Identification of olfactory dysfunction in carriers of X-linked Kallmann's syndrome

PHR1 is a vesicle-bound protein abundantly expressed in mature olfactory neurons

OBJECTIVES/HYPOTHESIS

To characterize the role of Phr1, a gene highly expressed in primary sensory neurons where it encodes an integral membrane protein with an N-terminal pleckstrin homology domain and a C-terminal transmembrane domain, in the olfactory system.

METHODS

We studied the immunelocalization of the PHR1 protein in mouse olfactory epithelium both at steady state and during regeneration following methyl bromide (MeBr) exposure using scanning confocal microscopy. Additionally, we examined the electrophysiologic role of Phr1 in olfaction and short-term olfactory adaptation.

RESULTS

We found that PHR1 is abundantly and specifically expressed in olfactory neurons. It is widely distributed in punctate, vesiculated organelles throughout the cell bodies, axons, and glomeruli of primary olfactory neurons but is specifically excluded from the olfactory cilia. In the regenerating olfactory epithelium, PHR1 expression appears at 14 days following MeBr ablation coinciding with the onset of olfactory neuron maturity. Despite the abundant and specific expression throughout the olfactory neurons, mice lacking Phr1 did not exhibit differences in the distribution of the components of olfactory signal transduction system, the rate of olfactory regeneration following MeBr exposure, olfactory function, or short-term adaptation to odors.

CONCLUSIONS

Phr1 is widely and abundantly expressed throughout mature olfactory neurons and other primary sensory neurons, but its absence does not appear to affect olfactory morphology, regeneration, sensory function, or adaptation. The exact function of Phr1 remains to be discovered.

Functional MRI of congenital hyposmia: brain activation to odors and imagination of odors and tastes

PURPOSE

Our goal was to use functional MRI (fMRI) to define brain activation in response to odors and imagination ("memory") of odors and tastes in patients who never recognized odors (congenital hyposmia).

METHOD

Functional MR brain scans were obtained in nine patients with congenital hyposmia using multislice echo planar imaging (EPI) in response to odors of amyl acetate, menthone, and pyridine and to imagination ("memory") of banana and peppermint odors and to salt and sweet tastes. Functional MR brain scans were compared with those in normal subjects and patients with acquired hyposmia. Activation images were derived using correlation analysis, and ratios of areas of brain activated to total and hemispheric brain areas were calculated. Total and hemispheric activated pixel counts were used to quantitate regional brain activation.

RESULTS

Brain activation in response to odors was present in patients with congenital hyposmia. Activation was significantly lower than in normal subjects and patients with acquired hyposmia and did not demonstrate differential vapor pressure-dependent detection responsiveness or odor response lateralization. Regional activation localization was in anterior frontal and temporal cortex similar to that in normal subjects and patients with acquired hyposmia. Activation in response to presented odors was diverse, with a larger group exhibiting little or no activation with localization only in anterior frontal and temporal cortex and a smaller group exhibiting greater activation with localization extending to more complex olfactory integration sites. "Memory" of odors and tastes elicited activation in the same central nervous system (CNS) regions in which activation in response to presented odors occurred, but responses were significantly lower than in normal subjects and patients with acquired hyposmia and did not lateralize.

CONCLUSION

Odors induced CNS activation in patients with congenital hyposmia, which distinguishes olfaction from vision and audition since neither light nor acoustic stimuli induce CNS activation. Odor activation localized to anterior frontal and temporal cortex, consistent with the hypothesis that olfactory pathways are hard-wired into the CNS and that further pathways are undeveloped with primary olfactory system CNS connections but lack of secondary connections. However, some patients exhibited greater odor activation with response localization extending to cingulate and opercular cortex, indicating some olfactory signals impinge on and maintain secondary connections consistent with similar functions in vision and audition. Activation localization of taste "memory" to anterior frontal and temporal cortex is consistent with CNS plasticity and cross-modal CNS reorganization as described for vision and audition. Thus, there are differences and similarities between olfaction, vision, and audition, the differences dependent on unique qualities of olfaction, perhaps due to its diffuse, primitive, fundamental role in survival. Response heterogeneity to odors may reflect heterogeneous genetic abnormalities, independent of anatomic or hormonal changes but dependent on molecular abnormalities in growth factor function interfering with growth factor/stem cell interactions. Patients with congenital hyposmia offer an unique model system not previously explored in which congenital smell lack as measured by fMRI is reflective of congenital dysfunction of a major sensory system.

A molecular and genetic view of human renal and urinary tract malformations

Malformations of the kidney and lower urinary tract are common causes of chronic renal failure in infants and young children, but little is known about the molecular pathogenesis of these disorders. In animal experiments, the main causes of malformation are mutations, chemical and pharmaceutical teratogens, obstruction of fetal urinary flow, and alterations of maternal nutrition. The focus of this review is to consider how mutations and other alterations of gene expression during development cause human urinary tract malformations. Some of these disorders are associated with congenital anomalies in multiple organ systems, and two such syndromes are considered in detail: first, the renal-coloboma syndrome, in which mutations of the PAX2 transcription factor cause partial failure of urinary tract growth; second, Kallmann's syndrome, in which mutations of a cell-signaling molecule are associated with the absence of the urinary tract. In patients seen by nephrologists and urologists, however, most urinary tract malformations occur in isolation, and in some of these individuals, a genetic pathogenesis is strongly suggested by a positive family history and genetic linkage studies. One common example is primary vesicoureteric reflux. Furthermore, sporadic malformations have been shown to be associated with polymorphisms of genes expressed during construction of the urinary tract. In the long term, an understanding of the genetic aspects of human urinary tract malformations will help to unravel the pathogenesis of these disorders and may facilitate the design of genetic screening tests with a view to early diagnosis.