Molecular genetics in neurology

Physiological and Pharmacological overview of the Gonadotropin Releasing Hormone

Gonadotropin-releasing Hormone (GnRH) is a decapeptide responsible for the control of the reproductive functions. It shows C- and N-terminal aminoacid modifications and two other distinct isoforms have been so far identified. The biological effects of GnRH are mediated by binding to high-affinity G-protein couple receptors (GnRHR), showing characteristic very short C tail. In mammals, including humans, GnRH-producing neurons originate in the embryonic nasal compartment and during early embryogenesis they undergo rapid migration towards the hypothalamus; the increasing knowledge of such mechanisms improved diagnostic and therapeutic approaches to infertility. The pharmacological use of GnRH, or its synthetic peptide and non-peptide agonists or antagonists, provides a valid tool for reproductive disorders and assisted reproduction technology (ART). The presence of GnRHR in several organs and tissues indicates additional functions of the peptide. The identification of a GnRH/GnRHR system in the human endometrium, ovary, and prostate has extended the functions of the peptide to the physiology and tumor transformation of such tissues. Likely, the activity of a GnRH/GnRHR system at the level of the hippocampus, as well as its decreased expression in mice brain aging, raised interest in its possible involvement in neurogenesis and neuronal functions. In conclusion, GnRH/GnRHR appears to be a fascinating biological system that exerts several possibly integrated pleiotropic actions in the complex control of reproductive functions, tumor growth, neurogenesis, and neuroprotection. This review aims to provide an overview of the physiology of GnRH and the pharmacological applications of its synthetic analogs in the management of reproductive and non-reproductive diseases.

GnRH in the Human Female Reproductive Axis

Gonadotropin-releasing hormone (GnRH) is recognized as the central regulator of the functions of the pituitary-gonadal axis. The increasing knowledge on the mechanisms controlling the development and the function of GnRH-producing neurons is leading to a better diagnostic and therapeutic approach for hypogonadotropic hypogonadisms and for alterations of the puberty onset. During female life span, the function of the GnRH pulse generator may be affected by a number of inputs from other neuronal systems, offering alternative strategies for diagnostic and therapeutic interventions. Moreover, the identification of a GnRH/GnRH receptor system in both human ovary and endometrium has widened the spectrum of action of the peptide outside its hypothalamic functions. The pharmacological use of GnRH itself or its synthetic analogs (agonists and antagonists) provides a valid tool to either stimulate or block gonadotropin secretion and to modulate the female fertility in several reproductive disorders and in assisted reproduction technology. The use of GnRH agonists in young female patients undergoing chemotherapy is also considered a promising therapeutic approach to counteract iatrogenic ovarian failure.

GnRH and GnRH receptors in the pathophysiology of the human female reproductive system

BACKGROUND

Human reproduction depends on an intact hypothalamic-pituitary-gonadal (HPG) axis. Hypothalamic gonadotrophin-releasing hormone (GnRH) has been recognized, since its identification in 1971, as the central regulator of the production and release of the pituitary gonadotrophins that, in turn, regulate the gonadal functions and the production of sex steroids. The characteristic peculiar development, distribution and episodic activity of GnRH-producing neurons have solicited an interdisciplinary interest on the etiopathogenesis of several reproductive diseases. The more recent identification of a GnRH/GnRH receptor (GnRHR) system in both the human endometrium and ovary has widened the spectrum of action of the peptide and of its analogues beyond its hypothalamic function.

METHODS

An analysis of research and review articles published in international journals until June 2015 has been carried out to comprehensively summarize both the well established and the most recent knowledge on the physiopathology of the GnRH system in the central and peripheral control of female reproductive functions and diseases.

RESULTS

This review focuses on the role of GnRH neurons in the control of the reproductive axis. New knowledge is accumulating on the genetic programme that drives GnRH neuron development to ameliorate the diagnosis and treatment of GnRH deficiency and consequent delayed or absent puberty. Moreover, a better understanding of the mechanisms controlling the episodic release of GnRH during the onset of puberty and the ovulatory cycle has enabled the pharmacological use of GnRH itself or its synthetic analogues (agonists and antagonists) to either stimulate or to block the gonadotrophin secretion and modulate the functions of the reproductive axis in several reproductive diseases and in assisted reproduction technology. Several inputs from other neuronal populations, as well as metabolic, somatic and age-related signals, may greatly affect the functions of the GnRH pulse generator during the female lifespan; their modulation may offer new possible strategies for diagnostic and therapeutic interventions. A GnRH/GnRHR system is also expressed in female reproductive tissues (e.g. endometrium and ovary), both in normal and pathological conditions. The expression of this system in the human endometrium and ovary supports its physiological regulatory role in the processes of trophoblast invasion of the maternal endometrium and embryo implantation as well as of follicular development and corpus luteum functions. The GnRH/GnRHR system that is expressed in diseased tissues of the female reproductive tract (both benign and malignant) is at present considered an effective molecular target for the development of novel therapeutic approaches for these pathologies. GnRH agonists are also considered as a promising therapeutic approach to counteract ovarian failure in young female patients undergoing chemotherapy.

CONCLUSIONS

Increasing knowledge about the regulation of GnRH pulsatile release, as well as the therapeutic use of its analogues, offers interesting new perspectives in the diagnosis, treatment and outcome of female reproductive disorders, including tumoral and iatrogenic diseases.

Brain development, infant communication, and empathy disorders: Intrinsic factors in child mental health

Disorders of emotion, communication, and learning in early childhood are considered in light of evidence on human brain growth from embryo stages. We cite microbehavioral evidence indicating that infants are born able to express the internal activity of their brains, including dynamic “motive states” that drive learning. Infant expressions stimulate the development of imitative and reciprocal relations with corresponding dynamic brain states of caregivers. The infant's mind must have an “innate self-with-other representation” of the inter-mind correspondence and reciprocity of feelings that can be generated with an adult.

Primordial motive systems appear in subcortical and limbic systems of the embryo before the cerebral cortex. These are presumed to continue to guide the growth of a child's brain after birth. We propose that an “intrinsic motive formation” is assembled prenatally and is ready at birth to share emotion with caregivers for regulation of the child's cortical development, on which cultural cognition and learning depend.

The intrinsic potentiality for “intersubjectivity” can be disorganized if the epigenetic program for the infant's brain fails. Indeed, many psychological disorders of childhood can be traced to faults in early stages of brain development when core motive systems form.

Down syndrome: advances in molecular biology and the neurosciences

The entire DNA sequence for human chromosome 21 is now complete, and it is predicted to contain only about 225 genes, which is approximately three-fold fewer than the number initially predicted just 10 years ago. Despite this remarkable achievement, very little is known about the mechanism(s) whereby increased gene copy number (gene dosage) results in the characteristic phenotype of Down syndrome. Although many of the phenotypic traits show large individual variation, neuromotor dysfunction and cognitive and language impairment are observed in virtually all individuals. Currently, there are no efficacious biomedical treatments for these central nervous system-associated impairments. To develop novel therapeutic strategies, the effects of gene dosage imbalance need to be understood within the framework of those critical biological events that regulate brain organization and function.

Conclusions of the symposium

On the basis of twenty-one kindreds and three cases from uninformative families, the Symposium has confirmed that fatal familial insomnia (FFI) is genotypically and phenotypically distinct and, likely, the third most common inherited prion disease. The genotype, characterized by the D178N mutation on the prion protein (PrP) gene coupled with the methionine codon at position 129 has been demonstrated in all cases. The immunoblot pattern of the PrPres associated with FFI shows a molecular mass of approximately 19kDa for the core protein and a marked underrepresentation of the unglycosylated form. The histopathology, characterized by marked thalamic and inferior olivary atrophy with a variable degree of cerebral cortical spongiosis has been observed in all but two cases. The disease duration was found to be significantly shorter in the FFI subjects homozygous at codon 129 than in the heterozygous subjects. The FFI sleep disorder is characterized by lack of spindle activity and disruption of the wake-sleep cycle which can only be established , or excluded, by polysomnography. Autonomic, endocrine and cognitive impairments also require careful assessment in each case. A condition lacking the D178N mutation and pathologically identical to FFI has been reported. Presence of sleep, autonomic and endocrine abnormalities needs to be demonstrated to identify this condition as a sporadic form of FFI. The pathophysiology of the sleep disorder, the pathogenic mechanisms, fine and early structural changes, including the role of apoptosis, and disease penetrance are the major unresolved issues in FFI.

A Dutch family with benign hereditary chorea of early onset: differentiation from Huntington's disease

A large Dutch family of 88 members, running through five generations, is described with benign hereditary chorea of early onset. The clinical presentation was heterogeneous. The chorea manifested in late infancy or childhood, interfered with writing, was non-disabling, stable or even improved in adulthood in most cases, but was slowly progressive with gait impairment in some. There was mild dysarthria and normal intelligence. EEG brain CT-scanning and MRI were normal. Huntington's disease was excluded by analysis of the I T 15 gene, which showed a normal number of the CAG trinucleotide repeats in two patients. It is concluded that benign hereditary chorea of early onset is an entity different from Huntington's disease and that in cases of early onset chorea the diagnostic accuracy is markedly improved by DNA testing.

Pediatric epilepsy syndromes: an update and critical review

Epilepsy syndromes occupy an important position in the current nosology of the epilepsies, describing and classifying seizure disorders with shared clinical and EEG features. Increasingly, this schema is being refined as new information becomes available and our understanding of etiology and presentation of each syndrome widens. Advances in neuroimaging and neurogenetics have been particularly important and are likely to fundamentally change our concepts of syndrome classification. At present, the International League Against Epilepsy classification of epilepsy syndromes according to presumed localization (partial, generalized, undetermined) and etiology (idiopathic, cryptogenic, symptomatic). In clinical practice, it is often useful to conceptualize epilepsy syndromes according to their usual age at presentation, which greatly facilitates syndrome identification in new patients and recognizes the age-related expression of many childhood epilepsies. Definitional problems exist for many pediatric epilepsy syndromes, particularly the epileptic encephalopathies of early infancy, the benign epilepsies of infancy and childhood, the myoclonic epilepsies of infancy and early childhood, and the idiopathic generalized epilepsies of childhood and adolescence. It is likely that further input from the fields of molecular genetics and neuroimaging will enable the classification of epilepsies to become more etiologically oriented and disease specific.

Relationship between trinucleotide repeats and neuropathological changes in Huntington's disease

The discovery of the Huntington's disease (HD) gene has provided the impetus to determine the association between the triplet repeat sequences and clinical manifestations of the disease. The present study is directed toward determining the relationship between the triplet repeat sequences and severity of the neurodegenerative process. Nineteen HD postmortem cases were evaluated for neuropathological changes as well as for the number of trinucleotide repeat sequences, each in a blinded fashion. Each case was assigned a gross grade according to the scale of Vonsattel and colleagues (1985); neuronal counts were then performed on both the caudate and the putamen. For 7 of the postmortem cases, blood had been collected prior to death and was analyzed for the HD gene. For the 12 remaining cases for which blood was unavailable, DNA from the frontal neocortex and striatum was extracted from frozen or formalin-fixed paraffinized tissue and subsequently analyzed for the HD gene. When correlation was made for age at death, greater numbers of trinucleotide repeats were associated with greater neuronal loss, in both the caudate (r = 0.9641, p < 0.001) and the putamen (r = 0.9652, p < 0.001). When correction was made for disease duration, the correlation was again significant, for both the caudate (r = 0.6396, p < 0.01) and the putamen (r = 0.6710, p < 0.001). This suggests that in HD, longer trinucleotide repeat length is associated with a faster rate of deterioration and greater pathological severity. A comparison of trinucleotide repeat length in different brain regions in 4 of the HD postmortem cases associated with greater numbers of repeats consistently demonstrated fewer repeats in the cerebellum than in the frontal cortex, striatum or blood.

Parents do matter: genomic imprinting and parental sex effects in neurological disorders

Genomic imprinting is a recently recognized phenomenon of differential expression of genetic material depending upon whether the genetic material has come from the male or female parent. This process of differential phenotypic expression involves mammalian development both in the normal and abnormal situations, resulting in parental sex effects. However, some parental sex effects may be due to other mechanisms such as mitochondrial inheritance. In the following article, evidence for genomic imprinting in experimental animals and in diseases are summarized. Relevant human neurological disorders manifesting parental sex effects discussed here include myotonic dystrophy, Huntington's disease, fragile X syndrome, spinocerebellar ataxia type 1, and neurofibromatosis type 1 and 2. A possible mechanism of imprinting involves the processes of methylation imprint and replication imprint. The knowledge of imprinting is helpful in clinical practice particularly in the areas of genetic counseling, prenatal diagnosis, and possible future gene therapy.

Investigation of peripheral neuropathy

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Biotechnology domain

Biotechnology and the use of biologically based agents for the betterment of mankind is an active field which is founded on the interaction between many basic sciences. This is achieved in coordination with engineering and technology for scaling up purposes. The application of modern recombinant DNA technology gave momentum and new horizons to the field of biotechnology both in the academic setting and in industry. The applications of biotechnology are being used in many fields including agriculture, medicine, industry, marine science and the environment. The final products of biotechnological applications are diverse. In the medical applications of biotechnology, for example, the field has been evolving in such a way that the final product could be a small molecule (e.g. drug/antibiotic) that can be developed based on genetic information by drug design or drug screening using a cloned and expressed target protein.

Fatal familial insomnia and familial Creutzfeldt-Jakob disease: clinical, pathological and molecular features

Fatal familial insomnia (FFI) and a subtype of familial Creutzfeldt-Jakob disease (CJD178) are two prion diseases that have different clinical and pathological features, the same aspartic acid to asparagine mutation (D178N) at codon 178 of the prion protein (PrP) gene, but distinct genotypes generated by the methionine-valine polymorphism at codon 129 (129M or 129V) in the mutant allele of the PrP gene. The D178N, 129M allele segregates with FFI while the D178N, 129V allele segregates with CJD178. The proteinase K resistant PrP (PrPres) isoforms present in FFI and CJD178 differ in degree of glycosylation and size. Thus, the amino acid, methionine or valine, at position 129 of the mutant allele, in conjunction with D178N mutation results in significant alterations of PrPres in FFI and CJD178. The 129 polymorphic site also exerts influence through the normal allele: the course of the disease is shorter in the patients homozygous at codon 129 and other minor but consistent phenotypic differences occur between homozygous and heterozygous FFI patients. The comparative study of PrPres distribution in FFI homozygotes and heterozygotes at codon 129 has lead to the conclusion that the phenotypic differences observed between these two FFI patient populations may be the result of different rates of conversion of normal PrP into PrPres, at least in some brain regions.

Gene therapy and pharmacological treatment of inherited neurological disorders

The identification of mutant genes responsible for inherited neurological disorders gives an opportunity to consider new approaches to their treatment. Although replacement of defective genes in postmitotic neurons is unlikely to be possible in the near future, the identification of gene products, and definitive delineation of the cellular dysfunction and death that result from mutated gene products, may suggest new therapeutic options. This article reviews these advances and considers approaches that may provide hope for alleviation of these disorders.

Plasma lysosomal enzyme levels in patients with motor neuron disease

beta-Hexosaminidase and acid-alpha-mannosidase were estimated in 17 adult patients with motor neuron disease. Normal plasma levels of beta-hexosaminidase ((A+B) and A) were found in all patients studied. Plasma acid alpha-mannosidase levels were normal in all but two patients with the spinal muscular atrophy type of the disorder. In addition, altered biochemical properties of acid alpha-mannosidase (i.e. Km, thermal stability) were found in the low-activity cases.

APOE is a major susceptibility gene for Alzheimer's disease

The initial report on APOE as a susceptibility gene for late-onset Alzheimer's disease was presented a little more than two years ago. During the past year, several significant events have given added impetus to research into Alzheimer's. The association of increased allele frequency of APOE4 with Alzheimer's disease has been reproduced in several dozen laboratories around the world. The protective effect of the APOE2 allele has been reported and also rapidly verified. No evidence exists to support the notion of linkage disequilibrium with any nearby locus on chromosome 19. The neuropathological demonstration of apolipoprotein E (apoE) within neuronal cytoplasm in a location suitable for proposed interaction with microtubule-associated protein tau and MAP2c has introduced a new view of neuronal neurobiology. As apoE is not known to be expressed in neurons, its relationship with cellular receptors, such as the low-density lipoprotein related receptor, and the mechanism of intracellular trafficking are now important research problems. The role of apoE as a metabolic co-factor in neuronal metabolism presents new possibilities for neuronal mechanisms of maintenance and response to stress.

Neurology

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Genetic factors in the etiology of idiopathic Parkinson's disease

Overshadowed by a vigorous search for an environmentally-derived toxin that would be possibly relevant for the pathogenesis of idiopathic Parkinson's disease (PD), genetic factors have largely been neglected for this condition during the last two decades. Recent descriptions of kindreds over three or more generations with several family members affected have renewed the interest in genetics of PD. Concurring with this, diagnostic concepts and pathologic criteria for PD and for idiopathic Lewy-body (LB) disease have been reevaluated such that LB-proven parkinsonism is sufficiently differentiated from familial parkinsonism without LB pathology. Surveys on genetic epidemiology in PD have confirmed the 19th century's notion that 10 to 15% of PD index cases report a further family member with PD. These figures were, however, substantiated on a statistical basis only in single surveys when comparisons were made with the numbers of PD relatives in control index cases. Twin studies did not reveal a higher rate of concordance within monozygotic pairs than in dizygotic pairs. Tests of striatal 18-F-Dopa uptake in clinically unaffected mono- and dizygotic co-twins did not alter the ratio between the concordance rates. Though not excluded by the twin studies, multifactorial (or polygenic) inheritance as well as mitochondrial inheritance are at present less likely to cover most of the inheritance pattern in familial LB parkinsonism. Instead, autosomal dominant inheritance with reduced penetrance is the most probable inheritance pattern for most of the reported pedigrees. Molecular genetic investigations have to consider the biochemical basis of the age- and region-specific pathology of PD. The first analyses of linkage and allelic associations gave inconclusive results in sporadic and familial PD. The hunt for metabolic factors that link geno- and phenotype expression in PD will continue.