Familial hydrocephalus of prenatal onset

The Genetic Basis of Hydrocephalus

Studies of syndromic hydrocephalus have led to the identification of >100 causative genes. Even though this work has illuminated numerous pathways associated with hydrocephalus, it has also highlighted the fact that the genetics underlying this phenotype are more complex than anticipated originally. Mendelian forms of hydrocephalus account for a small fraction of the genetic burden, with clear evidence of background-dependent effects of alleles on penetrance and expressivity of driver mutations in key developmental and homeostatic pathways. Here, we synthesize the currently implicated genes and inheritance paradigms underlying hydrocephalus, grouping causal loci into functional modules that affect discrete, albeit partially overlapping, cellular processes. These in turn have the potential to both inform pathomechanism and assist in the rational molecular classification of a clinically heterogeneous phenotype. Finally, we discuss conceptual methods that can lead to enhanced gene identification and dissection of disease basis, knowledge that will potentially form a foundation for the design of future therapeutics.

Genetics of human hydrocephalus

Human hydrocephalus is a common medical condition that is characterized by abnormalities in the flow or resorption of cerebrospinal fluid (CSF), resulting in ventricular dilatation. Human hydrocephalus can be classified into two clinical forms, congenital and acquired. Hydrocephalus is one of the complex and multifactorial neurological disorders.

A growing body of evidence indicates that genetic factors play a major role in the pathogenesis of hydrocephalus. An understanding of the genetic components and mechanism of this complex disorder may offer us significant insights into the molecular etiology of impaired brain development and an accumulation of the cerebrospinal fluid in cerebral compartments during the pathogenesis of hydrocephalus. Genetic studies in animal models have started to open the way for understanding the underlying pathology of hydrocephalus. At least 43 mutants/loci linked to hereditary hydrocephalus have been identified in animal models and humans. Up to date, 9 genes associated with hydrocephalus have been identified in animal models. In contrast, only one such gene has been identified in humans. Most of known hydrocephalus gene products are the important cytokines, growth factors or related molecules in the cellular signal pathways during early brain development. The current molecular genetic evidence from animal models indicate that in the early development stage, impaired and abnormal brain development caused by abnormal cellular signaling and functioning, all these cellular and developmental events would eventually lead to the congenital hydrocephalus.

Owing to our very primitive knowledge of the genetics and molecular pathogenesis of human hydrocephalus, it is difficult to evaluate whether data gained from animal models can be extrapolated to humans. Initiation of a large population genetics study in humans will certainly provide invaluable information about the molecular and cellular etiology and the developmental mechanisms of human hydrocephalus.

This review summarizes the recent findings on this issue among human and animal models, especially with reference to the molecular genetics, pathological, physiological and cellular studies, and identifies future research directions.

[Importance of the clinical genetics evaluation on hydrocephalus]

The aim of this study was to characterize the possibility of genetic etiology in a group of individuals with congenital hydrocephalus in which the etiology was indeterminate and to confirm that earlier diagnosed. The casuistry was composed by 16 individuals with congenital hydrocephalus. Investigation protocol included anamnesis, familial investigation, physical examination, computerized tomography or magnetic resonance image of head, vertebral column X-ray, karyotype and dysmorphological study. Results were analyzed in two groups. In Group I (3M:9F) was composed by hydrocephalus associated with unspecific signs. Group II (7 males) had findings of epectrum of L1 disease. Genetic counseling could be offered in 11 cases. These results demonstrate the great etiological heterogeneity of congenital hydrocephalus and reinforce the importance of dysmphology evaluation as an important complementary investigation.

Autosomal recessive hydrocephalus due to aqueduct stenosis: report of a further family and implications for genetic counselling

We report on two abortuses with hydrocephalus due to congenital stenosis of the aqueduct of Silvius. The occurrence of this disorder in two siblings (a male and a female) with normal parents supports the autosomal recessive pattern of inheritance. Such a mechanism of inheritance should be taken into account when counselling families with congenital hydrocephaly due to aqueduct stenosis.

The frequency of inherited hydrocephalus is influenced by intrauterine factors in H-Tx rats

H-Tx rats have fetal-onset inherited hydrocephalus. Linkage analysis has determined the genetics is complex, with at least three loci associated with hydrocephalus. In addition, maternal and/or intrauterine factors influence the frequency of expression. The aim of this study was to characterize nongenetic (epigenetic) factors that affect hydrocephalus in this strain. Groups of primiparous and multiparous females were used to breed fetuses for examination in utero. Multiparous females were manipulated to have either gestation with lactation or, by removal of pups at birth, gestation without lactation. In addition, hydrocephalus expression in postnatal rats from the breeding colony was analyzed for primiparous and multiparous females. The latter were subdivided according to the interval between the litter examined and the previous litter. There was no particular uterine position or horn that favored hydrocephalus and hydrocephalic fetuses were the same weight as normal littermates. The frequency of hydrocephalus was 16-20% in primiparous females and twofold higher in multiparous females that were lactating during pregnancy. Removal of the suckling pups prevented this increase. The severity of hydrocephalus was measured on 1-mm-thick fixed brain slices. Fetuses from lactating females had hydrocephalus that was significantly more severe than the nonlactating groups. However, all fetus groups had hydrocephalus that was very much less severe than the postnatal pups, suggesting that severity increases after birth. It is concluded that there is an epigenetic factor that increases the frequency of inherited hydrocephalus in fetuses if suckling pups are present during gestation. Future experiments will examine possible mechanisms for this genotype-environment interaction.

Molecular basis of autosomal recessive diseases among the Palestinian Arabs

In the review of the literature, 71 different autosomal recessive diseases have been delineated that are relatively frequent among Palestinian Arabs. Among those, in 40 the mutation(s) responsible for the diseases are known. Fourteen of these disorders were caused by a single mutation, while the other 26 were due to multiple mutations. Most of the mutations were found in homozygosity among the affected patients. It is probable that the high frequency of most of the genetic diseases among the Palestinian Arabs is due to a founder effect as the result of the high consanguinity rates in this population. However, in some cases the high frequency was demonstrated to be secondary to the presence of multiple mutations, either allelic or in different genes in a small geographic region. This phenomenon remains unexplained but may be secondary to a selective advantage to the carriers, either specific to the region or to the population.

Parental consanguinity in specific types of congenital anomalies

Parental consanguinity, as a recognized risk factor for congenital anomalies, has mainly been studied with a focus on the types of parental relationships and their effects on genetic syndromes or birth defects in general. The present work analyzed the association between parental consanguinity and congenital anomalies, split, when possible, into clinical subtypes, in an attempt to obtain some insight into their recognized etiological heterogeneity. The material consisted of 34,102 newborn infants, affected by one of 47 selected congenital anomaly types, ascertained by the Latin-American Collaborative Study of Congenital Malformations (ECLAMC) during the period from 1967 to 1997. The consanguinity rate for each congenital anomaly type was compared with that of the population under study (0.96%), and the potentially confounding effect of six selected variables was controlled through a conditional logistic regression analysis for those congenital anomalies significantly associated with consanguinity. Pre-occurrence rates for the same congenital anomaly in sibships of consanguineous and non-consanguineous cases were compared. A significant association with parental consanguinity was observed for three congenital anomaly types: hydrocephalus, postaxial hand polydactyly, and bilateral cleft lip +/- cleft palate, while three additional anomalies, namely, cephalocele, microcephaly, and hand + foot postaxial polydactyly, showed a positive association, but statistical significance disappeared after adjustment for confounders, probably owing to sample size reduction. The association between consanguinity and Down syndrome was mainly due to the confounding effect of maternal age, while for hydrops fetalis and 2-3 toe syndactyly, the observed positive association could not be tested for confounders due to sample size reduction.

Congenital hydrocephalus: nosology and guidelines for clinical approach and genetic counselling

Congenital hydrocephalus is a serious condition that can arise from multiple causes. It comprises a diverse group of conditions which result in impaired circulation and absorption of cerebrospinal fluid. Congenital malformations of the central nervous system, infections, haemorrhage, trauma, teratogens and, occasionally, tumours can all give rise to hydrocephalus. In this paper we focus on the genetic aspects of hydrocephalus, excluding neural tube defects. The incidence is 0.4-0.8 per 1000 liveborns and stillbirths. X-linked hydrocephalus comprises approximately 5% of all cases. This condition is caused by mutations in the gene at Xq28 encoding for L1, a neural cell adhesion molecule. Carrier detection and prenatal diagnosis can be offered to affected families by means of chorionic villus biopsy and linkage analysis or L1 mutation analysis. In general, recurrence risk for congenital hydrocephalus excluding X-linked hydrocephalus, is low; empiric risk figures found in various studies range from <1% to 4%. Unfortunately, prenatal diagnosis based on an early ultrasound scan is not always reliable as ventriculomegaly usually starts after 20 weeks of gestation. We stress the importance of additional clinical investigations. Prognosis in the prenatally diagnosed patients depends on additional malformations but in general, is not very good.

CONCLUSION

Congenital hydrocephalus may be non-syndromic and syndromic. Prognosis depends primarily on the underlying cause and/or associated malformations, which have to be delineated on the basis of clinical, cytogenetic and molecular analysis.

Genetic disorders among Palestinian Arabs. 2. Hydrocephalus and neural tube defects

Congenital hydrocephalus and/or open neural tube defect was present in at least one individual of 98 families out of the 2,000 Palestinian Arabic families who have visited the Genetic clinic at the Hadassah Medical Center. In 22 families the brain malformation was part of a syndrome: Meckel syndrome in 10, Warburg syndrome in another 5, Carpenter in one, and undiagnosed in 6 families. In 76 of the families the neural tube defect and/or the hydrocephalus were non-syndromal. It seems that most of the cases of isolated non-syndromal hydrocephalus represented autosomal recessive traits and that an abnormal allele is common among Palestinian Muslim Arabs.

Autosomal recessive hydrocephalus with aqueductal stenosis

We report the case histories of three sisters with congenital hydrocephalus associated with stenosis of the cerebral aqueduct. The parents were a young consanguineous couple. In two cases hydrocephalus was detected before birth by ultrasonography. We consider these three cases to be of the rare autosomal form of hereditary hydrocephalus.