Expression of Nek1 during kidney development and cyst formation in multiple nephron segments in the Nek1-deficient kat2J mouse model of polycystic kidney disease

BACKGROUND

Neks, mammalian orthologs of the fungal protein kinase never-in-mitosis A, have been implicated in the pathogenesis of polycystic kidney disease. Among them, Nek1 is the primary protein inactivated in kat2J mouse models of PKD.

RESULT

We report the expression pattern of Nek1 and characterize the renal cysts that develop in kat2J mice. Nek1 is detectable in all murine tissues but its expression in wild type and kat2J heterozygous kidneys decrease as the kidneys mature, especially in tubular epithelial cells. In the embryonic kidney, Nek1 expression is most prominent in cells that will become podocytes and proximal tubules. Kidney development in kat2J homozygous mice is aberrant early, before the appearance of gross cysts: developing cortical zones are thin, populated by immature glomeruli, and characterized by excessive apoptosis of several cell types. Cysts in kat2J homozygous mice form postnatally in Bowman's space as well as different tubular subtypes. Late in life, kat2J heterozygous mice form renal cysts and the cells lining these cysts lack staining for Nek1. The primary cilia of cells lining cysts in kat2J homozygous mice are morphologically diverse: in some cells they are unusually long and in others there are multiple cilia of varying lengths.

CONCLUSION

Our studies indicate that Nek1 deficiency leads to disordered kidney maturation, and cysts throughout the nephron.

Ex vivo modeling of chemical synergy in prenatal kidney cystogenesis

Cyclic adenosine monophosphate (cAMP) drives genetic polycystic kidney disease (PKD) cystogenesis. Yet within certain PKD families, striking differences in disease severity exist between affected individuals, and genomic and/or environmental modifying factors have been evoked to explain these observations. We hypothesized that PKD cystogenesis is accentuated by an aberrant fetal milieu, specifically by glucocorticoids. The extent and nature of cystogenesis was assessed in explanted wild-type mouse embryonic metanephroi, using 8-Br-cAMP as a chemical to mimic genetic PKD and the glucocorticoid dexamethasone as the environmental modulator. Cysts and glomeruli were quantified by an observer blinded to culture conditions, and tubules were phenotyped using specific markers. Dexamethasone or 8-Br-cAMP applied on their own produced cysts predominantly arising in proximal tubules and descending limbs of loops of Henle. When applied together, however, dexamethasone over a wide concentration range synergized with 8-Br-cAMP to generate a more severe, glomerulocystic, phenotype; we note that prominent glomerular cysts have been reported in autosomal dominant PKD fetal kidneys. Our data support the idea that an adverse antenatal environment exacerbates renal cystogenesis.

Distinct roles and regulations for HoxD genes in metanephric kidney development

Hox genes encode homeodomain-containing proteins that control embryonic development in multiple contexts. Up to 30 Hox genes, distributed among all four clusters, are expressed during mammalian kidney morphogenesis, but functional redundancy between them has made a detailed functional account difficult to achieve. We have investigated the role of the HoxD cluster through comparative molecular embryological analysis of a set of mouse strains carrying targeted genomic rearrangements such as deletions, duplications, and inversions. This analysis allowed us to uncover and genetically dissect the complex role of the HoxD cluster. Regulation of metanephric mesenchyme-ureteric bud interactions and maintenance of structural integrity of tubular epithelia are differentially controlled by some Hoxd genes during renal development, consistent with their specific expression profiles. We also provide evidence for a kidney-specific form of colinearity that underlies the differential expression of two distinct sets of genes located on both sides and overlapping at the Hoxd9 locus. These insights further our knowledge of the genetic control of kidney morphogenesis and may contribute to understanding certain congenital kidney malformations, including polycystic kidney disease and renal hypoplasia.

Hox genes encode proteins that control embryonic development along the head-to-tail axis and in multiple organs. Here, we show that several members of this gene family are necessary for the normal development of the mammalian kidneys. These genes are clustered in one site on the chromosome and their respective positions within the group determine which component of the kidneys they will contribute to. Using a large collection of engineered mutations in this system, we show that these genes are required both for the growth of the kidneys and for their proper organization, such that mutations in some genes reduce the size of the organs, whereas mutations in others induce polycystic kidneys. Our set of genetic rearrangements also allowed us to localize the position of regulatory sequences, which control the expression of these genes during kidney development.

Are therapeutic stem cells justified in bilateral multicystic kidney disease? A review of literature with insights into the embryology

Aim was to describe the challenges faced in the management of bilateral multicystic kidney disease (MCKD). A case of antenatally detected bilateral polycystic disease was referred at 28 weeks of gestation. The patient was advised to continue pregnancy till term and be in regular follow-up. Postnatally, the male baby passed urine in normal stream and was diagnosed as bilateral multicystic kidney disease on ultrasonography. He developed symptoms of renal failure. The baby was operated with right pyeloplasty and left pyelostomy, as the left ureter was atretic. The histopathology was consistent with bilateral multicystic kidney disease. Postoperatively, the baby was stable with intermittent episodes of metabolic acidosis that were managed medically and with peritoneal dialysis. Autologous stem cells were injected at the age of 1 year into the aorta at the level of the renal arteries clamping the aorta below. Repeat biopsy at time of stem cell injection showed 5/10 glomeruli showing global sclerosis on right side and 5/15 glomeruli showing global sclerosis on left side. The only improvement seen was in decreased doses of medicines to keep the child metabolically stable. The baby kept struggling but succumbed at the age of 17 months and 15 days. Post mortem bilateral renal biopsies demonstrated presence of primitive renal tubules and blastemal cells that were not demonstrated earlier. Survival for few months in bilateral multicystic kidney disease is thus possible with adequate treatment, the novel use of stem cells in these cases may prove beneficial in future though it is too early to comment further.

Differential diagnosis of fetal hyperechogenic cystic kidneys unrelated to renal tract anomalies: A multicenter study

OBJECTIVES

To identify important factors in the differential diagnosis of renal cysts associated with hyperechogenic kidneys.

METHODS

This was a retrospective multicenter study. We identified 93 fetuses presenting between 1990 and 2002 with hyperechogenic kidneys and which had a diagnosis of nephropathy confirmed later. We analyzed retrospectively the prenatal ultrasound findings of those fetuses which were found sonographically to have renal cysts.

RESULTS

Of the 93 fetuses presenting with hyperechogenic kidneys and with a later diagnosis of nephropathy, there were 28 with autosomal dominant polycystic kidney disease (ADPKD), 31 with autosomal recessive polycystic kidney disease (ARPKD), 11 with Bardet-Biedl syndrome, nine with Meckel-Gruber syndrome, six with Ivemark II syndrome, one with Jarcho-Levin syndrome, one with Beemer syndrome and one with Meckel-like syndrome. One third of the fetuses (30/93) had renal cysts. Cystic characteristics (size, location, number) were not very useful for diagnosis; more useful was diagnosis of an associated malformation. Three (11%) of the fetuses with ADPKD had cysts, as did nine (29%) of those with ARPKD, three (27%) of those with Bardet-Biedl syndrome, all (100%) of those with Meckel-Gruber syndrome, three (50%) of those with Ivemark II syndrome, and each of the three cases with other syndromes (Jarcho-Levin, Beemer and Meckel-like syndromes). None of the cases with trisomy 13 had cysts. There were no associated malformations in the 12 cases with renal cysts and polycystic kidney disease; the other 18 cases with renal cysts were associated with malformations that were often specific, such as polydactyly in Bardet-Biedl and Beemer syndromes, occipital defect and Dandy-Walker malformation in Meckel-Gruber or Meckel-Gruber-like syndromes, and thoracic and/or vertebral abnormalities in Jarcho-Levin and Beemer syndromes.

CONCLUSION

Renal cysts associated with hyperechogenic kidneys are not rare. The clue to diagnosis is the demonstration of an associated malformation. If no malformation is found, the main diagnosis remains polycystic kidney disease, i.e. ARPKD or ADPKD.

Early embryonic renal tubules of wild-type and polycystic kidney disease kidneys respond to cAMP stimulation with cystic fibrosis transmembrane conductance regulator/Na(+),K(+),2Cl(-) Co-transporter-dependent cystic dilation

Metanephric organ culture has been used to determine whether embryonic kidney tubules can be stimulated by cAMP to form cysts. Under basal culture conditions, wild-type kidneys from embryonic day 13.5 to 15.5 mice grow in size and continue ureteric bud branching and tubule formation over a 4- to 5-d period. Treatment of these kidneys with 8-Br-cAMP or the cAMP agonist forskolin induced the formation of dilated tubules within 1 h, which enlarged over several days and resulted in dramatically expanded cyst-like structures of proximal tubule and collecting duct origin. Tubule dilation was reversible upon withdrawal of 8-Br-cAMP and was inhibited by the cAMP-dependent protein kinase inhibitor H89 and the cystic fibrosis transmembrane conductance regulator (CFTR) inhibitor CFTR(inh)172. For further testing of the role of CFTR, metanephric cultures were prepared from mice with a targeted mutation of the Cftr gene. In contrast to kidneys from wild-type mice, those from Cftr -/- mice showed no evidence of tubular dilation in response to 8-Br-cAMP, indicating that CFTR Cl(-) channels are functional in embryonic kidneys and are required for cAMP-driven tubule expansion. A requirement for transepithelial Cl(-) transport was demonstrated by inhibiting the basolateral Na(+),K(+),2Cl(-) co-transporter with bumetanide, which effectively blocked all cAMP-stimulated tubular dilation. For determination of whether cystic dilation occurs to a greater extent in PKD kidneys in response to cAMP, Pkd1(m1Bei) -/- embryonic kidneys were treated with 8-Br-cAMP and were found to form rapidly CFTR- and Na(+),K(+),2Cl(-) co-transporter-dependent cysts that were three- to six-fold larger than those of wild-type kidneys. These results suggest that cAMP can stimulate fluid secretion early in renal tubule development during the time when renal cysts first appear in PKD kidneys and that PKD-deficient renal tubules are predisposed to abnormally increased cyst expansion in response to elevated levels of cAMP.

Fetal hyperechogenic kidney with normal amniotic fluid volume: a diagnostic dilemma

OBJECTIVE

To determine the prognostic value of sonographically detected fetal hyperechogenic kidneys with normal amniotic fluid volume.

METHODS

Seven cases of hyperechogenic fetal kidneys were identified by sonography over a 7-year period (1996--2002). Increased renal echogenicity was diagnosed when the renal parenchyma was of greater echogenicity than adjacent liver tissue. Amniotic fluid volume was measured by the semiquantitative sonographic technique known as the amniotic fluid index (AFI).

RESULTS

Three of the live-born infants had autosomal dominant polycystic kidney disease and one had autosomal recessive polycystic kidney. In the remainder, autopsy study revealed multifocal renal dysplasia in two cases and normal kidneys in one.

CONCLUSIONS

Increased renal echogenicity with normal amniotic fluid volume in a fetus without other anomalies is a difficult diagnostic dilemma. Although it is usually indicative of renal parenchymal disease with possible renal failure after birth or in early childhood, in some cases, it represents a normal variant. .

Kidney development and disease in the zebrafish

Unraveling the molecular pathogenesis of human disease presents many experimental challenges, not the least of which is that experiments on humans are generally frowned upon. Model organisms, including the zebrafish, allow for experimental analysis of gene function and the detailed characterization of disease processes. Zebrafish have matured as a vertebrate model organism now that genetic tools for targeted "knockdowns" and unbiased mutagenesis approaches are in hand. The fish larval pronephros is a relevant kidney in which to pursue many aspects of human kidney development and disease. This short review outlines recent progress in applying the zebrafish pronephros to issues of human health and development.

Prenatal diagnosis of the Meckel-Gruber syndrome from 11th to 20th gestational week

INTRODUCTION

The Meckel-Gruber syndrome (MKS) is a rare autosomal recessive disorder that is characterized by typical sonographical findings: occipital encephalocele, postaxial polydactyly and cystic enlargement of the kidneys. Its recurrence risk of 25 % demands an exact diagnosis.

METHOD

Retrospective analysis of the sonographic characteristics in relation to the gestational age in eight cases with the pathologic diagnosis of MKS.

RESULTS

The sonographic characteristics depend on the gestational age. The classic trias was solely seen in the case diagnosed before 14 (th) week of gestation. In the other seven cases, diagnosed between the 17 (th) and 20 (th) week of gestational age, only two of three characteristic signs of MKS could be visualised by US. Polydactyly was missed by ultrasound in all seven cases due to the marked oligohydramnion.

CONCLUSION

The Meckel-Gruber syndrome can be confidently detected and diagnosed by sonography at the 11th to 14th gestational week. Later in the pregnancy, severe oligohydramnion makes it more difficult to establish the diagnosis by US alone. In these cases a meticulous autopsy is necessary to establish the diagnosis of MKS.

A genetic screen in zebrafish identifies cilia genes as a principal cause of cystic kidney

Polycystic kidney disease (PKD) is a common human genetic illness. It is characterized by the formation of multiple kidney cysts that are thought to result from over-proliferation of epithelial cells. Zebrafish larvae can also develop kidney cysts. In an insertional mutagenesis screen in zebrafish, we identified 12 genes that can cause cysts in the glomerular-tubular region when mutated and we cloned 10 of these genes. Two of these genes, vhnf1 (tcf2) and pkd2, are already associated with human cystic kidney diseases. Recently, defects in primary cilia have been linked to PKD. Strikingly, three out of the 10 genes cloned in this screen are homologues of Chlamydomonas genes that encode components of intraflagellar transport (IFT) particles involved in cilia formation. Mutation in a fourth blocks ciliary assembly by an unknown mechanism. These results provide compelling support for the connection between cilia and cystogenesis. Our results also suggest that lesions in genes involved in cilia formation and function are the predominant cause of cystic kidney disease, and that the genes identified here are excellent candidates for novel human PKD genes.

Three-dimensional imaging of embryonic mouse kidney by two-photon microscopy

Developing mammalian embryonic kidney becomes progressively more elaborate as the ureteric bud branches into undifferentiated mesenchyme. Morphological perturbations of nephrogenesis, such as those seen in inherited renal diseases or induced in transgenic animals, require careful and often tedious documentation by multiple methodologies. We have applied a relatively quick and simple approach combining two-photon microscopy and advanced three-dimensional (3-D) imaging techniques to visualize and evaluate these complex events. As compared with laser confocal microscopy, two-photon microscopy offers superior optical sectioning deep into biological tissues, permitting analysis of large, heterogeneous, 3-D structures such as developing mouse kidney. Embryonic and newborn mouse kidneys were fluorescently labeled with lectins, phalloidin, or antibody. Three-dimensional image volumes were then collected. The resulting volume data sets were processed using a novel 3-D visualization technique. Reconstructed image volumes demonstrate the dichotomous branching of ureteric bud as it progresses from a simple, symmetrical structure into an elaborate, asymmetrical collecting system of multiple branches. Detailed morphology of in situ cysts was elucidated in a transgene-induced mouse model of polycystic kidney disease. We expect this integration of two-photon microscopy with advanced 3-D image analysis will provide a powerful tool for illuminating a variety of complex developmental processes in multiple dimensions.

Mosaic partial trisomy of chromosome 5 (q33-q ter) associated with fetal polycystic kidneys

A case of de novo mosaic partial trisomy of chromosome 5 (q33-q ter) in a stillborn male fetus with bilateral polycystic kidneys, and atrial septal defect, is reported. Fetal cord blood sampling was carried out at 25 weeks of gestation because of bilateral polycystic kidneys with severe oligohydramnios observed on ultrasound examination of the fetus. The family history was notable for the presence of similar phenotypic abnormality in the mother and sibling. However, no chromosomal abnormality was detected in other family members. Significance of this rare chromosomal abnormality and its association with congenital malformations in the fetus and in the family is being discussed.

Abnormal nephron development associated with a frameshift mutation in the transcription factor hepatocyte nuclear factor-1 beta

BACKGROUND

The transcription factor hepatocyte nuclear factor (HNF)-1 beta functions as a homodimer or as a heterodimer with the structurally related protein HNF-1 alpha. Both are expressed sequentially in rat kidney development, with HNF-1 beta being detected from the earliest inductory phases. HNF-1 beta gene mutations are associated with a unique disorder characterized by maturity-onset diabetes of the young (MODY) and early-onset and progressive nondiabetic renal dysfunction, which may lead to chronic renal failure.

METHODS

The HNF-1 beta gene was screened for mutations in six subjects with early-onset diabetes and a history of renal dysfunction in the subjects or their families.

RESULTS

A novel frameshift mutation in exon 4 of the HNF-1 beta gene and a deletion of CCTCT at codons 328 to 329 were detected in one subject. She was diagnosed as diabetic at the age of 21 in her second pregnancy. Glucose tolerance rapidly deteriorated over 18 months as a result of beta-cell dysfunction. The HNF-1 beta mutation arose de novo on a paternal chromosome and cosegregated with renal abnormalities in her family. The proband had bilateral small cysts in normal-sized kidneys and a reduced creatinine clearance of 66 mL/min (NR 80-120). Her first pregnancy was terminated at 17 weeks following an ultrasound diagnosis of bilateral, nonfunctioning cystic kidneys. Her first-born child had a small multicystic, dysplastic right kidney and a dysplastic left kidney with a reduced creatinine clearance (40 mL/min per 1.73 m2). Histologic examination of the large (5.8 vs. 1.4 g), polycystic fetal kidneys showed no normal nephrogenesis.

CONCLUSIONS

These studies indicate that HNF-1 beta plays a central role in normal kidney development and pancreatic beta-cell function, and suggest that one mechanism by which HNF-1 beta gene mutations may cause renal dysfunction are by their effects on nephron development.

The pathogenesis of dysplastic kidney in a urinary tract obstruction in the female fetal lamb

BACKGROUND/PURPOSE

The type of renal dysplasia resulting from obstructive uropathy depends on the completeness of the obstruction and its timing with respect to the stage of glomerulogenesis at the time of the obstruction. The authors created a successful obstructive uropathy model in the female fetal lamb to demonstrate the differing pathogenesis of renal dysplasia.

METHODS

Female fetal lambs at 60 and 90 days' gestation had their urethra and urachus ligated transabdominally and were delivered by cesarean section at 145 days (full term). Kidney length and cortical thickness were measured, and samples were examined histologically. In the lambs operated on at 90 days, the urine was collected at delivery and Na and CI were measured and compared with the results obtained from normal full-term lambs.

RESULTS

Seven of 10 female lambs had hydronephrosis or dysplastic kidneys. The cortext to kidney length ratio was 10+/-3% in the 90-days hydronephrotic group versus 29+/-6% in the controls (P<.001). Morphologically, the 90-day model had dilatation of the collecting tubules with normal glomerular numbers. The 60-day model had tubular cysts with fibromuscular cuffing and reduced glomerular numbers. The fetal urine Na was 47+/-3.3 mmol/L in controls versus 78+/-24 mmol/L in the hydropnephrotic lambs (P<.05). The urine CI in these lambs was 38+/-8.6 mmol/L in controls versus 55+/-14.5 mmol/L in the hydronephrotic lambs (P<.05).

CONCLUSIONS

An obstructive uropathy model was created in female fetal lambs. There were no dysplastic changes in the kidneys in lambs operated on at 90 days' gestation, but there were definite dysplastic changes in those operated on at 60 days. Concentrations of Na and CI in the fetal urine are higher than normal in the 90-day model.

Skeletal malformations in fetuses with Meckel syndrome

In six fetuses with Meckel syndrome (gestational age 16-23 weeks, crown-rump length 130-170 mm) the skeleton was examined as part of the autopsy procedure using whole body radiography and special radiographic techniques. In the upper and lower limbs we found similar types of polydactyly. We noted four types, based on the number and morphology of metacarpals and metatarsals. In the individual fetus there was more often similarity in the pattern of malformation in the two hands or in the two feet than there was between the pattern of malformation seen in the hands and that seen in the feet. Only one foot was normal. Malformations of the cranial base (the basilar part of the occipital bone or the postsphenoid bone) occurred in five cases, and the vertebral bodies in the lumbar region of the spine were malformed (cleft) in three cases. It is proposed that a skeletal analysis be included in the future evaluation of phenotypes in Meckel syndrome.

[Prenatal diagnosis of bilateral polycystic kidney disease in a twin pregnancy]

Polycystic renal dysplasia is a lethal malformation when it is bilateral. The authors report a rare case of polycystic dysplasia observed in both foetuses of a twin pregnancy, one of whom survived despite bilateral polycystic kidney disease. These biamniotic monoplacental twins were delivered prematurely at 33 weeks of amenorrhoea. The diagnosis was made by antenatal ultrasound. The first twin presented bilateral renal lesions: right polycystic kidney, segmental polycystic dysplasia of the superior pole of the left kidney on a completely duplicated system. The second twin presented a right polycystic kidney. In the light of this case report, the authors describe the various antenatal presentations of polycystic kidney and the associated urological malformations. Involvement of both foetuses of a twin pregnancy raises a discussion of the aetiopathogenesis of polycystic renal dysplasia.

Insights into the pathogenesis and natural history of fetuses with multicystic dysplastic kidney disease

To better delineate the natural history of multicystic displastic kidney disease (MCDKD) and provide insights into the pathogenesis of this condition, we report our experience in 102 prenatally detected cases. MCDKD is most commonly an incidental finding on prenatal ultrasound examination. The abnormality may be unilateral (76 per cent) or bilateral (24 per cent). In unilateral cases, abnormality of the contralateral kidney is common (33 per cent). Associated non-renal abnormalities occur frequently with both unilateral (26 per cent) and bilateral (67 per cent) MCDKD, and increase the risk for an abnormal chromosome study. Males are more likely to be affected than females with a ratio of 2.4:1, but females are twice as likely to have bilateral MCDKD and associated non-renal abnormalities, and four times more likely to have an abnormal chromosome study. We suggest that the option of chromosomal analysis should be discussed with all patients diagnosed with MCDKD in their fetus, if there is bilateral renal involvement or if an associated non-renal abnormality is present. Unilateral MCDKD without associated renal or non-renal abnormalities was not associated with an abnormal chromosome study, and resulted in favourable outcomes. While unilateral MCDKD, lack of associated anomalies, normal chromosome study and adequate amniotic fluid are all reassuring findings, a complete neonatal urologic work-up should be performed in all newborns. We believe the evaluation should include voiding cystourethrography to rule out vesicoureteral reflux. Our findings allow more precise counselling of patients regarding prognosis, and subsequent management of the fetus found to have MCDKD.

Multicystic kidney joined to the homolateral testis by an ectopic vas deferens: embryological hypothesis for a new description

Ectopic location of the vas deferens is a rare congenital anomaly with multiple variations. The frequent association with ano-rectal abnormalities and hypospadias is well known. We report two cases of a newborn and a 3-year-old child with ectopic vas deferens coupled with a left multicystic kidney without any ureteral structure. Furthermore, the latter had a contralateral vesicoureteral reflux and anal agenesis with recto-bulbar fistula. Our attempt with this report is to explain the development of such anomalous deferential outlet into the multicystic kidney, according to the most qualified theory of the Wolffian duct embryology.

Interstitial deletion del(3)(p12p21) in a malformed child subsequent to paternal paracentric insertion (or intraarm shift) 46,XY, ins(3)(p24.1p12.1p21.31)

We report on a malformed stillborn with deletion 3p subsequent to direct paracentric insertion (intraarm shift) in the normal father which had been first mistaken for paracentric inversion. The corrected diagnosis was supported by FISH of mapped markers on metaphase chromosomes. In addition we looked for recombinants in sperm. This observation reminds similar cases that had been considered exceptions to the expected meiotic recombination of paracentric inversions and points to a cytogenetic pitfall. Published deletions and paracentric inversions in 3p are briefly quoted.

Rearrangement of the human CDC5L gene by a t(6;19)(p21;q13.1) in a patient with multicystic renal dysplasia

Genetic studies have implicated the short arm of chromosome 6 in congenital hydronephrosis. In previous studies, we described a fetus carrying a t(6;19)(p21;q13.1) as the sole cytogenetic anomaly and suffering from bilateral multicystic renal dysplasia caused by a bilateral complete pelviureteric junction obstruction, resulting in a massive hydronephrosis. Characterization of the chromosome 19 breakpoint region revealed that the transcription factor-encoding USF2 gene is affected. In this report, we show that the CDC5L gene on chromosome 6p is rearranged in the cells of the fetus. CDC5L encodes a protein that is related to the product of the Schizosaccharomyces pombe Cdc5 gene, which exerts its effects at the G2/M transition during cell cycle progression. We have established the genomic organization of the CDC5L gene and found that it consists of at least 16 exons spanning approximately 50 kb of chromosome segment 6p21. Northern blot analysis indicated that the gene is ubiquitously expressed as a single mRNA of about 3.4 kb in both fetal and adult tissues. The translation product of the CDC5L gene has an electrophoretic mobility of about 100 kDa and is predicted to be a nuclear protein, since it contains a Myb-related DNA binding domain and potential nuclear localization signals in its aminoterminal region. Immunocytochemical analysis confirmed the nuclear localization of the CDC5L protein. CDC5L was also predicted to contain a hydrophilic, proline-rich region in its central part, which might function as a transcriptional activating domain. The chromosome 6 breakpoint was found in the intron between exons 9 and 10, indicating that, as a direct result of the 6;19 translocation, the Myb-related DNA binding domains and the nuclear localization signals are separated from the putative transactivating domain. Northern blot and RT-PCR experiments revealed that the other CDC5L allele is unaffected, and in Western blot experiments, expression of the 100-kDa protein was detected in fibroblasts of the fetus. Expression of a truncated or hybrid CDC5L transcript resulting from the CDC5L rearrangement could not be demonstrated.

Polycystic kidney disease in SBM transgenic mice: role of c-myc in disease induction and progression

SBM mouse is a unique transgenic model of polycystic kidney disease (PKD) produced by dysregulation of c-myc in the kidneys. Our previous demonstration that c-myc is overexpressed in human autosomal polycystic kidney disease (ADPKD) prompted us to investigate the pathogenetic role of c-myc in the induction and progression of the cystogenic phenotype in our mouse model. In young SBM kidneys, c-myc was two- to threefold increased with persistent expression levels into adulthood, an age when c-myc is normally undetectable. In situ hybridization analysis of the c-myc transgene demonstrated intense signal specifically overlying glomerular and tubular epithelium of developing cysts in fetal and young kidneys. Increased expression of c-myc correlated with the initiation and progression of the PKD phenotype as evidenced by early tubular and glomerular cysts at E16.5. Cyst number and size increased with age, with co-development of glomerular and tubular epithelial hyperplasia. Consistently, the mean renal proliferative index was increased approximately 5- to 20-fold in noncystic and cystic tubules of newborn SBM animals compared with littermate controls. Similarly, in fetal and newborn kidneys the tubular apoptotic indices were increased approximately three- to ninefold over controls. Both proliferation and apoptotic rates in cystic tubules approached levels in developing tubules from the normal nephrogenic zone. We conclude that the pathogenesis of PKD hinges on a critical imbalance in c-myc regulation of the opposing processes of cell proliferation and apoptosis, recapitulating the cellular phenomena in developing fetal kidney.

Epithelial galectin-3 during human nephrogenesis and childhood cystic diseases

Galectin-3 is a beta-galactoside-binding protein with putative roles in development, oncogenesis, and inflammation. Its expression in human nephrogenesis has not been previously reported. This study examines galectin-3 expression in early human embryos by Western blot and immunohistochemistry. This 33-kD protein was detected in the apical domain of distal tubules of the mesonephros and also in the mesonephric duct. In the metanephros, the adult kidney precursor, galectin-3 was detected in the apical domains of ureteric bud branches, and there was intense expression in fetal medullary and papillary collecting ducts in both the cytoplasm and plasma membranes. Low levels of galectin-3 were detected in the cytoplasm of a subset of cells in adult collecting ducts; these were alpha-intercalated cells because they expressed basal band 3 protein. In human multicystic dysplastic kidneys, all diseased epithelia had an embryonic apical expression pattern of galectin-3 and, in addition, all cystic epithelia in autosomal recessive polycystic kidneys expressed this molecule. It is concluded that galectin-3 is expressed by cells of the mesonephric duct/ureteric bud lineage, and it is speculated that the different subcellular locations may be implicated in both the regulation of normal growth and differentiation of this lineage, as well as in the pathogenesis of cystic epithelia.

Expression of hepatocyte growth factor/scatter factor and its receptor, MET, suggests roles in human embryonic organogenesis

Hepatocyte growth factor/scatter factor (HGF/SF) is secreted by mesenchymal cells and elicits proliferation, motility, differentiation, and morphogenesis of epithelia and other cells. These effects are mediated by binding to MET, a receptor tyrosine kinase. Genetically engineered mice lacking HGF/SF die in utero due to a failure of placental and hepatocyte differentiation, but little information exists regarding the expression of this signaling system in human development. Using reverse transcriptase-polymerase chain reaction, Western blots, and immunohistochemistry, we report that HGF/SF and MET are expressed during critical early periods of human organogenesis from 6 to 13 wk of gestation. Organs that expressed both genes included liver, metanephric kidney, intestine, and lung, each of which develop by inductive interactions between mesenchyme and epithelia. Of all organs studied, the placenta contained the highest levels of HGF/SF protein, and MET was detected in trophoblastic cells of chorionic villi as early as the 5th wk of gestation. Finally, examination of a human multicystic dysplastic kidney demonstrated that malformed, hyperproliferative tubules expressed MET, whereas HGF/SF protein was immunolocalized to the same epithelia and also to the surrounding undifferentiated cells. Hence HGF/SF might be an important growth factor in normal human embryogenesis and may additionally play a role in human organ malformations.

Insulin-like growth factor (IGF) and IGF binding protein gene expression in multicystic renal dysplasia

Multicystic dysplastic kidney disease is the most common form of renal dysplasia that leads to ESRD in children. This study describes the histopathological changes of multicystic dysplasia that occur from early fetal life to the postnatal period. At 14 wk gestation, early cystic enlargement of various segments of the nephron have been identified, in addition to a displaced metanephric blastema adjacent to zones of normal nephrogenesis. At later stages, the predominant features include cyst enlargement with marked fibromuscular collars, architectural disorganization, and replacement of the interstitium with a disarray of mesenchymal tissue. This study investigated the expression of the mRNA encoding the insulin-like growth factors (IGF) and IGF binding proteins (IGFBP) and have demonstrated IGF-II, IGFBP-2, and IGFBP-3 to be altered. Apart from their expression in the displaced metanephric blastema, both IGF-II and IGFBP-2 were overexpressed in abnormal tissue elements in all kidneys from fetal to postnatal life. IGF-II gene expression was localized to mesenchymal tissue, specifically in the periductal fibromuscular collars. IGFBP-2 mRNA was found to be expressed exclusively in the cyst epithelia of all cysts at all ages studied, whereas IGFBP-3 mRNA was absent from these epithelia. This study details the failure of normal IGF expression in the development of multicystic renal dysplasia and suggests a role for the IGF system in the progressive histopathological changes of this disorder.

The pathogenesis of multicystic dysplastic kidney disease: insights from the study of fetal kidneys

The pathogenesis of multicystic dysplastic kidney disease (MCDKD) is unknown. Most morphologic studies of MCDKD kidneys have been performed when the kidneys are resected postnatally, when their architecture has been distorted by massive cyst enlargement. We obtained two MCDKD kidneys at an early stage of development (14 and 19 weeks' gestation) and examined the pattern of nephrogenesis in detail. In both affected kidneys, we identified islands of spatially dislocated metanephric blastema adjacent to zones containing all the normal structural elements of nephrogenesis, including aggregates of induced mesenchyme, S-shaped bodies and maturing glomerull, and proximal and distal tubules. Metanephric blastemal cells displayed characteristic vimentin and smooth muscle actin immunoreactivity and insulin-like growth factor II gene expression, whereas induced elements exhibited appropriate cytokeratin immunoreactivity and Wilms' tumor gene expression. In most other zones, renal cysts were lined with epithelia varying from a flattened squamous to a cuboidal morphology and expression of markers suggested their origin to be from all portions of the nephron including Bowman's space, proximal tubule, and collecting duct. In some cysts, small clusters of epithelial cells were identified within the cyst lumen. These studies suggest that in the early stages of MCDKD, normal nephrogenesis occurs in what seems to be a normal metanephric blastema; however, an intrinsic abnormality in the branching morphogenesis of the ureteric duct might be responsible for the development of the histopathologic changes described.

Isolation of cosmids corresponding to the chromosome breakpoints of a de novo autosomal translocation, t(6;19)(p21;q13.1), in a patient with multicystic renal dysplasia

Hydronephrosis caused by pelvi-ureteric junction obstruction (PUJO) is a frequent urological malformation assumed to result from a deficient development of the ureteric bud. The exact etiology of pelvi-ureteric junction stenosis is unknown, but there is convincing evidence for a genetic cause, with linkage analysis predicting a hereditary hydronephrosis locus on chromosome 6p. We encountered a patient with a de novo autosomal t(6;19)(p21;q13.1) and attendant bilateral multicystic renal dysplasia (MRD), bilateral PUJO resulting in massive hydronephrosis, and an associated von Mayer-Rokitansky-Kuster disorder. On the basis of the presumption that in this patient the putative hydronephrosis gene might be disrupted by the translocation, we sought to isolate DNA from the breakpoint regions as the initial step in a strategy to identify genes affected by the t(6; 19). Using sequential rounds of fluorescence in situ hybridization (FISH) with cosmids selected from a detailed integrated map of the long arm of chromosome 19, we have identified a cosmid clone that spans the breakpoint. The position of the breakpoint was further localized by Southern blot analysis. Using a vectorette PCR approach, rearranged DNA fragments were isolated and, by comparative nucleotide sequence analysis, these were shown to contain ectopic sequences. A cosmid clone containing these ectopic sequences was isolated and shown by CASH (chromosome assignment using somatic cell hybrids) and FISH (fluorescence in situ hybridization) analysis to map to the short arm of chromosome 6 and to span the breakpoint found in the MRD patient. The isolated cosmid clones are useful reagents for analysis of other MRD patients and for the search for genes at or flanking the breakpoints.

Distribution and ontogenesis of tenascin in normal and cystic human fetal kidneys

BACKGROUND

Tenascin is a mesenchymal extracellular matrix glycoprotein transiently expressed during development, mainly at the site of epithelial-mesenchymal interactions. It is thought to play a key role in morphogenesis. Little is known about the distribution of tenascin in normal human fetal kidney, and, so far, no data have been reported concerning the distribution of the protein in fetal cystic kidneys.

EXPERIMENTAL DESIGN

Using specific mAb and the immunofluorescence technique, we analyzed the distribution of tenascin in normal human embryonic (n = 3), fetal (n = 15), and mature kidneys (n = 4) and in fetuses affected with autosomal recessive polycystic disease (n = 3), autosomal dominant polycystic disease (n = 3), and cystic dysplasia (n = 3). We compared the distribution of this protein with that of fibronectin and types I, III, V, and VI collagens.

RESULTS

In normal developing kidneys, tenascin is present in the uninduced blastema and in the mesenchyme around differentiating nephrons. It is homogeneously distributed in the inner cortex and in the medulla. During maturation, tenascin expression persists in the medulla but progressively decreases in the cortex. Tenascin is present in the mesangial area from the S-shaped body stage. Both types of polycystic diseases are characterized by a marked and diffuse increase in cortical and medullary expression of tenascin as well as types III, V, and VI collagen. In cystic dysplasia, two types of changes were observed: (a) increased tenascin and interstitial collagen expression in the subcapsular strips of condensed mesenchyme; and (b) heterogeneous medullary tenascin distribution with positive labeling of the condensed mesenchyme surrounding cysts and primitive ducts and negative labeling of the loose interstitial mesenchyme, contrasting with the diffuse accumulation of types III, V, and VI collagen.

CONCLUSIONS

In the human fetal kidney, tenascin is expressed by blastema cells and disappears when converted to epithelium. In polycystic diseases, an early increase in tenascin and interstitial collagen expression suggests that renal mesenchyme per se may contribute to the progressive alteration of the kidney. In cystic dysplasia, phenotypic changes in metanephric blastema indicate inappropriate commitment of blastema cells into interstitial cells, leading to the definitive arrest of nephrogenesis; the heterogeneity in tenascin medullary expression underlines the heterogeneity in the mesenchymal cell population.

Nodular renal blastoma in kidney with multicystic dysplasia. Report of a case

The clinico-pathologic association of nodular renal blastema, multicystic kidney and obstructive uropathy has been recently identified. We report on a female patient diagnosed as having unilater multicystic dysplasia by prenatal ultrasonography. The patient was nephrectomized at the age of 6 1/2 months. Examination of the resected kidney revealed multiple unilocular cysts in the cortex and hypoplasia of the homolateral ureter; histological study confirmed the presence of multiple cysts limited to the renal cortex, and revealed, among them, multiple cortical metanephric blastema cells islands. Our case supports a relationship between nodular renal blastema, cortical cysts and obstructive uropathy; ureter hypoplasia could cause intraluminal back pressure, with consequent abnormal development of the ampullae, normally endowed in nephronic anlagens induction, cystic tubular ectasia and persistence of nodular renal blastema. The peripheral location of renal nodular blastema and cysts supports a late error in nephrogenesis, at the time of formation of the last generation of nephrons.

[Multilocular cysts of the kidney in the adult]

Multilocular cyst of the adult kidney is a benign lesion of uncertain pathogenesis. We report a case studied by immunohistochemical techniques. A malformative histogenesis is suggested.

Fetal urine production at different gestational ages: correlation to various compromised fetuses in utero

To reveal which fetal life-threatening diseases significantly contribute to impairment of in-utero urine production and also to determine the gestational age at which time aberrant urine production becomes manifest, we observed 376 compromised fetuses (subject group) at 21-42 weeks' gestation using ultrasonography. A total of 358 uncomplicated fetuses, aged 21-40 weeks, were separately chosen as a control group. Statistical differences in the urine production rate between subject- and control-group fetuses were analysed using the Grubbs-Smirnoff test at corresponding gestational ages. Significant decreases were evident in: bilateral renal agenesis (100%) at 21-23 weeks; bilateral infantile polycystic kidney (100%) at 21-28 weeks; bilateral multicystic kidney disease (100%) at 21-31 weeks; donor fetuses with twin transfusion syndrome (TTS) (100%) at 21-28 weeks; post-term fetuses (100%) at 42 weeks; bilateral hydronephrosis (60%) at 21-38 weeks; non-immunologic hydrops fetalis (42%) at 21-35 weeks; intrauterine growth retardation (41%) at 29-40 weeks; and upper gastrointestinal tract obstruction (36%) at 30-38 weeks. Significant increases were noted in: recipient fetuses with TTS (100%) at 21-28 weeks, and unilateral hydronephrosis (36%) at 27-32 weeks. All indicate that urine production clearly delineates various fetal conditions in utero, in a closely disease-dependent relation to gestational age.

Hydronephrotic type of bilateral multicystic dysplastic kidney. An unusual case

25 year-old pregnant woman was admitted at week 29 of fetal development for routine ultrasonic evaluation of growth. Sonography of the fetal body revealed two cystic anechoic septated structures bilaterally. At autopsy of the stillborn neonate pathology confirmed congenital multicystic dysplastic kidney. We believe this is the first case reported.

Unilateral renal agenesis may result from in utero regression of multicystic renal dysplasia

Renal agenesis is generally thought to result from a lack of induction of the metanephric blastema by the ureteral bud, which may be secondary to ureteral bud maldevelopment and/or to a problem with the formation of the mesonephric duct. Multicystic dysplasia is thought to result from early ureteral obstruction as evidenced by the high frequency of associated proximal ureteral atresia. The recent obstetrical practice of large scale screening of large numbers of fetuses with sonography has resulted in a significant increase in the detection of this and other genitourinary anomalies. These findings have contributed to our understanding of the natural history of many of these malformations, resulting in ongoing reassessment and refinement of current management modalities. Thus, it is now well established that a significant number of multicystic dysplastic kidneys, initially detected in utero and followed postnatally, involute and disappear with time. We report the unequivocal presence of unilateral multicystic dysplasia detected during maternal sonography in 3 fetuses, which could not be seen on subsequent studies during the fetal or immediate postnatal period. To our knowledge, these cases constitute the first report of complete in utero regression of multicystic kidneys. This novel observation indicates that some cases of unilateral renal agenesis result from in utero regression of multicystic dysplastic kidneys. This phenomenon may explain the presence of an ipsilateral blind ending ureter found in some patients with unilateral renal agenesis. However, this infrequent observation does not explain all cases of renal agenesis. Thus, the etiology of renal agenesis remains multifactorial.

Polycystic kidney disease in the CBA/N immunodeficient mouse

We describe a polycystic lesion of the kidney in the CBA/N mouse with an X-linked recessive immunodeficient syndrome. There is progressive cystic dilatation affecting all parts of the nephron. The cyst lining is composed of a single layered epithelium with focal nuclear crowding and the formation of micropapillary structures. The cystic epithelial cells show subnuclear vacuolation. Focal basement membrane thickening is also a feature. There is no significant inflammatory infiltrate present within these kidneys. Electron microscopic examination reveals that the subnuclear vacuolation is due to loss of the membrane infoldings at the basal pole of the epithelial cell with fluid accumulation within the extracellular space. The basement membrane thickening is due to expansion of the lamina densa. These changes are not present at birth but develop progressively with age. The finding of a polycystic kidney lesion in these mice offers an opportunity to investigate the relationship between the immune system and renal cyst formation.

[Echographic screening for autosomal dominant polycystic kidney disease from intrauterine life to adult life]

ADPKD is the most widespread genetic nephropathy. Only twenty-five per cent of patients are symptomatic. In order to prevent the disease it is important early screening by ultrasonography that shows a typical picture only in adults. Familiar history is determinant for diagnosis in intrauterine age, in newborns and in infants. Ultrasonographic diagnosis is certain only after twenty-five weeks of pregnancy.

Cystic hamartomata of lung and kidney: a spectrum of developmental abnormalities

We report on a developmental malformation of the lung and kidney which has not been previously described and which we have chosen to call "cystic hamartomata of the lung and kidney" to emphasize the non-malignant nature of these lesions. We also confirm a previous case report by Weinberg and Zumwalt [1977] as a different distinct disorder that results in a multifocal cystic hamartomata of the lung with associated marked parenchymal overgrowth of the kidney (the Weinberg-Zumwalt syndrome). These cases represent a spectrum of abnormal morphogenesis affecting both kidney and lung. Patients 1 and 2 presented during infancy with abdominal masses and hypertension due to bilateral multilocular cysts of the kidney with associated hamartomatous pulmonary cysts; patient 2 also had one area of cellular mesoblastic nephroma. Patient 3 demonstrated markedly hyperplastic renomegaly with medullary dysplasia in association with bilateral cystic hamartomata of the lungs. During the fifth week of gestation, the ureteric bud invades the unsegmented mesoderm that becomes the metanephric system, and the lung bud invades the splanchic mesoderm, which provides the stimulus for its growth. We suggest that the predominant pattern of a congenital kidney or lung hamartoma might reflect the timing of a prenatal neoplastic event affecting these developmental processes.

Ultrasonographic anatomy and diagnosis of fetal uropathies affecting the upper urinary tract. I. Obstructive uropathies

The authors describe the ultrasonographic anatomy and semiology of allowing detection of the main types of fetal uropathies. The results of the author's personal experience in this domain are compared to data from the literature. Differential features of the uropathies are given and the limitations and practical significance of prenatal and postnatal ultrasonography are discussed.

[7 cases of congenital multicystic kidney with special reference to its embryogenesis]

We have experienced 7 cases of multicystic kidney. The latest two cases, etiologically of interest, are reported herein with special reference to its embryogenesis. Case 6: A 4-year-old girl was referred to our clinic for further evaluation of mild azotemia and nonvisualization of left kidney. Left kidney was strongly thought to be multicystic kidney from abdominal CT, whereas her contralateral kidney exhibited hydrocalycosis resembling infundibular stenosis with diminished calyceal numbers. Nephrectomy of her left kidney was performed and histological studies confirmed renal dysplasia (primitive duct, metaplastic cartilage, etc.). Case 7: A 7-year-old girl was referred to Hakodate Kyokai Hospital for the evaluation of azotemia and low stature. Her right kidney was not visualized on IVP and her left kidney exhibited hydronephrosis with diminished calyceal numbers. Her right kidney was diagnosed as multicystic kidney on CT-scan. Pyeloplasty of her left kidney was performed. Multicystic kidney is a rather rare congenital disease. Association of various anomalies in contralateral kidney has been emphasized as well as the notion that infundibulopelvic stenosis is a linked in the clinical spectrum extending from cystic dysplasia of the kidney to hydronephrosis. Our last two cases seem to be included in this category of obstruction theory. As shown by microdissection technique (Potter), however, severe ampullary inhibition early in fetal life is also an attractive hypothesis. Diminished calyceal number of contralateral kidneys seen in our recent two cases is compatible with possibility of ampullary damage. Recent experimental study also showed that renal dysplasia is not solely caused by simply mechanical obstruction to urinary drainage, even when the obstruction is imposed at an early stage of renal development.

Ultrasound diagnosis and perinatal management of fetal genito-urinary abnormalities

Approximately 50% of fetal abdominal masses originate in the urinary system and those recognizable ultrasonically include renal dysplasia, renal agenesis and obstruction of the lower excretory channels. Fetal renal anomalies may be discovered co-incidentally during the course of sonographic evaluation of uterine size-dates discrepancy, because they are commonly associated with fetal growth retardation and/or oligohydramnios, or during a planned sonographic follow-up of pregnancies in patients who are at risk of recurrence of such anomalies. The sonographic demonstration of renal anomalies under these circumstances may allow for elective termination of pregnancy, may modify the obstetric management and/or facilitate pediatric and surgical care of the newborn. In the collaboration study at three ultrasonic centers there were 81 cases of genito-urinary tract anomalies detected antenatally in a five years period. Among the detected anomalies there were 30 hydronephrotic fetuses, 12 with multicystic disease, 15 with Potter's syndrome, 10 with polycystic kidney, 9 with Prune Belly syndrome, 4 with isolated renal cysts and 1 with an ovarian cyst. Perinatal management of the fetus with urinary tract abnormalities greatly depends on the accuracy of the diagnosis. It would be justifiable to suggest that an inexperienced observer should not make the final diagnosis. He could be of great help, if one kept a high index of suspicion in patients with a significant family history of oligohydramnios and of unexplained abnormal cystic structures in the fetal abdomen and seek the help of a special referral center where experience in related cases is concentrated. Once an accurate diagnosis is made, various alternatives are open to the obstetrician. This is primarily dependent upon the type and degree of the abnormality. Unilateral multicystic kidney and hydronephrosis due to obstruction above the level of the urethra appear to be compatible with extrauterine life and should be approached accordingly. If there is massive enlargement of the fetal abdomen, elective cesarean delivery should be considered to prevent the dystocia which may occur with vaginal delivery and to prevent further damage of these vital organs. If bilateral renal agenesis, bilateral multicystic kidneys, or bilateral infantile polycystic kidneys are demonstrated early in gestation, the obstetrician and parents may choose to terminate the pregnancy because these conditions are not compatible with extrauterine life.(ABSTRACT TRUNCATED AT 400 WORDS)

Development of the embryonic murine kidney in normal and congenital polycystic kidney disease: characterization of a proximal tubular degenerative process as the first observable light microscopic defect

The current report presents findings from a comparative histological and histochemical investigation of murine congenital polycystic kidney disease. The studies revealed that the morphological changes are initiated in the developing proximal tubules of the nephron; differences from control sections first become evident at 16 days' gestation. As the disease progresses, obvious changes include hyperplasia and dilation of the tubule, cellular vacuolization, and alterations in the apical cell brush border. Included among the latter changes are decreases in enzyme (alkaline phosphatase) staining and decreases in glycoprotein staining (periodic acid Schiff). All such changes continue until the kidney is markedly cystic and apical cell cytochemical staining is absent. Some cellular vacuolization, assumed to be a normal developmental event, is also seen within the same segment of the proximal tubule at 17 days' gestation through the 1st postnatal day. Dilation of the collecting duct is noted to be a later or secondary change evident after the initial onset of the disease.

The pathogenesis of renal dysplasia. III. Complete and incomplete urinary obstruction

We graded obstructed kidneys of infants on the hypodysplasia scale to assess the influence of complete and partial obstruction on the pathogenesis of hypodysplasia. Kidneys with complete obstruction exhibited severe grades; those with partial ureteral obstruction had near normal grades. Those kidneys subjected to partial urethral obstruction ranged from mild to severe grades which correlated with degrees of lateral ectopy of the urethral office. Renal parenchymal development was impaired by complete obstruction but was tolerant to incomplete obstruction. Abnormal orifice positions associated with urethral obstructions were considered to be manifestations of ectopic ureteric buds and the hypodysplasia to be evidence of abnormal induction of abnormal renal blastema.

Prenatal morphology in Meckel's syndrome

Prenatal morphology of Meckel's syndrome was studied in five fetuses of different gestational age, that had been aborted because ultrasonography and elevated amniotic AFP-levels indicated neural tube defect. Histologically, the enlarged polycystic kidneys were completely alike with respect to the type of involvement and differed only in the severity of changes. They could be identified at type III cystic kidneys according to the classification of Potter. Proliferation of hepatic bile ducts and slight cystic dilatation of pancreatic ducts is already evident in the youngest fetus. Additional cyst formation in the epididymis was found in one of the cases. Occipital encephalocele, located within an apical occipital bone defect was always associated with a second mostly occult encephalocele protruding through a separated defect of the basal occipital squame and of the first and second vertebral arch. It is assumed that double encephalocele represents a constant finding in Meckel's syndrome, indicating a specific pattern within the disturbance of neural tube closure.