Progressive ankylosis (Ank) protein is expressed by neurons and Ank immunohistochemical reactivity is increased by limbic seizures

The Role of ANK in Calcium Pyrophosphate Deposition Disease

The protein product of the progressive ankylosis gene, known as ANK, is a 492-amino acid multi-pass transmembrane protein. This protein is critical for the regulation of pyrophosphate, and gain of function ANK mutations is associated with calcium pyrophosphate deposition disease. Much about the structure, function, and regulation of ANK remain unstudied. This review of the current literature examines recent contributions to our understanding of ANK. We focus on new work on the function, binding partners, and regulators of ANK. A more complete understanding of this important protein may help to identify future therapeutic targets for the treatment of calcium pyrophosphate deposition disease.

The progressive ankylosis protein ANK facilitates clathrin- and adaptor-mediated membrane traffic at the trans-Golgi network-to-endosome interface

Dominant or recessive mutations in the progressive ankylosis gene ANKH have been linked to familial chondrocalcinosis (CCAL2), craniometaphyseal dysplasia (CMD), mental retardation, deafness and ankylosis syndrome (MRDA). The function of the encoded membrane protein ANK in cellular compartments other than the plasma membrane is unknown. Here, we show that ANK localizes to the trans-Golgi network (TGN), clathrin-coated vesicles and the plasma membrane. ANK functionally interacts with clathrin and clathrin associated adaptor protein (AP) complexes as loss of either protein causes ANK dispersion from the TGN to cytoplasmic endosome-like puncta. Consistent with its subcellular localization, loss of ANK results in reduced formation of tubular membrane carriers from the TGN, perinuclear accumulation of early endosomes and impaired transferrin endocytosis. Our data indicate that clathrin/AP-mediated cycling of ANK between the TGN, endosomes, and the cell surface regulates membrane traffic at the TGN/endosomal interface. These findings suggest that dysfunction of Golgi-endosomal membrane traffic may contribute to ANKH-associated pathologies.

Neuronal RING finger protein 11 (RNF11) regulates canonical NF-κB signaling

Background

The RING domain-containing protein RING finger protein 11 (RNF11) is a member of the A20 ubiquitin-editing protein complex and modulates peripheral NF-κB signaling. RNF11 is robustly expressed in neurons and colocalizes with a population of α-synuclein-positive Lewy bodies and neurites in Parkinson disease patients. The NF-κB pathway has an important role in the vertebrate nervous system, where the absence of NF-κB activity during development can result in learning and memory deficits, whereas chronic NF-κB activation is associated with persistent neuroinflammation. We examined the functional role of RNF11 with respect to canonical NF-κB signaling in neurons to gain understanding of the tight association of inflammatory pathways, including NF-κB, with the pathogenesis of neurodegenerative diseases.

Methods and results

Luciferase assays were employed to assess NF-κB activity under targeted short hairpin RNA (shRNA) knockdown of RNF11 in human neuroblastoma cells and murine primary neurons, which suggested that RNF11 acts as a negative regulator of canonical neuronal NF-κB signaling. These results were further supported by analyses of p65 translocation to the nucleus following depletion of RNF11. Coimmunoprecipitation experiments indicated that RNF11 associates with members of the A20 ubiquitin-editing protein complex in neurons. Site-directed mutagenesis of the myristoylation domain, which is necessary for endosomal targeting of RNF11, altered the impact of RNF11 on NF-κB signaling and abrogated RNF11’s association with the A20 ubiquitin-editing protein complex. A partial effect on canonical NF-κB signaling and an association with the A20 ubiquitin-editing protein complex was observed with mutagenesis of the PPxY motif, a proline-rich region involved in Nedd4-like protein interactions. Last, shRNA-mediated reduction of RNF11 in neurons and neuronal cell lines elevated levels of monocyte chemoattractant protein 1 and TNF-α mRNA and proteins, suggesting that NF-κB signaling and associated inflammatory responses are aberrantly regulated in the absence of RNF11.

Conclusions

Our findings support the hypothesis that, in the nervous system, RNF11 negatively regulates canonical NF-κB signaling. Reduced or functionally compromised RNF11 could influence NF-κB-associated neuronal functions, including exaggerated inflammatory responses that may have implications for neurodegenerative disease pathogenesis and progression.

Identification of the inorganic pyrophosphate metabolizing, ATP substituting pathway in mammalian spermatozoa

Inorganic pyrophosphate (PPi) is generated by ATP hydrolysis in the cells and also present in extracellular matrix, cartilage and bodily fluids. Fueling an alternative pathway for energy production in cells, PPi is hydrolyzed by inorganic pyrophosphatase (PPA1) in a highly exergonic reaction that can under certain conditions substitute for ATP-derived energy. Recombinant PPA1 is used for energy-regeneration in the cell-free systems used to study the zymology of ATP-dependent ubiquitin-proteasome system, including the role of sperm-borne proteasomes in mammalian fertilization. Inspired by an observation of reduced in vitro fertilization (IVF) rates in the presence of external, recombinant PPA1, this study reveals, for the first time, the presence of PPi, PPA1 and PPi transporter, progressive ankylosis protein ANKH in mammalian spermatozoa. Addition of PPi during porcine IVF increased fertilization rates significantly and in a dose-dependent manner. Fluorometric assay detected high levels of PPi in porcine seminal plasma, oviductal fluid and spermatozoa. Immunofluorescence detected PPA1 in the postacrosomal sheath (PAS) and connecting piece of boar spermatozoa; ANKH was present in the sperm head PAS and equatorial segment. Both ANKH and PPA1 were also detected in human and mouse spermatozoa, and in porcine spermatids. Higher proteasomal-proteolytic activity, indispensable for fertilization, was measured in spermatozoa preserved with PPi. The identification of an alternative, PPi dependent pathway for ATP production in spermatozoa elevates our understanding of sperm physiology and sets the stage for the improvement of semen extenders, storage media and IVF media for animal biotechnology and human assisted reproductive therapies.

Animal models with pathological mineralization phenotypes

Extracellular matrix mineralization is important for mechanical stability of the skeleton and for calcium and phosphate storage. Professional mineral-disposing cell types are hypertrophic chondrocytes, odontoblasts, ameloblasts and osteoblasts. Since ectopic mineralization causes tissue dysfunction mineralization inhibitors and promoting factors have to be kept in close balance. The most prominent inhibitors are fetuin-A, matrix-Gla-protein (MGP), SIGBLING proteins and pyrophosphate. In spite of their ubiquitous presence, their loss entails a specific rather than a stereotypic pattern of ectopic mineralization. Typical sites of pathological mineral accumulation are connective tissues, articular cartilage, and vessels. Associated common human pathologies are degenerative joint disorders and arteriosclerosis. This article gives a summary on what we have learned from different mouse models with pathologic mineralization phenotypes about the role of these inhibitors and the regulation of mineralization promoting factors.

Autosomal recessive mental retardation, deafness, ankylosis, and mild hypophosphatemia associated with a novel ANKH mutation in a consanguineous family

CONTEXT

Mutations in ANKH cause the highly divergent conditions familial chondrocalcinosis and craniometaphyseal dysplasia. The gene product ANK is supposed to regulate tissue mineralization by transporting pyrophosphate to the extracellular space.

OBJECTIVE

We evaluated several family members of a large consanguineous family with mental retardation, deafness, and ankylosis. We compared their skeletal, metabolic, and serological parameters to that of the autosomal recessive progressive ankylosis (ank) mouse mutant, caused by a loss-of-function mutation in the murine ortholog Ank.

PARTICIPANTS

The studied patients had painful small joint soft-tissue calcifications, progressive spondylarthropathy, osteopenia, mild hypophosphatemia, mixed hearing loss, and mental retardation.

RESULTS

After mapping the disease gene to 5p15, we identified the novel homozygous ANK missense mutation L244S in all patients. Although L244 is a highly conserved amino acid, the mutated ANK protein was detected at normal levels at the plasma membrane in primary patient fibroblasts. The phenotype was highly congruent with the autosomal recessive progressive ankylosis (ank) mouse mutant. This indicates a loss-of-function effect of the L244S mutation despite normal ANK protein expression. Interestingly, our analyses revealed that the primary step of joint degeneration is fibrosis and mineralization of articular soft tissues. Moreover, heterozygous carriers of the L244S mutation showed mild osteoarthritis without metabolic alterations, pathological calcifications, or central nervous system involvement.

CONCLUSION

Beyond the description of the first human progressive ankylosis phenotype, our results indicate that ANK influences articular soft tissues commonly involved in degenerative joint disorders. Furthermore, this human disorder provides the first direct evidence for a role of ANK in the central nervous system.

The interaction between tumor necrosis factor-like weak inducer of apoptosis and its receptor fibroblast growth factor-inducible 14 promotes the recruitment of neutrophils into the ischemic brain

Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) and its receptor fibroblast growth factor-inducible 14 (Fn14) are expressed in endothelial cells and perivascular astrocytes. Here, we show that TWEAK induces a dose-dependent increase in the expression of the chemokine monocyte chemoattractant protein-1 (MCP-1) in astrocytes, and that this effect is mediated by its interaction with Fn14 via nuclear factor-kappaB pathway activation. Exposure to oxygen-glucose deprivation (OGD) conditions increases TWEAK and Fn14 mRNA expression in wild-type (Wt) astrocytic cultures. Likewise, incubation under OGD conditions induces the expression of MCP-1 in Wt astrocytes but not in astrocytes deficient on either TWEAK (TWEAK(-/-)) or Fn14 (Fn14(-/-)). We also found that TWEAK induces the passage of neutrophils to the abluminal side of an in vitro model of the blood-brain barrier. Our earlier studies indicate that cerebral ischemia increases the expression of TWEAK and Fn14 in the endothelial cell-basement membrane-astrocyte interface. Here, we report that middle cerebral artery occlusion increases the expression of MCP-1 and the recruitment of neutrophils into the ischemic tissue in Wt but not in TWEAK(-/-) or Fn14(-/-) mice. These novel results indicate that during cerebral ischemia, the interaction between TWEAK and Fn14 leads to the recruitment of leukocytes into the ischemic tissue.

The CPPDD-associated ANKH M48T mutation interrupts the interaction of ANKH with the sodium/phosphate cotransporter PiT-1

OBJECTIVE

Numerous dominant human homolog of progressive ankylosis (ANKH) mutations have been identified in familial calcium pyrophosphate dihydrate crystal deposition disease (CPPDD). Due to the dominant nature of these mutations, we investigated whether ANKH interacts with other proteins; and if so, whether any CPPDD-associated ANKH mutation might disrupt such protein interactions.

METHODS

Stable ATDC5 ANKH wt- and ANKH M48T-transfectants were generated. Lysates from these transfectants were used to identify candidate protein interaction with ANKH by coimmunoprecipitation followed by Western blot analysis. The effect of high phosphate on the expression of genes involved in modulating Pi (inorganic phosphate)/PPi (inorganic pyrophosphate) homeostasis in these transfectants was assessed.

RESULTS

We showed that ANKH protein associates with the sodium/phosphate cotransporter PiT-1, and that ANKH M48T mutant protein failed to interact with PiT-1. We also showed that upon high phosphate treatment, the normally coordinated upregulation of endogenous Ank and PiT1 transcript expression was disrupted in ANKH M48T transfectants.

CONCLUSION

Our results suggested that there is a coordinated interrelationship between 2 key participants of Pi and PPi metabolism, ANKH and PiT-1.

The low-density lipoprotein receptor-related protein 1 mediates tissue-type plasminogen activator-induced microglial activation in the ischemic brain

Microglia are the immune cells of the central nervous system (CNS) that become activated in response to pathological situations such as cerebral ischemia. Tissue-type plasminogen activator (tPA) is a serine proteinase that is found in the intravascular space and the CNS. The low-density lipoprotein receptor-related protein 1 (LRP1) is a member of the low-density lipoprotein receptor gene family found in neurons, astrocytes, and microglia. The present study investigated whether the interaction between tPA and microglial LRP1 plays a role in cerebral ischemia-induced microglial activation. We found that middle cerebral artery occlusion (MCAO) induces microglial activation in both wild-type and plasminogen-deficient (Plg(-/-)) mice. In contrast, MCAO-induced microglial activation is significantly decreased in tPA-deficient (tPA(-/-)) mice and in mice that lack LRP1 in microglial cells (macLRP(-)). We observed a significant increase in microglial activation when tPA(-/-) mice received treatment with murine tPA after MCAO. In contrast, treatment of macLRP(-) mice with tPA did not have an effect on the extent of microglial activation. Finally, both the volume of the ischemic lesion as well as inducible nitric oxide synthase production were significantly decreased in macLRP(-) mice and macLRP(-) microglia. In summary, our results indicate that the interaction between tPA and LRP1 induces microglial activation with the generation of an inflammatory response in the ischemic brain, suggesting a cytokine-like role for tPA in the CNS.

Tissue-type plasminogen activator and the low-density lipoprotein receptor-related protein induce Akt phosphorylation in the ischemic brain

Tissue-type plasminogen activator (tPA) is found in the intravascular space and in the central nervous system. The low-density lipoprotein receptor-related protein (LRP) is expressed in neurons and in perivascular astrocytes. During cerebral ischemia, tPA induces the shedding of LRP's extracellular domain from perivascular astrocytes, and this is followed by the development of cerebral edema. Protein kinase B (Akt) is a serine/threonine kinase that plays a critical role not only in cell survival but also in the regulation of the permeability of the blood-brain barrier. We found that, in the early phases of the ischemic insult, the interaction between tPA and LRP induces Akt phosphorylation (pAkt) in perivascular astrocytes and inhibits pAkt in neurons. Coimmunoprecipitation studies indicate that pAkt and LRP's intracellular domain interact in perivascular astrocytes and that this interaction is dependent on the presence of tPA and results in the development of edema. Together, these results indicate that, in the early stages of cerebral ischemia, the interaction between tPA and LRP in perivascular astrocytes induces the activation of a cell signaling event mediated by pAkt that leads to increase in the permeability of the blood-brain barrier.

The ANKH ΔE490Mutation in Calcium Pyrophosphate Dihydrate Crystal Deposition Disease (CPPDD) affects tissue non-specific Alkaline Phosphatase (TNAP) activities

ANKH (human homolog of progressive ankylosis) regulates inorganic pyrophosphate (PPi) transport. Dominant ANKH mutations were detected in at least five multiplex families with calcium pyrophosphate dihydrate crystal deposition disease (CPPPD). The objective of this study is to assess the functional consequences of one CPPDD-associated ANKH mutation (ΔE490) in chondrogenic ATDC5 cells. Stable ATDC5 transfectants bearing myc-tagged constructs of wild-type ANKH, mutant ANKH (ΔE490) and neo controls were generated. Upon ITS (insulin, transferrin and selenium) induction, expression of chondrocyte markers including alkaline phosphatase activity in the various transfectants was assessed. The ANKH ΔE490- transfectants had low alkaline phosphatase activities throughout ITS treatment due to lower TNAP protein expression and the presence of intracellular low-molecular-weight inhibitors. Our results suggest that the interplay of ANKH and TNAP activities is tightly regulated.

Regulated intramembrane proteolysis of the low-density lipoprotein receptor-related protein mediates ischemic cell death

The low-density lipoprotein receptor-related protein (LRP), a member of the low-density lipoprotein receptor gene family, mediates cellular signal transduction pathways. In this study we investigated the role of LRP in cell death. We found that incubation of mouse embryonic fibroblasts in serum-free media induces caspase-3 activation, an effect that is attenuated in LRP-deficient (LRP(-/-)) mouse embryonic fibroblasts. Since we previously demonstrated that middle cerebral artery occlusion (MCAO) in mice induces shedding of the LRP ectodomain, we investigated here whether cerebral ischemia induces regulated intramembrane proteolysis of LRP and whether this process is related to cell death. We found that MCAO induces an increase in gamma-secretase activity in the ischemic hemisphere and that treatment with the gamma-secretase inhibitor L-685,458 improves the neurological outcome and results in a 50% decrease in the volume of the ischemic lesion. Furthermore, MCAO caused nuclear translocation of the intracellular domain of LRP in neurons within the area of ischemic penumbra, and this effect was attenuated in mice treated with L-685,458. Finally, inhibition of either LRP or gamma-secretase attenuated cerebral ischemia-induced caspase-3 cleavage and apoptotic cell death. In summary, our results indicate that gamma-secretase-mediated regulated intramembrane proteolysis of LRP results in cell death under ischemic conditions.

Microcytosis in ank/ank mice and the role of ANKH in promoting erythroid differentiation

Progressive ankylosis (Ank and the human homolog, ANKH) is a transmembrane protein which regulates transport of inorganic pyrophosphate (PPi). ank/ank mice with a mutated ank gene, have calcification and bone ankylosis of the affected joints. In the course of studying these mutant mice, we found that they have microcytosis. These mutant mice have lower mean red blood cell volume (MCV) and lower hemoglobin content in red cells (mean corpuscular hemoglobin, MCH) than normal mice. Using quantitative real-time PCR analysis, we showed that Ank was expressed in the E/Meg bipotent precursor, BFU-E, CFU-E, but there was no Ank expression in the hemoglobinizing erythroblasts. Stable ANKH transfectants in K562 cells highly expressed two immature erythroid cell markers, E-cadherin and endoglin. Enhanced Erythropoietin (Epo) expression and downregulation of SHP-1 were detected in these transfectants. Consequently, the autocrine Epo-EpoR signaling pathway was activated, as evidenced by higher p-Tyr JAK2, p-Tyr EpoR and p-Tyr STAT5B in the ANKH transfectants. Our results revealed a novel function of ANKH in the promotion of early erythroid differentiation in K562 cells. We also showed that ank/ank mice have lower serum levels of Epo than the normal littermates, and this is the likely cause of microcytosis in these mutant mice.

Tissue-type plasminogen activator and the low-density lipoprotein receptor-related protein mediate cerebral ischemia-induced nuclear factor-kappaB pathway activation

Tissue-type plasminogen activator (tPA) is a serine proteinase found in the intravascular space and the central nervous system. The low-density lipoprotein receptor-related protein (LRP) is a member of the low-density lipoprotein receptor gene family found in neurons and astrocytes. Cerebral ischemia induces activation of the nuclear factor (NF)-kappaB pathway. The present study investigated the role that the interaction between tPA and LRP plays on middle cerebral artery occlusion (MCAO)-induced NF-kappaB-mediated inflammatory response. We found that MCAO increased LRP expression primarily in astrocytes and that this effect was significantly decreased in the absence of tPA. The onset of the ischemic insult induced activation of the NF-kappaB pathway in wild-type and plasminogen (Plg(-/-))-deficient mice, and this effect was attenuated after inhibition of LRP or genetic deficiency of tPA. Moreover, administration of tPA to tPA(-/-) mice resulted in activation of the NF-kappaB pathway comparable with that observed in wild-type and Plg(-/-) mice. We also report that inhibition of either tPA activity or LRP or genetic deficiency of tPA resulted in a significant decrease in MCAO-induced nitric oxide production and inducible nitric-oxide synthase expression. In conclusion, our results demonstrate that after MCAO the interaction between tPA and LRP results in NF-kappaB activation in astrocytes and induction of inducible nitric-oxide synthase expression in the ischemic tissue, suggesting a cytokine-like plasminogen-independent role for tPA during cerebral ischemia.

Tissue-type plasminogen activator-mediated shedding of astrocytic low-density lipoprotein receptor-related protein increases the permeability of the neurovascular unit

The low-density lipoprotein receptor-related protein (LRP) is a member of the LDL receptor gene family that binds several ligands, including tissue-type plasminogen activator (tPA). tPA is found in blood, where its primary function is as a thrombolytic enzyme, and in the central nervous system where it mediates events associated with cell death. Cerebral ischemia induces changes in the neurovascular unit (NVU) that result in brain edema. We investigated whether the interaction between tPA and LRP plays a role in the regulation of the permeability of the NVU during cerebral ischemia. We found that the ischemic insult induces shedding of LRP's ectodomain from perivascular astrocytes into the basement membrane. This event associates with the detachment of astrocytic end-feet processes and the formation of areas of perivascular edema. The shedding of LRP's ectodomain is significantly decreased in tPA deficient (tPA(-/-)) mice, is increased by incubation with tPA, and is inhibited by the receptor-associated protein (RAP). Furthermore, treatment with either RAP or anti-LRP IgG results in a faster recovery of motor activity and protection of the integrity of the NVU following middle cerebral artery occlusion (MCAO). Together, these results implicate tPA/LRP interactions as key regulators of the integrity of the NVU.

Immunolocalization of ecto-nucleotide pyrophosphatase/phosphodiesterase 1 (NPP1) in the rat forebrain

Immunohistochemical study was performed to determine distribution of ecto-nucleotide pyrophosphatase/phosphodiesterase1 (NPP1) in adult rat forebrain. The study revealed widespread distribution of NPP1 in rat forebrain, yet with regional differences in the expression pattern and abundance. Strong NPP1 immunoreaction was detected in pyramidal cell layer of cerebral cortex and hippocampus, and in the midline regions of hypothalamus and thalamus. In many immunopositive forebrain areas, NPP1 was mainly localized at neuronal cell bodies. However, prominent immunoreaction was also detected at ependymal cells, tanycytes, endothelial cells of the capillaries and cells of the choroid plexus, suggesting that NPP1 could be involved in some highly specialized transport process.

Mineral formation in joints caused by complete or joint-specific loss of ANK function

To reveal the ANK complete loss of function phenotype in mice, we generated conditional and null alleles. Mice homozygous for the null allele exhibited widespread joint mineralization, similar in severity to animals harboring the original ank allele. A delayed yet similar phenotype was observed in mice with joint-specific loss of ANK function.

INTRODUCTION

The ANK pyrophosphate regulator was originally identified and proposed to play a key role in articular cartilage maintenance based on a single spontaneous mouse mutation (ank) that causes severe generalized arthritis. A number of human mutations have subsequently been reported in the human ortholog (ANKH), some of which produce skull and long bone defects with no apparent defects in joints or articular cartilage. None of the currently known mouse or human mutations clearly eliminate the function of the endogenous gene.

MATERIALS AND METHODS

Two new Ank alleles were generated using homologous recombination in mouse embryonic stem (ES) cells. Joint range of motion assays and muCT studies were used to quantitatively assess phenotypic severity in wildtype, heterozygous, and homozygous mice carrying either the null (Anknull) or original (Ankank) allele. A Gdf5-Cre expressing line was crossed to mice harboring the conditional (Ankfloxp) allele to eliminate ANK function specifically in the joints. Histological stains and beta-galactosidase (LACZ) activity were used to determine the correlation between local loss of ANK function and defective joint phenotypes.

RESULTS

Anknull/Anknull mice develop severe ectopic postnatal crystal deposition in almost every joint of the body, leading to eventual joint fusion and loss of mobility. The severity of phenotype in these mice is indistinguishable from that of Ankank/Ankank mice. In addition, despite the widespread expression of Ank in many tissues, the specific deletion of Ank in joints also produces joint mineralization and ankylosis.

CONCLUSIONS

These studies show that ANK function is required locally in joints to inhibit mineral formation and that the Ank gene plays a key role in postnatal maintenance of joint mobility and function.

A soluble Fn14-Fc decoy receptor reduces infarct volume in a murine model of cerebral ischemia

Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) is a member of the tumor necrosis factor superfamily. TWEAK acts on responsive cells via binding to a small cell surface receptor named Fn14. Recent studies have demonstrated that TWEAK can stimulate numerous cellular responses including cell proliferation, migration, and proinflammatory molecule production, but the role of this cytokine in cardiovascular disease and stroke has not been established. The present study investigated whether TWEAK or Fn14 expression was regulated in a murine model of cerebral ischemia and whether TWEAK played a role in ischemia-mediated cell death. We found that TWEAK and Fn14 were expressed by primary mouse cerebral cortex-derived astrocytes and neurons cultured in vitro. Also, both the TWEAK and Fn14 proteins were present at elevated levels in the ischemic penumbra region after middle cerebral artery occlusion. Finally, we report that intracerebroventricular injection of a soluble Fn14-Fc decoy receptor immediately after middle cerebral artery occlusion significantly reduced infarct volume and the extent of microglial cell activation and apoptotic cell death in the ischemic penumbra. We conclude that the cytokine TWEAK may play an important role in ischemia-induced brain injury and that inhibition of TWEAK expression or function in the brain may represent a novel neuroprotective strategy to treat ischemic stroke.

Autosomal dominant early childhood seizures associated with chondrocalcinosis and a mutation in the ANKH Gene

We describe the pattern of early childhood seizures within a family with autosomal dominant chondrocalcinosis (CCAL, which causes adult-onset arthritis). All affected family members with CCAL experienced seizures in early childhood, usually, but not always, associated with fever. Similarities exist to the syndrome of generalized epilepsy with febrile seizures plus (GEFS+). A mutation within the ANKH gene on chromosome 5p has been found previously in this family; other patients with familial CCAL (but without seizures) have mutations in the same gene. ANKH codes for a transmembrane protein involved in the regulation of extracellular pyrophosphate ion levels, although its precise mechanism of action remains unclear. It is highly expressed in the brain, and its expression may be influenced by seizure activity. The mutation within this family creates a premature initiation codon, adding four amino acids to the N-terminus of the protein. We postulate that this may lead to a gain of function, causing seizure susceptibility as well as chondrocalcinosis. Mutations within this gene may underlie other forms of genetic epilepsy and febrile seizures.