Motor neuron disease due to neuropathy target esterase gene mutation: Clinical features of the index families

Recently, we reported that mutations in the neuropathy target esterase (NTE) gene cause autosomal recessive motor neuron disease (NTE-MND). We describe clinical, neurophysiologic, and neuroimaging features of affected subjects in the index families. NTE-MND subjects exhibited progressive lower extremity spastic weakness that began in childhood and was later associated with atrophy of distal leg and intrinsic hand muscles. NTE-MND resembles Troyer syndrome, except that short stature, cognitive impairment, and dysmorphic features, which often accompany Troyer syndrome, are not features of NTE-MND. Early onset, symmetry, and slow progression distinguish NTE-MND from typical amyotrophic lateral sclerosis. NTE is implicated in organophosphorus compound–induced delayed neurotoxicity (OPIDN). NTE-MND patients have upper and lower motor neuron deficits that are similar to OPIDN. Motor neuron degeneration in subjects with NTE mutations supports the role of NTE and its biochemical cascade in the molecular pathogenesis of OPIDN and possibly other degenerative neurologic disorders. Muscle Nerve, 2011Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/78477/1/21777_ftp.pd

Spinal cord magnetic resonance imaging in autosomal dominant hereditary spastic paraplegia

Hereditary spastic paraplegia (HSP) is a genetically heterogeneous group of neurodegenerative disorders characterized by progressive lower extremity weakness and spasticity. HSP pathology involves axonal degeneration that is most pronounced in the terminal segments of the longest descending (pyramidal) and ascending (dorsal columns) tracts. In this study, we compared spinal cord magnetic resonance imaging (MRI) in 13 HSP patients with four different types of autosomal dominant hereditary spastic paraplegia (SPG3A, SPG4, SPG6, and SPG8) with age-matched control subjects. The cross-section area of HSP subjects at cervical level C2 was 59.42±12.57 mm 2 and at thoracic level T9 was 28.58±5.25 mm 2 . Both of these values were less than in the healthy controls ( p <0.001). The degree of cord atrophy was more prominent in patients with SPG6 and SPG8 who had signs of severe cord atrophy (47.60±6.58 mm 2 at C2, 21.40±2.4 mm 2 at T9) than in subjects with SPG3 and SPG4 (66.0±8.94 mm 2 at C2, p <0.02; 31.75±2.76 mm 2 at T9, p <0.001). These observations indicate that spinal cord atrophy is a common finding in the four genetic types of HSP. Spinal cord atrophy was more severe in SPG6 and SPG8 HSP subjects than in other types of HSP we studied. This may suggest a different disease mechanism with more prominent axonal degeneration in these two types of HSP when compared with HSP due to spastin and atlastin mutations.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46666/1/234_2005_Article_1415.pd

Delayed Induction of Human NTE (PNPLA6) Rescues Neurodegeneration and Mobility Defects of Drosophila swiss cheese (sws) Mutants.

Human PNPLA6 gene encodes Neuropathy Target Esterase protein (NTE). PNPLA6 gene mutations cause hereditary spastic paraplegia (SPG39 HSP), Gordon-Holmes syndrome, Boucher-Neuhäuser syndromes, Laurence-Moon syndrome, and Oliver-McFarlane syndrome. Mutations in the Drosophila NTE homolog swiss cheese (sws) cause early-onset, progressive behavioral defects and neurodegeneration characterized by vacuole formation. We investigated sws5 flies and show for the first time that this allele causes progressive vacuolar formation in the brain and progressive deterioration of negative geotaxis speed and endurance. We demonstrate that inducible, neuron-specific expression of full-length human wildtype NTE reduces vacuole formation and substantially rescues mobility. Indeed, neuron-specific expression of wildtype human NTE is capable of rescuing mobility defects after 10 days of adult life at 29°C, when significant degeneration has already occurred, and significantly extends longevity of mutants at 25°C. These results raise the exciting possibility that late induction of NTE function may reduce or ameliorate neurodegeneration in humans even after symptoms begin. In addition, these results highlight the utility of negative geotaxis endurance as a new assay for longitudinal tracking of degenerative phenotypes in Drosophila

NIPA1 Gene Mutations Cause Autosomal Dominant Hereditary Spastic Paraplegia (SPG6)

The hereditary spastic paraplegias (HSPs) are genetically heterogeneous disorders characterized by progressive lower-extremity weakness and spasticity. The molecular pathogenesis is poorly understood. We report discovery of a dominant negative mutation in the NIPA1 gene in a kindred with autosomal dominant HSP (ADHSP), linked to chromosome 15q11-q13 (SPG6 locus); and precisely the same mutation in an unrelated kindred with ADHSP that was too small for meaningful linkage analysis. NIPA1 is highly expressed in neuronal tissues and encodes a putative membrane transporter or receptor. Identification of the NIPA1 function and ligand will aid an understanding of axonal neurodegeneration in HSP and may have important therapeutic implications

Delayed hNTE expression rescues endurance in <i>sws</i>^<i>5</i> flies.

<p>Endurance tolerance was assessed before (A, B) and after (C, D) mifepristone (RU486) application and induction of hNTE expression. (A) Berlin K flies exhibit wild-type endurance on day 3 of adulthood, while both <i>sws</i>^<i>5</i> mutant and <i>sws</i>^<i>5</i><i>;hNTE;elav GS</i> show a marked reduction in time-to-fatigue (n = 200 for all groups, log-rank, p<0.0001). (B) 48 hours later <i>sws</i>^<i>5</i> mutant and <i>sws</i>^<i>5</i><i>;hNTE;elav GS</i> cohorts continue to exhibit much lower endurance than Berlin K controls (n = 200 for all groups, long-rank, p<0.0001). At the end of the day-5-test, cohorts are divided in half and split into induced (RU+) and control (RU-) groups. (C) The same flies from (A) and (B) are tested for endurance 48 hours after mifepristone induction. Berlin K flies begin to decline in performance compared to day 5, independent of RU486 feeding (log rank, p≤0.0001 for RU+ and RU-). <i>sws</i>^<i>5</i> mutant and <i>sws</i>^<i>5</i><i>;hNTE;elav GS</i> cohorts show reduced endurance relative to Berlin K whether RU486-fed or not (n = 100 for all groups, long-rank, p<0.0001). (D) On day 10, after 120 hours RU486 induction, hNTE rescue flies’ (<i>sws</i>^<i>5</i><i>;hNTE;elav</i> GS RU+) time-to-fatigue is fully rescued to wild-type Berlin K endurance capacity (log rank, p = 0.9436). <i>sws</i>^<i>5</i> mutant and RU- control groups remain deficient in time-to-fatigue (log rank, p<0.0001). n = 100 for all cohorts.</p

Adult-specific hNTE expression restores NTE-like esterase activity and improves negative geotaxis in <i>sws</i>^<i>5</i> deficient flies.

<p>(A) hNTE protein is present in heads of adult hNTE rescue flies, but not controls or <i>sws</i>^<i>5</i> mutants. Loading control using anti-Tubulin is shown below. Representative image from 3 biological replicates. (n = 10 fly heads for each sample) (B) Esterase activity is reduced in <i>sws</i>^<i>5</i> mutants and control RU- flies in comparison to wild-type Berlin K (pairwise t-test, p = 0.006 and p = 0.0177, respectively). Flies expressing hNTE using elav-GAL4 increase esterase activity to the level of the wild type Berlin K (pairwise t-test, p = 0.9668). Data across groups were analyzed using two-way ANOVA with Bonferroni post-test and represent duplicate biological samples (n = 10, p≤0.0029, genotype effect, p<0.0001, RU effect, p = 0.0094, RU-by-genotype effect, p = 0.0038). (C) Age-matched <i>sws</i>^<i>5</i><i>;hNTE;elav GS</i> RU <i>+</i> flies display increased climbing vigor in comparison to flies without hNTE induction. Mifepristone (RU+) or vehicle (RU-) was fed to adult flies 3 days post-eclosion and maintained throughout life in order to induce transgene expression after development was complete. Photograph was taken 2 seconds after sharp rapping of vials onto a solid surface in order to induce negative geotaxis response.</p

Adult-specific, pan-neuronal hNTE expression partially rescues reduced lifespan of <i>sws</i>^<i>5</i> mutants at 25°C, 29°C.

<p>(A) <i>sws</i>^<i>5</i> mutants have reduced lifespan at 29°C in comparison to both Berlin K RU+/RU- and <i>sws</i>^<i>5</i><i>;hNTE;elav GS</i> (RU+/RU-) flies (n≥248, log rank, p<0.0001). <i>sws</i>^<i>5</i><i>;hNTE;elav GS</i> RU- (RU- control) flies have slightly reduced lifespan relative to Berlin K RU+/RU- and <i>sws</i>^<i>5</i><i>;hNTE;elav GS</i> RU+ (hNTE rescue) flies (n≥248, log rank, p = 0.006) but are longer lived than <i>sws</i>^<i>5</i> RU+/RU- flies (n≥248, log rank, p<0.0001). (B) <i>sws</i>^<i>5</i> mutants (RU+/RU-) and RU- control flies have reduced lifespan at 25°C in comparison to Berlin K (RU+/RU-) and hNTE rescue flies (n≥243, log rank, p<0.0001). Survival of hNTE rescue flies is nearly fully rescued to wild-type Berlin K lifespan at 25°C but is still statistically significant (n≥247, log rank, p<0.0001.</p

Continuous adult-specific hNTE expression improves climbing performance and endurance in <i>sws</i>^<i>5</i> flies at 2 ages.

<p>(A) Average climbing ability is increased in hNTE rescue flies during week 1 of adult life in comparison to age-matched flies without hNTE expression (p≤0.0001), but not to the level of the wild-type Berlin K flies (p = 0.0001). Flies were assessed daily on days 4 through 8 at 29°C. Climbing performance was assessed on a minimum of 2 cohorts. Data were analyzed using two-way ANOVA with Bonferroni post-test. (n≥112, p≤0.0001, genotype effect, p<0.0001, RU effect, p = 0.0233, RU-by-genotype effect, p = .0003). (B)Average climbing performance assessed on days 25–29 (week 4) of adulthood is improved in hNTE rescue flies in comparison to age-matched flies without hNTE expression (p≤0.0001), but not fully rescued to wild-type levels (p≤0.0001). Climbing was assessed on a minimum of 2 separate biological cohorts. Data were analyzed using two-way ANOVA with Bonferroni post-test. (n≥84, p≤0.0001, genotype effect, p<0.0001, RU effect, p = .0043,RU-by-genotype effect, p<0.0001). Data from both timepoints (2A and 2B) were combined to assess effects across age, age effect, p<0.0001, RU effect, p<0.0001, interaction, p = 0.8656. Thus, there is an age-independent effect of RU on climbing. (C) Time to fatigue is increased in hNTE rescue flies compared to <i>sws</i>^<i>5</i> flies and uninduced controls. Endurance experiments are analyzed statistically by log-rank (n≥150 p≤0.0001). Flies were aged at 29°C and assessed for time-to-fatigue on the 10^th day. (D) 24-day old control flies exhibit age-related decline in endurance relative to day 10. <i>sws</i>^<i>5</i> mutants and RU- control flies display marked reduction in time-to-fatigue- in comparison to Berlin K flies (log-rank, p≤0.0001). Time-to-fatigue is increased in hNTE rescue flies compared to <i>sws</i>^<i>5</i> and RU- controls (log rank, p≤0.0001), but not fully restored to wild-type (log rank with Pearson correlation, p = 0.0020). Endurance was assessed a minimum of 3 times to confirm reproducibility. n≥100 for all day-24 assessments.</p