Limb anomalies: Developmental and evolutionary aspects

Monodactyly in a patient with CHARGE syndrome: An additional case report

CHARGE syndrome is a rare autosomal dominant syndrome characterized by multiple congenital anomalies including coloboma, heart defects, ear anomalies, and developmental delay, caused by pathogenic variants in the CHD7 gene. The discovery of the molecular basis of this syndrome increased the number of cases reported and expanded the phenotype and clinical variability. Limb anomalies are occasional clinical findings in this syndrome, present in about 30% of reported cases. The occurrence of limb anomalies in this syndrome suggests that it should be considered as part of the phenotypic spectrum. Here, we describe an individual with CHARGE syndrome presenting unilateral monodactyly.

Identification of Transcription Factor Networks during Mouse Hindlimb Development

Mammalian hindlimb development involves a variety of cells and the regulation of spatiotemporal molecular events, but regulatory networks of transcription factors contributing to hindlimb morphogenesis are not well understood. Here, we identified transcription factor networks during mouse hindlimb morphology establishment through transcriptome analysis. We used four stages of embryonic hindlimb transcription profiles acquired from the Gene Expression Omnibus database (GSE30138), including E10.5, E11.5, E12.5 and E13.5, to construct a gene network using Weighted Gene Co-expression Network Analysis (WGCNA), and defined seven stage-associated modules. After filtering 7625 hub genes, we further prioritized 555 transcription factors with AnimalTFDB3.0. Gene ontology enrichment showed that transcription factors of different modules were enriched in muscle tissue development, connective tissue development, embryonic organ development, skeletal system morphogenesis, pattern specification process and urogenital system development separately. Six regulatory networks were constructed with key transcription factors, which contribute to the development of different tissues. Knockdown of four transcription factors from regulatory networks, including Sox9, Twist1, Snai2 and Klf4, showed that the expression of limb-development-related genes was also inhibited, which indicated the crucial role of transcription factor networks in hindlimb development.

Novel copy number variants and major limb reduction malformation: Report of three cases

Limb reduction malformations are highly heterogeneous in their clinical presentation and so, predicting the underlying mutation on a clinical basis can be challenging. Molecular karyotyping is a powerful genomic tool that has quickly become the mainstay for the study of children with malformation syndromes. We describe three patients with major limb reduction anomalies in whom pathogenic copy number variants were identified on molecular karyotyping. These include a patient with hypoplastic phalanges and absent hallux bilaterally with de novo deletion of 11.9 Mb on 7p21.1-22.1 spanning 63 genes including RAC1, another patient with severe Holt-Oram syndrome and a large de novo deletion 2.2 Mb on 12q24.13-24.21 spanning 20 genes including TBX3 and TBX5, and a third patient with acheiropodia who had a nullizygous deletion of 102 kb on 7q36.3 spanning LMBR1. We discuss the potential of these novel genomic rearrangements to improve our understanding of limb development in humans.

Split-hand/foot malformation - molecular cause and implications in genetic counseling

Split-hand/foot malformation (SHFM) is a congenital limb defect affecting predominantly the central rays of the autopod and occurs either as an isolated trait or part of a multiple congenital anomaly syndrome. SHFM is usually sporadic, familial forms are uncommon. The condition is clinically and genetically heterogeneous and shows mostly autosomal dominant inheritance with variable expressivity and reduced penetrance. To date, seven chromosomal loci associated with isolated SHFM have been described, i.e., SHFM1 to 6 and SHFM/SHFLD. The autosomal dominant mode of inheritance is typical for SHFM1, SHFM3, SHFM4, SHFM5. Autosomal recessive and X-linked inheritance is very uncommon and have been noted only in a few families. Most of the known SHFM loci are associated with chromosomal rearrangements that involve small deletions or duplications of the human genome. In addition, three genes, i.e., TP63, WNT10B, and DLX5 are known to carry point mutations in patients affected by SHFM. In this review, we focus on the known molecular basis of isolated SHFM. We provide clinical and molecular information about each type of abnormality as well as discuss the underlying pathways and mechanism that contribute to their development. Recent progress in the understanding of SHFM pathogenesis currently allows for the identification of causative genetic changes in about 50 % of the patients affected by this condition. Therefore, we propose a diagnostic flow-chart helpful in the planning of molecular genetic tests aimed at identifying disease causing mutation. Finally, we address the issue of genetic counseling, which can be extremely difficult and challenging especially in sporadic SHFM cases.

Clinical, genetic, and molecular aspects of split-hand/foot malformation: an update

We here provide an update on the clinical, genetic, and molecular aspects of split-hand/foot malformation (SHFM). This rare condition, affecting 1 in 8,500-25,000 newborns, is extremely complex because of its variability in clinical presentation, irregularities in its inheritance pattern, and the heterogeneity of molecular genetic alterations that can be found in affected individuals. Both syndromal and nonsyndromal forms are reviewed and the major molecular genetic alterations thus far reported in association with SHFM are discussed. This updated overview should be helpful for clinicians in their efforts to make an appropriate clinical and genetic diagnosis, provide an accurate recurrence risk assessment, and formulate a management plan.

Small nerve fibres, small hands and small feet: a new syndrome of pain, dysautonomia and acromesomelia in a kindred with a novel NaV1.7 mutation

The Na(V)1.7 sodium channel is preferentially expressed within dorsal root ganglion and sympathetic ganglion neurons and their small-diameter peripheral axons. Gain-of-function variants of Na(V)1.7 have recently been described in patients with painful small fibre neuropathy and no other apparent cause. Here, we describe a novel syndrome of pain, dysautonomia, small hands and small feet in a kindred carrying a novel Na(V)1.7 mutation. A 35-year-old male presented with erythema and burning pain in the hands since early childhood, later disseminating to the feet, cheeks and ears. He also experienced progressive muscle cramps, profound sweating, bowel disturbances (diarrhoea or constipation), episodic dry eyes and mouth, hot flashes, and erectile dysfunction. Neurological examination was normal. Physical examination was remarkable in revealing small hands and feet (acromesomelia). Blood examination and nerve conduction studies were unremarkable. Intra-epidermal nerve fibre density was significantly reduced compared to age- and sex-matched normative values. The patient's brother and father reported similar complaints including distal extremity redness and pain, and demonstrated comparable distal limb under-development. Quantitative sensory testing revealed impaired warmth sensation in the proband, father and brother. Genetic analysis revealed a novel missense mutation in the SCN9A gene encoding sodium channel Na(V)1.7 (G856D; c.2567G > A) in all three affected subjects, but not in unaffected family members. Functional analysis demonstrated that the mutation hyperpolarizes (-9.3 mV) channel activation, depolarizes (+6.2 mV) steady-state fast-inactivation, slows deactivation and enhances persistent current and the response to slow ramp stimuli by 10- to 11-fold compared with wild-type Na(V)1.7 channels. Current-clamp analysis of dorsal root ganglion neurons transfected with G856D mutant channels demonstrated depolarized resting potential, reduced current threshold, increased repetitive firing in response to suprathreshold stimulation and increased spontaneous firing. Our results demonstrate that the G856D mutation produces DRG neuron hyperexcitability which underlies pain in this kindred, and suggest that small peripheral nerve fibre dysfunction due to this mutation may have contributed to distal limb under-development in this novel syndrome.

Limb anomalies in patients with CHARGE syndrome: an expansion of the phenotype

CHARGE syndrome is characterized by a wide clinical variability. During the past years the phenotypic spectrum was markedly expanded. Limb anomalies were initially not recognized as part of the phenotype but more recently mild limb anomalies were described in approximately 30% of the patients. We report on three patients with several major features of CHARGE syndrome who, in addition, presented severe limb anomalies including monodactyly, tibia aplasia, and bifid femora. Three different heterozygous truncating mutations in the CHD7 gene were detected. It has been hypothesized before that the CHARGE syndrome is caused by a disruption of mesenchymal-epithelial interaction. Given the expression of the CHD7 gene in the developing limb bud, it was anticipated that limb defects would belong to the spectrum of manifestations of CHARGE syndrome. The present observations provide further support to this hypothesis.

Société Française d’Orthopédie Pédiatrique

Limb malformations are frequent. These malformations are isolated or associated with anomalies of other developmental fields and accurate diagnostic is essential for prognosis evaluation, treatment and genetic counseling. Animal embryology and molecular biology techniques, have given us a better understanding of the processes of growth and patterning of the limb buds. The key genes that are involved in these processes have been identified and their interactions recognized. Human genetics has been able to identify, or at least localize, several genes implicated in limb development. We here review the present knowledge on these genes and their mutations responsible for limb anomalies.

Oligosyndactylism mice have an inversion of chromosome 8

The radiation-induced mutation Oligosyndactylism (Os) is associated with limb and kidney defects in heterozygotes and with mitotic arrest and embryonic lethality in homozygotes. We reported that the cell cycle block in Os and in the 94-A/K transgene-induced mutations is due to disruption of the Anapc10 (Apc10/Doc1) gene. To understand the genetic basis of the limb and kidney abnormalities in Os mice we characterized the structural changes of chromosome 8 associated with this mutation. We demonstrate that the Os chromosome 8 has suffered two breaks that are 5 cM ( approximately 10 Mb) apart and the internal fragment delineated by the breaks is in an inverted orientation on the mutant chromosome. While sequences in proximity to the distal break are present in an abnormal Os-specific Anapc10 hybrid transcript, transcription of these sequences in normal mice is low and difficult to detect. Transfer of the Os mutation onto an FVB/N background indicated that the absence of dominant effects in 94-A/K mice is not due to strain background effects on the mutation. Further analysis of this mutation will determine if a gene interrupted by the break or a long-range effect of the rearrangement on neighboring genes is responsible for the dominant effects of Os.

A morpho-etiological description of congenital limb anomalies

BACKGROUND

Limb anomalies rank behind congenital heart disease as the most common birth defects observed in infants. More than 50 classifications for limb anomalies based on morphology and osseous anatomy have been drafted over the past 150 years. The present work aims to provide a concise summary of the most common congenital limb anomalies on a morpho-etiological basis.

PATIENTS AND METHODS

In a retrospective study, 70 newborns with anomalies of the upper and/or lower limbs were ascertained through clinical examination, chromosomal analysis, skeletal surveys and other relevant investigations.

RESULTS

Fetal causes of limb anomalies represented 55.8% of the cases in the form of 9 cases (12.9%) with chromosomal aberrations (trisomy 13, 18 and 21, duplication 13q and deletion 22q) and 30 cases (42.9%) with single gene disorders. An environmental etiology for limb anomalies was diagnosed in 11 cases (15.7%) as amniotic band disruption, monozygotic twin with abnormal circulation, vascular disruption (Poland sequence, sirenomelia and general vascular disruption) and an infant with a diabetic mother. Twenty cases (28.5%) had limb anomalies as part of sporadic syndromes of unknown etiology.

CONCLUSIONS

The morpho-etiological work-up of limb anomalies adopted in the present study is valuable for detecting the cause of the anomaly and is crucial for its prevention. Prevention can be achieved by proper genetic counseling, which includes recurrence risk estimation and prenatal diagnosis.

Speculations on the pathogenesis of CHARGE syndrome

To be seriously considered, a theory about the pathogenesis of a multiple congenital anomaly syndrome should meet three criteria: (1) it should explain all of the anomalies associated with the syndrome; (2) it should explain why certain anomalies are not associated with the syndrome; and (3) it should predict anomalies that could be associated with the syndrome, but have not yet been described. The theory must eventually pass the ultimate test, that is, molecular confirmation of the proposed mechanism. Several theories about the pathogenesis of CHARGE syndrome have been proposed, but none of these meet the three criteria stated above. In this study, the author proposes that CHARGE syndrome is due to a disruption of mesenchymal-epithelial interaction (epithelial includes ectoderm and endoderm). The theory is tested against the major, minor, and occasional anomalies that are used to make the clinical diagnosis of CHARGE syndrome. Review of the known embryology of the organs and tissues involved in CHARGE syndrome confirms that mesenchymal-epithelial interactions are necessary for proper formation of these organs and tissues. The presence of limb anomalies in approximately one-third of CHARGE syndrome patients fulfills criteria #3 above, in that limb anomalies were not felt to be a part of CHARGE syndrome until relatively recently. It is known that some patients with chromosomal abnormalities have a phenotype that overlaps with CHARGE syndrome. Given that critical developmental pathways must be robust and redundant in order to minimize errors, it may be that disruption of more than one gene is necessary to generate the CHARGE phenotype, as has been proposed for the holoprosencephaly sequence. Mutations and deletions of CHD7 have recently been identified as causing CHARGE syndrome in more than 50% of tested patients. Given this gene classes' putative role as a general controller of developmental gene expression as well as mesodermal patterning, it would fit the hypothesized mechanisms discussed in the study.

Transcriptome analysis of the murine forelimb and hindlimb autopod

To gain insight into the coordination of gene expression profiles during forelimb and hindlimb differentiation, a transcriptome analysis of mouse embryonic autopod tissues was performed using Affymetrix Murine Gene Chips (MOE-430). Forty-four transcripts with expression differences higher than 2-fold (T test, P < or = 0.05) were detected between forelimb and hindlimb tissues including 38 new transcripts such as Rdh10, Frzb, Tbx18, and Hip that exhibit differential limb expression. A comparison of gene expression profiles in the forelimb, hindlimb, and brain revealed 24 limb-signature genes whose expression was significantly enriched in limb autopod versus brain tissue (fold change >2, P < or = 0.05). Interestingly, the genes exhibiting enrichment in the developing autopod also segregated into significant fore- and hindlimb-specific clusters (P < or = 0.05) suggesting that by E 12.5, unique gene combinations are being used during the differentiation of each autopod type.

HOXA13 regulates the expression of bone morphogenetic proteins 2 and 7 to control distal limb morphogenesis

In humans and mice, loss of HOXA13 function causes defects in the growth and patterning of the digits and interdigital tissues. Analysis of Hoxa13 expression reveals a pattern of localization overlapping with sites of reduced Bmp2 and Bmp7 expression in Hoxa13mutant limbs. Biochemical analyses identified a novel series of Bmp2and Bmp7 enhancer regions that directly interact with the HOXA13 DNA-binding domain and activate gene expression in the presence of HOXA13. Immunoprecipitation of HOXA13-Bmp2 and HOXA13-Bmp7 enhancer complexes from the developing autopod confirm that endogenous HOXA13 associates with these regions. Exogenous application of BMP2 or BMP7 partially rescues the Hoxa13 mutant limb phenotype, suggesting that decreased BMP signaling contributes to the malformations present in these tissues. Together, these results provide conclusive evidence that HOXA13 regulates Bmp2 and Bmp7 expression, providing a mechanistic link between HOXA13, its target genes and the specific developmental processes affected by loss of HOXA13 function.

Mouse limb deformity mutations disrupt a global control region within the large regulatory landscape required for Gremlin expression

The mouse limb deformity (ld) mutations cause limb malformations by disrupting epithelial-mesenchymal signaling between the polarizing region and the apical ectodermal ridge. Formin was proposed as the relevant gene because three of the five ld alleles disrupt its C-terminal domain. In contrast, our studies establish that the two other ld alleles directly disrupt the neighboring Gremlin gene, corroborating the requirement of this BMP antagonist for limb morphogenesis. Further doubts concerning an involvement of Formin in the ld limb phenotype are cast, as a targeted mutation removing the C-terminal Formin domain by frame shift does not affect embryogenesis. In contrast, the deletion of the corresponding genomic region reproduces the ld limb phenotype and is allelic to mutations in Gremlin. We resolve these conflicting results by identifying a cis-regulatory region within the deletion that is required for Gremlin activation in the limb bud mesenchyme. This distant cis-regulatory region within Formin is also altered by three of the ld mutations. Therefore, the ld limb bud patterning defects are not caused by disruption of Formin, but by alteration of a global control region (GCR) required for Gremlin transcription. Our studies reveal the large genomic landscape harboring this GCR, which is required for tissue-specific coexpression of two structurally and functionally unrelated genes.

Probable second fetus with Marles-Chudley syndrome: cardiac calcifications with ulnar deficiency and absent/hypoplastic thumbs

In 1990 Marles and Chudley reported on an infant with absent ulnae and concomitant radial hypoplasia, oligodactyly, hydropsfetalis, and apparent endocardial fibroelastosis (EFE) and, on the basis of phenotype and parental consanguinity, postulated autosomal recessive inheritance. Recently we were privileged to study parts of a fetus who had presented at ultrasonography with cardiac calcifications, micrognathia, and severe ulnar dysgenesis. The small pieces of heart we received showed neither endocardial fibroelastosis nor calcifications. Thus, we had initial doubts that we were dealing with the Marles-Chudley syndrome. However, a review by Chudley of the heart findings in his cases did show the calcifications usually seen in primary or secondary EFE. The parents of Dr. Chudley's patient were Flipino; the father of our patient was a Samoan. This suggests that there exists a gene for autosomal recessive Marles-Chudley syndrome in the Poynesian population with pleiotropic effects on upper limb development and cardiac histogenesis.

Review of the Trematode Genus Ribeiroia (Psilostomidae): Ecology, Life History and Pathogenesis with Special Emphasis on the Amphibian Malformation Problem

Trematodes in the genus Ribeiroia have an indirect life cycle involving planorbid snails as first intermediate hosts, fishes or amphibians as second intermediate hosts and birds or mammals as definitive hosts. Although rarely pathogenic in definitive hosts, Ribeiroia infection can cause severe pathology and mortality in snails and amphibians. This group of parasites has gained notoriety for its prominent rol in the recent rash of amphibian deformities in North America. Under some circumstances, these malformations may enhance parasite transmission by rendering infected amphibian hosts more susceptible to definitive host predators. However, increasing reports of malformations in North American amphibian populations emphasize the importance of understanding infection patterns. Here we review important aspects of the biology, ecology, life cycle and pathogenesis of parasites in the genus Ribeiroia and identify priorities for future research. Based on available morphological descriptions and preliminary molecular data, three species of Ribeiroia are recognized: R. ondatrae in the Americas, R. marini in the Caribbean and R. congolensis/C. lileta in Africa. We further evaluate the influence of abiotic and biotic factors in determining the intensity and prevalence of Ribeiroia infection and malformations in amphibians, highlighting the importance of habitat alteration and secondary factors (e.g. aquatic eutrophication, contaminants) in promoting infection. Although not a "new" parasite, Ribeiroia may have increased in range, prevalence, or intensity in recent years, particularly within amphibian hosts. Nevertheless, while much is known about this intriguing group of parasites, there remains much that we do not know. Particular importance for future research is placed on the following areas: evaluating the phylogenetic position of the genus, establishing the molecular mechanism of parasite-induced malformations in amphibians, isolating the drivers of parasite transmission under field conditions and studying the consequences of malformations for parasite and host populations. Investigation of these questions will benefit enormously from a multidisciplinary approach that effectively integrates parasitology, developmental biology, immunology, herpetology and aquatic ecology.