Olfactory system and demyelination

Olfactory disorders in childhood: A comparative study of olfaction in children with adenoid hyperplasia versus a control group and the postoperative effects of adenoidectomy with respect to olfactory ability

PURPOSE

Hyposmia in childhood is poorly characterized. The "U-Sniff Test", validated for children with anosmia, can be used to objectify olfactory impairment but has not been used to distinguish between hyposmia and normosmia. Therefore, we investigated children with enlarged adenoids with respect to hyposmia, its correlation with adenoid size, and the sensitivity of questionnaires to predict olfactory impairment.

METHODS

In a prospective comparison, olfaction was assessed by "U-Sniff Test" (score 0-12; <8 hyposmia) in 41 children (5-18 years) with adenoid hyperplasia and compared with 196 children without any respiratory affection (control) after exclusion of previous SARS-Cov2-infection from December 2020 to December 2021. ENT-related complaints were collected using a self-designed questionnaire. We were able to include 13 children in a follow-up examination to compare preoperative performance in the "U-Sniff Test" with postoperative outcome after adenoidectomy.

STATISTICS

chi-square-test (p < 0.05), odds-ratio, Spearman's rho, ROC-, cluster analysis.

RESULTS

Severe hyposmia was present in 36.6% of children with adenoid-hyperplasia compared to 3.1% of the control-group. Adenoid-children scored significantly more often between 8 and 10 points (58.5%) than the control (31.6%; p < 0.01). Adenoid size and olfactory performance correlate significantly (r: 0.83; CI -0.89 … -0.72). Hyposmia in the adenoid group is characterized predominately by loss of the odors banana, butter and rose. None of children with hyposmia or parents reported impaired olfactory performance. Postoperatively, olfactory function improved significantly in 85% of cases (p 0.01, SD ± 1.71, Δ3.54points).

CONCLUSION

Questionnaires are insufficient to detect hyposmia in this cohort. In contrast, the "U-Sniff Test" detects even reduced olfactory performance without reaching the cut-off value, which represents the majority of test results in the adenoid group. Therefore, we recommend the classification of moderate hyposmia (8-10 points) to be included for our study population.

Unilaterally disrupted structural and functional connectivity of the fronto-limbic system in idiopathic hypogonadotropic hypogonadism

OBJECTIVE

Idiopathic hypogonadotropic hypogonadism (IHH) is rare and can either be associated with normal or defective olfactory sensation, classified as normosmic IHH (nIHH) or Kallmann syndrome (KS). We do not yet understand the central processing pathways in the olfactory system. We aimed to compare the resting-state structural and functional connectivity (FC) of olfactory neural pathways in patients with IHH. We hypotheses that alterations of structural connectivity and FC may exist in the olfactory cortex pathways in IHH patients.

DESIGN

STRUCTURAL AND FUNCTIONAL CONNECTIVITY DATA RESULTS BETWEEN TWO GROUPS WERE ANALYZED: Patients: Twenty-five IHH patients (13 nIHH patients and 12 KS patients) were recruited from the Department of Endocrinology and were assessed. A total of 25 age-matched healthy male controls were recruited from the community.

MEASUREMENTS

All subjects underwent diffusion tensor imaging and functional magnetic resonance imaging (fMRI) scans. Structural and functional connectivity data analyses were then performed. Pearson's correlation analyses were performed to investigate the correlations between the fractional anisotropy (FA) value and FC strength, showing significant differences among the three groups separately.

RESULTS

Compared with the HC group, FA value in the right uncinate fasciculus (UF) decreased significantly in the IHH group. The olfactory cortex FC values of the right gyrus rectus, orbitofrontal cortex (OFC) and right middle temporal gyrus in the IHH group were decreased compared with those in the HC group. Moreover, there were significant negative correlations between right UF FA and olfactory cortex-FC to both the gyrus rectus and OFC within the HC group (p &lt; .05).

CONCLUSION

Our findings suggest that alterations of structural and FC support the presence of neurobiological disruptions in IHH patients, particularly a specific structural-functional asymmetry disruption may exist in the olfactory cortex pathways in IHH patients.

Molecular characterization of myelin basic protein a (mbpa) gene from red-bellied pacu (Piaractus brachypomus)

Background

Myelin basic protein (MBP) is one of the most important structural components of the myelin sheaths in both central and peripheral nervous systems. MBP has several functions including organization of the myelin membranes, reorganization of the cytoskeleton during the myelination process, and interaction with the SH3 domain in signaling pathways. Likewise, MBP has been proposed as a marker of demyelination in traumatic brain injury and chemical exposure.

Methods

The aim of this study was to molecularly characterize the myelin basic protein a (mbpa) gene from the Colombian native fish, red-bellied pacu, Piaractus brachypomus. Bioinformatic tools were used to identify the phylogenetic relationships, physicochemical characteristics, exons, intrinsically disordered regions, and conserved domains of the protein. Gene expression was assessed by qPCR in three models corresponding to sublethal chlorpyrifos exposure, acute brain injury, and anesthesia experiments.

Results

mbpa complete open reading frame was identified with 414 nucleotides distributed in 7 exons that encode 137 amino acids. MBPa was recognized as belonging to the myelin basic protein family, closely related with orthologous proteins, and two intrinsically disordered regions were established within the sequence. Gene expression of mbpa was upregulated in the optic chiasm of the chlorpyrifos exposed fish in contrast to the control group.

Conclusions

The physicochemical computed features agree with the biological functions of MBP, and basal gene expression was according to the anatomical distribution in the tissues analyzed. This study is the first molecular characterization of mbpa from the native species Piaractus brachypomus.

Novel Microdeletion in the X Chromosome Leads to Kallmann Syndrome, Ichthyosis, Obesity, and Strabismus

Background

A large deletion in Xp22.3 can result in contiguous gene syndromes, including X-linked ichthyosis (XLI) and Kallmann syndrome (KS), presenting with short stature, chondrodysplasia punctata, intellectual disability, and strabismus. XLI and KS are caused by the deletion of STS and ANOS1, respectively.

Method

Two KS patients with XLI were screened to identify possible pathogenic mutations using whole exome sequencing. The clinical characteristics, molecular genetics, treatment outcomes, and genotype–phenotype association for each patient were analyzed.

Results

We identified a novel 3,923 kb deletion within the Xp22.31 region (chrX: 5810838–9733877) containing STS, ANOS1, GPR143, NLGN4X, VCX-A, PUDP, and PNPLA4 in patient 1, who presented with KS, XLI, obesity, hyperlipidemia, and strabismus. We identified a novel 5,807 kb deletion within the Xp22.31-p22.33 regions (chrX: 2700083–8507807) containing STS, ANOS1, and other 24 genes in patient 2, who presented with KS, XLI, obesity, and strabismus. No developmental delay, abnormal speech development, or autistic behavior were noticed in either patient.

Conclusion

We identified two novel microdeletions in the X chromosome leading to KS and XLI. These findings contribute to the understanding of the molecular mechanisms that drive contiguous gene syndromes. Our research confirmed that the Kallmann-Ichthyosis phenotype is caused by microdeletions at the chromosome level.

Involvement of the Olfactory Apparatus by Gliomas

The olfactory bulbs and tracts are central nervous system white matter tracts maintained by central neuroglia. Although rare, gliomas can originate from and progress to involve the olfactory apparatus. Through a Health Insurance Portability and Accountability Act-compliant retrospective review of the institutional teaching files and brain MR imaging reports spanning 10 years, we identified 12 cases of gliomas involving the olfactory bulbs and tracts, including 6 cases of glioblastoma, 2 cases of anaplastic oligodendroglioma, and 1 case each of pilocytic astrocytoma, diffuse (grade II) astrocytoma, anaplastic astrocytoma (grade III), and diffuse midline glioma. All except the pilocytic astrocytoma occurred in patients with known primary glial tumors elsewhere. Imaging findings of olfactory tumor involvement ranged from well-demarcated enhancing masses to ill-defined enhancing infiltrative lesions to nonenhancing masslike FLAIR signal abnormality within the olfactory tracts. Familiarity with the imaging findings of glioma involvement of the olfactory nerves is important for timely diagnosis and treatment of recurrent gliomas and to distinguish them from other disease processes.

Distribution and classification of the extracellular matrix in the olfactory bulb

Extracellular matrix (ECM) became an important player over the last few decades when studying the plasticity and regeneration of the central nervous system. In spite of the established role of ECM in these processes throughout the central nervous system (CNS), only few papers were published on the ECM of the olfactory system, which shows a lifelong plasticity, synaptic remodeling and postnatal neurogenesis. In the present study, we have described the localization and organization of major ECM molecules, the hyaluronan, the lecticans, tenascin-R and HAPLN1 link protein in the olfactory bulb (OB) of the rat. We detected all of these molecules in the OB showing differences in the molecular composition, staining intensity, and organization of ECM between the layers and in some cases within a single layer. One of the striking features of ECM staining pattern in the OB was that the reactions are shown dominantly in the neuropil, the PNNs were found rarely and they exhibited thin or diffuse appearance Similar organization was shown in human and mice samples. As the PNN limits the neural plasticity, its rare appearance may be related to the high degree of plasticity in the OB.

Olfactory ensheathing cells from the nasal mucosa and olfactory bulb have distinct membrane properties

Transplantation of olfactory ensheathing cells (OECs) is a potential therapy for the regeneration of damaged neurons. While they maintain tissue homeostasis in the olfactory mucosa (OM) and olfactory bulb (OB), their regenerative properties also support the normal sense of smell by enabling continual turnover and axonal regrowth of olfactory sensory neurons (OSNs). However, the molecular physiology of OECs is not fully understood, especially that of OECs from the mucosa. Here, we carried out whole-cell patch-clamp recordings from individual OECs cultured from the OM and OB of the adult rat, and from the human OM. A subset of OECs from the rat OM cultured 1-3 days in vitro had large weakly rectifying K⁺ currents, which were sensitive to Ba²⁺ and desipramine, blockers of Kir4-family channels. Kir4.1 immunofluorescence was detectable in cultured OM cells colabeled for the OEC marker S100, and in S100-labeled cells found adjacent to OSN axons in mucosal sections. OECs cultured from rat OB had distinct properties though, displaying strongly rectifying inward currents at hyperpolarized membrane potentials and strongly rectifying outward currents at depolarized potentials. Kir4.1 immunofluorescence was not evident in OECs adjacent to axons of OSNs in the OB. A subset of human OECs cultured from the OM of adults had membrane properties comparable to those of the rat OM that is dominated by Ba²⁺ -sensitive weak inwardly rectifying currents. The membrane properties of peripheral OECs are different to those of central OECs, suggesting they may play distinct roles during olfaction.

The Divalent Metal Transporter 1 (DMT1) Is Required for Iron Uptake and Normal Development of Oligodendrocyte Progenitor Cells

The divalent metal transporter 1 (DMT1) is a multimetal transporter with a primary role in iron transport. Although DMT1 has been described previously in the CNS, nothing was known about the role of this metal transporter in oligodendrocyte maturation and myelination. To determine whether DMT1 is required for oligodendrocyte progenitor cell (OPC) maturation, we used siRNAs and the Cre-lox system to knock down/knock out DMT1 expression in vitro as well as in vivo Blocking DMT1 synthesis in primary cultures of OPCs reduced oligodendrocyte iron uptake and significantly delayed OPC development. In vivo, a significant hypomyelination was found in DMT1 conditional knock-out mice in which DMT1 was postnatally deleted in NG2- or Sox10-positive OPCs. The brain of DMT1 knock-out animals presented a decrease in the expression levels of myelin proteins and a substantial reduction in the percentage of myelinated axons. This reduced postnatal myelination was accompanied by a decrease in the number of myelinating oligodendrocytes and a rise in proliferating OPCs. Furthermore, using the cuprizone model of demyelination, we established that DMT1 deletion in NG2-positive OPCs lead to less efficient remyelination of the adult brain. These results indicate that DMT1 is vital for OPC maturation and for the normal myelination of the mouse brain.SIGNIFICANCE STATEMENT To determine whether divalent metal transporter 1 (DMT1), a multimetal transporter with a primary role in iron transport, is essential for oligodendrocyte development, we created two conditional knock-out mice in which DMT1 was postnatally deleted in NG2- or Sox10-positive oligodendrocyte progenitor cells (OPCs). We have established that DMT1 is necessary for normal OPC maturation and is required for an efficient remyelination of the adult brain. Since iron accumulation by OPCs is indispensable for myelination, understanding the iron incorporation mechanism as well as the molecules involved is critical to design new therapeutic approaches to intervene in diseases in which the myelin sheath is damaged or lost.

ANOS1: a unified nomenclature for Kallmann syndrome 1 gene (KAL1) and anosmin-1

It is accepted that confusion regarding the description of genetic variants occurs when researchers do not use standard nomenclature. The Human Genome Organization Gene Nomenclature Committee contacted a panel of consultants, all working on the KAL1 gene, to propose an update of the nomenclature of the gene, as there was a convention in the literature of using the ‘KAL1’ symbol, when referring to the gene, but using the name ‘anosmin-1’ when referring to the protein. The new name, ANOS1, reflects protein name and is more transferrable across species.

Comparative study of chemical neuroanatomy of the olfactory neuropil in mouse, honey bee, and human

Despite divergent evolutionary origins, the organization of olfactory systems is remarkably similar across phyla. In both insects and mammals, sensory input from receptor cells is initially processed in synaptically dense regions of neuropil called glomeruli, where neural activity is shaped by local inhibition and centrifugal neuromodulation prior to being sent to higher-order brain areas by projection neurons. Here we review both similarities and several key differences in the neuroanatomy of the olfactory system in honey bees, mice, and humans, using a combination of literature review and new primary data. We have focused on the chemical identity and the innervation patterns of neuromodulatory inputs in the primary olfactory system. Our findings show that serotonergic fibers are similarly distributed across glomeruli in all three species. Octopaminergic/tyraminergic fibers in the honey bee also have a similar distribution, and possibly a similar function, to noradrenergic fibers in the mammalian OBs. However, preliminary evidence suggests that human OB may be relatively less organized than its counterparts in honey bee and mouse.

Olfactory Development, Part 1: Function, From Fetal Perception to Adult Wine-Tasting

Discrimination of odorous molecules in amniotic fluid occur after 30 weeks' gestation; fetuses exhibit differential responses to maternal diet. Olfactory reflexes enable reliable neonatal testing. Olfactory bulbs can be demonstrated reliably by MRI after 30 weeks' gestation, and their hypoplasia or aplasia also documented by late prenatal and postnatal MRI. Olfactory axons project from nasal epithelium to telencephalon before olfactory bulbs form. Fetal olfactory maturation remains incomplete at term for neuronal differentiation, synaptogenesis, myelination, and persistence of the transitory fetal ventricular recess. Immaturity does not signify nonfunction. Olfaction is the only sensory system without thalamic projection because of its own intrinsic thalamic equivalent. Diverse malformations of the olfactory bulb can be diagnosed by clinical examination, imaging, and neuropathology. Some epileptic auras might be primarily generated in the olfactory bulb. Cranial nerve 1 should be tested in all neonates and especially in patients with brain malformations, endocrinopathies, chromosomopathies, and genetic/metabolic diseases.

Unilateral olfactory sensitivity in multiple sclerosis

It is not known whether lateralized olfactory sensitivity deficits are present in MS. Since projections from the olfactory bulb to the olfactory cortex are largely ipsilateral, and since both functional imaging and psychophysical studies suggest that the right side of the brain may be more involved in olfactory processing than the left, we addressed this issue by administering well-validated tests of odor detection, along with tests of odor identification, to each side of the nose of 73 MS patients and 73 age-, gender-, and race-matched normal controls. We also determined, in 63 of the MS patients, whether correlations were present between the olfactory test measures and MRI-determined lesions in brain regions ipsilateral and contralateral to the nose side that was tested. No significant left:right differences in either olfactory sensitivity or identification were present, although in both cases mean performance was lower in the MS than in the control subjects (ps<0.0001). Scores on the two sides of the nose were positively correlated with one another (threshold r=0.56, p<0.0001; Identification r=0.71, p<0.0001). The percent of MS patients whose bilateral test scores fell below the 10th percentile of controls did not differ between the odor identification and detection threshold tests. Both left and right odor identification and detection test scores were weakly correlated with lesion volumes in temporal and frontal lobe brain regions (r's<0.40). Our findings demonstrate that MS does not differentially influence odor perception on left and right sides of the nose, regardless of whether sensitivity or identification is being measured. They also indicate that tests of odor identification and detection are similarly influenced by MS and that such influences are associated with central brain lesions.

Kallmann syndrome patient with gender dysphoria, multiple sclerosis, and thrombophilia

One of the challenging issues in patients with complex problems is that the various diseases and their treatment can influence each other and present unusual hurdles in management. We investigated one such complex case. A 34-year-old XY male presented with azoospermia, detected on semen analysis for pre-orchidectomy sperm banking. He had a 20-year history of gender dysphoria and bilateral breast swelling. The patient suffered a deep vein thrombosis at the age of 19 years. Examination confirmed clinical features of Kallmann syndrome including unilateral cryptorchidism, micropenis, congenital anosmia, and bimanual synkinesis (mirror movements), with reduced serum testosterone and normal gonadotropin levels demonstrating hypogonadotropic hypogonadism. MRI showed missing olfactory bulbs. Osteopenia and reduced vitamin D levels of 21 nmol/L were identified. He was found to harbor a heterozygous factor-V-Leiden mutation. The genetic basis of Kallmann syndrome remains unknown: his screening tests were negative for mutations in CHD7, FGF8, FGFR1, GNRH1, GNRHR, HS6ST1, KAL1, KISS1R, KISS1, NELF, PROK2, PROKR2, TAC3, and TACR3. The patient initially declined testosterone therapy with a view to undergo gender reassignment. Over the next 2 years, the patient experienced recurrent episodes of weakness and paresthesia, associated with classical MRI appearances of multiple sclerosis-related demyelination in the spinal cord and brain. Although it was difficult to elucidate an association between the patient's gender dysphoria and untreated congenital hypogonadism, his desire to become female together with his co-existing thrombophilia, presented challenges to the administration of hormone treatment. Furthermore, we have considered an association between multiple sclerosis and hypogonadotropic hypogonadism.

Impaired sense of smell and altered olfactory system in RAG-1(-∕-) immunodeficient mice

Immune deficiencies are often associated with a number of physical manifestations including loss of sense of smell and an increased level of anxiety. We have previously shown that T and B cell-deficient recombinase activating gene (RAG-1)(-∕-) knockout mice have an increased level of anxiety-like behavior and altered gene expression involved in olfaction. In this study, we expanded these findings by testing the structure and functional development of the olfactory system in RAG-1 (-∕-) mice. Our results show that these mice have a reduced engagement in different types of odors and this phenotype is associated with disorganized architecture of glomerular tissue and atrophy of the main olfactory epithelium. Most intriguingly this defect manifests specifically in adult age and is not due to impairment in the patterning of the olfactory neuron staining at the embryo stage. Together these findings provide a formerly unreported biological evidence for an altered function of the olfactory system in RAG-1 (-∕-) mice.

GnRH, anosmia and hypogonadotropic hypogonadism--where are we?

Gonadotropin releasing hormone (GnRH) neurons originate the nasal placode and migrate into the brain during prenatal development. Once within the brain, these cells become integral components of the hypothalamic-pituitary-gonadal axis, essential for reproductive function. Disruption of this system causes hypogonadotropic hypogonadism (HH). HH associated with anosmia is clinically defined as Kallman syndrome (KS). Recent work examining the developing nasal region has shed new light on cellular composition, cell interactions and molecular cues responsible for the development of this system in different species. This review discusses some developmental aspects, animal models and current advancements in our understanding of pathologies affecting GnRH. In addition we discuss how development of neural crest derivatives such as the glia of the olfactory system and craniofacial structures control GnRH development and reproductive function.

Olfactory Pathology in Central Nervous System Demyelinating Diseases

Olfactory dysfunction is common in multiple sclerosis (MS). Olfactory bulb and tract pathology in MS and other demyelinating diseases remain unexplored. A human autopsy cohort of pathologically confirmed cases encompassing the spectrum of demyelinating disease (MS; n = 17), neuromyelitis optica [(NMO); n = 3] and acute disseminated encephalomyelitis [(ADEM); n = 7] was compared to neuroinflammatory [herpes simplex virus encephalitis (HSE); n = 3], neurodegenerative [Alzheimer's disease (AD); n = 4] and non-neurologic (n = 8) controls. For each case, olfactory bulbs and/or tracts were stained for myelin, axons and inflammation. Inferior frontal cortex and hippocampus were stained for myelin in a subset of MS and ADEM cases. Olfactory bulb/tract demyelination was frequent in all demyelinating diseases [MS 12/17 (70.6%); ADEM 3/7 (42.9%); NMO 2/3 (66.7%)] but was absent in HSE, AD and non-neurologic controls. Inflammation was greater in the demyelinating diseases compared to non-neurologic controls. Olfactory bulb/tract axonal loss was most severe in MS where it correlated significantly with the extent of demyelination (r = 0.610, P = 0.009) and parenchymal inflammation (r = 0.681, P = 0.003). The extent of olfactory bulb/tract demyelination correlated with that found in the adjacent inferior frontal cortex but not hippocampus. We provide unequivocal evidence that olfactory bulb/tract demyelination is frequent, can occur early and is highly inflammatory, and is specific to demyelinating disease.

ERK1/2 signaling is essential for the chemoattraction exerted by human FGF2 and human anosmin-1 on newborn rat and mouse OPCs via FGFR1

Signaling through fibroblast growth factor receptors (FGFRs) is essential for many cellular processes including proliferation and migration, as well as differentiation events such as myelination. Anosmin-1 is an extracellular matrix (ECM) glycoprotein that interacts with the fibroblast growth factor receptor 1 (FGFR1) to exert its biological actions through this receptor, although the intracellular pathways underlying anosmin-1 signaling remain largely unknown. This protein is defective in the X-linked form of Kallmann syndrome (KS) and has a prominent role in the migration of neuronal and oligodendroglial precursors. We have shown that anosmin-1 exerts a chemotactic effect via FGFR1 on neuronal precursors from the subventricular zone (SVZ) and the essential role of the ERK1/2 signaling. We report here the positive chemotactic effect of FGF2 and anosmin-1 on rat and mouse postnatal OPCs via FGFR1. The same effect was observed with the truncated N-terminal region of anosmin-1 (A1Nt). The introduction in anosmin-1 of the missense mutation F517L found in patients suffering from KS annulled the chemotactic activity; however, the mutant form carrying the disease-causing mutation E514K also found in KS patients, behaved as the wild-type protein. The chemoattraction exhibited by FGF2 and anosmin-1 on OPCs was blocked by the mitogen-activated protein kinase (MAPK) inhibitor U0126, suggesting that the activation of the ERK1/2 MAPK signaling pathway following interaction with the FGFR1 is necessary for FGF2 and anosmin-1 to exert their chemotactic effect. In fact, both proteins were able to induce the phosphorylation of the ERK1/2 kinases after the activation of the FGFR1 receptor.

Early treatment of Kallmann syndrome may prevent eunuchoid appearance and behavior

Kallmann syndrome (KS) is a genetic disorder which combines hypogonadotropic hypogonadism and anosmia. Hypogonadism is characterized by the absence or reduced levels of gonadotropin-releasing hormone and anosmia due to olfactory bulb aplasia. KS treatment usually begins just before puberty, but brain sexual maturation occurs long before puberty normally at perinatal age. As brain cells implicated in the development of the olfactory and reproductive system have a rostral and a caudal origin, and the rostral origin is affected by aplasia in KS and the caudal origin does not seem to be affected, the early treatment of KS, as proposed in this paper, is to attain brain sexual maturation at the most appropriate age possible to prevent the eunuchoid behavior and appearance observed in KS.