Cerebro-reno-digital (Meckel-like) syndrome with Dandy-Walker malformation, cystic kidneys, hepatic fibrosis, and polydactyly

Aberrant Wnt signalling and cellular over-proliferation in a novel mouse model of Meckel-Gruber syndrome

Meckel-Gruber syndrome (MKS) is an embryonic lethal ciliopathy resulting from mutations in genes encoding proteins localising to the primary cilium. Mutations in the basal body protein MKS1 account for 7% of cases of MKS. The condition affects the development of multiple organs, including brain, kidney and skeleton. Here we present a novel Mks1(tm1a(EUCOMM)Wtsi) knockout mouse which accurately recapitulates the human condition, consistently developing pre-axial polydactyly, complex posterior fossa defects (including the Dandy-Walker malformation), and renal cystic dysplasia. TOPFlash Wnt reporter assays in mouse embryonic fibroblasts (MEFs) showed general de-regulated high levels of canonical Wnt/β-catenin signalling in Mks1(-/-) cells. In addition to these signalling defects, we also observed ectopic high proliferation in the brain and kidney of mutant animals at mid- to late-gestation. The specific role of Mks1 in regulating cell proliferation was confirmed in Mks1 siRNA knockdown experiments which showed increased levels of proliferation after knockdown, an effect not seen after knockdown of other ciliopathy genes. We suggest that this is a result of the de-regulation of multiple signalling pathways (Wnt, mTOR and Hh) in the absence of functional Mks1. This novel model system offers insights into the role of MKS1 in Wnt signalling and proliferation, and the impact of deregulation of these processes on brain and kidney development in MKS, as well as expanding our understanding of the role of Mks1 in multiple signalling pathways.

The Meckel-Gruber syndrome gene, MKS3, is mutated in Joubert syndrome

Joubert syndrome (JS) is an autosomal recessive disorder characterized by cerebellar vermis hypoplasia associated with hypotonia, developmental delay, abnormal respiratory patterns, and abnormal eye movements. The association of retinal dystrophy and renal anomalies defines JS type B. JS is a genetically heterogeneous condition with mutations in two genes, AHI1 and CEP290, identified to date. In addition, NPHP1 deletions identical to those that cause juvenile nephronophthisis have been identified in a subset of patients with a mild form of cerebellar and brainstem anomaly. Occipital encephalocele and/or polydactyly have occasionally been reported in some patients with JS, and these phenotypic features can also be observed in Meckel-Gruber syndrome (MKS). MKS is a rare, autosomal recessive lethal condition characterized by central nervous system malformations (typically, occipital meningoencephalocele), postaxial polydactyly, multicystic kidney dysplasia, and ductal proliferation in the portal area of the liver. Since there is obvious phenotypic overlap between JS and MKS, we hypothesized that mutations in the recently identified MKS genes, MKS1 on chromosome 17q and MKS3 on 8q, may be a cause of JS. After mutation analysis of MKS1 and MKS3 in a series of patients with JS (n=22), we identified MKS3 mutations in four patients with JS, thus defining MKS3 as the sixth JS locus (JBTS6). No MKS1 mutations were identified in this series, suggesting that the allelism is restricted to MKS3.

Antenatal presentation of Bardet-Biedl syndrome may mimic Meckel syndrome

Bardet-Biedl syndrome (BBS) is a multisystemic disorder characterized by postaxial polydactyly, progressive retinal dystrophy, obesity, hypogonadism, renal dysfunction, and learning difficulty. Other manifestations include diabetes mellitus, heart disease, hepatic fibrosis, and neurological features. The condition is genetically heterogeneous, and eight genes (BBS1-BBS8) have been identified to date. A mutation of the BBS1 gene on chromosome 11q13 is observed in 30%-40% of BBS cases. In addition, a complex triallelic inheritance has been established in this disorder--that is, in some families, three mutations at two BBS loci are necessary for the disease to be expressed. The clinical features of BBS that can be observed at birth are polydactyly, kidney anomaly, hepatic fibrosis, and genital and heart malformations. Interestingly, polydactyly, cystic kidneys, and liver anomalies (hepatic fibrosis with bile-duct proliferation) are also observed in Meckel syndrome, along with occipital encephalocele. Therefore, we decided to sequence the eight BBS genes in a series of 13 antenatal cases presenting with cystic kidneys and polydactyly and/or hepatic fibrosis but no encephalocele. These fetuses were mostly diagnosed as having Meckel or "Meckel-like" syndrome. In six cases, we identified a recessive mutation in a BBS gene (three in BBS2, two in BBS4, and one in BBS6). We found a heterozygous BBS6 mutation in three additional cases. No BBS1, BBS3, BBS5, BBS7, or BBS8 mutations were identified in our series. These results suggest that the antenatal presentation of BBS may mimic Meckel syndrome.

Molecular pathology and genetics of congenital hepatorenal fibrocystic syndromes

The hepatorenal fibrocystic (HRFC) syndromes are a heterogeneous group of severe monogenic conditions that may be detected before birth. Commonly, HRFC syndromes present in the neonatal and paediatric age, with consistent developmental abnormalities mostly involving the liver and kidney. The changes include the proliferation and dilatation of epithelial ducts in these tissues with abnormal deposition of extracellular matrix. In this review, we examine the clinical features and differential diagnoses of this group of syndromes, including autosomal recessive polycystic kidney disease (ARPKD), juvenile nephronophthisis (NPHP), Meckel-Gruber syndrome (MKS), Bardet-Biedl syndrome (BBS), and Jeune asphyxiating thoracic dystrophy (JATD). Extrahepatic manifestations include mostly bone and central nervous system abnormalities, dysmorphic features, and developmental delay. Previously, it has been suggested that ARPKD, JATD, and Ellis-van Creveld syndrome (EvC) may arise from defects in differentiation in a common developmental pathway. We review recent molecular advances in the recessive HRFC syndromes and discuss this hypothesis.

Liver fibrocystic disease and polydactyly: proposal of a new syndrome

Liver fibrocystic disease (LFCD), characterized by dilatation of the intrahepatic bile ducts and variable degree of fibrosis, can be present alone or as part of many syndromes, such as Bardet-Biedl syndrome (BBS), Meckel syndrome, Jeune asphyxiating thoracic dysplasia, and Fraser-Jequier-Chen syndrome. We report two cases of LFCD and polydactyly with features similar, but not diagnostic of, BBS. Patient 1 was an 18-month-old boy with mental retardation, polydactyly, chronic renal failure, convergent strabismus, and hepatic fibrosis. Patient 2 was a male neonate with LFCD and polydactyly. Their manifestations could not be diagnosed as any of the previous mentioned entities. Difficulties in the early diagnosis of BBS have been previously reported and this could explain the clinical variability and heterogeneity of manifestations at the time of diagnosis. On the other hand, the existence of liver abnormalities in association with BBS has been previously described, but is rare. Our patients' malformations might represent a new entity where autosomal recessive inheritance is probable, but other patterns cannot be ruled out.

Cystic kidney disease presenting in infancy

AIM

The clinical, histological and imaging findings of 12 children with ultrasound features of severe renal cystic disease presenting in the first year of life were reviewed.

METHODS AND RESULTS

Two children had cystic dysplasia and four had autosomal dominant polycystic disease. Two had a malformation syndrome, one a variant of Meckel syndrome and the other Bardet Biedl syndrome. One had autosomal recessive polycystic disease and in three there was no final diagnosis. Intravenous urography gave non-specific information. In six cases clinical findings combined with imaging established a diagnosis. Diagnosis was established by biopsy in two and gave supportive evidence in one. Outlook for renal function is variable. One child has had a transplant and one is on dialysis awaiting a transplant. Three have a degree of renal failure and one has died. Six have normal renal function. Renal cystic disease is the common pathway for a heterogeneous group of disorders as shown in these children.

CONCLUSION

It is emphasized that a specific diagnosis could not be made from the renal sonographic appearances alone, nor could any prognostic implications for renal function be made. Contrast retention on intravenous urography was also insufficiently specific to be of value. Ultrasound of the parents was the most useful imaging procedure and should be done in all cases.

A gene for Meckel syndrome maps to chromosome 11q13

Meckel syndrome (MKS) is a rare autosomal recessive lethal condition of unknown origin, characterized by (i) an occipital meningo-encephalocele with (ii) enlarged kidneys, with multicystic dysplasia and fibrotic changes in the portal area of the liver and with ductal proliferation, and (iii) postaxial polydactyly. A gene responsible for MKS in Finland has been mapped to chromosome 17q21-q24. Studying a subset of Middle Eastern and northern African MKS families, we have recently excluded the chromosome 17 region and have suggested a genetic heterogeneity. In the present study, we report on the mapping of a second MKS locus (MKS2) to chromosome 11q13, by homozygosity mapping in seven families that do not show linkage to chromosome 17q21-q24 (maximum LOD score 4.41 at recombination fraction .01). Most interestingly, the affected fetuses of southern Tunisian ancestry shared a particular haplotype at loci D11S911 and D11S906, suggesting that a founder effect is involved. Our observation gives support to the clinical and genetic heterogeneity of MKS.

Meckel syndrome

Meckel syndrome (MKS) is a lethal syndrome with a central nervous system malformation, usually occipital meningoencephalocele, bilaterally large multicystic kidneys with fibrotic changes of the liver, and polydactyly in most cases. Additional anomalies are frequent. A common characteristic of the parenchymal changes of many organs is a proliferation of the stromal connective tissue and increase and dilatation of the associated epithelial ducts. Autosomal recessive inheritance is well confirmed and the gene locus has been mapped to chromosome 17q21-24 by genome wide linkage study. The locus was later refined to within a less than 1 cM region (17q22), in which most of the Finnish MKS patients share a common chromosomal haplotype suggesting one major and relatively old mutation. However, in most of the non-Finnish MKS families studied, this linkage could not be confirmed. The linkage studies provide evidence that more than one locus is involved in bringing about the combination of CNS malformations, cystic kidneys, and polydactyly, maybe even in typical cases of MKS. Prenatal diagnosis of MKS by vaginal ultrasound scan is possible from 11-12 weeks of pregnancy, especially in families where there is a known risk. In those families where linkage to 17q22 is established, prenatal diagnosis by DNA analysis is possible.

COACH syndrome: report of two brothers with congenital hepatic fibrosis, cerebellar vermis hypoplasia, oligophrenia, ataxia, and mental retardation

Congenital hepatic fibrosis (CHF) is probably the most common cause of non-icteric hepatosplenomegaly and is encountered mainly in children and young adults. We describe here two brothers from healthy, non-consanguineous parents. The patients showed early hepatosplenomegaly, portal hypertension, and no apparent kidney involvement. Clinical and laboratory findings were similar in both patients. Liver biopsies showed the presence of broad septa of fibrous tissue containing abundant bile ducts, portal tracts enlarged by fibrosis, and preserved lobular architecture. The histological findings were suggestive of CHF. Ophthalmological assessment demonstrated visual impairment with mild exotropia, nystagmus, and oculomotor apraxia. Neurological examination showed moderate mental retardation and cerebellar ataxia. Brain MRI confirmed cerebellar malformation with inferior vermis hypoplasia. This pattern of defects is consistent with COACH syndrome (Cerebellar vermis hypoplasia, Oligophrenia, congenital Ataxia, Coloboma, Hepatic fibrocirrhosis) which has previously been reported in five other cases. Our report may contribute to a better delineation of the COACH syndrome phenotype in the spectrum of oculo-encephalohepato-renal disorders.

The Meckel syndrome: report of two Japanese sibs and a review of literature

Two Japanese sibs with the Meckel syndrome are reported. Both babies showed the classical triad of this conditions: occipital encephalocele, cystic kidneys, and postaxial polydactyly of all four limbs. The diagnostic criteria and differential diagnosis were reviewed.

Dandy-Walker malformation in the Meckel syndrome

The Meckel syndrome (MS) is an autosomal recessive disorder classically defined by the triad of occipital encephalocele, multicystic kidneys, and polydactyly. Here we describe 3 sibs with varying manifestations of MS. The propositus had isolated cystic renal disease. The other sibs were both prenatally diagnosed with renal disease, polydactyly, and the Dandy-Walker malformation, an unusual central nervous system defect in MS. These findings are discussed in the context of the phenotypic expression of MS and the nosology of this disorder and the cerebro-reno-digital (Meckel-like) syndromes.

Familial Dandy-Walker malformation associated with macrocephaly, facial anomalies, developmental delay, and brain stem dysgenesis: prenatal diagnosis and postnatal outcome in brothers. A new syndrome?

Brothers are reported with an apparently new constellation of manifestations including Dandy-Walker complex (DWC), migrational brain disorder, macrocephaly, and facial anomalies. The first brother presented at birth, the second was detected prenatally with DWC and the pregnancy terminated. Fetal brain histopathology showed DWC associated with brainstem dysgenesis. Inheritance is likely autosomal or X-linked recessive. An extensive review of the differential diagnosis of DWC is provided.