Whole gene deletion of the hepatocyte nuclear factor-1beta gene in a patient with the prune-belly syndrome

The Landscape of HNF1B Deficiency: A Syndrome Not Yet Fully Explored

The hepatocyte nuclear factor 1β (HNF1B) gene is involved in the development of specialized epithelia of several organs during the early and late phases of embryogenesis, performing its function mainly by regulating the cell cycle and apoptosis pathways. The first pathogenic variant of HNF1B (namely, R177X) was reported in 1997 and is associated with the maturity-onset diabetes of the young. Since then, more than 230 different HNF1B variants have been reported, revealing a multifaceted syndrome with complex and heterogenous genetic, pathologic, and clinical profiles, mainly affecting the pediatric population. The pancreas and kidneys are the most frequently affected organs, resulting in diabetes, renal cysts, and a decrease in renal function, leading, in 2001, to the definition of HNF1B deficiency syndrome, including renal cysts and diabetes. However, several other organs and systems have since emerged as being affected by HNF1B defect, while diabetes and renal cysts are not always present. Especially, liver involvement has generally been overlooked but recently emerged as particularly relevant (mostly showing chronically elevated liver enzymes) and with a putative relation with tumor development, thus requiring a more granular analysis. Nowadays, HNF1B-associated disease has been recognized as a clinical entity with a broader and more variable multisystem phenotype, but the reasons for the phenotypic heterogeneity are still poorly understood. In this review, we aimed to describe the multifaceted nature of HNF1B deficiency in the pediatric and adult populations: we analyzed the genetic, phenotypic, and clinical features of this complex and misdiagnosed syndrome, covering the most frequent, unusual, and recently identified traits.

Phenotypic Variability of 17q12 Microdeletion Syndrome – Three Cases and Review of Literature

Chromosome 17q12 microdeletion syndrome is a contiguous gene deletion syndrome caused by an 1–2 Mb loss, characterized by multicystic dysplastic kidneys or other urinary system anomalies starting in utero, including autism or maturity-onset diabetes of the young in its postnatal phenotype. Here, we report on three cases (two prenatal and one postnatal) with distinct and novel clinical presentations as compared with a large number of reviewed patients, thus emphasizing the phenotypic variability of this syndrome and the consequent difficulties in genetic counselling. Prenatal hyperechogenic multicystic kidneys, as well as other urinary tract anomalies, should be considered a marker, therefore indicating the necessity of comprehensive genetic testing, and autism should also be acknowledged as a possible clinical presentation, postnatally.

Prune Belly Syndrome Associated with Interstitial 17q12 Microdeletion

We report a term male neonate presenting with a “prune belly,” bilateral hydronephrosis, hydroureter, posterior urethral obstruction, and bilateral undescended testes. Analysis with the whole genome SNP microarray revealed an interstitial deletion of about 1.49 megabase (MB) at chromosome 17q12. We present a rare association of prune belly syndrome with a chromosomal deletion in this same region.

Prune belly syndrome in Finland - A population-based study on current epidemiology and hospital admissions

BACKGROUND

Prune belly syndrome (PBS) is a multisystem disease characterized by absent or deficient abdominal musculature with accompanying lax skin, urinary tract abnormalities, and cryptorchidism. Previous studies have estimated a birth prevalence of 1 in 35,000-50,000 live births.

OBJECTIVE

We set out to clarify the epidemiology and early hospital admissions of PBS in Finland through a population-based register study. Further, possible maternal risk factors for PBS were analyzed in a case-control setting.

STUDY DESIGN

The Finnish Register of Congenital Malformations was linked to the Care Register for Health Care, a population-based hospital admission data for PBS patients. Additionally, five matched controls were identified in the Birth Register and maternal risk factors of PBS were studied utilizing data from the Drugs and Pregnancy database.

RESULTS

We identified 31 cases of PBS during 1993-2015, 15 of which were live born and 16 elective terminations. The total prevalence was 1 in 44,000 births. Three patients (20%) died during infancy. On average, PBS-patients had 3.2 admissions and 10.6 hospital days per year in Finland during the study period years 1998-2015, 35- and 27-fold compared to children in Finland in general. Multiple miscarriages were significantly associated to PBS in maternal risk factor analyses.

DISCUSSION

The burden of disease is significant in PBS, demonstrated as a high infant mortality rate (20%), multiple hospital admissions, and inpatient care in days. The available variables are limited as a register-based study.

CONCLUSION

We present data on contemporary epidemiology in a population-based study and show that the total prevalence of PBS is 1 in 44,000 in Finland. PBS entails a significant disease burden with admissions and hospital days over 35- and 27-fold compared to the general pediatric population, further aggravated by an infant mortality rate of 20%.

Prune-belly syndrome in Africa: An analysis and systematic review of cases, etiology, treatment, and outcomes

Background:

Prune-belly syndrome is a rare congenital disorder characterized by a spectrum of three anomalies: bilateral undescended testes, dilated urinary tract, and anterior abdominal muscle deficiency.

Objectives:

In developing countries, inadequate access to health care may affect treatment and outcomes of prune-belly syndrome. This study’s goal was to review the anatomical features, etiology, genetics, management, and outcomes of cases in Africa.

Methods:

PubMed was searched to identify case reports and case studies describing prune-belly syndrome in Africa. Data collected from each study included the number of cases, age at diagnosis, sex, description of the abdominal muscles, testes, and urinary tract, as well as associated anomalies, management, and long-term outcomes.

Results:

A total of 16 publications that reported 58 cases in African countries were included. The prevalence of female patients (15.5%) was higher than in developed countries (3%). The abdominal muscles were deficient in all cases, and bilateral cryptorchidism was present in nearly all males (96%). Distension of the bladder was common, with normal anatomy reported in only one case. Bilateral hydroureters and hydronephrosis also were present in the majority of cases. Only six cases (10.3%) had no associated anomalies, such as musculoskeletal or cardiovascular. Karyotyping was performed in only three cases (5.2%) because of limited hospital facilities. Six parents (10.3%) declined treatment for their children, 12 cases (20.7%) were managed conservatively, and 25 (43.1%) received surgical intervention. Patients’ mortality rate was higher than in developed countries.

Conclusion:

Diagnosis and treatment of prune-belly syndrome remains a challenge in Africa, in which multiple factors, such as access to health care and cultural beliefs, affect mortality rates and outcomes. Patient education and support groups may improve compliance with treatment.

Level of evidence:

Not applicable for this multicenter audit.

Case Report: Novel Copy Number Variant 16p11.2 Duplication Associated With Prune Belly Syndrome

Prune belly syndrome (PBS) is a rare congenital disease that predominantly occurs in males and is identified by its classic triad of abdominal wall musculature deficiencies, cryptorchidism, and urinary tract abnormalities. However, numerous anomalies involving the kidneys, heart, lungs, and muscles have also been reported. A multitude of chromosomal abnormalities have been implicated in its pathogenesis. PBS can occur in association with trisomy 18 and 21. Gene duplications and deletions have also been reported; however, a definite cause of PBS is still unknown. We report the first PBS patient with a copy number variant in 16p11.2.

Recognition of maturity-onset diabetes of the young in China

Aims/Introduction

Given that mutations related to maturity‐onset diabetes of the young (MODY) are rarely found in Chinese populations, we aim to characterize the mutation spectrum of MODY pedigrees.

Materials and Methods

Maturity‐onset diabetes of the young candidate gene‐ or exome‐targeted capture sequencing was carried out in 76 probands from unrelated families fulfilling the clinical diagnostic criteria for MODY. MAF <0.01 in the GnomAD or ExAC database was used to filter significant variants. Sanger sequencing was then carried out to validate findings. Function prediction by SIFT, PolyPhen‐2 and PROVEAN or CADD was carried out in missense mutations.

Results

A total of 32 mutations in six genes were identified in 31 families, accounting for 40.79% of the potential MODY families. The MODY subtype detection rate was 18.42% for GCK, 15.79% for HNF1A, 2.63% for HNF4A, and 1.32% for KLF11, PAX4 and NEUROG3. Seven nonsense/frameshift mutations and four missense mutations with damaging prediction were newly identified novel mutations. The clinical features of MODY2, MODY3/1 and MODYX are similar to previous reports. Clinical phenotype of NEUROG3 p.Arg55Glufs*23 is characterized by hyperglycemia and mild intermittent abdominal pain.

Conclusions

This study adds to the emerging pattern of MODY epidemiology that the proportion of MODY explained by known pathogenic genes is higher than that previously reported, and found NEUROG3 as a new causative gene for MODY.

Prune belly syndrome in surviving males can be caused by Hemizygous missense mutations in the X-linked Filamin A gene

Background

Prune belly syndrome (PBS) is a rare, multi-system congenital myopathy primarily affecting males that is poorly described genetically. Phenotypically, its morbidity spans from mild to lethal, however, all isolated PBS cases manifest three cardinal pathological features: 1) wrinkled flaccid ventral abdominal wall with skeletal muscle deficiency, 2) urinary tract dilation with poorly contractile smooth muscle, and 3) intra-abdominal undescended testes. Despite evidence for a genetic basis, previously reported PBS autosomal candidate genes only account for one consanguineous family and single cases.

Methods

We performed whole exome sequencing (WES) of two maternal adult half-brothers with syndromic PBS (PBS + Otopalatodigital spectrum disorder [OPDSD]) and two unrelated sporadic individuals with isolated PBS and further functionally validated the identified mutations.

Results

We identified three unreported hemizygous missense point mutations in the X-chromosome gene Filamin A (FLNA) (c.4952 C > T (p.A1448V), c.6727C > T (p.C2160R), c.5966 G > A (p.G2236E)) in two related cases and two unrelated sporadic individuals. Two of the three PBS mutations map to the highly regulatory, stretch-sensing Ig19–21 region of FLNA and enhance binding to intracellular tails of the transmembrane receptor β-integrin 1 (ITGβ1).

Conclusions

FLNA is a regulatory actin-crosslinking protein that functions in smooth muscle cells as a mechanosensing molecular scaffold, transmitting force signals from the actin-myosin motor units and cytoskeleton via binding partners to the extracellular matrix. This is the first evidence for an X-linked cause of PBS in multiple unrelated individuals and expands the phenotypic spectrum associated with FLNA in males surviving even into adulthood.

Clinical manifestations of a sporadic maturity-onset diabetes of the young (MODY) 5 with a whole deletion of HNF1B based on 17q12 microdeletion

We report a sporadic case of maturity-onset diabetes of the young type 5 (MODY5) with a whole-gene deletion of the hepatocyte nuclear factor-1beta (HNF1B) gene. A 44-year-old Japanese man who had been diagnosed with early-onset non-autoimmune diabetes mellitus at the age of 23 was examined. He showed multi-systemic symptoms, including a solitary congenital kidney, pancreatic hypoplasia, pancreatic exocrine dysfunction, elevation of the serum levels of liver enzymes, hypomagnesemia, and hyperuricemia. These clinical characteristics, in spite of the absence of a family history of diabetes, prompted us to make the diagnosis of maturity-onset diabetes of the young 5 (MODY 5). One allele deletion of the entire HNF1B gene revealed by multiplex ligation-dependent probe amplification (MLPA) led us to the diagnoses of 17q12 microdeletion syndrome even though there were negative chromosomal analyses with array comparative genomic hybridization (CGH). 17q12 microdeletion syndrome, which is not rare especially in sporadic cases since 17q12 is a typical hot spot for chromosomal deletion, could have complicated the clinical heterogeneity of MODY5.

Prune belly syndrome: current perspectives

Prune belly syndrome (PBS) is a rare but morbid congenital disease, classically defined by a triad of cardinal features that includes cryptorchidism, urinary tract dilation and laxity of the abdominal wall musculature. Children often require numerous surgical interventions including bilateral orchidopexy as well as individually tailored urinary tract and abdominal wall reconstruction. Along with the classic features, patients with PBS often experience gastrointestinal, orthopedic, and cardiopulmonary comorbidities.

New insights into the role of HNF-1β in kidney (patho)physiology

Hepatocyte nuclear factor-1β (HNF-1β) is an essential transcription factor that regulates the development and function of epithelia in the kidney, liver, pancreas, and genitourinary tract. Humans who carry HNF1B mutations develop heterogeneous renal abnormalities, including multicystic dysplastic kidneys, glomerulocystic kidney disease, renal agenesis, renal hypoplasia, and renal interstitial fibrosis. In the embryonic kidney, HNF-1β is required for ureteric bud branching, initiation of nephrogenesis, and nephron segmentation. Ablation of mouse Hnf1b in nephron progenitors causes defective tubulogenesis, whereas later inactivation in elongating tubules leads to cyst formation due to downregulation of cystic disease genes, including Umod, Pkhd1, and Pkd2. In the adult kidney, HNF-1β controls the expression of genes required for intrarenal metabolism and solute transport by tubular epithelial cells. Tubular abnormalities observed in HNF-1β nephropathy include hyperuricemia with or without gout, hypokalemia, hypomagnesemia, and polyuria. Recent studies have identified novel post-transcriptional and post-translational regulatory mechanisms that control HNF-1β expression and activity, including the miRNA cluster miR17 ∼ 92 and the interacting proteins PCBD1 and zyxin. Further understanding of the molecular mechanisms upstream and downstream of HNF-1β may lead to the development of new therapeutic approaches in cystic kidney disease and other HNF1B-related renal diseases.

Phenotypic severity scoring system and categorisation for prune belly syndrome: application to a pilot cohort of 50 living patients

OBJECTIVE

To design a novel system of scoring prune belly syndrome (PBS) phenotypic severity at any presenting age and apply it to a large pilot cohort.

PATIENTS AND METHODS

From 2000 to 2017, patients with PBS were recruited to our prospective PBS study and medical records were cross-sectionally analysed, generating individualised RUBACE scores. We designed the pragmatic RUBACE-scoring system based on six sub-scores (R: renal, U: ureter, B: bladder/outlet, A: abdominal wall, C: cryptorchidism, E: extra-genitourinary, generating the acronym RUBACE), yielding a potential summed score of 0-31. The 'E' score was used to segregate syndromic PBS and PBS-plus variants. The cohort was scored per classic Woodard criteria and RUBACE scores compared to Woodard category.

RESULTS

In all, 48 males and two females had a mean (range) RUBACE score of 13.8 (8-25) at a mean age of 7.3 years. Segregated by phenotypic categories, there were 39 isolated PBS (76%), six syndromic PBS (12%) and five PBS-plus (10%) cases. The mean RUBACE scores for Woodard categories 1, 2, and 3 were 20.5 (eight patients), 13.8 (25), and 10.6 (17), respectively (P < 0.001).

CONCLUSIONS

RUBACE is a practical, organ/system level, phenotyping tool designed to grade PBS severity and categorise patients into isolated PBS, syndromic PBS, and PBS-plus groups. This standardised system will facilitate genotype-phenotype correlations and future prospective multicentre studies assessing medical and surgical treatment outcomes.

Copy number variations in a population with prune belly syndrome

Prune Belly Syndrome (PBS) is a congenital multisystem myopathy with mild to lethal severity. While of uncertain etiology, 95% male predominance and familial occurrence suggest a genetic basis. As copy number variations (CNVs) can cause unexplained genetic disorders, we tested for novel CNVs in a large PBS population. We genotyped 21 unrelated PBS patients by high-resolution array comparative genomic hybridization (aCGH) and phenotyped using a novel PBS severity scoring system. Available parents were screened for detected CNV via quantitative PCR (qPCR). We additionally screened for recurrence of identified novel candidate CNVs on 106 PBS probands by qPCR. We identified 10 CNVs in 8 of 21 PBS patients tested (38%). Testing confirmed inheritance from an unaffected biological parent in six patients; parental samples were unavailable in two probands. One candidate CNV includes duplication of the X-chromosome AGTR2 gene, known to function in urinary tract development. Subsequent screening of the larger PBS cohort did not identify any recurrent CNVs. Presence of CNV did not correlate with PBS severity scoring. CNVs were uncommon in this large PBS population, but analysis of identified variants may inform disease pathogenesis and reveal targets for therapeutic intervention for this rare, severe disorder.

Rare copy number variants identified in prune belly syndrome

Prune belly syndrome (PBS), also known as Eagle-Barrett syndrome, is a rare congenital disorder characterized by absence or hypoplasia of the abdominal wall musculature, urinary tract anomalies, and cryptorchidism in males. The etiology of PBS is largely unresolved, but genetic factors are implicated given its recurrence in families. We examined cases of PBS to identify novel pathogenic copy number variants (CNVs). A total of 34 cases (30 males and 4 females) with PBS identified from all live births in New York State (1998-2005) were genotyped using Illumina HumanOmni2.5 microarrays. CNVs were prioritized if they were absent from in-house controls, encompassed ≥10 consecutive probes, were ≥20 Kb in size, had ≤20% overlap with common variants in population reference controls, and had ≤20% overlap with any variant previously detected in other birth defect phenotypes screened in our laboratory. We identified 17 candidate autosomal CNVs; 10 cases each had one CNV and four cases each had two CNVs. The CNVs included a 158 Kb duplication at 4q22 that overlaps the BMPR1B gene; duplications of different sizes carried by two cases in the intron of STIM1 gene; a 67 Kb duplication 202 Kb downstream of the NOG gene, and a 1.34 Mb deletion including the MYOCD gene. The identified rare CNVs spanned genes involved in mesodermal, muscle, and urinary tract development and differentiation, which might help in elucidating the genetic contribution to PBS. We did not have parental DNA and cannot identify whether these CNVs were de novo or inherited. Further research on these CNVs, particularly BMP signaling is warranted to elucidate the pathogenesis of PBS.

Copy-number variation analysis in familial nonsyndromic congenital anomalies of the kidney and urinary tract: Evidence for the causative role of a transposable element-associated genomic rearrangement

Most congenital anomalies of the kidney and urinary tract (CAKUT) are sporadic, but familial occurrence has been described, suggesting a genetic contribution. Copy-number variations (CNVs) were detected in patients with CAKUT to identify possible novel genomic regions associated with CAKUT. CNVs were investigated in 7 children with CAKUT from three unrelated families using array comparative genomic hybridization: female monozygotic twins with bilateral duplex collecting system/vesicoureteral reflux (VUR)/unilateral renal hypodyspasia (URHD); two male siblings with VUR/URHD; 3 male second cousins, one with bilateral VUR/URHD, one with bilateral VUR and one with ureterovesical junction obstruction (UVJO). Five patients had a normal constitution of CNVs, one had a duplication of 0.2 Mb on the 5q-arm (5q23.3), probably unrelated to CAKUT, and one with UVJO had a 1.4 Mb deletion on the 17q-arm (17q12) which includes a known CAKUT gene, HNF1B. The phenotype of HNF1B deletion was extended including renal magnesium wasting. A higher coverage in transposable elements (TEs) was found in the deleted region compared with the expected density in any random genomic region. Notably, the 5′ breakpoint was mapped within a solo long terminal repeat (LTR) sequence. Moreover, highly similar members of solo LTR and mammalian interspersed repetitive (MIR) elements, as well as nucleotide sequence microhomology were detected at the breakpoint regions. In conclusion, the deletion detected in one patient suggests this genomic imbalance as causative for UVJO. A not very well known phenotype of HNF1B deletion resulting in both low urinary tract malformations and renal wasting of magnesium was described. The high load in TEs of the deleted region, the presence of highly similar elements, and the microhomology found at breakpoint regions may have contributed to the generation of the deletion. CNV analysis could reveal novel causative genomic regions in patients with CAKUT, and further studies in larger cohorts are needed.

HPSE2 mutations in urofacial syndrome, non-neurogenic neurogenic bladder and lower urinary tract dysfunction

BACKGROUND

Urofacial syndrome (UFS) is characterised by congenital bladder dysfunction accompanied by a characteristic abnormal grimace upon smiling and crying. In recent years, biallelic mutations of HPSE2 and LRIG2 have been reported in UFS patients. Non-neurogenic neurogenic bladder (NNNB) has a bladder identical to UFS without typical facial features. The aim of this study was to analyse HPSE2 mutations in patients with UFS and NNNB or severe lower urinary tract dysfunction (LUTD) without abnormal facial expression.

METHODS

Patients with UFS, NNNB and severe LUTD were enrolled in the study. We examined a total of 35 patients from 33 families. There were seven UFS patients from five different families, 21 patients with NNNB and seven with LUTD. HPSE2 gene mutation analysis was performed using the polymerase chain reaction protocol followed by Sanger sequencing in these patients.

RESULTS

A twin pair with UFS was found to be homozygous for c.457C>T (p.Arg153*) mutation. No other pathogenetic variant was detected.

CONCLUSION

HPSE2 mutations were found in one UFS family but not detected in patients with NNNB and severe LUTD. Considering the increasingly recognised cases of NNNB that were diagnosed in early childhood period, genetic factors appear to be responsible. Thus, further genetic studies are needed to discover novel associated gene variants in these bladder anomalies.

Prune belly syndrome with overlapping presentation of partial urorectal septum malformation sequence in a female newborn with absent perineal openings

Prune belly syndrome (PBS) is a rare congenital anomaly characterized in males by a triad of anomalous genitourinary tract, deficient development of abdominal wall muscles, and bilateral cryptorchidism. Although similar anomalies have been reported in females, by definition they do not full fill the classical triad. Urorectal septum malformation sequence (URSM) is a lethal condition characterized by presence of ambiguous genitalia, absent perineal openings (urogenital and anal), and lumbosacral abnormalities. In this original case report, the authors discuss the presentation and management of what would be analogous to a Woodhouse category 1 PBS in a female newborn associated with an overlapping presentation of URSM.

Prune-belly syndrome: an autopsy case report

Prune-belly syndrome (PBS) is a rare congenital anomaly characterized by a spectrum of mild-to-severe presentations of urinary tract malformations, deficient abdominal wall musculature, and cryptorchidism in male newborns or genital abnormalities in the female newborns. Currently, antenatal diagnosis is feasible with ultrasound examination, and treatment is based on case report experience. More recently, intrauterine management has been undertaken with encouraging results. The authors report a case of PBS diagnosed at the seventeenth gestation week, when ultrasonographic examination revealed the presence of ascites, distended bladder, thickened bladder wall and posterior urethral valve. The fetus was submitted to an intrauterine intervention at the nineteenth gestational week. Delivery occurred at 34 weeks of gestation and the newborn examination was consistent with PBS. On the second day of life, the newborn was submitted to abdominoplasty, colostomy, and orchiopexy. However, the outcome was unfavorable with respiratory failure and death on the fifteenth day of life. The autopsy confirmed the diagnosis of PBS, but the immediate cause of death was attributed to aspiration pneumonia.

Genetics of human congenital urinary bladder disease

Lower urinary tract and/or kidney malformations are collectively the most common cause of end-stage renal disease in children, and they are also likely to account for a major subset of young adults requiring renal replacement therapy. Advances have been made regarding the discovery of the genetic causes of human kidney malformations. Indeed, testing for mutations of key nephrogenesis genes is now feasible for patients seen in nephrology clinics. Unfortunately, less is known about defined genetic bases of human lower urinary tract anomalies. The focus of this review is the genetic bases of congenital structural and functional disorders of the urinary bladder. Three are highlighted. First, prune belly syndrome, where mutations of CHRM3, encoding an acetylcholine receptor, HNF1B, encoding a transcription factor, and ACTA2, encoding a cytoskeletal protein, have been reported. Second, the urofacial syndrome, where mutations of LRIG2 and HPSE2, encoding proteins localised in nerves invading the fetal bladder, have been defined. Finally, we review emerging evidence that bladder exstrophy may have genetic bases, including variants in the TP63 promoter. These genetic discoveries provide a new perspective on a group of otherwise poorly understood diseases.

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.

Prune-belly syndrome: case series and review of the literature regarding early prenatal diagnosis, epidemiology, genetic factors, treatment, and prognosis

Prune-belly syndrome (PBS) is a rare congenital syndrome characterized by deficient abdominal muscles, urinary tract malformation, and in males, cryptorchidism and has an estimated incidence of 1 in 35,000 to 1 in 50,000 live births. The syndrome might be due to severe bladder outlet obstruction or to abdominal muscle deficiency secondary to a migrational defect of the lateral mesoblast between weeks 6 and 7 of pregnancy. The current review of the medical record reports a special focus on epidemiology, genetic factors, early prenatal diagnosis clusters, treatment, and prognosis of PBS.

Pregnancy outcome in a woman with prune belly syndrome

Prune belly syndrome is a rare congenital syndrome that primarily affects male fetuses. Affected men are universally infertile; however, there is a paucity of information published on the reproductive potential of affected women. Pregnancy outcomes in affected women have not been described in the literature. We describe the case of pregnancy in an affected woman. Her pregnancy progressed without complication. Her fetus had no stigmata of the syndrome. Her labour and delivery were, however, complicated by a prolonged second stage of labour and need for vacuum-assisted vaginal delivery.

Prune belly syndrome

The majority of paediatric surgeons will encounter a patient with prune belly syndrome (PBS) only a few times in their clinical practice. There have been many opposing views in the literature regarding the pathogenesis and management of this complex condition. A detailed review was conducted using PubMed to identify key publications involving PBS. This article discusses the evolution of our understanding of the pathogenesis and diagnosis of PBS, including its typical characteristics. We describe the management options available for bilateral intra-abdominal testes, the deficient abdominal wall, the dilated urinary system and examine the evidence base used to support the current approaches employed.

Genetic basis of prune belly syndrome: screening for HNF1β gene

PURPOSE

Although the cause of prune belly syndrome is unknown, familial evidence suggests a genetic component. Recently 2 nonfamilial cases of prune belly syndrome with chromosome 17q12 deletions encompassing the HNF1β gene have made this a candidate gene for prune belly syndrome. To date, there has been no large-scale screening of patients with prune belly syndrome for HNF1β mutations. We assessed the role of HNF1β in prune belly syndrome by screening for genomic mutations with functional characterization of any detected mutations.

MATERIALS AND METHODS

We studied patients with prune belly syndrome who were prospectively enrolled in our Pediatric Genitourinary DNA Repository since 2001. DNA from patient samples was amplified by polymerase chain reaction, sequenced for coding and splice regions of the HNF1β gene, and compared to control databases. We performed functional assay testing of the ability of mutant HNF1β to activate a luciferase construct with an HNF1β DNA binding site.

RESULTS

From 32 prune belly syndrome probands (30 males, 2 females) HNF1β sequencing detected a missense mutation (V61G) in 1 child with prune belly syndrome. Absent in control databases, V61G was previously reported in 2 patients without prune belly syndrome who had congenital genitourinary anomalies. Functional testing showed similar luciferase activity compared to wild-type HNF1β, suggesting the V61G substitution does not disturb HNF1β function.

CONCLUSIONS

One genomic HNF1β mutation was detected in 3% of patients with prune belly syndrome but found to be functionally normal. Thus, functionally significant HNF1β mutations are uncommon in prune belly syndrome, despite case reports of HNF1β deletions. Further genetic study is necessary, as identification of the genetic basis of prune belly syndrome may ultimately lead to prevention and improved treatments for this rare but severe syndrome.

Muscarinic Acetylcholine Receptor M3 Mutation Causes Urinary Bladder Disease and a Prune-Belly-like Syndrome

Urinary bladder malformations associated with bladder outlet obstruction are a frequent cause of progressive renal failure in children. We here describe a muscarinic acetylcholine receptor M3 (CHRM3) (1q41-q44) homozygous frameshift mutation in familial congenital bladder malformation associated with a prune-belly-like syndrome, defining an isolated gene defect underlying this sometimes devastating disease. CHRM3 encodes the M3 muscarinic acetylcholine receptor, which we show is present in developing renal epithelia and bladder muscle. These observations may imply that M3 has a role beyond its known contribution to detrusor contractions. This Mendelian disease caused by a muscarinic acetylcholine receptor mutation strikingly phenocopies Chrm3 null mutant mice.

DNA hypomethylation, transient neonatal diabetes, and prune belly sequence in one of two identical twins

One known genetic mechanism for transient neonatal diabetes is loss of methylation at 6q24. The etiology of prune belly sequence is unknown but a genetic defect, affecting the mesoderm from which the triad abdominal muscle hypoplasia, urinary tract abnormalities, and cryptorchidism develop, has been suggested. We investigated a family, including one twin, with transient neonatal diabetes and prune belly sequence. Autoantibody tests excluded type 1 diabetes. Microsatellite marker analysis confirmed the twins being monozygotic. We identified no mutations in ZFP57, KCNJ11, ABCC8, GCK, HNF1A, HNF1B, HNF3B, IPF1, PAX4, or ZIC3. The proband had loss of methylation at the 6q24 locus TNDM and also at the loci IGF2R, DIRAS3, and PEG1, while the other family members, including the healthy monozygotic twin, had normal findings. The loss of methylation on chromosome 6q24 and elsewhere may indicate a generalized maternal hypomethylation syndrome, which accounts for both transient neonatal diabetes and prune belly sequence.

HNF1B mutations associate with hypomagnesemia and renal magnesium wasting

Mutations in hepatocyte nuclear factor 1B (HNF1B), which is a transcription factor expressed in tissues including renal epithelia, associate with abnormal renal development. While studying renal phenotypes of children with HNF1B mutations, we identified a teenager who presented with tetany and hypomagnesemia. We retrospectively reviewed radiographic and laboratory data for all patients from a single center who had been screened for an HNF1B mutation. We found heterozygous mutations in 21 (23%) of 91 cases of renal malformation. All mutation carriers had abnormal fetal renal ultrasonography. Plasma magnesium levels were available for 66 patients with chronic kidney disease (stages 1 to 3). Striking, 44% (eight of 18) of mutation carriers had hypomagnesemia (<1.58 mg/dl) compared with 2% (one of 48) of those without mutations (P < 0.0001). The median plasma magnesium was significantly lower among mutation carriers than those without mutations (1.68 versus 2.02 mg/dl; P < 0.0001). Because hypermagnesuria and hypocalciuria accompanied the hypomagnesemia, we analyzed genes associated with hypermagnesuria and detected highly conserved HNF1 recognition sites in FXYD2, a gene that can cause autosomal dominant hypomagnesemia and hypocalciuria when mutated. Using a luciferase reporter assay, we demonstrated HNF1B-mediated transactivation of FXYD2. These results extend the phenotype of HNF1B mutations to include hypomagnesemia. HNF1B regulates transcription of FXYD2, which participates in the tubular handling of Mg(2+), thus describing a role for HNF1B not only in nephrogenesis but also in the maintenance of tubular function.