Brief report: intragenic deletion of the KALIG-1 gene in Kallmann's syndrome

Antibody to neural cell adhesion molecule can disrupt the migration of luteinizing hormone-releasing hormone neurons into the mouse brain

The neurons which synthesize and release luteinizing hormone-releasing hormone (LHRH), are hypothesized to originate in the epithelium of the medial olfactory pit and to migrate into the brain along a scaffolding made up of neural cell adhesion molecule (NCAM)-immunoreactive branches of the terminal and vomeronasal nerves. These LHRH neurons, studied by immunocytochemical and autoradiographic procedures, were found to originate within a very short period of embryogenesis, specifically day 10, in mice, and to follow a remarkably ordered spatiotemporal course along the migration route into the brain. The purpose of the present experiments was to determine whether perturbation of the NCAM-immunoreactive migration route, at a particular time in development, would arrest the migration of LHRH neurons into the brain. We found that a 1 microliter injection of antiserum to NCAM into the area of the olfactory pit, on day 10 of embryogenesis, significantly reduced the number of LHRH-immunoreactive neurons seen in the epithelium of the medial olfactory pit, with a concomitant significant reduction in the number of LHRH-immunoreactive cells seen outside of the placode, on the migration route. These results confirm our initial hypothesis that LHRH neurons migrate from the epithelium of the olfactory pit to the brain and indicate that NCAM plays a causal role in this phenomenon.

Diagnosis of X-recessive Kallmann syndrome in early infancy. Evidence of hypoplastic rhinencephalon

A 3-month-old infant presented with hypogonadism, a small penis and bilateral cryptorchidism. He showed an insufficient response of luteotropic hormone (LH) and follicle stimulating hormone (FSH) to luteotropic hormone releasing hormone (LHRH) and of testosterone to human chorionic gonadotropin. The maternal uncle had hypogonadism and anosmia and also showed an impaired LH and FSH response to LHRH. MRI examination showed hypoplasia of the rhinencephalon in both cases. These findings in the son and brother of the clinically unaffected mother suggest X-linked recessive inheritance.

Molecular genetics in neurology

There has been remarkable progress in the identification of mutations in genes that cause inherited neurological disorders. Abnormalities in the genes for Huntington disease, neurofibromatosis types 1 and 2, one form of familial amyotrophic lateral sclerosis, fragile X syndrome, myotonic dystrophy, Kennedy syndrome, Menkes disease, and several forms of retinitis pigmentosa have been elucidated. Rare disorders of neuronal migration such as Kallmann syndrome, Miller-Dieker syndrome, and Norrie disease have been shown to be due to specific gene defects. Several muscle disorders characterized by abnormal membrane excitability have been defined as mutations of the muscle sodium or chloride channels. These advances provide opportunity for accurate molecular diagnosis of at-risk individuals and are the harbinger of new approaches to therapy of these diseases.

X-linked Kallmann syndrome. A neuronal targeting defect in the olfactory system?

Kallmann syndrome is a human genetic disorder characterized by the association of hypogonadism with the inability to smell, and is due to defects in the olfactory system development (i.e. incomplete migration of olfactory axons and of gonadotropin-releasing hormone producing neurons from the olfactory epithelium to the forebrain; aplasia or hypoplasia of olfactory bulbs and tracts). The human X-linked Kallmann syndrome gene and its chicken homologue have been cloned. Their protein products contain fibronectin type III repeats and a 'four-disulfide-core' domain also found in molecules that are involved in neural development. Consistent with the human phenotype, the chicken Kallmann gene is expressed in the developing olfactory bulb. At present the molecular and cellular mechanism of action of the Kallmann syndrome gene product is unknown. Based on expression studies and the characteristics domains of the predicted protein, it is hypothesized that the protein may be involved in targeting olfactory axons to the bulb. Alternatively, the Kallmann protein could be an extracellular matrix component required for the proper formation of the multilayered structure of the olfactory bulb.

Congenital heart disease associated with sporadic Kallmann syndrome

A 17-year-old boy with Kallmann syndrome had complex congenital heart disease that included double-outlet right ventricle, d-mal-position of the great arteries, right aortic arch, and hypoplastic main pulmonary artery. He had neurosensory hearing loss and mental retardation. The 7 previously reported patients with Kallmann syndrome and cardiac abnormalities were short with height > or = 2 standard deviations below the mean for age (5/7), lacked a family history of Kallmann syndrome (6/6), and were mentally retarded (4/4). Patients presenting with Kallmann syndrome and congenital heart defects appear to represent a distinct subgroup of patients with Kallmann syndrome. The cause of this association is unclear, but may involve either autosomal recessive inheritance, sporadic dominant mutation, or a shared teratogenic event during the first trimester of gestation.

Expression pattern of the Kallmann syndrome gene in the olfactory system suggests a role in neuronal targeting

Kallmann syndrome is a genetic disorder characterized by a defect in olfactory system development, which appears to be due to an abnormality in the migration of olfactory axons and gonadotropin releasing hormone (Gn-RH) producing neurons. The X-linked Kallmann syndrome gene shares significant similarities with molecules involved in neural development. We have now isolated the evolutionarily conserved chicken homologue of the Kallmann gene. In the developing and adult chicken, high levels of expression were found in the mitral cells of the olfactory bulb (the target of olfactory axons) and in the Purkinje cells of the cerebellar cortex, both areas affected in patients with Kallmann syndrome. We propose a model in which the Kallmann syndrome gene product is a signal molecule required for neuronal targeting throughout life.

Moebius syndrome associated with pituitary dwarfism and hypoplastic optic disc

A 17 year old male patient with Moebius syndrome with pituitary dwarfism and unilateral hypoplastic optic disc is presented. Although there have been several reports of an association of Moebius syndrome and pituitary dysfunction, growth hormone deficiency has not been reported previously. These associations may give some insight into the pathogenesis of Moebius syndrome.

Characterization of neuronal cell varieties migrating from the olfactory epithelium during prenatal development in the rat. Immunocytochemical study using antibodies against olfactory marker protein (OMP) and luteinizing hormone-releasing hormone (LH-RH)

The development of neurons located outside the olfactory epithelium was studied by using antisera against olfactory marker protein (OMP) and luteinizing hormone-releasing hormone (LH-RH) in the rat. The study was restricted to the localization of these cells in the nasal cavity and in the region of the olfactory bulb during development. We describe groups of cells that stain positively for OMP located principally on the ventro-lateral aspect of the olfactory bulbs. A comparison is made with the LH-RH-immunoreactive system of cells which predominate on the medial aspect following the known trajectory of the nervus terminalis. OMP-immunoreactive cells appeared along the course of the olfactory fibers when they were first detected at embryonic day 16. These cells became restricted to a small group above the cribriform plate, ventral to the olfactory bulbs that seemed to disappear shortly after birth. It is concluded that these cells, which like the LH-RH cells have most probably migrated from the olfactory placode, represent a group of intervening neurons between the olfactory receptor cells and the olfactory bulb, serving as hints for olfactory axons to reach their targets during prenatal development.

Molecular basis of the X-chromosome-linked Kallmann's syndrome

Kallmann's syndrome combines hypogonadotropic hypogonadism and anosmia. The most frequent form of the disease is linked to the X chromosome and has been proposed to be due to a defect in the embryonic migration of GnRH neurons and olfactory axons from the nose to the brain. A candidate gene for the X-linked form of the disease has been isolated by positional cloning. Mutations in the open reading frame have been identified in several patients, providing convincing evidence that this gene is the actual gene, KAL, responsible for the X-linked Kallmann's syndrome. Correlations between molecular and clinical data extend the role of the KAL gene to other neuronal pathways and kidney organogenesis. The deduced amino acid sequence led us to postulate that the KAL protein is an extracellular matrix component with possible antiprotease and adhesion functions. Such functions are known to be involved in neuronal migration, axonal guidance and targeting, and also in synaptogenesis. Further experiments will enable the elucidation of the role of the KAL protein.

Transient pattern of exuberant projections of olfactory axons during development in the rat

The purpose of our study was twofold: (1) to trace the development of the olfactory axons from early embryonic stages until the mature pattern of connectivity and (2) to determine whether a transient penetration of them exists beyond the olfactory glomeruli. Two techniques were employed: DiI applied in the olfactory epithelium after aldehyde fixation, and olfactory marker protein (OMP) immunostaining. At E13 and E14 olfactory axons were observed spreading over the telencephalic vesicle and entering deeply into the prospective olfactory bulb, extending near the ventricular zone. Growth cones were seen at the end of these axons. At E15, the bundles of olfactory axons form a network, in which axons, growth cones and cells were seen. Some of these axons entered the olfactory bulb. Using OMP immunostaining olfactory axons were observed along the external plexiform layer, the mitral cell layer and in the granular layer from E19 to P6. At P9 some OMP immunoreactive axons were observed in the external plexiform layer. No OMP immunostained axons could be observed outside the glomeruli at P10. Our conclusions are that a transient immature pattern of early invasion over the telencephalic vesicle and of the olfactory bulb by olfactory axons occurs in the olfactory system. By the second postnatal week the glomerular layer reaches its mature configuration, and no olfactory fibers are seen outside the glomerular layer.

Structure of the X-linked Kallmann syndrome gene and its homologous pseudogene on the Y chromosome

The gene for the X-linked Kallmann syndrome (KAL), a developmental disorder characterized by hypogonadotropic hypogonadism and anosmia, maps to Xp22.3 and has a homologous locus, KALP, on Yq11. We show here that KAL consists of 14 exons spanning 120-200 kilobases that correlate with the distribution of domains in the predicted protein including four fibronectin type III repeats. The KALP locus reveals several large deletions and a number of small insertions, deletions and base substitutions which indicate it is a non-processed pseudogene. The sequence divergence between KAL and KALP in humans, and the chromosomal location of KAL homologous sequences in other primates, suggest that KALP and the steroid sulphatase pseudogene on Yq11 were involved in the same rearrangement event on the Y chromosome during primate evolution.

Kallmann syndrome gene on the X and Y chromosomes: implications for evolutionary divergence of human sex chromosomes

The recently identified gene for X-linked Kallmann syndrome (hypogonadotropic hypogonadism and anosmia) has a closely related homologue on the Y chromosome. The X and Y copies of this gene are located in a large region of X/Y homology, on Xp22.3 and Yq11.2, respectively. Comparison of the structure of the X-linked Kallmann syndrome gene and its Y homologue shed light on the evolutionary history of this region of the human sex chromosomes. Our data show that the Y homologue is not functional. Comparative analysis of X/Y sequence identity at several loci on Xp22.3 and Yq11.2 suggests that the homology between these two regions is the result of a complex series of events which occurred in the recent evolution of sex chromosomes.

Kallmann syndrome due to a translocation resulting in an X/Y fusion gene

The X-linked Kallmann syndrome gene was recently cloned and homologous sequences of unknown functional significance identified on the Y chromosome. We now describe a patient with Kallmann syndrome carrying an X;Y translocation resulting from abnormal pairing and precise recombination between the X-linked Kallmann syndrome gene and its homologue on the Y. The translocation created a recombinant, non-functional Kallmann syndrome gene identical to the normal X-linked gene with the exception of the 3' end which is derived from the Y. Our findings indicate that the 3' portion of the Kallmann syndrome gene is essential for its function and cannot be substituted by the Y-derived homologous region, although a 'position' effect remains a formal possibility.

The gene for X-linked Kallmann syndrome: a human neuronal migration defect

A new gene from the distal short arm of the human X chromosome has recently been cloned and characterized. Mutations in this gene lead to the neuronal migration defect observed in Kallmann syndrome. Although there is no direct proof for the involvement of this gene in neuronal migration, significant similarities between its predicted protein product and neural adhesion molecules have been found. X-linked Kallmann syndrome represents the first example in vertebrates of a neuronal migration defect for which the gene has been isolated.