Mutations In ACP5 Research Articles

Novel Mutations in ACP5 and SAMHD1 in a Patient With Pediatric Systemic Lupus Erythematosus.

BackgroundThe study of genetic predisposition to pediatric systemic lupus erythematosus (pSLE) has brought new insights into the pathophysiology of SLE, as it is hypothesized that genetic predisposition is greater in children. Furthermore, identifying genetic variants and linking disrupted genes to abnormal immune pathways and clinical manifestations can be beneficial for both diagnosis and treatment. Here, we identified genetic alterations in a patient with childhood-onset SLE and analyzed the immunological mechanisms behind them to support future diagnosis, prognosis, and treatment.MethodsWhole exome sequencing (WES) was adopted for genetic analysis of a patient with childhood-onset SLE. Gene mutations were confirmed by Sanger sequencing. Clinical data of this patient were collected and summarized. Ingenuity Pathway Analysis was used to provide interacting genes of the perturbed genes. Online Enrichr tool and Cytoscape software were used to analysis the related pathways of these genes.ResultsWe present a case of a 2-year-old girl who was diagnosed with idiopathic thrombocytopenic purpura (ITP) and SLE. The patient was characterized by cutaneous bleeding spots on both lower extremities, thrombocytopenia, decreased serum complements levels, increased urinary red blood cells, and positive ANA and dsDNA. The patient was treated with methylprednisolone and mycophenolate, but clinical remission could not be achieved. The genomic analysis identified three novel mutations in this pSLE patient, a double-stranded missense mutation in ACP5 (c.1152G>T and c.420G>A) and a single-stranded mutation in SAMHD1 (c.1423G>A). Bioinformatic analysis showed that these two genes and their interacting genes are enriched in the regulation of multiple immune pathways associated with SLE, including cytokine signaling and immune cell activation or function. Analysis of the synergistic regulation of these two genes suggests that abnormalities in the type I interferon pathway caused by genetic variants may contribute to the pathogenesis of SLE.ConclusionThe combined complexity of polymorphisms in the coding regions of ACP5 and SAMHD1 influences the susceptibility to SLE. Alterations in these genes may lead to abnormalities in the type I interferon pathway. Our study extends the spectrum of mutations in the ACP5 and SAMHD1 genes. The identification of these mutations could aid in the diagnosis of SLE with genetic counseling and suggest potential precise treatments for specific pathways.

Autoimmune Hemolytic Anemia Due to Spondyloenchondrodysplasia with Spastic Paraparesis and Intracranial Calcification due to Mutation in ACP5.

Spondyloenchondrodysplasia (SPENCD) is a rare spondylometaphyseal skeletal dysplasia with characteristic lesions mimicking enchondromatosis and resulting in short stature. A large spectrum of immunologic abnormalities may be seen in SPENCD, including immune deficiencies and autoimmune disorders. SPENCD is caused by loss of tartrate-resistant acid phosphatase activity, due to homozygous mutations in ACP5 , playing a role in nonnucleic-acid-related stimulation/regulation of the type I interferon pathway. In this article, we presented a 19-year-old boy with SPENCD, presenting with recurrent autoimmune hemolytic anemia episodes since he was 5 years old. He had short stature, platyspondyly, metaphyseal changes, intracranial calcification, spastic paraparesis, and mild intellectual disability. He also had recurrent pneumonia attacks. The clinical diagnosis of SPENCD was confirmed by sequencing of the ACP5 gene, and a homozygous c.155A > C (p.K52T) variation was found, which was reported before as pathogenic. In conclusion, in early onset chronic autoimmune cytopenias an immune dysregulation may often have a role in the etiology. Associating findings and immunologic functions should be carefully evaluated in such patients in the light of the literature. The present case shows the importance of multisystemic evaluation for the detection of SPENCD that has a monogenic etiology.

Characterisation of ACP5 missense mutations encoding tartrate-resistant acid phosphatase associated with spondyloenchondrodysplasia.

Biallelic mutations in ACP5, encoding tartrate-resistant acid phosphatase (TRACP), have recently been identified to cause the inherited immuno-osseous disorder, spondyloenchondrodysplasia (SPENCD). This study was undertaken to characterize the eight reported missense mutations in ACP5 associated with SPENCD on TRACP expression. ACP5 mutant genes were synthesized, transfected into human embryonic kidney (HEK-293) cells and stably expressing cell lines were established. TRACP expression was assessed by cytochemical and immuno-cytochemical staining with a panel of monoclonal antibodies. Analysis of wild (WT) type and eight mutant stable cell lines indicated that all mutants lacked stainable enzyme activity. All ACP5 mutant constructs were translated into intact proteins by HEK-293 cells. The mutant TRACP proteins displayed variable immune reactivity patterns, and all drastically reduced enzymatic activity, revealing that there is no gross inhibition of TRACP biosynthesis by the mutations. But they likely interfere with folding thereby impairing enzyme function. TRACP exists as two isoforms. TRACP 5a is a less active monomeric enzyme (35kD), with the intact loop peptide and TRACP 5b is proteolytically cleaved highly active enzyme encompassing two subunits (23 kD and 16 kD) held together by disulfide bonds. None of the mutant proteins were proteolytically processed into isoform 5b intracellularly, and only three mutants were secreted in significant amounts into the culture medium as intact isoform 5a-like proteins. Analysis of antibody reactivity patterns revealed that T89I and M264K mutant proteins retained some native conformation, whereas all others were in "denatured" or "unfolded" forms. Western blot analysis with intracellular and secreted TRACP proteins also revealed similar observations indicating that mutant T89I is amply secreted as inactive protein. All mutant proteins were attacked by Endo-H sensitive glycans and none could be activated by proteolytic cleavage in vitro. In conclusion, determining the structure-function relationship of the SPENCD mutations in TRACP will expand our understanding of basic mechanisms underlying immune responsiveness and its involvement in dysregulated bone metabolism.

Tartrate-Resistant Acid Phosphatase Deficiency in the Predisposition to Systemic Lupus Erythematosus.

Mutations in the ACP5 gene, which encodes tartrate-resistant acid phosphatase (TRAP), cause the immuno-osseous disorder spondyloenchondrodysplasia, which includes as disease features systemic lupus erythematosus (SLE) and a type I interferon (IFN) signature. Our aims were to identify TRAP substrates, determine the consequences of TRAP deficiency in immune cells, and assess whether ACP5 mutations are enriched in sporadic cases of SLE. Interaction between TRAP and its binding partners was tested by a yeast 2-hybrid screening, confocal microscopy, and immunoprecipitation/Western blotting. TRAP knockdown was performed using small interfering RNA. Phosphorylation of osteopontin (OPN) was analyzed by mass spectrometry. Nucleotide sequence analysis of ACP5 was performed by Sanger sequencing or next-generation sequencing. TRAP and OPN colocalized and interacted in human macrophages and plasmacytoid dendritic cells (PDCs). TRAP dephosphorylated 3 serine residues on specific OPN peptides. TRAP knockdown resulted in increased OPN phosphorylation and increased nuclear translocation of IRF7 and P65, with resultant heightened expression of IFN-stimulated genes and IL6 and TNF following Toll-like receptor 9 stimulation. An excess of heterozygous ACP5 missense variants was observed in SLE compared to controls (P = 0.04), and transfection experiments revealed a significant reduction in TRAP activity in a number of variants. Our findings indicate that TRAP and OPN colocalize and that OPN is a substrate for TRAP in human immune cells. TRAP deficiency in PDCs leads to increased IFNα production, providing at least a partial explanation for how ACP5 mutations cause lupus in the context of spondyloenchondrodysplasia. Detection of ACP5 missense variants in a lupus cohort suggests that impaired TRAP functioning may increase susceptibility to sporadic lupus.

Erratum to: Spondyloenchondrodysplasia Due to Mutations in ACP5: A Comprehensive Survey

The online version of the original article can be found at http://dx.doi.org/10.1007/s10875-016-0252-y .

Spondyloenchondrodysplasia Due to Mutations in ACP5: A Comprehensive Survey

PurposeSpondyloenchondrodysplasia is a rare immuno-osseous dysplasia caused by biallelic mutations in ACP5. We aimed to provide a survey of the skeletal, neurological and immune manifestations of this disease in a cohort of molecularly confirmed cases.MethodsWe compiled clinical, genetic and serological data from a total of 26 patients from 18 pedigrees, all with biallelic ACP5 mutations.ResultsWe observed a variability in skeletal, neurological and immune phenotypes, which was sometimes marked even between affected siblings. In total, 22 of 26 patients manifested autoimmune disease, most frequently autoimmune thrombocytopenia and systemic lupus erythematosus. Four patients were considered to demonstrate no clinical autoimmune disease, although two were positive for autoantibodies. In the majority of patients tested we detected upregulated expression of interferon-stimulated genes (ISGs), in keeping with the autoimmune phenotype and the likely immune-regulatory function of the deficient protein tartrate resistant acid phosphatase (TRAP). Two mutation positive patients did not demonstrate an upregulation of ISGs, including one patient with significant autoimmune disease controlled by immunosuppressive therapy.ConclusionsOur data expand the known phenotype of SPENCD. We propose that the OMIM differentiation between spondyloenchondrodysplasia and spondyloenchondrodysplasia with immune dysregulation is no longer appropriate, since the molecular evidence that we provide suggests that these phenotypes represent a continuum of the same disorder. In addition, the absence of an interferon signature following immunomodulatory treatments in a patient with significant autoimmune disease may indicate a therapeutic response important for the immune manifestations of spondyloenchondrodysplasia.

Severe immune dysregulation with neurological impairment and minor bone changes in a child with spondyloenchondrodysplasia due to two novel mutations in the ACP5 gene

Spondyloenchondrodysplasia (SPENCD) is a rare skeletal dysplasia, characterized by metaphyseal lesions, neurological impairment and immune dysregulation associated with lupus-like features. SPENCD is caused by biallelic mutations in the ACP5 gene encoding tartrate-resistant phosphatase. We report on a child, who presented with spasticity, multisystem inflammation, autoimmunity and immunodeficiency with minimal metaphyseal changes due to compound heterozygosity for two novel ACP5 mutations. These findings extend the phenotypic spectrum of SPENCD and indicate that ACP5 mutations can cause severe immune dysregulation and neurological impairment even in the absence of metaphyseal dysplasia.

Mutations in PCYT1A, Encoding a Key Regulator of Phosphatidylcholine Metabolism, Cause Spondylometaphyseal Dysplasia with Cone-Rod Dystrophy

The spondylometaphyseal dysplasias (SMDs) are a group of about a dozen rare disorders characterized by short stature, irregular, flat vertebrae, and metaphyseal abnormalities. Aside from spondylometaphyseal dysplasia Kozlowski type (MIM 184252) caused by mutations in TRPV4 (MIM 605427) and spondyloenchondrodysplasia (MIM 607944) resulting from mutations in ACP5 (MIM 171640), the genetic etiologies of SMDs are unknown. 1 Two of these unexplained SMDs have ophthalmologic manifestations: SMD with cone-rod dystrophy (SMD-CRD [MIM 608940]) and axial SMD with retinal degeneration (MIM 602271). Delineated clinically a decade ago, SMD-CRD is a presumed autosomal-recessive disorder with postnatal growth deficiency leading to profound short stature; rhizomelia with bowing of the lower extremities; platyspondyly with anterior vertebral protrusions; progressive metaphyseal irregularity and cupping with shortened tubular bones; and early-onset, progressive visual impairment associated with a pigmentary maculopathy and electroretinographic evidence of cone-rod dysfunction. 2‐5 In contrast to retinitis pigmentosa, the CRDs have early involvement of cone photoreceptors. 6

Genetic and functional investigation of a Mendelian form of systemic lupus erythematosus

We have shown that bi-allelic mutations in ACP5 result in a deficiency of the encoded protein, tartrate-resistant acid phosphatase (TRAP), which causes the immuno-osseous disease spondyloenchondrodysplasia. In addition to having a bone and neurological phenotype, patients with spondyloenchondrodysplasia exhibit a wide spectrum of autoimmune manifestations, including autoantibody production, systemic lupus erythematosus, increased interferon α (IFNα), and an interferon signature. In bone, TRAP produced by osteoclasts regulates cell migration by dephosphorylation of osteopontin. However, TRAP is also produced by immune cells, particularly macrophages and dendritic cells (DCs). In murine plasmacytoid dendritic cells (pDC), phosphorylated osteopontin is integral to IFN-α production. Whereas osteopontin has been shown to be a TRAP substrate in murine bone cells, nothing is known about whether TRAP regulates osteopontin in immune cells. We hypothesise that TRAP dephosphorylates osteopontin in human pDCs and negatively regulates IFN-α production.We studied the interaction between TRAP and osteopontin. By confocal microscopy, we showed that TRAP co-localised with osteopontin in the Golgi in primary human macrophages, DCs, and pDCs. In a TRAP and osteopontin overexpression system in human embryonic kidney 293 cells, we co-immunoprecipitated TRAP and osteopontin, suggesting that they interact with each other. We also showed in an in-vitro assay that recombinant human TRAP could dephosphorylate osteopontin, demonstrating that osteoponin is a substrate for TRAP. These findings suggest that osteopontin is a target for TRAP in immune cells. To test whether TRAP deficiency leads to hyperphosphorylation of osteopontin and increased IFNα, we are generating TRAP knockdowns in a pDC cell line.Understanding of the mechanism by which TRAP regulates IFNα, potentially via osteopontin, may eventually allow for directed therapeutic approaches in spondyloenchondrodysplasia and other autoimmune diseases associated with an interferon signature, particularly systemic lupus erythematosus. FundingWellcome Trust.

Genetic deficiency of tartrate-resistant acid phosphatase associated with skeletal dysplasia, cerebral calcifications and autoimmunity

Vertebral and metaphyseal dysplasia, spasticity with cerebral calcifications, and strong predisposition to autoimmune diseases are the hallmarks of the genetic disorder spondyloenchondrodysplasia. We mapped a locus in five consanguineous families to chromosome 19p13 and identified mutations in ACP5, which encodes tartrate-resistant phosphatase (TRAP), in 14 affected individuals and showed that these mutations abolish enzyme function in the serum and cells of affected individuals. Phosphorylated osteopontin, a protein involved in bone reabsorption and in immune regulation, accumulates in serum, urine and cells cultured from TRAP-deficient individuals. Case-derived dendritic cells exhibit an altered cytokine profile and are more potent than matched control cells in stimulating allogeneic T cell proliferation in mixed lymphocyte reactions. These findings shed new light on the role of osteopontin and its regulation by TRAP in the pathogenesis of common autoimmune disorders.

Tartrate-resistant acid phosphatase deficiency causes a bone dysplasia with autoimmunity and a type I interferon expression signature.

We studied ten individuals from eight families showing features consistent with the immuno-osseus dysplasia spondyloenchondrodysplasia (SPENCD). Of particular note was the diverse spectrum of autoimmune phenotypes observed in these patients, including systemic lupus erythematosus (SLE), Sjögren's syndrome, haemolytic anemia, thrombocytopenia, hypothyroidism, inflammatory myositis, Raynaud's disease, and vitiligo. Haplotype data indicated the disease gene to be on chromosome 19p13 and linkage analysis yielded a combined multipoint lod score of 3.6. Sequencing of the ACP5 gene, encoding tartrate resistant acid phosphatase (TRAP), identified biallelic mutations in each of the patients studied, and in vivo testing confirmed a loss of expressed protein. All eight patients assayed demonstrated elevated serum interferon alpha activity, and gene expression profiling in whole blood defined a type I interferon signature. Our findings reveal a previously unrecognised link between TRAP activity and interferon metabolism, and highlight the importance of type I interferon in the genesis of autoimmunity.