Linkage mapping and phenotypic analysis of autosomal dominant Pallister-Hall syndrome

Two Novel Frameshift Mutations in the GLI3 Gene Underlie Non-Syndromic Polydactyly in Chinese Families

Objective: Polydactyly is characterized by multiple distinct heterogeneous phenotypes, the etiologies of which involve several genes. This study aimed to explore the genetic defects and further clarify the molecular mechanism of polydactyly in several Chinese families. Methods: Three families with diverse phenotypes of non-syndromic polydactyly were analyzed: two were cases of familial disease, whereas one was sporadic. PCR and Sanger sequencing were used to screen for pathogenic mutations in two known disease-associated genes, GLI3 and HOXD13, while bioinformatic analyses predicted the pathogenicity of the identified variants. Reverse transcription PCR was used to analyze the splicing effect of an intronic variant. Results: Two novel heterozygous frameshift mutations (c.4478delG/p.S1493Tfs*18; c.846_c.847insC/p.R283Qfs*21) were identified in the GLI3 gene from two of the pedigrees. Both c.4478delG and c.846_c.847insC were later confirmed in affected and unaffected members and normal controls, to truncate and disrupt the integrity of the GLI3 protein, reduce its level of expression, and disrupt its biological function through nonsense-mediated mRNA decay (NMD). In addition, a deep intron mutation (c.125-47 C>A) was detected in the GLI3 gene from the sporadic case, however, both bioinformatics analysis (HSF, splice AI, and CBS) and RT-PCR indicated that the variant c.125-47 C>A had minimal if any impact on splicing of the GLI3 gene. Conclusion: Two newly identified heterozygous frameshift mutations in the GLI3 gene were detected in two families with non-syndromic polydactyly, further extending the mutational spectrum of the GLI3 gene in non-syndromic polydactyly. Moreover, our study further expanded the phenotypic spectrum of non-syndromic polydactyly.

Advances in hypothalamic hamartoma research over the past 30 years (1992-2021): a bibliometric analysis

Background

Hypothalamic hamartoma (HH) is a rare intracranial disease whose manifestations include gelastic seizures and precocious puberty. The diagnosis and treatment of HH have changed substantially over the past three decades as medical care has improved. Bibliometrics can reveal the evolution and development of a scientific field.

Methods

Documents on HH were retrieved from the Web of Science Core Collection (WoSCC) database on September 8, 2022. The search terms were as follows: "hypothalamic hamartoma" or "hamartoma of the hypothalamus" or "hypothalamic hamartomas." The types of documents were restricted to articles, case reports, and reviews. VOSviewer, CiteSpace, and the R package "bibliometrix" were used for a bibliometric analysis.

Results

A total of 667 independent documents on HH were obtained from the WoSCC database. The most common types of documents were articles (n = 498, 75%) and reviews (n = 103, 15%). The number of annual publications fluctuated but showed an upward trend overall, and the annual growth rate was 6.85%. The cumulative publication data indicated that the most influential journals in the HH field include Epilepsia, Epileptic Disorders, Child's Nervous System, Neurosurgery, and the Journal of Neurosurgery. Kerrigan JF, Ng YT, Rekate HL, Regis J, and Kameyama S were among the most prominent authors in the field of HH, with numerous publications and citations. American research institutions, especially the Barrow Neurological Institute, occupied a pivotal position in HH research. Other countries and institutions were catching up and producing considerable research results. Research on HH has steadily switched its emphasis from Pallister-Hall syndrome (PHS) and precocious puberty to epilepsy and new diagnostic and therapeutic techniques, including Gamma Knife, laser ablation, and interstitial thermal therapy.

Conclusion

HH remains a special neurological disease with significant research prospects. The development of novel technologies, including MRI-guided laser-induced thermal therapy (MRg-LiTT) and stereotactic radiofrequency thermocoagulation (RF-TC), has enabled the efficient treatment of gelastic seizures in HH while minimizing the risks associated with craniotomies. Through bibliometric analysis, this study points out the direction for future HH research.

Novel GLI3 Mutations in Chinese Patients with Non-syndromic Post-axial Polydactyly

BACKGROUND

Polydactyly, characterized by supernumerary digits in the upper or lower extremities, is the most common congenital digital abnormalities. It derives from the defective patterning of anteroposterior axis of the developing limb, with various etiology and clinical heterogeneity. The patients with post-axial polydactyly type A (PAPA) have the typical symptom of a well-formed supernumerary digit outside the fifth digit.

OBJECTIVE

The aim of present study was to identify the causative mutations of two unrelated Han Chinese patients with non-syndromic PAPA.

METHODS

Two unrelated Han Chinese patients and 100 ethnicity-matched, unrelated normal controls were recruited for this study. BGISEQ-500 exome sequencing was performed in the two patients, followed by validation in the patients and 100 controls by using Sanger sequencing.

RESULTS

Two mutations in the GLI family zinc finger 3 gene (GLI3), including a frameshift mutation c.3437_3453delTCGAGCAGCCCTGCCCC (p.L1146RfsX95) and a nonsense mutation c.3997C>T (p.Q1333X), were identified in two patients but were absent in the 100 healthy controls.

CONCLUSION

The two GLI3 mutations, p.L1146RfsX95 and p.Q1333X, may account for non-syndromic PAPA in the two patients, respectively. The findings of this study may expand the mutational spectrum of GLI3-PAPA and provide novel insights into the genetic basis of polydactyly.

A GLI3 variant leading to polydactyly in heterozygotes and Pallister-Hall-like syndrome in a homozygote

Variants in transcriptional activator Gli Kruppel Family Member 3 (GLI3) have been reported to be associated with several phenotypes including Greig cephalopolysyndactyly syndrome (MIM #175700), Pallister-Hall syndrome (PHS) (MIM #146510), postaxial polydactyly types A1 (PAPA1) and B (PAPB) (MIM #174200), and preaxial polydactyly type 4 (MIM #174700). All these disorders follow an autosomal dominant pattern of inheritance. Hypothalamic hamartomas (MIM 241800) is associated with somatic variants in GLI3. We report a related couple with parents having PAPA1 and PAPB, who had a fetus with a phenotype most compatible with PHS. Molecular analyses demonstrated homozygosity for a pathogenic GLI3 variant (c.1927C > T; p. Arg643*) in the fetus and heterozygosity in the parents. The genetic analysis in this family demonstrates that heterozygosity and homozygosity for the same GLI3 variant can cause a different phenotype. Furthermore, the occurrence of Pallister-Hall-like syndrome in a homozygous patient should be taken into account in genetic counseling of families with PAPA1/PAPB.

A review of genetic factors contributing to the etiopathogenesis of anorectal malformations

BACKGROUND

Anorectal malformation (ARM) is a common congenital anomaly with a wide clinical spectrum. Recently, many genetic and molecular studies have been conducted worldwide highlighting the contribution of genetic factors in its etiology. We summarize the current literature on such genetic factors.

MATERIALS AND METHODS

Literature search was done using different combinations of terms related to genetics in anorectal malformations. From 2012 to June 2017, articles published in the English literature and studies conducted on human population were included.

OBSERVATIONS AND RESULTS

A paradigm shift was observed from the earlier studies concentrating on genetic aberrations in specific pathways to genome wide arrays exploring single nucleotide polymorphisms (SNPs) and copy number variations (CNVs) in ARM patients. Rare CNVs (including 79 genes) and SNPs have been found to genetically contribute to ARM. Out of disrupted 79 genes one such putative gene is DKK4. Down regulation of CDX-1 gene has also been implicated in isolated ARM patients. In syndromic ARM de novo microdeletion at 17q12 and a few others have been identified.

CONCLUSION

Major genetic aberrations proposed in the pathogenesis of ARM affect members of the Wnt, Hox (homebox) genes, Sonic hedgehog (Shh) and Gli2, Bmp4, Fgf and CDX1 signalling pathways; probable targets of future molecular gene therapy.

GLI3-related polydactyly: a review

GLI3 mutations are known to be associated with nine syndromes/conditions in which polydactyly is a feature. In this review, the embryology, pathogenesis, and animal models of GLI3-related polydactyly are discussed first. This is followed by a detailed review of the genotype-phenotype correlations. Based on our review of the literature and our clinical experiences, we recommend viewing GLI3-related syndromes/conditions as four separate entities; each characterized by a specific pattern of polydactyly. These four entities are: the preaxial polydactyly type IV-Greig-acrocallosal spectrum, postaxial polydactyly types A/B, Pallister-Hall syndrome (PHS), and oral-facial-digital overlap syndrome. We also provide illustrative clinical examples from our practice including a family with a novel GLI3 mutation causing PHS. The review also introduces the term 'Forme Fruste' preaxial polydactyly and gives several conclusions/recommendations including the recommendation to revise the current criteria for the clinical diagnosis of PHS.

Hypothalamic hamartoma with neurofibrillary tangles

Hypothalamic hamartomas are rare tumors that typically present in childhood, often with gelastic seizures, precocious puberty, or as a manifestation of Pallister-Hall syndrome. Neurofibrillary tangles are cytoplasmic aggregates of hyperphosphorylated tau that are best recognized in Alzheimer disease, other tau-associated neurodegenerative diseases, or as part of aging, but occasionally may be seen in low-grade neoplasms with a ganglion cell component as gangliocytoma or ganglioglioma. Herein, we report a case of hypothalamic hamartoma with neurofibrillary tangles.

Anorectal malformation: the etiological factors

Anorectal malformation (ARM) is a congenital anomaly commonly encountered in pediatric surgery practice. Although surgical procedures correct the anatomical anomalies, the post-operative bowel function is not universally satisfactory. The etiology of ARM remains unclear. In this review, we summarize the current understanding of the genetic and epigenetic factors contributing to the pathogenesis of ARM, based on published animal models, human genetics and epidemiological researches. Appreciation of these factors may be helpful in the management of ARM in the future.

Cis-regulatory underpinnings of human GLI3 expression in embryonic craniofacial structures and internal organs

The zinc finger transcription factor Gli3 is an important mediator of Sonic hedgehog (Shh) signaling. During early embryonic development Gli3 participates in patterning and growth of the central nervous system, face, skeleton, limb, tooth and gut. Precise regulation of the temporal and spatial expression of Gli3 is crucial for the proper specification of these structures in mammals and other vertebrates. Previously we reported a set of human intronic cis-regulators controlling almost the entire known repertoire of endogenous Gli3 expression in mouse neural tube and limbs. However, the genetic underpinning of GLI3 expression in other embryonic domains such as craniofacial structures and internal organs remain elusive. Here we demonstrate in a transgenic mice assay the potential of a subset of human/fish conserved non-coding sequences (CNEs) residing within GLI3 intronic intervals to induce reporter gene expression at known regions of endogenous Gli3 transcription in embryonic domains other than central nervous system (CNS) and limbs. Highly specific reporter expression was observed in craniofacial structures, eye, gut, and genitourinary system. Moreover, the comparison of expression patterns directed by these intronic cis-acting regulatory elements in mouse and zebrafish embryos suggests that in accordance with sequence conservation, the target site specificity of a subset of these elements remains preserved among these two lineages. Taken together with our recent investigations, it is proposed here that during vertebrate evolution the Gli3 expression control acquired multiple, independently acting, intronic enhancers for spatiotemporal patterning of CNS, limbs, craniofacial structures and internal organs.

Unraveling the disease pathogenesis behind lethal hydrolethalus syndrome revealed multiple changes in molecular and cellular level

BACKGROUND

Hydrolethalus syndrome (HLS) is a severe fetal malformation syndrome characterized by multiple developmental anomalies, including central nervous system (CNS) malformation such as hydrocephaly and absent midline structures of the brain, micrognathia, defective lobation of the lungs and polydactyly. Microscopically, immature cerebral cortex, abnormalities in radial glial cells and hypothalamic hamartoma are among key findings in the CNS of HLS fetuses. HLS is caused by a substitution of aspartic acid by glycine in the HYLS1 protein, whose function was previously unknown.

RESULTS

To provide insight into the disease mechanism(s) of this lethal disorder we have studied different aspects of HLS and HYLS1. A genome-wide gene expression analysis indicated several upregulated genes in cell cycle regulatory cascades and in specific signal transduction pathways while many downregulated genes were associated with lipid metabolism. These changes were supported by findings in functional cell biology studies, which revealed an increased cell cycle rate and a decreased amount of apoptosis in HLS neuronal progenitor cells. Also, changes in lipid metabolism gene expression were reflected by a significant increase in the cholesterol levels of HLS liver tissues. In addition, based on our functional studies of HYLS1, we propose that HYLS1 is a transcriptional regulator that shuffles between the cytoplasm and the nucleus, and that when HYLS1 is mutated its function is significantly altered.

CONCLUSION

In this study, we have shown that the HYLS1 mutation has significant consequences in the cellular and tissue levels in HLS fetuses. Based on these results, it can be suggested that HYLS1 is part of the cellular transcriptional regulatory machinery and that the genetic defect has a widespread effect during embryonic and fetal development. These findings add a significant amount of new information to the pathogenesis of HLS and strongly suggest an essential role for HYLS1 in normal fetal development.

Identification of somatic chromosomal abnormalities in hypothalamic hamartoma tissue at the GLI3 locus

Hypothalamic hamartomas (HH) are rare, benign congenital tumors associated with intractable epilepsy. Most cases are sporadic and nonsyndromic. Approximately 5% of HH cases are associated with Pallister-Hall syndrome (PHS), which is caused by haploinsufficiency of GLI3. We have investigated the possibility that HH pathogenesis in sporadic cases is due to a somatic (tumor-only) mutation in GLI3. We isolated genomic DNA from peripheral blood and surgically resected HH tissue in 55 patients with sporadic HH and intractable epilepsy. A genome-wide screen for loss of heterozygosity (LOH) and chromosomal abnormalities was performed with parallel analysis of blood and HH tissue with Affymetrix 10K SNP microarrays. Additionally, resequencing and fine mapping with SNP genotyping were completed for the GLI3 gene with comparisons between peripheral blood and HH tissue pairs. By analyzing chromosomal copy-number data for paired samples on the Affymetrix 10K array, we identified a somatic chromosomal abnormality on chromosome 7p in one HH tissue sample. Resequencing of GLI3 did not identify causative germline mutations but did identify LOH within the GLI3 gene in the HH tissue samples of three patients. Further genotyping of 28 SNPs within and surrounding GLI3 identified five additional patients exhibiting LOH. Together, these data provide evidence that the development of chromosomal abnormalities within GLI3 is associated with the pathogenesis of HH lesions in sporadic, nonsyndromic patients with HH and intractable epilepsy. Chromosomal abnormalities including the GLI3 locus were seen in 8 of 55 (15%) of the resected HH tissue samples. These somatic mutations appear to be highly variable.

The Histopathology of Hypothalamic Hamartomas

Hypothalamic hamartomas (HHs) are rare developmental tumors that cause seizures or pituitary axis dysfunction, usually beginning in childhood. We analyzed HH tissue from 57 patients whose tumors were resected through recently developed transcallosal interforniceal and transventricular endoscopic surgical approaches. All cases were composed of abnormally distributed but cytologically normal neurons and glia, including fibrillary astrocytes and oligodendrocytes. Neuronal elements predominated in most cases, but a relative increase in astrocytic elements was seen with increasing age. All had various sized nodular foci of neurons as well as areas of diffusely distributed neurons with interspersed glial cells. Smaller neurons predominated, and most cases had only a few interspersed large ganglion cells. Immunohistochemistry demonstrated extensive production of synapse-associated proteins. Immunohistochemistry for phosphorylated and nonphosphorylated neurofilament and alpha-internexin demonstrated staining patterns consistent with mature neurons. In contrast to cortical dysplasia, atypical large ganglion-like balloon cells were almost never seen. In summary, although their number and distribution vary, mature smaller neurons were the most prominent and most consistent histologic feature of HH. Nodules of these small neurons were a universal feature of the microarchitecture of HH lesions associated with epilepsy. Characterization of these neurons may aid in understanding the mechanism of seizure development in HH.

Hedgehog signaling in skeletal development

Hedgehog signaling coordinates a variety of patterning processes during early embryonic development. Drosophila hedgehog and its vertebrate orthologs, Sonic hedgehog, Indian hedgehog, and Desert hedgehog, share a generally conserved signal transduction cascade. However, the particular mechanisms by which the lipid-modified molecules specify embryonic tissues differ substantially. Vertebrate skeletal patterning is one of the most intensively studied biological processes. During skeletogenesis, Sonic and Indian hedgehog provide positional information and initiate or maintain cellular differentiation programs regulating the formation of cartilage and bone. They either signal directly to adjacent cells or form tightly regulated gradients that act over long distances to pattern the axial and appendicular skeleton and regulate crucial steps during endochondral ossification. As a consequence, malfunction of the hedgehog signaling network can cause severe skeletal disorders and tumors.

What you can learn from one gene: GLI3

The study of patients with rare multiple congenital anomaly syndromes can provide illuminating insights into normal development and the pathogenesis of congenital anomalies. The GLI3 gene is a particularly good example as it illuminates the phenomena of pleiotropy, phenocopies, syndrome families, and evolutionary conservation of pathogenesis, and raises questions about how diagnoses are conceptualised. These topics are reviewed in turn, in the context of the clinical and biological data derived from patients with mutations in GLI3 and experimental work in model systems.

Psychiatric and neuropsychological characterization of Pallister-Hall syndrome

Pallister-Hall syndrome (PHS) is a rare, single-gene, malformation syndrome that includes central polydactyly, hypothalamic hamartoma, bifid epiglottis, endocrine dysfunction, and other anomalies. The syndrome has variable clinical manifestations and is inherited in an autosomal dominant pattern. We sought to determine whether psychiatric disorders and/or neuropsychological impairment were characteristic of PHS. We prospectively conducted systematic neuropsychiatric evaluations with 19 PHS subjects ranging in age from 7 to 75 years. The evaluation included detailed clinical interviews, clinician-rated and self-report instruments, and a battery of neuropsychological tests. Seven of 14 adult PHS subjects met diagnostic criteria for at least one DSM-IV Axis I disorder. Three additional subjects demonstrated developmental delays and/or neuropsychological deficits on formal neuropsychological testing. However, we found no characteristic psychiatric phenotype associated with PHS, and the frequency of each of the diagnoses observed in these subjects was not different from that expected in this size sample. The overall frequency of psychiatric findings among all patients with PHS cannot be compared to point prevalence estimates of psychiatric disease in the general population because of biased ascertainment. This limitation is inherent to the study of behavioral phenotypes in rare disorders. The general issue of psychiatric evaluation of rare genetic syndromes is discussed in light of this negative result.

The hypothalamic hamartoma: a model of subcortical epileptogenesis and encephalopathy

Although uncommon, the hypothalamic hamartoma (HH) is often associated with a devastating clinical syndrome, which may include refractory epilepsy, progressive cognitive decline, and deterioration in behavioral and psychiatric functioning. Contrary to conventional thinking which attributed seizure origin to cortical structures, the hamartoma itself has now been firmly established as the site of intrinsic epileptogenesis for the gelastic seizures (i.e., characterized by unusual mirth) peculiar to this disorder. It also appears that the HH contributes to a process of secondary epileptogenesis, with eventual cortical seizure onset of multiple types in some patients. Anticonvulsant medications are known to be poorly effective in this disorder. Treatment, including some innovative approaches to surgical resection, is now targeted directly at the HH itself, with impressive results. Younger patients, in particular, may avoid the deteriorating course described earlier. Access to tissue from larger numbers of patients at single or collaborating centers specializing in HH surgery will allow for research into the fundamental mechanisms producing this little understood disorder. Refractory epilepsy associated with HH is the premier human model for subcortical epilepsy and an excellent model for secondary epileptogenesis and epileptic encephalopathy.

Molecular and clinical analyses of Greig cephalopolysyndactyly and Pallister-Hall syndromes: robust phenotype prediction from the type and position of GLI3 mutations

Mutations in the GLI3 zinc-finger transcription factor gene cause Greig cephalopolysyndactyly syndrome (GCPS) and Pallister-Hall syndrome (PHS), which are variable but distinct clinical entities. We hypothesized that GLI3 mutations that predict a truncated functional repressor protein cause PHS and that functional haploinsufficiency of GLI3 causes GCPS. To test these hypotheses, we screened patients with PHS and GCPS for GLI3 mutations. The patient group consisted of 135 individuals: 89 patients with GCPS and 46 patients with PHS. We detected 47 pathological mutations (among 60 probands); when these were combined with previously published mutations, two genotype-phenotype correlations were evident. First, GCPS was caused by many types of alterations, including translocations, large deletions, exonic deletions and duplications, small in-frame deletions, and missense, frameshift/nonsense, and splicing mutations. In contrast, PHS was caused only by frameshift/nonsense and splicing mutations. Second, among the frameshift/nonsense mutations, there was a clear genotype-phenotype correlation. Mutations in the first third of the gene (from open reading frame [ORF] nucleotides [nt] 1-1997) caused GCPS, and mutations in the second third of the gene (from ORF nt 1998-3481) caused primarily PHS. Surprisingly, there were 12 mutations in patients with GCPS in the 3' third of the gene (after ORF nt 3481), and no patients with PHS had mutations in this region. These results demonstrate a robust correlation of genotype and phenotype for GLI3 mutations and strongly support the hypothesis that these two allelic disorders have distinct modes of pathogenesis.

Feingold syndrome: clinical review and genetic mapping

Feingold syndrome is characterized by autosomal dominant inheritance of microcephaly and limb malformations, notably hypoplastic thumbs, and clinodactyly of second and fifth fingers. Syndactyly frequently involves the second and third, as well as the fourth and fifth toes. Approximately one in three Feingold syndrome patients have esophageal or duodenal atresia or both. Anal atresia has been reported in a single case. At least 79 patients in 25 families have been reported. The syndrome has autosomal dominant inheritance with full penetrance, and variable expressivity. Vertebral anomalies, cardiac malformations, and deafness have been noted in a minority of patients. Here, we report a patient with hydronephrosis of one kidney and cystic dysplasia of the other, necessitating nephrectomy. The overall pattern of malformations in Feingold syndrome shows considerable overlap with the VATER/VACTERL association. The gene for Feingold syndrome maps to 2p23-p24, but remains to be identified. Comparison of the pattern of anomalies that occurs in the Feingold syndrome in humans and malformations that are present in mice with mutations of genes in the sonic hedgehog signaling pathway suggest, that the elusive Feingold syndrome gene may involve this signaling pathway as well.

Pallister-Hall syndrome with hypoparathyroidism

We report on a 5 2/12 year-old boy who presented with convulsions, precocious puberty due to a 1.9 x 1.9 x 1.6 hypothalamic hamartoma of the tuber cinereum, and some dysmorphic features including polysyndactyly of hands and feet, suggesting the diagnosis of Pallister-Hall syndrome. Hypocalcemia due to hypoparathyroidism was demonstrated, and this combination has not been reported previously. Therefore, we can add hypoparathyroidism as another feature of Pallister-Hall syndrome.

Hirschprung's disease and imperforate anus in Pallister-Hall syndrome: a new association

Hirschprung's disease and imperforate anus are described concurrently in a newborn with Pallister-Hall syndrome as well as the difficulties in making this diagnosis. Awareness of this new association should prompt the exclusion of Hirschprung's disease before repair of imperforate anus in infants with Pallister-Hall syndrome. The known genetic parallels between these conditions is discussed briefly in terms of etiology.

Hypothalamic hamartomas: seven cases and review of the literature

Hypothalamic hamartomas constitute rare developmental lesions associated with gelastic epilepsy and/or precocious puberty (PP). We elected to review cases encountered at our center (7 patients) and the existing literature (277 patients) to obtain a better understanding of the clinical aspects, pathogenesis, and treatment of this entity. Evidence suggests that gelastic seizures are due to intrinsic epileptogenicity. The cause of the subsequent development of other seizure types, cognitive decline, and diffuse spike-and-wave pattern remains unresolved and is addressed. Anticonvulsants often fail to control seizures and different surgical options are available. Available evidence suggests that a resection through a subtemporal approach is best for lesions that are pedunculated or with a significant prepontine component, while a transcallosal approach is more appropriate for sessile lesions with an intraventricular component. Gamma knife surgery may be especially useful for small sessile lesions, failed partial resections, or patients not appropriate or refusing open surgery.

The amino-terminal region of Gli3 antagonizes the Shh response and acts in dorsoventral fate specification in the developing spinal cord

A concentration gradient of Shh is thought to pattern the ventral neural tube, and these ventral cell types are absent in shh-/- mice. Based on in vitro and genetic studies, the zinc finger-containing transcription factors Gli 1, 2, and 3 are mediators of the Shh intracellular response. The floorplate and adjacent cell types are absent in gli1-/-;gli2-/- mice, but part of the Shh-/- phenotype in the neural tube is alleviated in the Shh-/-;gli3-/- double mutant. This is consistent with the predicted role of Gli3 as a repressor of the Shh response. Gli3 repressor activity is blocked by Shh. In order to test the role of the repressor form of Gli3 in the neural tube, a truncated version of Gli3 (Gli3R*) was designed to mimic a Pallister Hall allele. Gli3R* acts as a constitutive repressor independent of Shh signaling. Misexpression of Gli3R* in the chick neural tube caused a ventral expansion of class-I, dorsal progenitor proteins and a loss of class-II, ventral progenitor proteins consistent with expected activity as a repressor of the Shh response. Activation of the BMP response is sufficient to maintain gli3 expression in neural plate explants, which might be a mechanism by which BMPs antagonize the Shh response.

Pallister-Hall syndrome: clinical and MR features

A 4-month-old boy with polydactyly and bifid epiglottis was found to have a large sellar and suprasellar mass. When the diagnosis of Pallister-Hall syndrome was made, conservative management was elected. When the patient was 2 years old, the tumor had grown proportionally with the patient, and he was developing appropriately. Although rare, this entity is important to recognize not only for clinical diagnosis but also for appropriate management and genetic counseling.

Assignment of the locus for hydrolethalus syndrome to a highly restricted region on 11q23-25

Hydrolethalus syndrome is a recessively inherited lethal malformation syndrome characterized by hydrocephaly with absent midline structures of the brain, micrognathia, polydactyly, and several other abnormalities, mostly in the midline structures. Hydrolethalus syndrome was described in 1981 in Finland, where the incidence is 1:20,000. Only a few cases have been reported elsewhere, and the pathogenesis has remained unknown. Here we report the assignment of the hydrolethalus syndrome locus to chromosome 11q23-25 in Finnish families. The initial genome scan was performed using DNA samples from only 15 affected individuals. In the next step, the hydrolethalus syndrome locus was assigned to an 8.5-cM interval between markers D11S4144 and D11S1351 by linkage analysis in eight families. Finally, the critical locus could be restricted by linkage disequilibrium and haplotype analyses to a 0.5-1-cM region between markers D11S933 and D11S934. Genealogical studies performed in 40 families affected by hydrolethalus revealed no regional clustering, suggesting a relatively early introduction of the disease mutation into the Finnish population and the spreading of the mutation with the inhabitation of the late-settlement area.

Craniofacial developmental abnormalities

Major advances have been made in the elucidation of the molecular basis of a number of human dysmorphic syndromes involving abnormalities of craniofacial development. This will lead, in turn, to a greater understanding of the mechanisms that underlie normal craniofacial development.