Mutations in the SPTLC2 Subunit of Serine Palmitoyltransferase Cause Hereditary Sensory and Autonomic Neuropathy Type I

Peripheral Neuropathy Group, VIB Department of Molecular Genetics, University of Antwerp, B-2610 Antwerp, Belgium.
The American Journal of Human Genetics (Impact Factor: 10.93). 10/2010; 87(4):513-22. DOI: 10.1016/j.ajhg.2010.09.010
Source: PubMed


Hereditary sensory and autonomic neuropathy type I (HSAN-I) is an axonal peripheral neuropathy associated with progressive distal sensory loss and severe ulcerations. Mutations in the first subunit of the enzyme serine palmitoyltransferase (SPT) have been associated with HSAN-I. The SPT enzyme catalyzes the first and rate-limiting step in the de novo sphingolipid synthesis pathway. However, different studies suggest the implication of other genes in the pathology of HSAN-I. Therefore, we screened the two other known subunits of SPT, SPTLC2 and SPTLC3, in a cohort of 78 HSAN patients. No mutations were found in SPTLC3, but we identified three heterozygous missense mutations in the SPTLC2 subunit of SPT in four families presenting with a typical HSAN-I phenotype. We demonstrate that these mutations result in a partial to complete loss of SPT activity in vitro and in vivo. Moreover, they cause the accumulation of the atypical and neurotoxic sphingoid metabolite 1-deoxy-sphinganine. Our findings extend the genetic heterogeneity in HSAN-I and enlarge the group of HSAN neuropathies associated with SPT defects. We further show that HSAN-I is consistently associated with an increased formation of the neurotoxic 1-deoxysphinganine, suggesting a common pathomechanism for HSAN-I.

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    • "Both genes encoding the additional subunits of SPT, SPTLC2 and SPTLC3, were screened for mutations in a cohort of typical HSAN patients. Heterozygous missense mutations were identified in SPTLC2 in a fraction of patients but no mutations were found in SPTLC3 (Rotthier et al., 2010). Consistent with a neuropathy ''disease gene,'' suppression of the sptlc3 ortholog in zebrafish embryos showed motor neuron axon defects that phenocopied suppression of other known CMT genes (Figures 2H and 2I). "
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    ABSTRACT: Charcot-Marie-Tooth (CMT) disease is a clinically and genetically heterogeneous distal symmetric polyneuropathy. Whole-exome sequencing (WES) of 40 individuals from 37 unrelated families with CMT-like peripheral neuropathy refractory to molecular diagnosis identified apparent causal mutations in ∼45% (17/37) of families. Three candidate disease genes are proposed, supported by a combination of genetic and in vivo studies. Aggregate analysis of mutation data revealed a significantly increased number of rare variants across 58 neuropathy-associated genes in subjects versus controls, confirmed in a second ethnically discrete neuropathy cohort, suggesting that mutation burden potentially contributes to phenotypic variability. Neuropathy genes shown to have highly penetrant Mendelizing variants (HPMVs) and implicated by burden in families were shown to interact genetically in a zebrafish assay exacerbating the phenotype established by the suppression of single genes. Our findings suggest that the combinatorial effect of rare variants contributes to disease burden and variable expressivity. Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.
    Cell Reports 08/2015; 12(7). DOI:10.1016/j.celrep.2015.07.023 · 8.36 Impact Factor
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    • "The HSAN1 mutations in SPT induce a permanent shift from L-serine toward L-alanine which results in a pathologically increased 1-deoxySL formation (Penno et al. 2010; Rotthier et al. 2010). Elevated 1-deoxySL levels were found in plasma and lymphoblasts of HSAN1 patients and in plasma and peripheral nerve tissue of transgenic mice (Penno et al. 2010; Rotthier et al. 2010; Garofalo et al. 2011). 1-deoxySL are neurotoxic and impair neurite formation in cultured neurons (Penno et al. 2010). "
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    ABSTRACT: 1-Deoxysphingolipids (1-deoxySL) are atypical sphingolipids that are formed by the enzyme serine palmitoyltransferase (SPT) due to a promiscuous use of l-alanine over its canonical substrate l-serine. Several mutations in SPT are associated with the hereditary sensory and autonomic neuropathy type I (HSAN1). The current hypothesis is that these mutations induce a permanent shift in the affinity from l-serine toward l-alanine which results in a pathologically increased 1-deoxySL formation in HSAN1 patients. Also, wild-type SPT forms 1-deoxySL under certain conditions, and elevated levels were found in individuals with the metabolic syndrome and diabetes. However, the molecular mechanisms which control the substrate shift of the wild-type enzyme are not understood. Here, we report a novel SPTLC2–S384F variant in two unrelated HSAN1 families. Affected patients showed elevated plasma 1-deoxySL levels and expression of the S384F mutant in HEK293 cells increased 1-deoxySL formation. Previously, S384 has been reported as one of the two (S384 and Y387) putative phosphorylation sites in SPTLC2. The phosphorylation of wild-type SPTLC2 was confirmed by isoelectric focusing. The impact of an S384 phosphorylation on SPT activity was tested by creating mutants mimicking either a constitutively phosphorylated (S384D, S384E) or non-phosphorylated (S384A, Y387F, Y387F+S384A) protein. The S384D but not the S384E variant was associated with increased 1-deoxySL formation. The other mutations had no influence on activity and substrate affinity. In summary, our data show that S384F is a novel mutation in HSAN1 and that the substrate specificity of wild-type SPT might by dynamically regulated by a phosphorylation at this position. Electronic supplementary material The online version of this article (doi:10.1007/s12017-014-8339-1) contains supplementary material, which is available to authorized users.
    NeuroMolecular Medicine 01/2015; 17(1). DOI:10.1007/s12017-014-8339-1 · 3.68 Impact Factor
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    • "[39] I504F G385 Surface exposed Sensory neuropathy, ulcerations, osteomyelitis, and anhidrosis. [39] A182P T79 Not surface exposed Sensory neuropathy. [42] "
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    ABSTRACT: The pyridoxal 5'-phosphate (PLP)-dependent enzyme serine palmitoyltransferase (SPT) catalyses the first step of de novo sphingolipid biosynthesis. The core human enzyme is a membrane-bound heterodimer composed of two subunits (hLCB1 and hLCB2a/b), and mutations in both hLCB1 (e.g., C133W and C133Y) and hLCB2a (e.g., V359M, G382V, and I504F) have been identified in patients with hereditary sensory and autonomic neuropathy type I (HSAN1), an inherited disorder that affects sensory and autonomic neurons. These mutations result in substrate promiscuity, leading to formation of neurotoxic deoxysphingolipids found in affected individuals. Here we measure the activities of the hLCB2a mutants in the presence of ssSPTa and ssSPTb and find that all decrease enzyme activity. High resolution structural data of the homodimeric SPT enzyme from the bacterium Sphingomonas paucimobilis (Sp SPT) provides a model to understand the impact of the hLCB2a mutations on the mechanism of SPT. The three human hLCB2a HSAN1 mutations map onto Sp SPT (V246M, G268V, and G385F), and these mutant mimics reveal that the amino acid changes have varying impacts; they perturb the PLP cofactor binding, reduce the affinity for both substrates, decrease the enzyme activity, and, in the most severe case, cause the protein to be expressed in an insoluble form.
    09/2013; 2013:194371. DOI:10.1155/2013/194371
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