Busulfan‐induced central polydactyly, syndactyly and cleft hand or foot: A common mechanism of disruption leads to divergent phenotypes

Polydactyly and syndactyly linked to GLI3 and TBX5 mutations: A pediatric case report

Background

Polydactyly and syndactyly, which are commonly encountered congenital limb deformities, rarely occur together and are linked with significant genetic mutations. This report sheds light on a unique co-presentation involving mutations in both the GLI3 and TBX5 genes, offering a deeper understanding of the genetic interactions that may influence limb development. This case report is important to increase our knowledge on genetic bases of limb malformations.

Case presentation

We report the case of an 8-month-old boy, born to non-consanguineous parents, presenting with both polydactyly and syndactyly in his limbs, in particular, complete syndactyly between the third to fifth fingers and post-axial polydactyly of the feet. His father showed a similar phenotype. Genetic testing identified a pathogenic heterozygous variant in the GLI3 gene (c .3762 T > A, p.(Tyr1254 *)) and a variant of uncertain significance in the TBX5 gene (c .1063 C>T, p.(Arg355Cys)).

Conclusions

This case highlights the complex nature of diagnosing and managing congenital limb deformities driven by genetic factors. It underscores the critical importance of comprehensive genetic testing in determining the etiology of limb malformations. The GLI3 variant, classified according to ACMG guidelines as a class IV mutation, likely results in a truncated protein due to a premature stop codon, confirmed by family segregation analysis indicating its paternal origin, suggesting autosomal dominant inheritance. Notably, the TBX5 gene variant, often associated with Holt-Oram syndrome-which is characterized by only hand skeletal anomalies and early-onset atrial fibrillation-suggests a risk of developing cardiac issues that are not currently present but may emerge as the child grows. This potential for evolving clinical manifestations necessitates vigilant long-term monitoring and may influence future medical management and therapeutic approaches.

The Oberg-Manske-Tonkin (OMT) Classification of Congenital Upper Extremities: Update for 2020

A new classification for congenital upper-extremity anomalies was first published in 2010. It has come to be known as the OMT classification highlighting the thought leaders behind it: Kerby Oberg, Paul Manske, and Michael Tonkin. Based on a dysmorphology framework, the OMT has been adopted by the International Federation of Society for Surgery of the Hand and surgeons who treat congenital upper-extremity anomalies. As predicted in the first publication, updates will be necessary based on an improved understanding of morphogenesis; the first update was in 2014 and this represents the second update to the original OMT classification. We carefully reviewed all aspects of the OMT classification, its current stratification, and updated literature on the developmental basis of limb anomalies. We also considered the clinical usefulness and challenges of the classification through discussions with stakeholders and those who care for patients with congenital upper-limb anomalies. These factors guided the current modifications of the OMT classification. In providing the updated classification, we provide the rationale for these changes. The updated OMT classification is by no means final. As our understanding of congenital anomalies progresses, we anticipate subsequent updates in the years to come.

A Case of Nonsyndromic Unilateral Cleft Hand with Central Polydactyly, Syndactyly, and Thumb Hypoplasia: Support for a Common Etiology

Experimental studies showed that central polydactyly, syndactyly, and cleft hand might appear when the same teratogenic factor acts on embryos at the same developmental stage. These observations and some clinical cases support the concept that a common etiologic mechanism is involved in the development of these malformations. We report a clinical case that demonstrates the association previously observed in experimental studies. Here, a patient with unilateral nonsyndromic cleft hand, central polydactyly, first web syndactyly, osseous syndactyly between the ring and long fingers, and minor thumb hypoplasia was presented.

Maternal exposure to busulfan reduces the cell number in the somatosensory cortex associated with delayed somatic and reflex maturation in neonatal rats

Busulfan is a bifunctional alkylating agent used for myeloablative conditioning and in the treatment of chronic myeloid leukemia due to its ability to cause DNA damage. However, in rodent experiments, busulfan presented a potential teratogenic and cytotoxic effect. Studies have evaluated the effects of busulfan on fetuses after administration in pregnancy or directly on pups during the lactation period. There are no studies on the effects of busulfan administration during pregnancy on offspring development after birth. We investigated the effects of busulfan on somatic and reflex development and encephalic morphology in young rats after exposure in pregnancy. The pregnant rats were exposed to busulfan (10 mg/kg, intraperitoneal) during the early developmental stage (days 12-14 of the gestational period). After birth, we evaluated the somatic growth, maturation of physical features and reflex-ontogeny during the lactation period. We also assessed the effects of busulfan on encephalic weight and cortical morphometry at 28 days of postnatal life. As a result, busulfan-induced pathological changes included: microcephaly, evaluated by the reduction of cranial axes, delay in reflex maturation and physical features, as well as a decrease in the morphometric parameters of somatosensory and motor cortex. Thus, these results suggest that the administration of a DNA alkylating agent, such as busulfan, during the gestational period can cause damage to the central nervous system in the pups throughout their postnatal development.

Distal Dorsal Dimelia: A Disturbance of Dorsal-Ventral Digit Development

PURPOSE

Congenital palmar nail (distal dorsal dimelia [dDD]) of the hand is a rare malformation most commonly affecting the little finger. The purpose of this report was to review the features and associations of this rare disorder and discuss the suspected underlying etiology in light of our current understanding of developmental biology.

METHODS

In this retrospective cohort study from 3 practices, we describe our collective experience and review the reported literature on this disorder both as an isolated condition and in conjunction with other anomalies.

RESULTS

We examined 15 fingers with dDD, 5 of which involved little fingers. We also found dDD in 6 cases with radial polydactyly (preaxial polydactyl type II [PPD2]) and in 1 case of cleft hand involving digits adjacent to the clefted web space (the index and middle fingers). Cases of little finger dDD were also associated with prominent clefting of the adjacent web space in 4 of 5 cases. All cases had stiffness of the interphalangeal joints and loss of palmar creases consistent with dorsalization of the palmar aspect of the digit. When combined with 63 fingers reported in the literature with dDD, 3 patterns were evident. The most common form occurred in little fingers (n = 50; 64%; dDDu). The next most common form was reported in association with cleft hands (n = 16; 21%; dDDc). Radial digits in association with either radial polydactyly (PPD2) or radial longitudinal deficiency were also susceptible to dDD (n = 12; 15%; dDDr).

CONCLUSIONS

Congenital dDD is a disturbance of terminal dorsal-ventral digit patterning. The distribution of this condition with little fingers, clefting, and altered radial digit formation (PPD2 or radial longitudinal deficiency), as well as recent genetic and animal studies, suggests that dDD and altered dorsal-ventral patterning are linked to abnormal apical ectodermal ridge boundary formation.

TYPE OF STUDY/LEVEL OF EVIDENCE

Diagnostic IV.

Classification of congenital upper limb anomalies: towards improved communication, diagnosis, and discovery

Recently the International Federation of Societies for Surgery of the Hand replaced the Swanson scheme for classifying congenital upper limb anomalies with the Oberg, Manske, Tonkin (OMT) classification. This review explores the reasons for this change after nearly 50 years of using the Swanson classification. In particular, it documents the state of our understanding regarding genetics and limb development at the time Swanson generated his classification. It also describes the continued progress in clinical genetics and developmental biology. Such progress drives the need to embrace and incorporate these changes within a new classification scheme; one that will improve communication, diagnosis, and support further discovery of the pathogenesis of congenital hand anomalies.

Progress on the study of the mechanism of busulfan cytotoxicity

The preparation of spermatogonial stem cell (SSC) transplant recipients laid the technical foundation for SSC transplant technology and the understanding of spermatogenesis mechanisms. Busulfan is commonly used to prepare recipients for mouse SSC transplantation; however, its safety and efficiency have been questioned. This review summarizes the relationship between SSCs and Sertoli cells (SCs), and the mechanism of busulfan toxicity against sperm cells. We concluded that the proliferation, differentiation, and apoptosis of SSCs are regulated by SCs. The endogenous spermatogenic cells are depleted by busulfan treatment via alkylation of DNA, destruction of vimentin filament distribution, disruption of SSC differentiation, promotion of SSC dormancy, and generation of oxidative stress. However, the mechanisms require further exploration. The recent establishment of a model in vitro culture system has provided a good technical foundation to further explore these mechanisms, which will help us to find more efficient methods of recipient preparation and optimal transplantation times.

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.

Hand/foot splitting and the 're-evolution' of mesopodial skeletal elements during the evolution and radiation of chameleons

Background

One of the most distinctive traits found within Chamaeleonidae is their split/cleft autopodia and the simplified and divergent morphology of the mesopodial skeleton. These anatomical characteristics have facilitated the adaptive radiation of chameleons to arboreal niches. To better understand the homology of chameleon carpal and tarsal elements, the process of syndactyly, cleft formation, and how modification of the mesopodial skeleton has played a role in the evolution and diversification of chameleons, we have studied the Veiled Chameleon (Chamaeleo calyptratus). We analysed limb patterning and morphogenesis through in situ hybridization, in vitro whole embryo culture and pharmacological perturbation, scoring for apoptosis, clefting, and skeletogenesis. Furthermore, we framed our data within a phylogenetic context by performing comparative skeletal analyses in 8 of the 12 currently recognized genera of extant chameleons.

Results

Our study uncovered a previously underappreciated degree of mesopodial skeletal diversity in chameleons. Phylogenetically derived chameleons exhibit a ‘typical’ outgroup complement of mesopodial elements (with the exception of centralia), with twice the number of currently recognized carpal and tarsal elements considered for this clade. In contrast to avians and rodents, mesenchymal clefting in chameleons commences in spite of the maintenance of a robust apical ectodermal ridge (AER). Furthermore, Bmp signaling appears to be important for cleft initiation but not for maintenance of apoptosis. Interdigital cell death therefore may be an ancestral characteristic of the autopodium, however syndactyly is an evolutionary novelty. In addition, we find that the pisiform segments from the ulnare and that chameleons lack an astragalus-calcaneum complex typical of amniotes and have evolved an ankle architecture convergent with amphibians in phylogenetically higher chameleons.

Conclusion

Our data underscores the importance of comparative and phylogenetic approaches when studying development. Body size may have played a role in the characteristic mesopodial skeletal architecture of chameleons by constraining deployment of the skeletogenic program in the smaller and earliest diverged and basal taxa. Our study challenges the ‘re-evolution’ of osteological features by showing that ‘re-evolving’ a ‘lost’ feature de novo (contrary to Dollo’s Law) may instead be due to so called ‘missing structures’ being present but underdeveloped and/or fused to other adjacent elements (cryptic features) whose independence may be re-established under changes in adaptive selective pressure.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-015-0464-4) contains supplementary material, which is available to authorized users.

Central and ulnar cleft hands: a review of concurrent deformities in a series of 47 patients and their pathogenesis

Two main types of cleft hands have been described. The ulnar cleft hand deformity is very rare and is characterized by two constant features: a deep cleft radial to the little finger and hypoplasia of the ulnar digits. The pathogenesis of ulnar clefts is unknown. The second type is the central cleft hand deformity, which is characterized by a soft tissue/bone defect in the hand centrally. Patients with central clefts also have several concurrent deformities in the remaining digits. This paper reviews the clinical features of three cases with ulnar cleft hands and 44 cases of central cleft hands, with special emphasis on concurrent deformities. The author's hypothesis of pathogenesis for both types of clefts and their concurrent deformities is then offered.

Gene dosage of the transcription factor Fingerin (bHLHA9) affects digit development and links syndactyly to ectrodactyly

Distal limb deformities are congenital malformations with phenotypic variability, genetic heterogeneity and complex inheritance. Among these, split-hand/foot malformation is an ectrodactyly with missing central fingers, yielding a lobster claw-like hand, which when combined with long-bone deficiency is defined as split-hand/foot malformation and long-bone deficiency (SHFLD) that is genetically heterogeneous. Copy number variation (CNV) consisting of 17p13.3 duplication was identified in unrelated pedigrees, underlying SHFLD3 (OMIM 612576). Although the transcription factor Fingerin (bHLHA9) is the only complete gene in the critical region, its biological role is not yet known and there are no data supporting its involvement in mammalian limb development. We have generated knockout mice in which only the entire coding region of Fingerin was deleted, and indeed found that most null mice display some limb defects. These include various levels of simple asymmetrical syndactyly, characterized by webbed fingers, generated by incomplete separation of soft, but not skeletal, tissues between forelimb digits 2 and 3. As expected, hand pads of Fingerin null embryos exhibited reduced apoptosis between digital rays 2 and 3. This defect was shown to cause syndactyly when the same limbs were grown ex vivo following the apoptosis assay. Extrapolating from mouse data, we suggest that Fingerin loss-of-function in humans may underlie MSSD syndactyly (OMIM 609432), which was mapped to the same locus. Taken together, Fingerin gene dosage links two different congenital limb malformations, syndactyly and ectrodactyly, which were previously postulated to share a common etiology. These results add limb disorders to the growing list of diseases resulting from CNV.

Busulfan-induced pathological changes of the cerebellar development in infant rats

Busulfan, an antineoplastic bifunctional-alkylating agent, is known to induce developmental anomalies and fetal neurotoxicity. We previously reported that busulfan induced p53-dependent neural progenitor cell apoptosis in fetal rat brain (Ohira et al., 2012). The present study was carried out to clarify the characteristics and sequence of busulfan-induced pathological changes in infant rat brain. Six-day-old male infant rats were treated with 10, 20, 30 or 50 mg/kg of busulfan, and their brains were examined at 1, 2, 4, 7, and 14 days after treatment (DAT). As a result, histopathological changes were selectively detected in the external granular layer (EGL), deep cerebellar nuclei (DCN) and cerebellar white matter (CWM) in the cerebellum with dose-dependent severity but not in the cerebrum. In the normal infant rat cerebellum, granular cells in the EGL were proliferating and moving to the internal granular layer during the normal developmental process. In the EGL of the busulfan group, apoptotic granular cells increased at 2 DAT simultaneously with increased numbers of p53- and p21-positive cells while mitotic granular cells decreased, suggesting an occurrence of p53-related apoptosis and depression of proliferative activity in granular cells. In the DCN, apoptotic glial cells increased at 2 DAT and glial cells showing abnormal mitosis increased at 4 DAT. In the CWN, edematous change accompanying a few apoptotic cells was found in the CWN, especially in the parafolliculus (PFL), from 2 to 7 DAT. The present study demonstrated for the first time the characteristics and sequence of busulfan-induced pathological changes in infant rat cerebellum.

Normal genetic variation of the human foot: Part 2: Population variance, epigenetic mechanisms, and developmental constraint in function

Congenital deformities of the foot have been reported to correlate with regulatory epigenetic mechanisms that are also responsible for the timing and sequencing of developmental growth of the lower limb. Developmental variance of normal morphologic features has also been shown to vary between populations despite the retention of human foot characteristics. The molecular evidence for genetically controlled expressions of common evolved physical features is highly suggestive of regulatory control mechanisms that act together with developmental constraints to homogenize the retained functional characteristics of the foot. Genetic variance in morphologic features and functional plasticity when linked to morphometric change during gait may prove influential in clarifying kinematic and kinetic relationships.

Sequence of busulfan-induced neural progenitor cell damage in the fetal rat brain

The sequence of neural progenitor cell (NPC) damage induced in fetal rat brain by transplacental exposure to busulfan, an antineoplastic bifunctional-alkylating agent, on gestational day 13 was examined by immunohistochemical and real-time RT-PCR analyses. Following busulfan treatment, pyknotic NPCs first appeared in the medial layer and then extended to the dorsal layer of the ventricular zone (VZ) of the telencephalon. Pyknotic NPCs that were immunohistochemically positive for cleaved caspase-3, i.e. apoptotic NPCs, began to increase at 24 h after treatment, peaked at 48 h, and returned to the control levels at 96 h. On the other hand, the index (%) of phospho-histone H3-positive NPCs, i.e. mitotic NPCs, and that of BrdU-positive NPCs, i.e. S-phase cells, decreased in accordance with the increase in the index of apoptotic NPCs. Prior to the peak time of apoptotic NPCs, the indices of p53- and p21-positive NPCs peaked at 36 h. In addition, the expression levels of p21 and Puma (p53-target genes) mRNAs were elevated in real-time RT-PCR analysis. These findings indicated that busulfan not only induced apoptosis through the p53-mediated intrinsic pathway but also inhibited cell proliferation in NPCs, resulting in a reduction of the width of the telencephalon. On the other hand, in spite of up-regulation of p21 expression, the expression of cyclin D1, part of the cell cycle machinery of the G1/S transition, and the expression levels of Cdc20 and cyclin B1 which are involved in G2/M transition, showed no changes, giving no possible information of busulfan-induced cell cycle arrest in NPCs.

Developmental biology and classification of congenital anomalies of the hand and upper extremity

Recent investigations into the mechanism of limb development have clarified the roles of several molecules, their pathways, and interactions. Characterization of the molecular pathways that orchestrate limb development has provided insight into the etiology of many limb malformations. In this review, we describe how the insights from developmental biology are related to clinically relevant anomalies and the current classification schemes used to define, categorize, and communicate patterns of upper limb malformations. We advocate an updated classification scheme for upper limb anomalies that incorporates our current molecular perspective of limb development and the pathogenetic basis for malformations using dysmorphology terminology. We anticipate that this scheme will improve the utility of a classification as a basis for diagnosis, treatment, and research.

Occurrence of central polydactyly, syndactyly, and cleft hand in a single family: report of five hands in three cases

Central polydactyly, syndactyly, and cleft hand are categorized separately in the International Federation of Societies for Surgery of the Hand classification. However, some investigators have proposed that these malformations should be classified into a single category: abnormal induction of finger rays. In this article, we report 5 hands with central polydactyly, syndactyly, and cleft hand in 3 patients from the same family and discuss the phenotypes in each hand.

Combined congenital radial and ulnar longitudinal deficiencies: report of 2 cases

Variation in longitudinal deficiencies is likely related to the timing and duration of an insult during early limb development. In experimental models, teratogenic insults induce ulnar deficiencies earlier in gestation than radial deficiencies. In this report, we describe the rare combination of right radial and left ulnar deficiencies in 2 cases. Interestingly, 1 case had a history of 2 separate and apparently distinct episodes of bleeding during early gestation, whereas the other demonstrated associated hematoma formation early in development. These cases also demonstrate the susceptibility for ulnar defects on the left and radial defects on the right. The authors discuss the relationship of prenatal insults on limb development and the mechanisms underlying longitudinal deficiencies.