Sonic Hedgehog Mutations Research Articles

The Role of Sonic Hedgehog in Human Holoprosencephaly and Short-Rib Polydactyly Syndromes.

The Hedgehog (HH) signalling pathway is one of the major pathways controlling cell differentiation and proliferation during human development. This pathway is complex, with HH function influenced by inhibitors, promotors, interactions with other signalling pathways, and non-genetic and cellular factors. Many aspects of this pathway are not yet clarified. The main features of Sonic Hedgehog (SHH) signalling are discussed in relation to its function in human development. The possible role of SHH will be considered using examples of holoprosencephaly and short-rib polydactyly (SRP) syndromes. In these syndromes, there is wide variability in phenotype even with the same genetic mutation, so that other factors must influence the outcome. SHH mutations were the first identified genetic causes of holoprosencephaly, but many other genes and environmental factors can cause malformations in the holoprosencephaly spectrum. Many patients with SRP have genetic defects affecting primary cilia, structures found on most mammalian cells which are thought to be necessary for canonical HH signal transduction. Although SHH signalling is affected in both these genetic conditions, there is little overlap in phenotype. Possible explanations will be canvassed, using data from published human and animal studies. Implications for the understanding of SHH signalling in humans will be discussed.

Mutations in phospholipase C eta-1 (PLCH1) are associated with holoprosencephaly

BackgroundHoloprosencephaly is a spectrum of developmental disorder of the embryonic forebrain in which there is failed or incomplete separation of the prosencephalon into two cerebral hemispheres. To date, dominant mutations...

Untangling Sources of Phenotypic Variation Characterizing the Craniofacial Disease Holoprosencephaly

Holoprosencaphly (HPE)—a craniofacial disorder in which the forebrain fails to develop into two hemispheres and the midface does not fully form—is characterized by a broad spectrum of severity. Phenotypes range from very mild midfacial narrowing to cyclopia. Mutations in Sonic hedgehog (SHH) and in SHH signaling pathway members are known to underlie HPE; however, the source of the highly variable craniofacial morphology manifesting in the HPE patient population is not understood. Previous research in a chick model suggests that reduced SHH‐signaling in the brain correlates with a continuous distribution of HPE‐like phenotypes, and that very small modifications in ligand concentration can result in highly heterogeneous morphologies. Here, we are probing the origins of morphological variation in a genetic mouse model. Although humans heterozygous for SHH mutations exhibit the full spectrum of HPE, mice heterozygous for Shh do not exhibit even mild HPE although homozygous mutants are cyclopic. Mice homozygous for mutations in the SHH‐signaling pathway member low‐density lipoprotein receptor‐related protein (Lrp) 2 however exhibit mild to severe forms of HPE, and are therefore a better model for examining sources of variation. LRP2 is an endocytic receptor required to induce proper SHH signaling in the forebrain. We used geometric morphometric analysis to quantify the shape of embryos with sequential, genetic loss of Shh and Lrp2 alleles, and qPCR was used to assess SHH signaling pathway activation. We found that there is no statistically significant difference in shape among wild‐type, Lrp2+/−, Shh+/−, and Lrp2+/−;Shh+/− embryos, while Lrp2−/− and Lrp2−/−;Shh+/− embryos diverged from the group, exhibiting a more narrow midface. Interestingly, there was increased phenotypic variance in Lrp2−/− and Lrp2−/−;Shh+/− embryos in comparison to the other genotypes, with a greater increase in variance seen in the Lrp2−/−;Shh+/− group. Our results support the hypothesis that very slight modifications to SHH pathway activation can yield large amounts of phenotypic variation.Support or Funding InformationThis work is supported by NIH/NIDCR‐R01DE018234, ‐R01DE019638, ‐T32DE730619, ‐F31DE02579001.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

ARX and SHH gene mutation analyses revealed no mutation in patients with agenesis/dysgenesis of the corpus callosum

Mutations in sonic hedgehog (SHH; OMIM *600725) and the aristaless-related homeobox gene (ARX; OMIM *300382) can both result in severe brain malformation. Haploinsufficiency of SHH has been shown to cause not only midline structure defects such as holoprosencephaly, corpus callosum agenesis but also developmental delay and/or craniofacial dysmorphic features including microcephaly, hypotelorism, or a single central incisor. Mutations in the ARX gene may result in different phenotypes as well, such as X-linked mental retardation (XLMR; OMIM #300419), X-linked lissencephaly with ambiguous genitalia (XLAG; OMIM #300215), Partington syndrome (OMIM #309510), X-linked myoclonic epilepsy (OMIM #300432), X-linked West syndrome (OMIM #308350), and agenesis of the corpus callosum with abnormal genitalia (OMIM #300004). In a total number of 27 patients with complete or partial absence of the corpus callosum, SHH and ARX genes were investigated in order to evaluate whether mutations in SHH and ARX result in partial (dysgenesis) or complete (agenesis) absence of the corpus callosum. No causative mutations could be detected suggesting that these genes may not play a major role in corpus callosum formation.

The role of the sonic hedgehog signalling pathway in patients with midline defects and congenital hypopituitarism.

The Gli family of zinc finger (GLI) transcription factors mediates the sonic hedgehog signalling pathway (HH) essential for CNS, early pituitary and ventral forebrain development in mice. Human mutations in this pathway have been described in patients with holoprosencephaly (HPE), isolated congenital hypopituitarism (CH) and cranial/midline facial abnormalities. Mutations in Sonic hedgehog (SHH) have been associated with HPE but not CH, despite murine studies indicating involvement in pituitary development. We aimed to establish the role of the HH pathway in the aetiology of hypothalamo-pituitary disorders by screening our cohort of patients with midline defects and/or CH for mutations in SHH, GLI2, Shh brain enhancer 2 (SBE2) and growth-arrest specific 1 (GAS1). Two variants and a deletion of GLI2 were identified in three patients. A novel variant at a highly conserved residue in the zinc finger DNA-binding domain, c.1552G > A [pE518K], was identified in a patient with growth hormone deficiency and low normal free T4. A nonsynonymous variant, c.2159G > A [p.R720H], was identified in a patient with a short neck, cleft palate and hypogonadotrophic hypogonadism. A 26·6 Mb deletion, 2q12·3-q21·3, encompassing GLI2 and 77 other genes, was identified in a patient with short stature and impaired growth. Human embryonic expression studies and molecular characterisation of the GLI2 mutant p.E518K support the potential pathogenicity of GLI2 mutations. No mutations were identified in GAS1 or SBE2. A novel SHH variant, c.1295T>A [p.I432N], was identified in two siblings with variable midline defects but normal pituitary function. Our data suggest that mutations in SHH, GAS1 and SBE2 are not associated with hypopituitarism, although GLI2 is an important candidate for CH.

The pathogenesis of preaxial polydactyly: Anatomical insights using a silkie chicken model with sonic hedgehog mutation enhancement

The pathogenesis of preaxial polydactyly: Anatomical insights using a silkie chicken model with sonic hedgehog mutation enhancement

Sonic Hedgehog mutations are not a common cause of congenital hypopituitarism in the absence of complex midline cerebral defects.

Sonic Hedgehog (SHH) and GLI2, an obligatory mediator of SHH signal transduction, are holoprosencephaly (HPE)-associated genes essential in pituitary formation. GLI2 variants have been found in patients with congenital hypopituitarism without complex midline cerebral defects (MCD). However, data on the occurrence of SHH mutations in these patients are limited. We screened for SHH and GLI2 mutations or copy number variations (CNV) in patients with congenital hypopituitarism without MCD or with variable degrees of MCD. Detailed data on clinical, laboratory and neuroimaging findings of 115 patients presenting with congenital hypopituitarism without MCD, septo-optic dysplasia or HPE were analysed. The SHH and GLI2 genes were directly sequenced, and the presence of gene CNV was analysed by multiplex ligation-dependent probe amplification (MLPA). Anterior pituitary deficiency was found in 74% and 53% of patients with SOD or HPE, respectively. Diabetes insipidus was common in patients with HPE (47%) but infrequent in patients with congenital hypopituitarism or SOD (7% and 8%, respectively). A single heterozygous nonsense SHH mutation (p.Tyr175Ter) was found in a patient presenting with hypopituitarism and alobar HPE. No other SHH mutations or CNV were found. Nine GLI2 variations (8 missense and 1 frameshift) including a homozygous and a compound heterozygous variation were found in patients with congenital hypopituitarism or SOD, but not in HPE patients. No GLI2 CNV were found. SHH mutations or copy number variations are not a common cause of congenital hypopituitarism in patients without complex midline cerebral defects. GLI2 variants are found in some patients with congenital hypopituitarism without complex midline cerebral defects or septo-optic dysplasia. However, functional analyses of these variants are needed to strengthen genotype-phenotype relationship.

Therapeutic Opportunities for Medulloblastoma Come of Age

In this issue of Cancer Cell, Kool and colleagues reveal clear genetically defined subclasses of the sonic hedgehog (SHH) subclass of medulloblastoma. This molecular dissection of the SHH subclass is not simply a cutting-edge advance; the data have profound impact on clinical trial design and decision-making.

Single‐nucleotide variants in two Hedgehog genes, SHH and HHIP, as genetic cause of combined pituitary hormone deficiency

Combined pituitary hormone deficiency (CPHD) is characterized by deficiencies of two or more anterior pituitary hormones. Its genetic cause is unknown in the majority of cases. The Hedgehog (Hh) signalling pathway has been implicated in disorders associated with pituitary development. Mutations in Sonic Hedgehog (SHH) have been described in patients with holoprosencephaly (with or without pituitary involvement). Hedgehog interacting protein (HHIP) has been associated with variations in adult height in genome wide association studies. We investigated whether mutations in these two genes of the Hh pathway, SHH and HHIP, could result in 'idiopathic' CPHD. We directly sequenced the coding regions and exon - intron boundaries of SHH and HHIP in 93 CPHD patients of the Dutch HYPOPIT study in whom mutations in the classical CPHD genes PROP1, POU1F1, HESX1, LHX3 and LHX4 had been ruled out. We compared the expression of Hh genes in Hep3B transfected cells between wild-type proteins and mutants. We identified three single-nucleotide variants (p.Ala226Thr, c.1078C>T and c.*8G>T) in SHH. The function of the latter was severely affected in our in vitro assay. In HHIP, we detected a new activating variant c.-1G>C, which increases HHIP's inhibiting function on the Hh pathway. Our results suggest involvement of the Hedgehog pathway in CPHD. We suggest that both SHH and HHIP are investigated as a second screening in CPHD, after mutations in the classical CPHD genes have been ruled out.

Cdon Mutation and Fetal Ethanol Exposure Synergize to Produce Midline Signaling Defects and Holoprosencephaly Spectrum Disorders in Mice

Holoprosencephaly (HPE) is a remarkably common congenital anomaly characterized by failure to define the midline of the forebrain and midface. HPE is associated with heterozygous mutations in Sonic hedgehog (SHH) pathway components, but clinical presentation is extremely variable and many mutation carriers are unaffected. It has been proposed that these observations are best explained by a multiple-hit model, in which the penetrance and expressivity of an HPE mutation is enhanced by a second mutation or the presence of cooperating, but otherwise silent, modifier genes. Non-genetic risk factors are also implicated in HPE, and gene–environment interactions may provide an alternative multiple-hit model to purely genetic multiple-hit models; however, there is little evidence for this contention. We report here a mouse model in which there is dramatic synergy between mutation of a bona fide HPE gene (Cdon, which encodes a SHH co-receptor) and a suspected HPE teratogen, ethanol. Loss of Cdon and in utero ethanol exposure in 129S6 mice give little or no phenotype individually, but together produce defects in early midline patterning, inhibition of SHH signaling in the developing forebrain, and a broad spectrum of HPE phenotypes. Our findings argue that ethanol is indeed a risk factor for HPE, but genetically predisposed individuals, such as those with SHH pathway mutations, may be particularly susceptible. Furthermore, gene–environment interactions are likely to be important in the multifactorial etiology of HPE.

Genotypic and phenotypic analysis of 396 individuals with mutations in Sonic Hedgehog

BackgroundHoloprosencephaly (HPE), the most common malformation of the human forebrain, may result from mutations in over 12 genes. Sonic Hedgehog (SHH) was the first such gene discovered; mutations in SHH...

Maternal genetic effect in DNA analysis: Egg on your traits

A dilemma of penetrance parallels the uncertainty principle as array analyses uncover a disturbing continuity of human molecular variation. Among mechanisms for altered penetrance is maternal genetic effect, hypothesized to explain mother-offspring discordance from 12/13 translocation [Wilson et al., 1991] and important to consider when confronting identical genetic changes in normal mothers and their abnormal children. A boy with developmental delays, autistic features, minimal dysmorphology, and maternally inherited 17p13.3 microduplication could exemplify maternal genetic effect, as could a boy with altered brain pattern and maternally inherited Sonic Hedgehog mutation reported by Schell-Apacik et al. [2009]. Maternal genetic effects, characterized in fly, fish, and mouse, are important to consider in human DNA analysis so that identical findings in mother and child are not routinely dismissed as benign variations. Suspect families can define relevant maternal-zygote transition (MZT) genes, provide assays for oocyte function and disruption, and shift anomaly emphasis from pattern recognition to pattern restoration.

Hedgehog pathway does not play a role in hidradenitis suppurativa pathogenesis

Hidradenitis suppurativa is a chronically relapsing skin disorder with onset after puberty and is characterized by inflammatory lesions in hair follicle and apocrine sweat gland-bearing skin that manifests as abscesses with formation of cysts and sinus tracts. Hedgehog family genes are required in normal embryonic skin, hair follicle, sebaceous and sweat gland development. Mutations of hedgehog pathway in adult skin have previously been found in basal cell carcinomas and in alopecia as well as in epidermal cysts and in odontogenic keratocysts. Therefore, we suggested that the hedgehog pathway might play a role in formation of sinus tracts and cysts as newly formed structures in hidradenitis suppurativa patients. None of the sinus tracts or cysts in 81 hidradenitis suppurativa histological slides from 34 patients showed positive finding for sonic hedgehog mutation. According to our findings, we have to conclude that there is no evidence that sonic hedgehog pathway is part of hidradenitis suppurativa pathogenesis.

Novel Sonic Hedgehog Mutation in a Couple with Variable Expression of Holoprosencephaly

Holoprosencephaly (HPE) is the most common developmental defect of the forebrain and midface in humans. sporadic and inherited mutations in the human sonic hedgehog (SHH) gene cause 37% of familial HPE. A couple was referred to our unit with a family history of two spontaneous first trimester miscarriages and a daughter with HPE who presented early neonatal death. The father had a repaired median cleft lip, absence of central incisors, facial medial hypoplasia, and cleft palate. Intelligence and a brain CT scan were normal. Direct paternal sequencing analysis showed a novel nonsense mutation (W127X). Facial characteristics are considered as HPE microforms, and the pedigree suggested autosomal dominant inheritance with a variable expression of the phenotype. This study reinforces the importance of an exhaustive evaluation of couples with a history of miscarriages and neonatal deaths with structural defects.

Sonic hedgehog mutations are an uncommon cause of developmental eye anomalies

Sonic hedgehog mutations are an uncommon cause of developmental eye anomalies

Detection of poliovirus-infected macrophages in thymus of patients with myasthenia gravis

Genetic and environmental factors are thought to contribute to the etiology of the autoimmune disease myasthenia gravis (MG). Viral involvement has long been suspected, but direct evidence of involvement has not been found. We recently reported that Toll-like receptor 4 (TLR4)-a key activator of innate immunity-was overexpressed in the thymus of some patients with MG, suggesting that thymic infection by pathogens might be involved in MG pathogenesis. We searched for evidence of intrathymic infection in patients with MG. Twenty-seven MG thymuses (6 involuted, 7 hyperplastic, 5 thymitis, and 9 thymoma) previously tested for TLR4 expression, 18 nonpathologic control thymuses, and 10 pathologic control thymuses from patients without MG (8 thymoma and 2 hyperplastic) were analyzed for cytomegalovirus, varicella-zoster virus, herpes simplex virus types 1 and 2, eubacteria, respiratory syncytial virus, and enteroviruses using PCR techniques. Immunohistochemistry and double immunofluorescence were used to detect enterovirus capsid protein VP1 in thymic specimens and analyze TLR4 expression in VP1-positive cells. Poliovirus was detected in 4 MG thymuses (14.8%; 2 thymitis and 2 thymoma). No virus was detected in any control thymus. A linear correlation between plus and minus strand poliovirus RNA levels was observed in all 4 thymuses, suggesting persistent thymic infection. VP1 protein was detected in the cytoplasm of CD68-positive macrophages scattered through thymic medulla in all PV-positive thymuses. VP1 and TLR4 colocalized in infected cells. Poliovirus-infected macrophages are present in thymus of some patients with myasthenia gravis, suggesting a viral contribution to the intrathymic alterations leading to the disease.

Sonic hedgehog mutation analysis in patients with VACTERL association

Sonic hedgehog mutation analysis in patients with VACTERL association

Sonic hedgehog mutations identified in holoprosencephaly patients can act in a dominant negative manner

Sonic hedgehog (SHH) plays an important instructional role in vertebrate development, as exemplified by the numerous developmental disorders that occur when the SHH pathway is disrupted. Mutations in the SHH gene are the most common cause of sporadic and inherited holoprosencephaly (HPE), a developmental disorder that is characterized by defective prosencephalon development. SHH HPE mutations provide a unique opportunity to better understand SHH biogenesis and signaling, and to decipher its role in the development of HPE. Here, we analyzed a panel of SHH HPE missense mutations that encode changes in the amino-terminal active domain of SHH. Our results show that SHH HPE mutations affect SHH biogenesis and signaling at multiple steps, which broadly results in low levels of protein expression, defective processing of SHH into its active form and protein with reduced activity. Additionally, we found that some inactive SHH proteins were able to modulate the activity of wt SHH in a dominant negative manner, both in vitro and in vivo. These findings show for the first time the susceptibility of SHH driven developmental processes to perturbations by low-activity forms of SHH. In conclusion, we demonstrate that SHH mutations found in HPE patients affect distinct steps of SHH biogenesis to attenuate SHH activity to different levels, and suggest that these variable levels of SHH activity might contribute to some of the phenotypic variation found in HPE patients.

Mutational analyses of UPIIIA, SHH, EFNB2, and HNF1β in persistent cloaca and associated kidney malformations

Objectives ‘Persistent cloaca’ is a severe malformation affecting females in which the urinary, genital and alimentary tracts share a single conduit. Previously, a Uroplakin IIIA ( UPIIIA) mutation was reported in one individual with persistent cloaca, and UPIIIA, Sonic Hedgehog (SHH), Ephrin B2 (EFNB2) and Hepatocyte Nuclear Factor 1β (HNF1β) are expressed during the normal development of organs that are affected in this condition. HNF1β mutations have been associated with uterine malformations in humans, and mutations of genes homologous to human SHH or EFNB2 cause persistent cloaca in mice. Patients and methods We sought mutations of coding regions of UPIIIA, SHH, EFNB2 and HNF1β genes by direct sequencing in a group of 20 patients with persistent cloaca. Most had associated malformations of the upper renal tract and over half had impaired renal excretory function. The majority of patients had congenital anomalies outside the renal/genital tracts and two had the VACTERL association. Results Apart from a previously described index case, we failed to find UPIIIA mutations, and no patient had a SHH, EFNB2 or HNF1β mutation. Conclusion Persistent cloaca is only rarely associated with UPIIIA mutation. Despite the fact that SHH and EFNB2 are appealing candidate genes, based on their expression patterns and mutant mice phenotypes, they were not mutated in these humans with persistent cloaca. Although HNF1β mutations can perturb paramesonephric duct fusion in humans, HNF1β was not mutated in persistent cloaca.

Functional Characterization of Sonic Hedgehog Mutations Associated with Holoprosencephaly

Mutations of the developmental gene Sonic hedgehog (SHH) and alterations of SHH signaling have been associated with holoprosencephaly (HPE), a rare disorder characterized by a large spectrum of brain and craniofacial anomalies. Based on the crystal structure of mouse N-terminal and Drosophila C-terminal hedgehog proteins, we have developed three-dimensional models of the corresponding human proteins (SHH-N, SHH-C) that have allowed us to identify within these two domains crucial regions associated with HPE missense mutations. We have further characterized the functional consequences linked to 11 of these mutations. In transfected HEK293 cells, the production of the active SHH-N fragment was dramatically impaired for eight mutants (W117R, W117G, H140P, T150R, C183F, L271P, I354T, A383T). The supernatants from these cell cultures showed no significant SHH-signaling activity in a reporter cell-based assay. Two mutants (G31R, D222N) were associated with a lower production of SHH-N and signaling activity. Finally, one mutant harboring the A226T mutation displays an activity comparable with the wild-type protein. This work demonstrates that most of the HPE-associated SHH mutations analyzed have a deleterious effect on the availability of SHH-N and its biological activity. However, because of the lack of correlation between genotype and phenotype for SHH-associated mutations, our study suggests that other factors intervene in the development of the spectrum of HPE anomalies.