreous solid mass-occupying lesions with calcification in the right eye. Ocular CT showed flaky high-density and calcification in the right eye. This was classified as an International Retinoblastoma Staging System group E retinoblastoma with an indication for enucleation. Enucleation and orbital implantation were performed on the child's right eye. Karyotype analysis revealed an abnormal 46, XY, 15pstk+ karyotype, and the mother exhibited diploidy of the short arm of chromosome 15. The Alx-4 development factor, 13q deletion syndrome, and the PAPA2 gene have been reported as potential mechanisms for Rb combined with polydactyly.

CONCLUSION

We report the case of a baby boy with Rb and polydactyly exhibiting a 46, XY, 15pstk+ Karyotype. We discuss potential genetic factors related to both Rb and polydactyly. Furthermore, there is a need for further exploration into the impact of chromosomal polymorphisms in Rb with polydactyly.

A case-control study characterizing polydactyly risk factors in Bogotá and Cali, Colombia between 2002 and 2020

BACKGROUND

Polydactyly is a congenital abnormality characterized by the presence of additional fingers on one or more extremities. In Colombia, polydactyly accounted for 17% of musculoskeletal congenital abnormalities in 2021, with a prevalence of 6.03 per 10,000 live births. The purpose of this study was to determine the prevalence of polydactyly and identify associated risk factors in Bogotá and Cali, Colombia, from 2002 to 2020.

METHODS

A retrospective case-control study design was employed, analyzing data from birth defect reports provided by the Program for the Prevention and Follow-up of Congenital Defects and Orphan Diseases surveillance system. Cases included live births or stillbirths with polydactyly, while controls consisted of infants without congenital abnormality, matched in terms of birth date and hospital. Prevalence of polydactyly was calculated and risk factors were assessed through odds ratios obtained by logistic regression models, considering a 95% confidence interval.

RESULTS

Among the 558,255 births included in the study, 848 cases of polydactyly were identified, resulting in a prevalence rate of 15.19 per 10,000 live births. Risk factors associated with polydactyly included male newborn sex, pregestational diabetes, and a family history of malformation among first-degree relatives.

CONCLUSION

These findings highlight the importance a surveillance system aimed to characterize populations with congenital abnormalities, providing a better option for analyzing risk factors, help improving prevention, diagnosis, notification, and optimal treatment in patients.

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.

A variant in the LDL receptor-related protein encoding gene LRP4 underlying polydactyly and phalangeal synostosis in a family of Pakistani origin

A family of Pakistani origin, segregating polydactyly, and phalangeal synostosis in an autosomal dominant manner, has been investigated and presented in the present report. Whole-exome sequencing (WES), followed by segregation analysis using Sanger sequencing, revealed a heterozygous missense variant [c.G1696A, p.(Gly566Ser)] in the LRP4 gene located on human chromosome 11p11.2. Homology protein modeling revealed the mutant Ser566 generated new interactions with at least four other amino acids and disrupted protein folding and function. Our findings demonstrated the first direct evidence of involvement of LRP4 in causing polydactyly and phalangeal synostosis in the same family. This study highlighted the importance of inclusion of LRP4 gene in screening individuals presenting polydactyly in hands and feet, and phalangeal synostosis in the same family.

Variants in EFCAB7 underlie nonsyndromic postaxial polydactyly

Polydactyly is the most common limb malformation that occurs in 1.6-10.6 per one thousand live births, with incidence varying with ancestry. The underlying gene has been identified for many of the ~100 syndromes that include polydactyly. While for the more common form, nonsydromic polydactyly, eleven candidate genes have been reported. We investigated the underlying genetic cause of autosomal recessive nonsyndromic postaxial polydactyly in four consanguineous Pakistani families. Some family members with postaxial polydactyly also present with syndactyly, camptodactyly, or clinodactyly. Analysis of the exome sequence data revealed two novel homozygous frameshift deletions in EFCAB7: [c.830delG;p.(Gly277Valfs*5)]; in three families and [c.1350_1351delGA;p.(Asn451Phefs*2)] in one family. Sanger sequencing confirmed that these variants segregated with postaxial polydactyly, i.e., family members with postaxial polydactyly were found to be homozygous while unaffected members were heterozygous or wild type. EFCAB7 displays expressions in the skeletal muscle and on the cellular level in cilia. IQCE-EFCAB7 and EVC-EVC2 are part of the heterotetramer EvC complex, which is a positive regulator of the Hedgehog (Hh) pathway, that plays a key role in limb formation. Depletion of either EFCAB7 or IQCE inhibits induction of Gli1, a direct Hh target gene. Variants in IQCE and GLI1 have been shown to cause nonsyndromic postaxial polydactyly, while variants in EVC and EVC2 underlie Ellis van Creveld and Weyers syndromes, which include postaxial polydactyly as a phenotype. This is the first report of the involvement of EFCAB7 in human disease etiology.

Engineering Inflammation-Resistant Cartilage: Bridging Gene Therapy and Tissue Engineering

Articular cartilage defects caused by traumatic injury rarely heal spontaneously and predispose into post-traumatic osteoarthritis. In the current autologous cell-based treatments the regenerative process is often hampered by the poor regenerative capacity of adult cells and the inflammatory state of the injured joint. The lack of ideal treatment options for cartilage injuries motivated the authors to tissue engineer a cartilage tissue which would be more resistant to inflammation. A clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 knockout of TGF-β-activated kinase 1 (TAK1) gene in polydactyly chondrocytes provides multivalent protection against the signals that activate the pro-inflammatory and catabolic NF-κB pathway. The TAK1-KO chondrocytes encapsulate into a hyaluronan hydrogel deposit copious cartilage extracellular matrix proteins and facilitate integration onto native cartilage, even under proinflammatory conditions. Furthermore, when implanted in vivo, compared to WT fewer pro-inflammatory M1 macrophages invade the cartilage, likely due to the lower levels of cytokines secreted by the TAK1-KO polydactyly chondrocytes. The engineered cartilage thus represents a new paradigm-shift for the creation of more potent and functional tissues for use in regenerative medicine.

Identification of a Novel IQCE Large Deletion through Copy Number Variant Analysis from Whole-Exome Sequencing Data of a Patient with Postaxial Polydactyly Type A7

Introduction

Non-syndromic polydactyly has been associated with pathogenic variants in 11 genes until today, including IQCE gene. More precisely, loss-of-function of IQCE is associated with the autosomal recessive disorder postaxial polydactyly type A7 (PAPA7, MIM #617642).

Case Presentation

A 3-year-old female patient was referred to our genetics department with postaxial polydactyly, syndactyly, brachydactyly, and hypoplastic teeth. Through whole-exome sequencing (WES), a pathogenic IQCE variant was identified (c.895_904del) in the homozygous state, which adequately explained the disease phenotype of our patient. However, copy number variant (CNV) analysis from WES data, using ExomeDepth, revealed a novel, likely pathogenic large deletion involving IQCE genomic regions (DEL:chr7:2606751_2641098) encompassing exons 2-18 of the gene.

Conclusion

IQCE gene codes for a 695-amino acid protein located at the base of the primary cilia that positively regulates the Hedgehog signaling pathway. This case report represents the first description of a large deletion in IQCE and indicates that implementation of ExomeDepth in routine WES analysis can contribute valuable information toward elucidating the correct etiology of rare genetic diseases, increasing the diagnostic yield, and minimizing the need for additional tests.

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.

A Rare Combination of Heptadactyl and Hexadactyl Polydactyly in a Neonate

Heptadactyly and hexadactyly are rare congenital disorders from the polydactyly family. This type of polydactyly is usually classified into three major groups: preaxial (medial ray), postaxial (lateral ray), and central polydactyly. The most common presentation is both preaxial and postaxial polydactyly. The occurrence of heptadactyly and hexadactyly has been reported but the presence of both in the same infant has not been reported yet. We report the presence of both these abnormalities in the same infant.

Thumb Duplication Surgical Treatment: Outcomes and Results

Aim

This study aims to evaluate functional and esthetic outcomes of thumb duplication correction in pediatric age.

Methods

Retrospective study including all pediatric patients with thumb duplication undergoing surgical treatment between 2012 and 2017. We analyzed demographic data, surgical technique, and surgical outcomes considering Tada, Horii, and Tien scores, according to the following parameters: active mobility of the metacarpophalangeal and interphalangeal joints, stability, alignment, and family's opinion about cosmetic and function of the thumb. The Wassel-Flatt classification was used to classify the duplicated thumbs.

Results

A total of 11 patients were included, predominantly male (ratio 1.8:1), with a median age at time of surgery of 19[10-26] months and a median follow-up time after surgery of 23 [3-63] months. The Wassel- Flatt type IV thumb was the most frequent (73%). The postoperative evaluation revealed that 82% of patients had good results in Tada score, 73% had good results in Horii score, and all patients showed good results in Tien score. We found a relation between lower age and fair postoperative alignment (P = .047) and between fair postoperative alignment and fair final Tada (P = .022), Horii (P = .006), and Tien (P = .009) scores.

Conclusions

Excision and reconstruction procedures are good options in the treatment of thumb duplication providing good clinical results, with excellent parent satisfaction. Timing of surgery is important for favorable esthetic outcomes, while angular deformity is a determining factor that for postoperative dissatisfaction.

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.

Human thumb consists of three phalanges and lacks metacarpal? A morphometric study on the long bones of the hand

PURPOSE

For many years, it was thought that the thumb consists of just two phalanges that differentiate it from the other four medial triphalangeal fingers. But there are some old reports that few former scientists believed the thumb has three phalanges and it lacked a metacarpal, and the thumb metacarpal is a phalanx. So this anthropometric study was carried out by investigating the morphology of the long bones of the hand and correlations between the thumb metacarpal and other miniature long bones of the hand.

METHODS

We studied anterior-posterior X-ray images of the right hands of 80 individuals from 18 to 65 years old. The exploration targets were the length of all metacarpals (MC), proximal phalanges (PP), middle phalanges (MP), and distal phalanges (DP). Friedman Repeated Measures Analysis of Variance and Dunn's post hoc test were carried out to compare the means of all variables. The correlation between all quantitative factors was done by Spearman Rank Correlation (Spearman's Rho) coefficient.

RESULTS

Our results showed that the length of the phalanges and the total length of the fingers are independent of the related metacarpal length (P < 0.001). Also, the thumb metacarpal length in comparison to all bones of the hand was significantly different from all long bones of the hand except the proximal phalanx of the middle finger (P = 1).

CONCLUSION

Based on the morphology of the long bones of the hand and the high similarity between the thumb metacarpal and phalanges especially the proximal phalanx of the middle finger, it can be suggested that the current thumb metacarpal is a proximal phalanx of the thumb.

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.

Case Report: Prenatal Diagnosis of Postaxial Polydactyly With Bi-Allelic Variants in Smoothened (SMO)

Postaxial polydactyly is a common congenital malformation which involves complex genetic factors. This retrospective study analyzed the cytogenetic and molecular results of a Chinese fetus diagnosed with postaxial polydactyly of all four limbs. Fetal karyotyping and chromosomal microarray analysis (CMA) did not find any abnormality while trio whole-exome sequencing (trio-WES) identified bi-allelic variants in smoothened (SMO) and (NM_005631.5: c.1219C > G, NP_005622.1: p. Pro407Ala, and NM_005631.5: c.1619C > T, NP_005622.1: p. Ala540Val). Sanger sequencing validated these variants. The mutations are highly conserved across multiple species. In-depth bioinformatics analysis and familial co-segregation implied the compound heterozygous variants as the likely cause of postaxial polydactyly in this fetus. Our findings provided the basis for genetic counseling and will contribute to a better understanding of the complex genetic mechanism that underlies postaxial polydactyly.

Identification of homozygous missense variant in SIX5 gene underlying recessive nonsyndromic hearing impairment

Hearing impairment (HI) is a heterogeneous condition that affects many individuals globally with different age groups. HI is a genetically and phenotypically heterogeneous disorder. Over the last several years, many genes/loci causing rare autosomal recessive and dominant forms of hearing impairments have been identified, involved in various aspects of ear development. In the current study, two affected individuals of a consanguineous family exhibiting autosomal recessive nonsyndromic hearing impairment (AR-NSHI) were clinically and genetically characterized. The single affected individual (IV-2) of the family was subjected to whole-exome sequencing (WES) accompanied by traditional Sanger sequencing. Clinical examinations using air conduction audiograms of both the affected individuals showed profound hearing loss across all frequencies. WES revealed a homozygous missense variant (c.44G>C) in the SIX5 gene located on chromosome 19q13.32. We report the first case of autosomal recessive NSHI due to a biallelic missense variant in the SIX5 gene. This report further supports the evidence that the SIX5 variant might cause profound HI and supports its vital role in auditory function. Identification of novel candidate genes might help in application of future gene therapy strategies that may be implemented for NSHI, such as gene replacement using cDNA, gene silencing using RNA interference, and gene editing using the CRISPR/Cas9 system.

De Novo GLI3 Pathogenic Variants May Cause Hypotonia and a Range of Brain Malformations Without Skeletal Abnormalities

BACKGROUND

GLI3 encodes a zinc finger transcription factor that plays a role in the sonic hedgehog pathway. Germline pathogenic GLI3 variants are associated with Greig cephalopolysyndactyly and Pallister-Hall syndromes, two syndromes involving brain malformation and polydactyly.

METHODS

We identified patients with pathogenic GLI3 variants and brain malformations in the absence of polydactyly or other skeletal malformation.

RESULTS

Two patients were identified. Patient #1 is a 4-year-old boy with hypotonia and global developmental delay. Brain MRI showed a focal cortical dysplasia, but he had no history of seizures. Genetic testing identified a de novo likely pathogenic GLI3 variant: c.4453A>T, p.Asn1485Tyr. Patient #2 is a 4-year-old boy with hypotonia, macrocephaly, and global developmental delay. His brain MRI showed partial agenesis of the corpus callosum, dilatation of the right lateral ventricle, and absent hippocampal commissure. Genetic testing identified a de novo pathogenic GLI3 variant: c.4236_4237del, p.Gln1414AspfsTer21. Neither patient had polydactyly or any apparent skeletal abnormality.

CONCLUSIONS

These patients widen the spectrum of clinical features that may be associated with GLI3 pathogenic variants to include hypotonia, focal cortical dysplasia, and other brain malformations, in the absence of apparent skeletal malformation. Further study is needed to determine if GLI3 pathogenic variants are a more common cause of focal cortical dysplasia or corpus callosum agenesis than presently recognized.

A novel variant of GLI3, p.Asp1514Thrfs*5, is identified in a Chinese family affected by polydactyly

Background

Polydactyly is a common congenital malformation characterized by the presence of supernumerary fingers or toes. In this case study, we sought to identify the causative pathogenic factor in a family from a northern region of China affected by non‐syndromic postaxial polydactyly (PAP).

Methods

After recruiting a three‐generation family with PAP, whole‐exome sequencing was performed to identify the causative variant. In silico analysis and Sanger sequencing were used to validate the variant.

Results

We identified a novel heterozygous frameshift variant (NM_000168.6:c.4540delG, p.Asp1514Thrfs*5) in the transcriptional activator (TA1) domain of the GLI3 gene.

Conclusion

The novel frameshift variant identified in this study further confirms the relationship between non‐syndromic PAP and GLI3 and extends the previously established mutational and phenotypic spectra of GLI3.

Comparison of the Infant and Adult Adipose-Derived Mesenchymal Stem Cells in Proliferation, Senescence, Anti-oxidative Ability and Differentiation Potential

BACKGROUND

Infant adipose-derived mesenchymal stem cells (ADSCs) collected from excised polydactyly fat tissue, which was surgical waste, could be cultured and expanded in vitro in this study. In addition, the collecting process would not cause pain in the host. In this study, the proliferation, reduction of senescence, anti-oxidative ability, and differentiation potential in the infant ADSCs were compared with those in the adult ADSCs harvested from thigh liposuction to determine the availability of infant ADSCs.

METHODS

Proliferation was determined by detecting the fold changes in cell numbers and doubling time periods. Senescence was analyzed by investigating the age-related gene expression levels and the replicative stress. The superoxide dismutase (SOD) gene expression, adipogenic, neurogenic, osteogenic, and tenogenic differentiation were compared by RT-qPCR. The chondrogenic differentiation efficiency was also determined using RT-qPCR and immunohistochemical staining.

RESULTS

The proliferation, SOD (SOD1, SOD2 and SOD3) gene expression, the stemness-related gene (c-MYC) and telomerase reverse transcriptase of the infant ADSCs at early passages were enhanced compared with those of the adults'. Cellular senescence related genes, including p16, p21 and p53, and replicative stress were reduced in the infant ADSCs. The adipogenic genes (PPARγ and LPL) and neurogenic genes (MAP2 and NEFH) of the infant ADSC differentiated cells were significantly higher than those of the adults' while the expression of the osteogenic genes (OCN and RUNX) and tenogenic genes (TNC and COL3A1) of both demonstrated opposite results. The chondrogenic markers (SOX9, COL2 and COL10) were enhanced in the infant ADSC differentiated chondrogenic pellets, and the expression levels of SODs were decreased during the differentiation process.

CONCLUSION

Cultured infant ADSCs demonstrate less cellular senescence and replicative stress, higher proliferation rates, better antioxidant defense activity, and higher potential of chondrogenic, adipogenic and neurogenic differentiation.

Genes, Heritability, 'Race', and Intelligence: Misapprehensions and Implications

The role of genetics in determining measured differences in mean IQ between putative racial groups has been a focus of intense discussion and disagreement for more than 50 years. While the last several decades of research have definitively demonstrated that genetic variation can influence measures of cognitive function, the inferences drawn by some participants in the controversy regarding the implications of these findings for racial differences in cognitive ability are highly dubious. Of equal importance, there is no compelling scientific rationale for focusing on and devoting substantial effort to determining mean differences in intelligence or other cognitive functions between groups with incompletely defined and dynamic (and therefore not definitively definable) boundaries.

ZPA Regulatory Sequence Variants in Chinese Patients With Preaxial Polydactyly: Genetic and Clinical Characteristics

Preaxial polydactyly (PPD) is a common congenital abnormality with an incidence of 0.8-1.4% in Asians, characterized by the presence of extra digit(s) on the preaxial side of the hand or foot. PPD is genetically classified into four subtypes, PPD type I-IV. Variants in six genes/loci [including GLI family zinc finger 3 (GLI3), ZPA regulatory sequence (ZRS), and pre-ZRS region] have been identified in PPD cases. Among these loci, ZRS is, perhaps, the most special and well known, but most articles only reported one or a few cases. There is a lack of reports on the ZRS-variant frequency in patients with PPD. In this study, we recruited 167 sporadic or familial cases (including 154 sporadic patients and 13 families) with PPD from Central-South China and identified four ZRS variants in four patients (2.40%, 4/167), including two novel variants (ZRS131A > T/chr7:g.156584439A > T and ZRS474C > G/chr7:g.156584096C > G) and two known variants (ZRS428T > A/chr7:g.156584142T > A and ZRS619C > T/chr7:g.156583951C > T). ZRS131A > T and ZRS428T > A were detected in PPD I cases and ZRS474C > G and ZRS619C > T combinedly acted to cause PPD II. The detectable rate of ZRS variants in PPD I was 1.60% (2/125), while PPD II was significantly higher (9.52%, 2/21). Three bilateral PPD cases harbored ZRS variants (13.64%, 3/22), suggesting that bilateral PPD was more possibly caused by genetic etiologies. This study identified two novel ZRS variants, further confirmed the association between ZRS and PPD I and reported a rare PPD II case resulted from the compound heterozygote of ZRS. This investigation preliminarily evaluated a ZRS variants rate in patients with PPD and described the general picture of PPD in Central-South China.

Complex Hand Polydactyly: A Case Report and Literature Review

Polydactyly is a common congenital malformation in which extra digits are present in at least one extremity. It has various presentations, and it can be an isolated anomaly or part of other diseases. Most isolated polydactyly cases are sporadic and unilateral, but there is an increased incidence in some populations. Polydactyly is multifactorial and can occur in different forms. Its main line of treatment is surgery to improve cosmesis and functioning. In this report, we present a rare case of bilateral complex hand polydactyly in a one-year-seven-months old girl of African descent. She is otherwise healthy with no family history of malformations. The pattern is not consistent with any syndromic disease. She subsequently underwent surgical resection of the extra digits.

Current Trends in Genetics and Neonatal Care

BACKGROUND

Genetic and genomic health applications are rapidly changing. A clear and updated description of these applications for the neonatal population is needed to guide current nursing practice.

PURPOSE

To provide scientific evidence and guidance on the current genetic and genomic applications pertinent to neonatal care.

METHODS

A search of CINAHL and PubMed was conducted using the search terms "newborn/neonatal" and "genetics," "genomics," "newborn screening," "pharmacogenomics," "ethical," and "legal." Google searches were also conducted to synthesize professional guidelines, position statements, and current genetic practices.

FINDINGS/RESULTS

Components of the newborn genetic assessment, including details on the newborn physical examination, family history, and laboratory tests pertinent to the newborn, are reported. The history and process of newborn screening are described, in addition to the impact of advancements, such as whole exome and genome sequencing, on newborn screening. Pharmacogenomics, a genomic application that is currently utilized primarily in the research context for neonates, is described and future implications stated. Finally, the specific ethical and legal implications for these genetic and genomic applications are detailed, along with genetic/genomic resources for nurses.

IMPLICATIONS FOR PRACTICE

Providing nurses with the most up-to-date evidence on genetic and genomic applications ensures their involvement and contributions to quality neonatal care.

IMPLICATIONS FOR RESEARCH

Ongoing genetic/genomic research is needed to understand the implications of genetic/genomic applications on the neonatal population and how these new applications will change neonatal care.

A Novel Homozygous Missense Mutation in the Zinc Finger DNA Binding Domain of GLI1 Causes Recessive Post-Axial Polydactyly

Background: Polydactyly is a prevalent digit abnormality characterized by having extra digits/toes. Mutations in eleven known genes have been associated to cause nonsyndromic polydactyly: GLI3, GLI1, ZRS regulating LMBR1, IQCE, ZNF141, PITX1, MIPOL1, FAM92A, STKLD1, KIAA0825, and DACH1. Method: A single affected family member (IV-4) was subjected to whole-exome sequencing (WES) to identify the causal gene. Bi-directional Sanger sequencing was performed to segregate the identified variant within the family. In silico analysis was performed to investigate the effect of the variant on DNA binding properties. Results: whole-exome sequencing identified a bi-allelic missense variant (c.1010C > T; p. Ser337Leu) in exon nine of GLI1 gene located on chromosome 12q13.3. With the use of Sanger sequencing, the identified variant segregated perfectly with the disease phenotype. Furthermore, in silico analysis of this DNA binding protein revealed that the variant weakened the DNA binding interaction, resulting in indecorous GLI1 function. Conclusion: Herein, we report a novel variant in GLI1 gene, causing autosomal recessive post-axial polydactyly type A (PAPA) type 8. This confirms the critical role of GLI1 in digit development and might help in genotype-phenotype correlation in the future.

Homozygous GLI3 variants observed in three unrelated patients presenting with syndromic polydactyly

Polydactyly is a hallmark of GLI3 pathogenic variants, with Greig cephalopolysyndactyly syndrome and Pallister-Hall syndrome being the two main associated clinical presentations. Homozygous GLI3 variants are rare instances in the literature, and mendelian dominance is the accepted framework for GLI3-related diseases. Herein, we report three unrelated probands, presenting with polydactyly, and homozygous variants in the GLI3 gene. First, a 10-year-old girl, whose parents were first-degree cousins, presented with bilateral postaxial polydactyly of the hands, developmental delay and multiple malformations. Second, a male newborn, whose parents were first-degree cousins, presented with isolated bilateral postaxial polysyndactyly of the hands and the feet. Third, an adult male, whose parents were first-degree cousins, had bilateral mesoaxial polydactyly of the hands, with severe intellectual disability and multiple malformations. All three probands carried homozygous GLI3 variants. Strikingly, the parents also carried the child's variant, in the heterozygous state, without any clinical sign of GLI3 disease. Given the clinical presentation of our patients, the rarity and predicted high pathogenicity of the variants observed, and the absence of other pathogenic variants, we suggest that these GLI3 homozygous variants are causal. Moreover, the parents were heterozygous for the observed variants, but were clinically unremarkable, suggesting that these variants are hypomorphic alleles.

Identification of the genetic basis of sporadic polydactyly in China by targeted sequencing

Purpose

Polydactyly is a highly heterogeneous group of skeletal deformities in clinical and genetic background. The variation spectrum in Chinese sporadic polydactyly has not been comprehensively analyzed. To elucidate genetic variation spectrum and genotype-phenotype correlations in Chinese patients with polydactyly, we conducted comprehensive genetic analysis of patients nationwide using targeted sequencing.

Methods

A total of 181 patients diagnosed with polydactylies were recruited. We designed a targeted capture panel for sequencing 721 genes that are associated with the pathogenesis of skeletal dysplasia. We performed rigorous variant- and gene-level filtrations to identify potentially damaging variants, followed by enrichment analysis and gene prioritization.

Results

A total of 568 deleterious variants of 293 genes were identified in 173 of 181 patients with a positive rate of 95.6% by targeted sequencing. For each sample, an average of 3.17 deleterious variants were identified. Especially, 14 pathogenic or likely pathogenic variants were identified in 10 genes in 14 patients out of the 181 patients, providing a positive molecular diagnostic rate of 7.7%.

Conclusion

Targeted sequencing analysis provides a high efficiency approach for the genetic diagnosis of polydactyly. This is the largest next generation sequencing study performed to date in patients with polydactyly and represents the genetic basis of polydactyly typically encountered in genetics clinics.

An intrafamilial phenotypic variability in Ellis-Van Creveld syndrome due to a novel 27 bps deletion mutation

Ellis-van Creveld (EvC) syndrome is an autosomal recessive disease, characterized by ectodermal, skeletal, and cardiac anomalies. We report intrafamilial phenotypic variability in three new EvC syndrome cases. Affected males in this study showed only ectodermal abnormalities, whereas an affected female showed the classical presentation of EvC Syndrome, including bilateral postaxial polydactyly of hands and feet, and congenital heart defects. Whole exome sequencing was performed to identify the causative variant, followed by validation and segregation analysis using Sanger sequencing. A homozygous deletion variant (c.731_757del) was identified in exon 6 of the EVC gene (NM_153717.2). The identified variant is considered to be the most likely candidate variant for the EvC syndrome in the family based on previous reports validating the role of EVC variants in the EvC syndrome. The disease correctly segregated in the family members, as all affected members were homozygous, and obligate carriers were heterozygous. Our family is remarkable in highlighting the variable expressivity of the EvC phenotype within the same family, due to a homozygous deletion mutation in the EVC gene. The variable expressivity might be due to the hypomorphic nature of mutation, or the presence of additional variants in modifier genes or in the regulatory regions of the EVC/EVC2 genes.

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.

Signaling Pathways in Bone Development and Their Related Skeletal Dysplasia

Bone development is a tightly regulated process. Several integrated signaling pathways including HH, PTHrP, WNT, NOTCH, TGF-β, BMP, FGF and the transcription factors SOX9, RUNX2 and OSX are essential for proper skeletal development. Misregulation of these signaling pathways can cause a large spectrum of congenital conditions categorized as skeletal dysplasia. Since the signaling pathways involved in skeletal dysplasia interact at multiple levels and have a different role depending on the time of action (early or late in chondrogenesis and osteoblastogenesis), it is still difficult to precisely explain the physiopathological mechanisms of skeletal disorders. However, in recent years, significant progress has been made in elucidating the mechanisms of these signaling pathways and genotype-phenotype correlations have helped to elucidate their role in skeletogenesis. Here, we review the principal signaling pathways involved in bone development and their associated skeletal dysplasia.

Wolf-Hirschhorn syndrome: Prenatal diagnosis and molecular cytogenetic characterization of a de novo distal deletion of 4p (4p16.1 → pter) in a fetus with facial cleft and preaxial polydactyly

OBJECTIVE

We present prenatal diagnosis and molecular cytogenetic characterization of Wolf-Hirschhorn syndrome (WHS) in a fetus with facial cleft and preaxial polydactyly.

MATERIALS AND METHODS

A 37-year-old woman underwent amniocentesis at 18 weeks of gestation because of advanced maternal age, and the result showed an aberrant chromosome 4 or 46,XX,add(4) (p15.3). The woman consulted our clinics at 22 weeks of gestation and requested for repeat amniocentesis. Prenatal ultrasound revealed intrauterine growth restriction, facial cleft, vermian hypoplasia of cerebellum, micrognathia and absent stomach. Conventional cytogenetic analysis was performed on cultured amniocytes, parental bloods and cord blood. Array comparative genomic hybridization (aCGH) and quantitative fluorescent polymerase chain reaction (QF-PCR) were performed on the DNAs extracted from uncultured amniocytes and parental bloods. Fluorescence in situ hybridization (FISH) analysis was performed on cultured metaphase amniocytes.

RESULTS

aCGH analysis on uncultured amniocytes revealed arr 4p16.3p16.1 (74,447-8,732,731) × 1.0 [GRCh37 (hg19)] with an 8.66-Mb deletion of 4p16.3-p16.1 encompassing 70 [Online Mendelian Inheritance of in Man (OMIM)] genes including ZNF141, FGFRL1, TACC3, LETM1, NSD2 and NELFA. QF-PCR revealed a paternal origin of the distal 4p deletion. Conventional cytogenetic analysis revealed 46,XX,del(4) (p16.1)dn in the fetus. Metaphase FISH analysis confirmed a 4p16 deletion. The parental karyotypes were normal. The pregnancy was subsequently terminated, and a malformed fetus was delivered with typical WHS facial dysmorphism, bilateral cleft lip and palate, and preaxial polydactyly on the right hand.

CONCLUSION

aCGH, QF-PCR and FISH help to delineate the nature of a prenatally defected aberrant chromosome, and the acquired information is useful for genetic counseling.