Prenatal diagnosis of polycystic kidneys and encephalocele (Meckel syndrome)

Meckel Syndrome

Meckel syndrome is a rare, lethal, genetic disorder that can be diagnosed sonographically. Five cases of Meckel syndrome were sonographically observed prenatally between 18 and 33 weeks. In all five cases, the fetal kidneys were large and echogenic. Two of four fetuses with encephaloceles were correctly identified sonographically, and two of four fetuses with polydactyly were identified with ultrasound. Major sonographic findings in 24 previously reported cases are reviewed. Differential diagnoses are also discussed. In any fetus with large, echogenic kidneys, one should suspect Meckel syndrome and should search for the other associated abnormalities, chiefly, encephalocele, polydactyly, hydrocephalus, and cleft lip and palate.

A new syndrome with features of the Smith-Lemli-Opitz and Meckel-Gruber syndromes in a sibship with cerebellar defects

The Smith-Lemli-Opitz syndrome (SLOS) and the Meckel syndrome (MS) have been regarded as separate autosomal recessive entities. Recently, overlap of these two syndromes has been discussed. A sibship containing a probable new syndrome with features reminiscent of the SLOS and the MS is presented. The literature is reviewed with regard to the frequency of various malformations in these syndromes. Clinical manifestations and cerebellar abnormalities in these sibs are similar to those described in the Joubert syndrome (JS). These three cases may represent a new syndrome with features in common with SLOS, MS, and JS resulting from the same mutant gene, which exhibits considerable pleiotropy.

Pathology of renal and hepatic anomalies in Meckel syndrome

We describe 9 cases of Meckel syndrome (dysencephalia splanchnocystica), ranging in gestational age from 17 to 39 weeks. Five were liveborn, and the longest survival was 30 hours. Six of the 9 had all 3 elements of the classically defined triad, namely occipital encephalocele, renal cystic dysplasia, and postaxial polydactyly. The remaining 3 cases had only 2 elements of the triad. The renal abnormalities in the 9 cases resembled one another closely, varying only slightly in severity. They consisted of renal cystic dysplasia with different degrees of nephronic differentiation. The 8 available livers all contained intrahepatic bile duct anomalies. Seven of them had the classic "ductal plate malformation," as defined by Jorgensen [1977]; the remaining case had a less severe form of this malformation. The livers of the Meckel syndrome fetuses were compared to those of age-matched control fetuses, and it was concluded that the hepatic abnormality represents an arrested development of the intrahepatic biliary system at the stage of biliary cylinders with varying degrees of reactive bile duct proliferation, bile duct dilatation, portal fibrosis, and portal fibrous vascular obliteration superimposed on the arrested pattern. The case showing the least severe hepatic lesion also had the least severe renal lesion. The anomalies that were present are listed. The relationship of the different lesions to each other is briefly discussed. It was concluded that the hepatic lesion appears to be a consistent manifestation in Meckel syndrome and is of diagnostic value as the renal lesion has previously been shown to be.

Visceral anomalies in the Meckel syndrome

The visceral abnormalities of 32 autopsied Meckel's syndrome cases were analysed macroscopically and histologically in order to observe the distribution and spectrum of internal abnormalities in this hereditary malformation syndrome. All cases showed the classical triad of central nervous system anomaly, postaxial polydactyly, and cystic kidneys. Five cases were midterm fetuses and 27 cases were perinatal deaths. The kidneys were grossly enlarged in almost all of the cases (29) and showed a uniform histological pattern of fibrocystic proliferation, which is considered characteristic of MS. Fibrosis and proliferation of the bile ducts in the hepatic portal tracts were found in each case. Severe hypoplasia of the male genitalia associated with cryptorchidism was the third consistent anomaly. Derivatives of the müllerian ducts were present in four males, and the initial sex determination of the male infants was sometimes difficult. Epididymal cysts (39%) and ductal dilatation as well as fibrosis of the pancreas (31%) were further common anomalies. This series showed that a number of gross and microscopic abnormalities are consistently present in MS and that histological investigation is invaluable in defining the syndrome in doubtful cases.

The Meckel syndrome in Finland: epidemiologic and genetic aspects

Estimates of the incidence of the Meckel syndrome (MS) from different parts of the world vary from 1:140,000 to 1:13,250 births. In this nationwide study performed in Finland, the incidence of 1:14,400 births was found by retrospective ascertainment during the period 1970-1979, while the incidence was 1:8,500 births when prospective monitoring was performed in 1980-1981. The most probable incidence in Finland is about 1:9,000 births. Autosomal recessive inheritance of MS is confirmed in this study. The ratio of affected sibs, corrected for truncate complete ascertainment, was 0.261. No consanguinity between parents was found, as marriages between close relatives are rare in Finland and the ancestors were not traced back far enough to find remote consanguinities.

The Meckel syndrome: clinicopathological findings in 67 patients

A nationwide study on the Meckel syndrome (MS) was carried out covering retrospectively the years 1970-1979 and prospectively the years 1980-1981. Sixty-seven cases from 48 Finnish families were found. The clinical and pathological findings were studied. Cystic dysplasia of the kidneys was present in all the cases where sufficient information was available. In all 41 cases with specimens available from the liver, a typical fibrotic change with proliferation and dilatation of the bile ducts was found. This series and a review of the literature give convincing evidence that cystic dysplasia of the kidneys with fibrosis of the liver is a constant finding in the "true" Meckel syndrome. In conclusion, it is proposed that cystic dysplasia of the kidneys with fibrotic changes of the liver and occipital encephalocele or some other central nervous system malformation are considered as minimal diagnostic criteria of MS. Thus, a histologic investigation of the kidneys and liver is essential in diagnosing MS in doubtful cases. Heterozygote manifestations were not found.

Prenatal diagnosis of Meckel syndrome: case reports and literature review

We report on 2 couples at risk to have Meckel syndrome (MS) offspring. Three pregnancies were monitored by ultrasonography and alpha-fetoprotein (AFP) assay in midtrimester. Of the 2 involving an affected fetus, one was thought to be unaffected. A literature survey was undertaken. Sources of error seem to lie in the heterogeneity of clinical manifestations and the variable onset and rate of progression of clinical components of MS and limitations in ultrasonographic resolution inherent in the scanner or due to the associated oligohydramnios. The following observations/suggestions are made concerning the prenatal diagnosis of MS: 1) Utilize as many tests as are available. 2) Amniotic fluid AFP is more likely to show significant elevation than serum AFP. 3) Ultrasonography should concentrate on presence of oligohydramnios, small head diameter, cystic mass at the occiput, large kidneys, and absent bladder. 4) Use serial AFP and sonographic examination if findings are initially normal or equivocal.

Cystic kidneys. Genetics, pathologic anatomy, clinical picture, and prenatal diagnosis

According to the classification of Osathanondh and Potter of cystic kidneys we give an overview of the different types of cystic changes taking genetic aspects into account. Usually pathoanatomic types do not represent genetic entities: All type I kidneys are transmitted in an autosomal recessive way with varying clinical symptoms; in rare cases they even present in adults. The relationship to "congenital hepatic fibrosis", "cystic liver", and to the "Caroli syndrome" is discussed. Type II kidneys are usually not genetic in origin; but they may occur as part of several syndromes. Rarely genetic factors might contribute to type II kidneys that may present as familial cases of Potter syndrome ("renal non-function syndrome"). Type IV kidneys, although different in their pathoanatomic picture can be regarded according to a common pathogenetic theory as part of the spectrum of malformations as in type II. Therefore the genetic interpretation of type II kidneys also applies to type IV lesions. Type III kidneys include autosomal dominant polycystic kidney disease. This type may already present in childhood; the first prenatal diagnosis by ultrasonography is described in detail. Furthermore type III changes are part of syndromes or non-hereditary malformation complexes, and often present only as mild manifestations. Diseases with isolated involvement of the medulla (juvenile nephronophthisis/medullary cystic disease) or cortex are described as part of the differential diagnosis, they are heterogeneous and genetically only partly understood. Syndromes with cystic kidneys are reviewed as well as the possibilities of prenatal diagnosis of cystic diseases. Reliable prenatal diagnosis is only possible in type II, and possible in some of the other types. The nosology is improved if genetic information is taken into account.

Are bowing of long tubular bones and preaxial polydactyly signs of the Meckel syndrome?

We describe four cases with signs resembling those of Meckel syndrome. Two cases demonstrated postaxial polydactyly; one case, preaxial polydactyly; and one case, pre- and postaxial polydactyly. Since there is at least one other reported case with preaxial polydactyly, it may be a rare sign of the Meckel syndrome. In all four cases, various degrees of bowing of the long tubular bones were observed. Since at least two cases exhibited typical Meckel syndrome and since in a few further reported cases X-ray examination revealed bowing of long tubular bones, this sign is considered to be a further, hitherto not well recognized sign of the Meckel syndrome, and not grounds for delineation of a new syndrome. An extensive review of the literature revealed, that shortened and bowed extremities may be present in about one-sixth of all cases with Meckel syndrome.

Prenatal diagnosis--a compilation of diagnosed conditions

This article provides physicians with an up-to-date listing of 182 fetal conditions diagnosed prenatally. This information is presented in two key tables: the first an alphabetical listing of the conditions and the second a grouping of them according to disease categories. The latter table also presents the technique(s) used to establish the diagnosis, as well as pertinent references. Chromosomal abnormalities, diagnosed from amniotic fluid cell karyotypes, have not been individually tabulated in either table. Current techniques utilized for prenatal diagnosis are presented (see Comment).

Genetics of microphthalmos

This is a survey of the genetics of microphthalmos and the heritable syndromes in which microphthalmos occurs. New syndromes are delineated such as the autosomal dominant anophthalmos-microphthalmos-coloboma syndrome, the autosomal dominant microphthalmos, microcephaly, lacunar retinal atrophy syndrome, the autosomal recessive anophthalmos-microphthalmos-coloboma syndrome, the autosomal recessive syndrome with anophthalmos or microphthalmos and genital malformations, and the autosomal recessive syndrome with microphthalmos, microcephaly and retinal falciform folds. Nanophthalmos is described as a poorly defined phenotype and rejected as a genotype. Several other genetic entities with microphthalmos are reviewed and recent descriptions are surveyed.

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.

Spectrum of anomalies in the Meckel syndrome, or: "Maybe there is a malformation syndrome with at least one constant anomaly"

The Meckel syndrome comprises a variety of defects including the classical triad of occipital encephalocele, cystic kidneys, and polydactyly. The frequencies of the various defects are more accurately represented in the affected sibs of probands than in the probands themselves, since the latter are selected according to severity and preconceived notions of what constitutes the syndrome. In a series of 38 such sibs, all had cystic dysplasia of the kidney, 63% had an occipital meningocele, 55% had polydactyly, and 18% had no reported brain malformation. In families in which the proband had the classical triad, only 68% of the affected sibs had it. It is concluded that the diagnosis of Meckel syndrome may not be valid in the absence of cystic kidney dysplasia. In babies with encephalocele or anencephaly, pathologic examination, particularly of the kidneys, is important in determining risk of recurrence. This approach to estimating the variability of a syndrome might profitably be extended to other genetically determined pleiotropic conditions.

Inherited renal disease and genetic counseling

Inherited renal abnormalities and diseases are less common than acquired disorders. However, they are of great interest because their study results in increased understanding of the embryogenesis and physiology of the kidney, the pathogenesis of acquired disease, improved therapeutic approaches and accuracy of genetic counseling. Inherited defects of the kidney may be structural, functional or part of genetically transmitted systemic diseases that have major effects on renal structure and/or functions. Most structural defects of the kidney, with the exception of varying forms of cystic disease and the hereditary nephritides, are congenital and only rarely inherited in a Mendelian sense. The majority of genetically transmitted abnormalities of proximal and distal tubular function are caused by inborn metabolic errors or enzyme defects and deficiencies. Amniocentesis, ultrasonography and enzymatic assays have made the prenatal diagnosis of many inherited renal diseases possible so that more accurate counseling early therapeutic intervention may be provided.