Variable expression of subclinical phenotypes instead of reduced penetrance in families with mild triphalangeal thumb phenotypes

BackgroundThe of zone of polarizing activity regulatory sequence (ZRS) is a regulatory element residing in intron 5 of LMBR1 and regulates Sonic Hedgehog expression in the limb bud. Variants in the ZRS are generally fully penetrant and can cause triphalangeal thumb (TPT) and polydactyly in affected families.ObjectiveIn this report, we describe two families with mild phenotypical presentation.MethodsWe performed a field study for clinical evaluation and sequenced the ZRS for variantsusing Sanger sequencing.ResultsIn family I, a novel 165A>G variant in the ZRS (g.156584405A>G, GRCh37/Hg19) was found. In family II, we identified a 295T>C variant in the ZRS (g.156584535T>C, GRCh37/Hg19). Family members of both families who were presumed to be unaffected shared the variant in the ZRS with affected family members, suggesting reduced penetrance of the genotype. However, clinical examination of these unaffected family members revealed minor anomalies like broad thumbs and lack of thumb opposition. As the phenotype in affected patients is remarkably mild, we suggest that these ZRS variants are minimally disruptive for Sonic Hedgehog expression and therefore can result in subclinical phenotypes.ConclusionOur study underlines the importance of accurate clinical examination and appropriate genetic counselling in families with mild cases of TPT.

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Zone of Polarizing Activity Regulatory Sequence Mutations/Duplications with Preaxial Polydactyly and Longitudinal Preaxial Ray Deficiency in the Phenotype: A Review of Human Cases, Animal Models, and Insights Regarding the Pathogenesis

BioMed Research International ◽

10.1155/2018/1573871 ◽

2018 ◽

Vol 2018 ◽

pp. 1-9 ◽

Cited By ~ 4

Author(s):

Mohammad M. Al-Qattan

Keyword(s):

Developmental Biology ◽

Animal Models ◽

Sonic Hedgehog ◽

Ectopic Expression ◽

Point Mutations ◽

Limb Bud ◽

Regulatory Sequence ◽

Preaxial Polydactyly ◽

Zone Of Polarizing Activity

Clinicians and scientists interested in developmental biology have viewed preaxial polydactyly (PPD) and longitudinal preaxial ray deficiency (LPAD) as two different entities. Point mutations and duplications in the zone of polarizing activity regulatory sequence (ZRS) are associated with anterior ectopic expression of Sonic Hedgehog (SHH) in the limb bud and usually result in a PPD phenotype. However, some of these mutations/duplications also have LPAD in the phenotype. This unusual PPD-LPAD association in ZRS mutations/duplications has not been specifically reviewed in the literature. The author reviews this unusual entity and gives insights regarding its pathogenesis.

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The mesenchymal factor, FGF10, initiates and maintains the outgrowth of the chick limb bud through interaction with FGF8, an apical ectodermal factor

Development ◽

10.1242/dev.124.11.2235 ◽

1997 ◽

Vol 124 (11) ◽

pp. 2235-2244 ◽

Cited By ~ 67

Author(s):

H. Ohuchi ◽

T. Nakagawa ◽

A. Yamamoto ◽

A. Araga ◽

T. Ohata ◽

...

Keyword(s):

Sonic Hedgehog ◽

Limb Bud ◽

Fibroblast Growth ◽

Lateral Plate Mesoderm ◽

Lateral Plate ◽

Bud Formation ◽

Limb Mesenchyme ◽

Vertebrate Limb ◽

Fgf10 Expression ◽

Zone Of Polarizing Activity

Vertebrate limb formation has been known to be initiated by a factor(s) secreted from the lateral plate mesoderm. In this report, we provide evidence that a member of the fibroblast growth factor (FGF) family, FGF10, emanates from the prospective limb mesoderm to serve as an endogenous initiator for limb bud formation. Fgf10 expression in the prospective limb mesenchyme precedes Fgf8 expression in the nascent apical ectoderm. Ectopic application of FGF10 to the chick embryonic flank can induce Fgf8 expression in the adjacent ectoderm, resulting in the formation of an additional complete limb. Expression of Fgf10 persists in the mesenchyme of the established limb bud and appears to interact with Fgf8 in the apical ectoderm and Sonic hedgehog in the zone of polarizing activity. These results suggest that FGF10 is a key mesenchymal factor involved in the initial budding as well as the continuous outgrowth of vertebrate limbs.

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Relationship between retinoic acid and sonic hedgehog, two polarizing signals in the chick wing bud

Development ◽

10.1242/dev.120.11.3267 ◽

1994 ◽

Vol 120 (11) ◽

pp. 3267-3274 ◽

Cited By ~ 7

Author(s):

J. Helms ◽

C. Thaller ◽

G. Eichele

Keyword(s):

Retinoic Acid ◽

Sonic Hedgehog ◽

Positional Information ◽

Limb Bud ◽

Dependent Manner ◽

All Trans Retinoic Acid ◽

Wing Bud ◽

Zone Of Polarizing Activity ◽

Dose Dependent

Local application of all-trans-retinoic acid (RA) to the anterior margin of chick limb buds results in pattern duplications reminescent of those that develop after grafting cells from the zone of polarizing activity (ZPA). RA may act directly by conferring positional information to limb bud cells, or it may act indirectly by creating a polarizing region in the tissue distal to the RA source. Here we demonstrate that tissue distal to an RA-releasing bead acquires polarizing activity in a dose-dependent manner. Treatments with pharmacological (beads soaked in 330 micrograms/ml) and physiological (beads soaked in 10 micrograms/ml) doses of RA are equally capable of inducing digit pattern duplication. Additionally, both treatments induce sonic hedgehog (shh; also known as vertebrate hedgehog-1, vhh-1), a putative ZPA morphogen and Hoxd-11, a gene induced by the polarizing signal. However, tissue transplantation assays reveal that pharmacological, but not physiological, doses create a polarizing region. This differential response could be explained if physiological doses induced less shh than pharmacological doses. However, our in situ hybridization analyses demonstrate that both treatments result in similar amounts of mRNA encoding this candidate ZPA morphogen. We outline a model describing the apparently disparate effects of pharmacologic and physiological doses RA on limb bud tissue.

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Embryonic retinoic acid synthesis is required for forelimb growth and anteroposterior patterning in the mouse

Development ◽

10.1242/dev.129.15.3563 ◽

2002 ◽

Vol 129 (15) ◽

pp. 3563-3574 ◽

Cited By ~ 11

Author(s):

Karen Niederreither ◽

Julien Vermot ◽

Brigitte Schuhbaur ◽

Pierre Chambon ◽

Pascal Dollé

Keyword(s):

Retinoic Acid ◽

Sonic Hedgehog ◽

Acid Synthesis ◽

Limb Bud ◽

Anteroposterior Patterning ◽

Limb Morphogenesis ◽

Functional Zone ◽

Mutant Mouse Embryos ◽

Bud Growth ◽

Zone Of Polarizing Activity

Numerous studies, often performed on avian embryos, have implicated retinoic acid (RA) in the control of limb bud growth and patterning. Here we have investigated whether the lack of endogenous RA synthesis affects limb morphogenesis in mutant mouse embryos deficient for the retinaldehyde dehydrogenase 2 (Raldh2/Aldh1a2). These mutants, which have no detectable embryonic RA except in the developing retina, die at E9.5-E10 without any evidence of limb bud formation, but maternal RA supplementation through oral gavage from E7.5 can extend their survival. Such survivors exhibit highly reduced forelimb rudiments, but apparently normal hindlimbs. By providing RA within maternal food, we found both a stage- and dose-dependency for rescue of forelimb growth and patterning. Following RA supplementation from E7.5 to 8.5, mutant forelimbs are markedly hypoplastic and lack anteroposterior (AP) patterning, with a single medial cartilage and 1-2 digit rudiments. RA provided until E9.5 significantly rescues forelimb growth, but cannot restore normal AP patterning. Increasing the RA dose rescues the hypodactyly, but leads to lack of asymmetry of the digit pattern, with abnormally long first digit or symmetrical polydactyly. Mutant forelimb buds are characterized by lack of expression or abnormal distal distribution of Sonic hedgehog (Shh) transcripts, sometimes with highest expression anteriorly. Downregulation or ectopic anterior expression of Fgf4 is also seen. As a result, genes such as Bmp2 or Hoxd genes are expressed symmetrically along the AP axis of the forelimb buds, and/or later, of the autopod. We suggest that RA signaling cooperates with a posteriorly restricted factor such as dHand, to generate a functional zone of polarizing activity (ZPA).

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A Novel ZRS Mutation in a Chinese Patient with Preaxial Polydactyly and Triphalangeal Thumb

Cytogenetic and Genome Research ◽

10.1159/000448820 ◽

2016 ◽

Vol 149 (3) ◽

pp. 171-175 ◽

Cited By ~ 9

Author(s):

Pan-Feng Wu ◽

Shuai Guo ◽

Xue-Feng Fan ◽

Liang-Liang Fan ◽

Jie-Yuan Jin ◽

...

Keyword(s):

De Novo ◽

Novel Mutation ◽

Genetic Diagnosis ◽

Chinese Patient ◽

Regulatory Sequence ◽

Preaxial Polydactyly ◽

Thumb Duplication ◽

Zone Of Polarizing Activity ◽

The Right ◽

Triphalangeal Thumb

Preaxial polydactyly (PPD; OMIM 603596), which is characterized as having supernumerary fingers, is an unusual congenital hand abnormality. Triphalangeal thumb (TPT; OMIM 190600) is identified by an extra phalangeal bone and is often found in association with PPD. When in combination, the disease is referred to as PPD type II (PPD II; OMIM 174500). Previous studies have demonstrated that variations in the zone of polarizing activity regulatory sequence (ZRS; chr7:156,583,796-156,584,569; hg19) region are associated with PPD II. In this study, our patient was diagnosed with PPD II, having bilateral thumb duplication and unilateral TPT (on the right hand). Further investigation of possible causative genes identified a de novo heterozygous ZRS mutation (ZRS 428T>A). This novel mutation was neither found in 200 normal controls nor reported in online databases. Moreover, the bioinformatics program Genomic Evolutionary Rate Profiling (GERP) revealed this site (ZRS428) to be evolutionarily highly conserved, and the 428T>A point mutation was predicted to be deleterious by MutationTaster. In conclusion, the affected individual shows bilateral thumb duplication, but unilateral TPT making this case special. Thus, our findings not only further support the important role of ZRS in limb morphogenesis and expand the spectrum of ZRS mutations, but also emphasize the significance of genetic diagnosis and counseling of families with digit number and identity alterations as well.

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A variant in the sonic hedgehog regulatory sequence (ZRS) is associated with triphalangeal thumb and deregulates expression in the developing limb

Human Molecular Genetics ◽

10.1093/hmg/ddn141 ◽

2008 ◽

Vol 17 (16) ◽

pp. 2417-2423 ◽

Cited By ~ 58

Author(s):

Dominic Furniss ◽

Laura A. Lettice ◽

Indira B. Taylor ◽

Paul S. Critchley ◽

Henk Giele ◽

...

Keyword(s):

Sonic Hedgehog ◽

Regulatory Sequence ◽

Triphalangeal Thumb

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Slug, a zinc finger gene previously implicated in the early patterning of the mesoderm and the neural crest, is also involved in chick limb development

Development ◽

10.1242/dev.124.9.1821 ◽

1997 ◽

Vol 124 (9) ◽

pp. 1821-1829

Author(s):

M.A. Ros ◽

M. Sefton ◽

M.A. Nieto

Keyword(s):

Zinc Finger ◽

Sonic Hedgehog ◽

Limb Development ◽

Limb Bud ◽

Mesenchymal Phenotype ◽

Signalling Molecules ◽

Slug Expression ◽

Snail Family ◽

Zone Of Polarizing Activity ◽

Signalling Systems

The great advances made over the last few years in the identification of signalling molecules that pattern the limb bud along the three axes make the limb an excellent model system with which to study developmental mechanisms in vertebrates. The understanding of the signalling networks and their mutual interactions during limb development requires the characterisation of the corresponding downstream genes. In this study we report the expression pattern of Slug, a zinc-finger-containing gene of the snail family, during the development of the limb, and its regulation by distinct axial signalling systems. Slug expression is highly dynamic, and at different stages of limb development can be correlated with the zone of polarizing activity, the progress zone and the interdigital areas. We show that the maintenance of its expression is dependent on signals from the apical ectodermal ridge and independent of Sonic Hedgehog. We also report that, in the interdigit, apoptotic cells lie outside of the domains of Slug expression. The correlation of Slug expression with areas of undifferentiated mesenchyme at stages of tissue differentiation is consistent with its role in early development, in maintaining the mesenchymal phenotype and repressing differentiation processes. We suggest that Slug is involved in the epithelial-mesenchymal interactions that lead to the maintenance of the progress zone.

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Relationship between dose, distance and time in Sonic Hedgehog-mediated regulation of anteroposterior polarity in the chick limb

Development ◽

10.1242/dev.124.21.4393 ◽

1997 ◽

Vol 124 (21) ◽

pp. 4393-4404 ◽

Cited By ~ 17

Author(s):

Y. Yang ◽

G. Drossopoulou ◽

P.T. Chuang ◽

D. Duprez ◽

E. Marti ◽

...

Keyword(s):

Alkaline Phosphatase ◽

Long Range ◽

Sonic Hedgehog ◽

Mirror Image ◽

Limb Bud ◽

Limb Mesenchyme ◽

Significant Difference ◽

Zone Of Polarizing Activity ◽

Anteroposterior Polarity ◽

Dose Dependent

Anteroposterior polarity in the vertebrate limb is thought to be regulated in response to signals derived from a specialized region of distal posterior mesenchyme, the zone of polarizing activity. Sonic Hedgehog (Shh) is expressed in the zone of polarizing activity and appears to mediate the action of the zone of polarizing activity. Here we have manipulated Shh signal in the limb to assess whether it acts as a long-range signal to directly pattern all the digits. Firstly, we demonstrate that alterations in digit development are dependent upon the dose of Shh applied. DiI-labeling experiments indicate that cells giving rise to the extra digits lie within a 300 microm radius of a Shh bead and that the most posterior digits come from cells that lie very close to the bead. A response to Shh involves a 12–16 hour period in which no irreversible changes in digit pattern occur. Increasing the time of exposure to Shh leads to specification of additional digits, firstly digit 2, then 3, then 4. Cell marking experiments demonstrate that cells giving rise to posterior digits are first specified as anterior digits and later adopt a more posterior character. To monitor the direct range of Shh signalling, we developed sensitive assays for localizing Shh by attaching alkaline phosphatase to Shh and introducing cells expressing these forms into the limb bud. These experiments demonstrate that long-range diffusion across the anteroposterior axis of the limb is possible. However, despite a dramatic difference in their diffusibility in the limb mesenchyme, the two forms of alkaline phosphatase-tagged Shh proteins share similar polarizing activity. Moreover, Shh-N (aminoterminal peptide of Shh)-coated beads and Shh-expressing cells also exhibit similar patterning activity despite a significant difference in the diffusibility of Shh from these two sources. Finally, we demonstrate that when Shh-N is attached to an integral membrane protein, cells transfected with this anchored signal also induce mirror-image pattern duplications in a dose-dependent fashion similar to the zone of polarizing activity itself. These data suggest that it is unlikely that Shh itself signals digit formation at a distance. Beads soaked in Shh-N do not induce Shh in anterior limb mesenchyme ruling out direct propagation of a Shh signal. However, Shh induces dose-dependent expression of Bmp genes in anterior mesenchyme at the start of the promotion phase. Taken together, these results argue that the dose-dependent effects of Shh in the regulation of anteroposterior pattern in the limb may be mediated by some other signal(s). BMPs are plausible candidates.

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The bHLH transcription factor dHAND controls Sonic hedgehog expression and establishment of the zone of polarizing activity during limb development

Development ◽

10.1242/dev.127.11.2461 ◽

2000 ◽

Vol 127 (11) ◽

pp. 2461-2470 ◽

Cited By ~ 9

Author(s):

J. Charite ◽

D.G. McFadden ◽

E.N. Olson

Keyword(s):

Transcription Factor ◽

Sonic Hedgehog ◽

Limb Development ◽

Target Genes ◽

Ectopic Expression ◽

Tissue Growth ◽

Limb Bud ◽

Bhlh Transcription Factor ◽

Expression Domain ◽

Zone Of Polarizing Activity

Limb outgrowth and patterning of skeletal elements are dependent on complex tissue interactions involving the zone of polarizing activity (ZPA) in the posterior region of the limb bud and the apical ectodermal ridge. The peptide morphogen Sonic hedgehog (SHH) is expressed specifically in the ZPA and, when expressed ectopically, is sufficient to mimic its functions, inducing tissue growth and formation of posterior skeletal elements. We show that the basic helix-loop-helix transcription factor dHAND is expressed posteriorly in the developing limb prior to Shh and subsequently occupies a broad domain that encompasses the Shh expression domain. In mouse embryos homozygous for a dHAND null allele, limb buds are severely underdeveloped and Shh is not expressed. Conversely, misexpression of dHAND in the anterior region of the limb bud of transgenic mice results in formation of an additional ZPA, revealed by ectopic expression of Shh and its target genes, and resulting limb abnormalities that include preaxial polydactyly with duplication of posterior skeletal elements. Analysis of mouse mutants in which Hedgehog expression is altered also revealed a feedback mechanism in which Hedgehog signaling is required to maintain the full dHAND expression domain in the developing limb. Together, these findings identify dHAND as an upstream activator of Shh expression and important transcriptional regulator of limb development.

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