Genital abnormalities in Pallister-Hall syndrome: Report of two patients and review of the literature

Pallister-Hall syndrome, GLI3, and kidney malformation

Pallister-Hall syndrome (PHS) is a rare autosomal dominant disease diagnosed by the presence of hypothalamic hamartoma, mesoaxial polydactyly and a truncating variant in the middle third of the GLI-Kruppel family member 3 (GLI3) gene. PHS may also include a wide range of clinical phenotypes affecting multiple organ systems including congenital anomalies of the kidney and urinary tract (CAKUT). The observed clinical phenotypes are consistent with the essential role of GLI3, a transcriptional effector in the hedgehog (Hh) signaling pathway, in organogenesis. However, the mechanisms by which truncation of GLI3 in PHS results in such a variety of clinical phenotypes with variable severity, even within the same organ, remain unclear. In this study we focus on presentation of CAKUT in PHS. A systematic analysis of reported PHS patients (n = 78) revealed a prevalence of 26.9% (21/78) of CAKUT. Hypoplasia (± dysplasia) and agenesis were the two main types of CAKUT; bilateral and unilateral CAKUT were reported with equal frequency. Examination of clinical phenotypes with CAKUT revealed a significant association between CAKUT and craniofacial defects, bifid epiglottis and a Disorder of Sex Development, specifically affecting external genitalia. Lastly, we determined that PHS patients with CAKUT predominately had substitution type variants (as opposed to deletion type variants in non-CAKUT PHS patients) in the middle third of the GLI3 gene. These results provide a foundation for future work aimed at uncovering the molecular mechanisms by which variant GLI3 result in the wide range and severity of clinical features observed in PHS.

Distinctive functioning of STARD1 in the fetal Leydig cells compared to adult Leydig and adrenal cells. Impact of Hedgehog signaling via the primary cilium

STARD1 stimulates cholesterol transfer to mitochondrial CYP11A1 for conversion to pregnenolone. A cholesterol-binding START domain is guided by an N-terminal domain in a cell selective manner. Fetal and adult Leydig cells (FLC, ALC) show distinct Stard1 regulation. sm- FISH microscopy, which resolves individual molecules of Stard1 mRNA, shows uniformly high basal expression in each FLC. In ALC, in vivo, and cultured MA-10 cells, basal Stard1 expression is minimal. PKA activates loci asynchronously, with delayed splicing/export of 3.5 kb mRNA to mitochondria. After 60 min, ALC transition to an integrated mRNA delivery to mitochondria that is seen in FLC. Sertoli cells cooperate in Stard1 stimulation in FLC by delivering DHH to the primary cilium. There PTCH, SMO and cholesterol cooperate to release GLI3 to activate the Stard1 locus, probably by directing histone changes. ALC lack cilia. PKA then primes locus activation. FLC and ALC share similar SIK/CRTC/CREB regulation characterized for adrenal cells.

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.

GLI3 resides at the intersection of hedgehog and androgen action to promote male sex differentiation

Urogenital tract abnormalities are among the most common congenital defects in humans. Male urogenital development requires Hedgehog-GLI signaling and testicular hormones, but how these pathways interact is unclear. We found that Gli3^XtJ mutant mice exhibit cryptorchidism and hypospadias due to local effects of GLI3 loss and systemic effects of testicular hormone deficiency. Fetal Leydig cells, the sole source of these hormones in developing testis, were reduced in numbers in Gli3^XtJ testes, and their functional identity diminished over time. Androgen supplementation partially rescued testicular descent but not hypospadias in Gli3^XtJ mutants, decoupling local effects of GLI3 loss from systemic effects of androgen insufficiency. Reintroduction of GLI3 activator (GLI3A) into Gli3^XtJ testes restored expression of Hedgehog pathway and steroidogenic genes. Together, our results show a novel function for the activated form of GLI3 that translates Hedgehog signals to reinforce fetal Leydig cell identity and stimulate timely INSL3 and testosterone synthesis in the developing testis. In turn, exquisite timing and concentrations of testosterone are required to work alongside local GLI3 activity to control development of a functionally integrated male urogenital tract.

Disorders in male sex differentiation (DSD) are among the most common defects in all live births, yet in many cases, pediatric patient families are reluctant to address the issue and endure lifelong consequences. Urogenital tract development, as in many organ systems, depends on exquisite timing among layers of a number of signaling pathways. Here, we show that interactions between the hedgehog and androgen signaling pathways are required for the development of internal and external male sex characteristics, but results for each tissue is distinct. This new knowledge will aid in discovering the means by which congenital malformations might occur, identify potential developmental targets that might be vulnerable to environmental exposures, and promote new ideas for how they might be prevented.

Lineage-specific roles of hedgehog-GLI signaling during mammalian kidney development

Aberrant hedgehog (Hh) signaling during embryogenesis results in various severe congenital abnormalities, including renal malformations. The molecular mechanisms that underlie congenital renal malformations remain poorly understood. Here, we review the current understanding of the lineage-specific roles of Hh signaling during renal morphogenesis and how aberrant Hh signaling during embryonic kidney development contributes to renal malformation.

Pituitary Transcription Factor Mutations Leading to Hypopituitarism

Congenital pituitary hormone deficiency is a disabling condition. It is part of a spectrum of disorders including craniofacial midline developmental defects ranging from holoprosencephaly through septo-optic dysplasia to combined and isolated pituitary hormone deficiency. The first genes discovered in the human disease were based on mouse models of dwarfism due to mutations in transcription factor genes. High-throughput DNA sequencing technologies enabled clinicians and researchers to find novel genetic causes of hypopituitarism for the more than three quarters of patients without a known genetic diagnosis to date. Transcription factor (TF) genes are at the forefront of the functional analysis of novel variants of unknown significance due to the relative ease in in vitro testing in a research lab. Genetic testing in hypopituitarism is of high importance to the individual and their family to predict phenotype composition, disease progression and to avoid life-threatening complications such as secondary adrenal insufficiency.This chapter aims to highlight our current understanding about (1) the contribution of TF genes to pituitary development (2) the diversity of inheritance and phenotype features in combined and select isolated pituitary hormone deficiency and (3) provide an initial assessment on how to approach variants of unknown significance in human hypopituitarism. Our better understanding on how transcription factor gene variants lead to hypopituitarism is a meaningful step to plan advanced therapies to specific genetic changes in the future.

Hedgehog signaling pathway: Epigenetic regulation and role in disease and cancer development

The evolutionarily conserved Hedgehog (Hh) signaling pathway have critical roles in development and homeostasis of tissues. Under physiological conditions, Hh is controlled at different levels via stem cell maintenance and tissue regeneration. Aberrant activation of this signaling pathway may occur in a wide range of human diseases including different types of cancer. In this review we present a concise overview on the key genes composing Hh signaling pathway and provide recent advances on the molecular mechanisms that regulate Hh signaling pathway from extracellular and receptors to the cytoplasmic and nuclear machinery with a highlight on the role of microRNAs. Furthermore, we focus on critical studies demonstrating dysregulation of the Hh pathway in human disease development, and potential therapeutic implications. Finally, we introduce recent therapeutic drugs acting as Shh signaling pathway inhibitors, including those in clinical trials and preclinical studies.

A novel missense variant in the GLI3 zinc finger domain in a family with digital anomalies

Mutations in GLI3, which encodes a transcription factor of the Hedgehog signaling pathway, cause several developmental anomalies linked to inappropriate tissue patterning. Here, we report a novel missense variant in the fifth zinc finger domain of GLI3 (c.1826G>A; p.(Cys609Tyr)) initially identified in a proband with preaxial polydactyly type IV, developmental delay, sensorineural hearing loss, skeletal, and genitourinary anomalies. Additional family members exhibited various digital anomalies such as preaxial polydactyly, syndactyly, and postaxial polydactyly either in isolation or combined. Functional studies of Cys609Tyr GLI3 in cultured cells showed abnormal GLI3 processing leading to decreased GLI3 repressor production, increased basal transcriptional activity, and submaximal GLI reporter activity with Hedgehog pathway activation, thus demonstrating an intriguing molecular mechanism for this GLI3-related phenotype. Given the complexity of GLI3 post-translational processing and opposing biological functions as a transcriptional activator and repressor, our findings highlight the importance of performing functional studies of presumed GLI3 variants. This family also demonstrates how GLI3 variants are variably expressed.

Genetics of Combined Pituitary Hormone Deficiency: Roadmap into the Genome Era

The genetic basis for combined pituitary hormone deficiency (CPHD) is complex, involving 30 genes in a variety of syndromic and nonsyndromic presentations. Molecular diagnosis of this disorder is valuable for predicting disease progression, avoiding unnecessary surgery, and family planning. We expect that the application of high throughput sequencing will uncover additional contributing genes and eventually become a valuable tool for molecular diagnosis. For example, in the last 3 years, six new genes have been implicated in CPHD using whole-exome sequencing. In this review, we present a historical perspective on gene discovery for CPHD and predict approaches that may facilitate future gene identification projects conducted by clinicians and basic scientists. Guidelines for systematic reporting of genetic variants and assigning causality are emerging. We apply these guidelines retrospectively to reports of the genetic basis of CPHD and summarize modes of inheritance and penetrance for each of the known genes. In recent years, there have been great improvements in databases of genetic information for diverse populations. Some issues remain that make molecular diagnosis challenging in some cases. These include the inherent genetic complexity of this disorder, technical challenges like uneven coverage, differing results from variant calling and interpretation pipelines, the number of tolerated genetic alterations, and imperfect methods for predicting pathogenicity. We discuss approaches for future research in the genetics of CPHD.

Urogenital development in Pallister-Hall syndrome is disrupted in a cell-lineage-specific manner by constitutive expression of GLI3 repressor

Pallister-Hall syndrome (PHS) is a rare disorder caused by mutations in GLI3 that produce a transcriptional repressor (GLI3R). Individuals with PHS present with a variably penetrant variety of urogenital system malformations, including renal aplasia or hypoplasia, hydroureter, hydronephrosis or a common urogenital sinus. The embryologic mechanisms controlled by GLI3R that result in these pathologic phenotypes are undefined. We demonstrate that germline expression of GLI3R causes renal hypoplasia, associated with decreased nephron number, and hydroureter and hydronephrosis, caused by blind-ending ureters. Mice with obligate GLI3R expression also displayed duplication of the ureters that was caused by aberrant common nephric duct patterning and ureteric stalk outgrowth. These developmental abnormalities are associated with suppressed Hedgehog signaling activity in the cloaca and adjacent vesicular mesenchyme. Mice with conditional expression of GLI3R were utilized to identify lineage-specific effects of GLI3R. In the ureteric bud, GLI3R expression decreased branching morphogenesis. In Six2-positive nephrogenic progenitors, GLI3R decreased progenitor cell proliferation reducing the number of nephrogenic precursor structures. Using mutant mice with Gli3R and Gli3 null alleles, we demonstrate that urogenital system patterning and development is controlled by the levels of GLI3R and not by an absence of full-length GLI3. We conclude that the urogenital system phenotypes observed in PHS are caused by GLI3R-dependent perturbations in nephric duct patterning, renal branching morphogenesis and nephrogenic progenitor self-renewal.

Sequencing of the DKK1 gene in patients with anorectal malformations and hypospadias

Anorectal malformations (ARM) are rare congenital malformations of the gastrointestinal tract. Approximately 60% of the patients have additional congenital malformations, such as hypospadias. A recently published article showed that deletion of one single gene, dickkopf WNT signaling pathway inhibitor-1 (Dkk1), resulted in an imperforate anus with rectourinary fistula and preputial hypospadias in mice. To determine whether DKK1 also plays a role in the etiology of ARM and hypospadias in humans, we sequenced the four exons of the DKK1 gene in 17 patients affected with both ARM and hypospadias. No new potential disease-causing variant was identified. However, we detected a known non-synonymous variant in one patient, which was predicted in silico to be damaging, and the corresponding unaffected amino acid is highly conserved.

CONCLUSION

In this human study, a potential interesting non-synonymous variant was found in the DKK1 gene. Whether this variant plays a contributory role in the genesis of ARM or hypospadias would require a much larger study.

Total colonic aganglionosis and imperforate anus in a severely affected infant with Pallister-Hall syndrome

Pallister-Hall syndrome is a complex malformation syndrome characterized by a wide range of anomalies including hypothalamic hamartoma, polydactyly, bifid epiglottis, and genitourinary abnormalities. It is usually caused by truncating frameshift/nonsense and splicing mutations in the middle third of GLI3. The clinical course ranges from mild to lethal in the neonatal period. We present the first patient with Pallister-Hall syndrome reported with total colonic aganglionosis, a rare form of Hirschsprung disease with poor long-term outcome. The patient also had an imperforate anus, which is the third individual with Pallister-Hall syndrome reported with both Hirschsprung disease and an imperforate anus. Molecular testing via amniocentesis showed an apparently de novo novel nonsense mutation c.2641 C>T (p.Gln881*). His overall medical course was difficult and was complicated by respiratory failure and pan-hypopituitarism. Invasive care was ultimately withdrawn, and the patient expired at three months of age. This patient's phenotype was complex with unusual gastrointestinal features ultimately leading to a unfavorable prognosis and outcome, highlighting the range of clinical severity in patients with Pallister-Hall syndrome.

Associations of anorectal malformations and related syndromes

Anorectal malformations (ARMs) represent a complex group of congenital anomalies resulting from abnormal development of the hindgut, allantois and Mullerian duct resulting in complete or partial urorectal septal malformations. There is a wide variety of phenotypic expression, ranging from mild anorectal to very complex severe ARM with >75 % having other associated malformations. 50 % of cases are syndromic although many may have other associated anomalies. This suggests a genetic link but the genetics of ARM are highly complex with a number of candidate genes being identified. Many can be classified as "field defects" as a result of a complex set of genetic interactions. Patients with associated malformations can be classified into those with multiple congenital anomalies (non-syndromic), those with chromosomal abnormalities and those with non-chromosomal syndromic associations, also, those with non-chromosomal syndromes and the influence of environmental factors (e.g. drugs in pregnancy). Although much is not known about the aetiology of ARM, the weight of evidence points to genetic factors as major causes for the condition. In this review, we look at the chromosomal and genetic associations and their underlying signalling pathways, to obtain a better understanding of the pathogenetic mechanisms involved in developing ARM. The spectrum of ARM phenotypic expression probably results from involvement and crosstalk between a number of critical signalling systems involved in development of this region. As a result, it may be expressed as a "field developmental defect" with many associated abnormalities. The role of environmental factors in the development of ARM is probably less.

Lower urinary tract development and disease

Congenital anomalies of the lower urinary tract (CALUT) are a family of birth defects of the ureter, the bladder, and the urethra. CALUT includes ureteral anomaliesc such as congenital abnormalities of the ureteropelvic junction (UPJ) and ureterovesical junction (UVJ), and birth defects of the bladder and the urethra such as bladder-exstrophy-epispadias complex (BEEC), prune belly syndrome (PBS), and posterior urethral valves (PUVs). CALUT is one of the most common birth defects and is often associated with antenatal hydronephrosis, vesicoureteral reflux (VUR), urinary tract obstruction, urinary tract infections (UTI), chronic kidney disease, and renal failure in children. Here, we discuss the current genetic and molecular knowledge about lower urinary tract development and genetic basis of CALUT in both human and mouse models. We provide an overview of the developmental processes leading to the formation of the ureter, the bladder, and the urethra, and different genes and signaling pathways controlling these developmental processes. Human genetic disorders that affect the ureter, the bladder and the urethra and associated gene mutations are also presented. As we are entering the postgenomic era of personalized medicine, information in this article may provide useful interpretation for the genetic and genomic test results collected from patients with lower urinary tract birth defects. With evidence-based interpretations, clinicians may provide more effective personalized therapies to patients and genetic counseling for their families.