Autosomal recessive nonsyndromal hydrocephalus

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.

Heterogeneous expression of hydrocephalic phenotype in the hyh mice carrying a point mutation in α-SNAP

The hyh mouse carrying a point mutation in the gene encoding for soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein alpha (alpha-SNAP) develops inherited hydrocephalus. The investigation was designed to study: (i) the clinical evolution of hyh mice; (ii) factors other than the alpha-SNAP mutation that may influence the expression of hydrocephalus; (iii) the neuropathological features underlying the different forms of clinical evolution. The study included 3017 mice, 22.4% of which were hydrocephalic. The neuropathological study was performed in 112 mice by use of light and electron microscopy. It was found that maternal- and sex-related factors are involved in the heterogeneous expression of hyh phenotype. The clinical evolution recorded throughout a 4-year period also revealed a heterogeneous expression of the hydrocephalic phenotype. Two subpopulations were distinguished: (i) 70% of mice underwent a rapidly progressive hydrocephalus and died during the first 2 months of life; they presented macrocephaly, extremely large expansion of the ventricles, equilibrium impairment and decreased motor activity. (ii) Mice with slowly progressive hydrocephalus (30%) survived for periods ranging between 2 months and 2 years. They had no or moderate macrocephaly; moderate ventricular dilatation and preserved general motor activity; they all presented spontaneous ventriculostomies communicating the ventricles with the subarachnoid space, indicating that such communications play a key role in the long survival of these mice. The hyh mutant represents an ideal animal model to investigate how do the brain "adapt" to a virtually life-lasting hydrocephalus.

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.

Late onset X-linked hydrocephalus with normal cerebrospinal fluid pressure

A family with X-linked hydrocephalus with normal cerebrospinal fluid (CSF) pressure and in which three brothers and a grandson of case 1, a proband, were affected is reported. The symptoms at onset were epileptic attacks that started in adulthood in the three brothers and at the age of 6 years in the grandson. In the three brothers, from 10 to 27 years after the onset of epileptic episodes, disorganization of intelligence and psychiatric deterioration were gradually noticed by their families. At the same time, they showed occasional urinary incontinence. Brain computed tomography (CT) scans revealed dilatation of the ventricular systems. Based on the results of the measurement of CSF pressure and radioactive-iodinated human serum albumin (RISA)-cysternography, two of the brothers were diagnosed as having normal pressure hydrocephalus (NPH), and they were treated neurosurgically. However, no obvious improvement in clinical symptoms was observed. Although the grandson had shown normal psychomotor development during his early childhood, temporal epilepsy and temper tantrums started at the age of 6 years. Computed tomography-scanning revealed dilatation of the ventricular system similar to the other three cases at the age of 8 years. With the diagnosis of NPH, the patient underwent a shunt operation, which resulted in no obvious effects. As it is reasonable to surmise that the pathological gene would have been transferred via the daughter of the proband to the grandson, it is suggested that the inheritance manner might be X-linked recessive. The cases presented here are different from the cases of hydrocephalus due to stenosis of the aqueduct Sylvius (HSAS) and other types of X-linked hydrocephalus reported previously in terms of the age of onset, course, symptoms, and CT findings. Thus, it is suggested that the present cases might be a new type of X-linked hydrocephalus.

Pleiotropic skeletal and ocular phenotypes of the mouse mutation congenital hydrocephalus (ch/Mf1) arise from a winged helix/forkhead transcriptionfactor gene

Congenital hydrocephalus is an etiologically diverse, poorly understood, but relatively common birth defect. Most human cases are sporadic with familial forms showing considerable phenotypic and etiologic heterogeneity. We have studied the autosomal recessive mouse mutation congenital hydrocephalus ( ch ) to identify candidate human hydrocephalus genes and their modifiers. ch mice have a congenital, lethal hydrocephalus in association with multiple developmental defects, notably skeletal defects, in tissues derived from the cephalic neural crest. We utilized positional cloning methods to map ch in the vicinity of D13Mit294 and confirm that the ch phenotype is caused by homozygosity for a nonsense mutation in a gene encoding a winged helix/forkhead transcription factor ( Mf1 ). Based on linked genetic markers, we performed detailed phenotypic characterization of mutant homozygotes and heterozygotes to demonstrate the pleiotropic effects of the mutant gene. Surprisingly, ch heterozygotes have the glaucoma-related distinct phenotype of multiple anterior segment defects resembling Axenfeld-Rieger anomaly. We also localized a second member of this gene family ( Hfh1 ), a candidate for other developmental defects, approximately 470 kb proximal to Mf1.

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.

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.

Autosomal recessive disorders among Arabs: an overview from Kuwait

Kuwait has a cosmopolitan population of 1.7 million, mostly Arabs. This population is a mosaic of large and small minorities representing most Arab communities. In general, Kuwait's population is characterized by a rapid rate of growth, large family size, high rates of consanguineous marriages within the Arab communities with low frequency of intermarriage between them, and the presence of genetic isolates and semi-isolates in some extended families and Bedouin tribes. Genetic services have been available in Kuwait for over a decade. During this time it has become clear that Arabs have a high frequency of genetic disorders, and in particular autosomal recessive traits. Their pattern is unique and some disorders are relatively common. Examples are Bardet-Biedl and Meckel syndromes, phenylketonuria, and familial Mediterranean fever. A relatively large number of new syndromes and variants have been delineated in Kuwait's population, many being the result of homozygosity for autosomal recessive genes that occurred because of inbreeding. Some of these syndromes have subsequently been found in other parts of the world, negating the concept of the private syndrome. This paper provides an overview of autosomal recessive disorders among the Arabs in Kuwait from a personal perspective and published studies, and highlights the need for genetic services in Arab countries with the goal of prevention and treatment of genetic disorders.

Familial hydrocephalus of prenatal onset

Fourteen families in which more than one child was diagnosed with hydrocephalus of prenatal onset were seen in our genetic counseling clinic. In 7 families only males were affected: in 2 X-linked hydrocephalus was diagnosed while X-linked inheritance was suspected in 3 other families. These 5 families were of Jewish origin. In the 8 families of Arab origin, the parents of the affected children were consanguineous. In 6 of these families at least one female was affected and the hydrocephalus was most probably inherited as an autosomal recessive trait. This type of hydrocephalus of prenatal onset appears to be frequent among Palestinian Arabs.

Assignment of X-linked hydrocephalus to Xq28 by linkage analysis

X-linked recessive hydrocephalus (HSAS) occurs at a frequency of approximately 1 per 30,000 male births and consists of hydrocephalus, stenosis of the aqueduct of Sylvius, mental retardation, spastic paraparesis, and clasped thumbs. Prenatal diagnosis of affected males by ultrasonographic detection of hydrocephalus is unreliable because hydrocephalus may be absent antenatally. Furthermore, carrier detection in females is not possible because they are asymptomatic. Using four families segregating HSAS, we performed linkage analysis with a panel of X-linked probes that detect restriction fragment length polymorphisms. We report here that HSAS, in all tested families, is closely linked to marker loci mapping in Xq28 (DXS52, lod = 6.52 at theta of 0.03; F8, lod = 4.32 at theta of 0.00; DXS15, lod = 3.40 at theta of 0.00). These data assign HSAS to the gene-dense chromosomal band Xq28 and allow for both prenatal diagnosis and carrier detection by linkage analysis.

Autosomal recessive hydrocephalus with third ventricle obstruction

Here we report a brother and sister who presented in the neonatal period with hydrocephalus. Ultrasonography showed marked dilatation of the lateral ventricles but not the third ventricle. One child with postnatal onset was shunted and had normal development at 3 years. The other child had severe hydrocephalus at birth and was not treated. Neuropathologic studies demonstrated dilatation of the lateral ventricles and marked narrowing of the posterior part of the third ventricle but no other malformations other than those that result directly from hydrocephalus. The potential for a good prognosis is emphasized.