Chorea-amyotrophy with chronic hemolytic anemia: a variant of chorea-amyotrophy with acanthocytosis

Obscurin and KCTD6 regulate cullin-dependent small ankyrin-1 (sAnk1.5) protein turnover

Small ankyrin-1 isoform 5 (sAnk1.5) turnover is regulated by posttranslational modification (ubiquitylation, neddylation, and acetylation), the presence of obscurin, and KCTD6 (a novel tissue-specific interaction partner). KCTD6 links sAnk1.5 to cullin-3. The absence of obscurin results in translocation of sAnk1.5/KCTD6 to the Z-disk and loss of sAnk1.5 on the protein level.

Protein turnover through cullin-3 is tightly regulated by posttranslational modifications, the COP9 signalosome, and BTB/POZ-domain proteins that link cullin-3 to specific substrates for ubiquitylation. In this paper, we report how potassium channel tetramerization domain containing 6 (KCTD6) represents a novel substrate adaptor for cullin-3, effectively regulating protein levels of the muscle small ankyrin-1 isoform 5 (sAnk1.5).

Binding of sAnk1.5 to KCTD6, and its subsequent turnover is regulated through posttranslational modification by nedd8, ubiquitin, and acetylation of C-terminal lysine residues. The presence of the sAnk1.5 binding partner obscurin, and mutation of lysine residues increased sAnk1.5 protein levels, as did knockdown of KCTD6 in cardiomyocytes. Obscurin knockout muscle displayed reduced sAnk1.5 levels and mislocalization of the sAnk1.5/KCTD6 complex. Scaffolding functions of obscurin may therefore prevent activation of the cullin-mediated protein degradation machinery and ubiquitylation of sAnk1.5 through sequestration of sAnk1.5/KCTD6 at the sarcomeric M-band, away from the Z-disk–associated cullin-3. The interaction of KCTD6 with ankyrin-1 may have implications beyond muscle for hereditary spherocytosis, as KCTD6 is also present in erythrocytes, and erythrocyte ankyrin isoforms contain its mapped minimal binding site.

Familial temporal lobe epilepsy as a presenting feature of choreoacanthocytosis

PURPOSE

Choreoacanthocytosis (ChAc) is an autosomal recessive disorder caused by mutations in VPS13A on chromosome 9q21 and characterized by neurodegeneration and red cell acanthocytosis. Seizures are not uncommon in ChAc but have not been well characterized in the literature. We report two ChAc families in which patients presented with temporal lobe epilepsy.

METHODS

Detailed medical and family histories were obtained. EEG, video-telemetry, brain magnetic resonance imaging (MRI) with volumetric studies of amygdala and hippocampus, as well as neuropsychological testing were performed. Blood smears were examined for acanthocytosis. Mutation analysis of VPS13A was carried out in five patients.

RESULTS

Six patients in three sibships were initially seen with seizures. Age at seizure onset ranged from 22 to 38 years. Seizures preceded other clinical manifestations of ChAc by < or = 15 years. The epileptic aura consisted of a sensation of déjà-vu, fear, hallucinations, palpitations, or vertigo. EEG with video-telemetry showed epileptiform discharges originating either from one or both temporal lobes. Epilepsy was generally well controlled, but some patients had periods of increased seizure frequency requiring treatment with multiple antiepileptic drugs (AEDs). Both families shared a deletion of exons 70-73 of VPS13A, extending to exons 6-7 of GNA14.

CONCLUSIONS

Temporal lobe epilepsy may be the presenting feature of ChAc and may delay its diagnosis. Epilepsy in ChAc patients represents a challenge, because seizures may at times be difficult to control, and some AEDs may worsen the involuntary movements. Mutations in VPS13A or GNA14 or both may be associated with clinical features of temporal lobe epilepsy.

Neuroacanthocytosis: new developments in a neglected group of dementing disorders

Neurological abnormalities associated with spiculated, "acanthocytic" red cells in blood have been summarized as neuroacanthocytosis. This is a heterogeneous group of conditions that can now be clearly subdivided on the basis of genetic discoveries. The core neuroacanthocytosis syndromes are autosomal recessive chorea-acanthocytosis (ChAc) and the X-linked McLeod syndrome (MLS). Huntington's disease-like 2 (HLD2) and pantothenate kinase associated neurodegeneration (PKAN) can now also be included. All of these share dyskinesias, cognitive deterioration and progressive neurodegeneration mainly of the basal ganglia, but they are sufficiently distinct to permit a specific working diagnosis on the basis of clinical, laboratory and imaging findings. In addition, the VPS13A (formerly called CHAC), XK, JPH3 and PANK2 genes, respectively, may be examined for mutations. Unfortunately, little is yet known about the normal and abnormal physiology of the protein products of these genes, but they appear to be involved in membrane function and intracellular protein sorting. Since no cures are yet available, development and study of disease models in experimental animals (mouse, C. elegans) is a priority for current research. From a clinical point of view, the common occurrence of cardiomyopathy in MLS, the transfusion hazards due to the McLeod Kell phenotype and the possibility of improving the violent trunk spasms and orofacial dyskinesias typical for ChAc (with subsequent lip or tongue mutilations and feeding dystonia) by deep brain surgery or stimulation should be considered in patient management.

An alternate promoter directs expression of a truncated, muscle-specific isoform of the human ankyrin 1 gene

Ankyrin 1, an erythrocyte membrane protein that links the underlying cytoskeleton to the plasma membrane, is also expressed in brain and muscle. We cloned a truncated, muscle-specific ankyrin 1 cDNA composed of novel 5' sequences and 3' sequences previously identified in the last 3 exons of the human ankyrin 1 erythroid gene. Northern blot analysis revealed expression restricted to cardiac and skeletal muscle tissues. Deduced amino acid sequence of this muscle cDNA predicted a peptide of 155 amino acids in length with a hydrophobic NH2 terminus. Cloning of the corresponding chromosomal gene revealed that the ankyrin 1 muscle transcript is composed of four exons spread over approximately 10 kilobase pairs of DNA. Reverse transcriptase-polymerase chain reaction of skeletal muscle cDNA identified multiple cDNA isoforms created by alternative splicing. The ankyrin 1 muscle promoter was identified as a (G + C)-rich promoter located > 200 kilobase pairs from the ankyrin 1 erythroid promoter. An ankyrin 1 muscle promoter fragment directed high level expression of a reporter gene in cultured C2C12 muscle cells, but not in HeLa or K562 (erythroid) cells. DNA-protein interactions were identified in vitro at a single Sp1 and two E box consensus binding sites contained within the promoter. A MyoD cDNA expression plasmid transactivated an ankyrin 1 muscle promoter fragment/reporter gene plasmid in a dose-dependent fashion in both HeLa and K562 cells. A polyclonal antibody raised to human ankyrin 1 muscle-specific sequences reacted with peptides of 28 and 30 kDa on immunoblots of human skeletal muscle.

Mutation of a highly conserved residue of betaI spectrin associated with fatal and near-fatal neonatal hemolytic anemia

We studied an infant with severe nonimmune hemolytic anemia and hydrops fetalis at birth. His neonatal course was marked by ongoing hemolysis of undetermined etiology requiring repeated erythrocyte transfusions. He has remained transfusion-dependent for more than 2 yr. A previous sibling born with hemolytic anemia and hydrops fetalis died on the second day of life. Peripheral blood smears from the parents revealed rare elliptocytes. Examination of their erythrocyte membranes revealed abnormal mechanical stability as well as structural and functional abnormalities in spectrin. Genetic studies revealed that the proband and his deceased sister were homozygous for a mutation of betaIsigma1 spectrin, L2025R, in a region of spectrin that is critical for normal function. The importance of leucine in this position of the proposed triple helical model of spectrin repeats is highlighted by its evolutionary conservation in all beta spectrins from Drosophila to humans. Molecular modeling demonstrated the disruption of hydrophobic interactions in the interior of the triple helix critical for spectrin function caused by the replacement of the hydrophobic, uncharged leucine by a hydrophilic, positively charged arginine. This mutation must also be expressed in the betaIsigma2 spectrin found in muscle, yet pathologic and immunohistochemical examination of skeletal muscle from the deceased sibling was unremarkable.

Hereditary spherocytosis: a review of the clinical and molecular aspects of the disease

Hereditary spherocytosis is a common and very heterogeneous hemolytic anemia caused by defects of the red cell membrane proteins. In recent years, major advances in our understanding of the red cell membrane skeleton and a better characterization of its individual components have allowed a brighter insight into the pathogenesis of the disease. In this article, we present an overview of the erythrocyte skeleton and its individual constituents. We also review the clinical aspects of the disease and describe the currently known molecular defects involving the membrane proteins which have been shown to play an essential role in the underlying mechanism of hereditary spherocytosis. Finally we examine several models that have been proposed in an attempt to clarify the mechanism leading from the initial molecular insult to the clinical phenotype.

Isolated weakness of the extensor hallucis longus in a patient with hereditary spherocytosis

A 24-year-old woman with a history of hereditary spherocytosis and oral contraceptive use presented with a spontaneous, isolated loss of great toe extension. She had clinical and electrodiagnostic evidence of a localized lesion affecting the nerve supply to the extensor hallucis longus (EHL). Full clinical recovery was apparent within 6 months with nonoperative therapy. Isolated EHL weakness may occur as a rare neurologic complication of procedures such as high tibial osteotomies, but, to our knowledge, this has not been reported in the absence of trauma or surgery. While the coexistence of hereditary spherocytosis and a peripheral neuropathy may have been purely coincidental, it is plausible that the isolated lesion in this patient was due to ischemic changes from underlying rheologic conditions, possibly in association with a variation in the neural or nutrient vessel supply to the EHL.

Choreo-acanthocytosis like phenotype without acanthocytes: clinicopathological case report. A contribution to the knowledge of the functional pathology of the caudate nucleus

Detailed clinical and neuropathological findings in two unrelated patients with a chorea-acanthocytosis-like phenotype (CA) are reported. One case met all the diagnostic criteria of CA and had a deceased brother with the same disease. The second case had a virtually identical phenotype to the former but without acanthocytes. These findings suggest that both patients are affected by the same disease and that acanthocytes are not essential to the diagnosis. Neuropathological autopsy studies on the brain of the second case showed selective atrophy of the caudate nucleus that seemed to correspond to the movement disorder and behavioural abnormalities prominent in this patient. In both subjects, morphometric and ultrastructural examination of the peripheral nerve showed loss of myelinated fibres, more accentuated distally, and cytoskeletal changes in the axoplasm. These findings support the hypothesis that peripheral neuropathy in CA is caused by distal axonopathy.

[Homologies between membrane proteins result in expected or unexpected relations between neuromuscular and erythrocyte diseases]

The advances achieved in biochemistry and molecular genetics have made it possible to demonstrate that the membrane proteins of the erythrocytes belong to protein "families" that are present in most cell membranes and share remarkable structural and functional homologies. Abnormalities of erythrocyte membrane proteins might then totally or partially reflect lesions of other cell membranes that are intrinsically more severe than those of the erythrocytes. Examples of these physiopathogenetic links can be found in congenital diseases where muscular and erythrocytic pathologies coexist. Such are: (1) choreaacanthocytosis supported by molecular abnormalities of the so-called band 3 protein or anion channel; (2) Mac Leod syndrome by deficiency of a membrane protein precursor of Kell antigens; (3) some cases of hereditary spherocytosis associated with qualitative and quantitative ankyrin alterations. Yet, despite the homologies that are known to exist between spectrin and dystrophin, all attempts to use spectrin analysis as marker of Duchenne-Becker muscular dystrophy have met with complete failure, which shows that at this early stage one should refrain from drawing firm physiopathological conclusions from the available data.

Parkinsonism with neuroacanthocytosis

Two patients with neuroacanthocytosis are described. One presented with parkinsonism and the other resembled diurnal dystonia of the Segawa type. Both patients responded well to dopaminomimetic therapy. A PET scan with fluorodopa revealed a nigrostriatal deficit in the first patient.

Chorea-acanthocytosis: report of a family and neuropathological study of two cases

We report three siblings, offspring of normal consanguineous parents, with a progressive neurological illness that began in midlife and was characterized primarily by chorea and leading to death in the fourth decade. The proband had erythrocyte acanthocytosis with normal serum beta-lipoprotein. Biopsy of left gastrocnemius muscle showed neurogenic muscular atrophy. There was a decrease in the numbers of large myelinated axons of the sural nerve. Postmortem examination of two cases showed marked atrophy, neuronal loss and gliosis of the caudate nucleus and putamen. Autosomal recessive inheritance is likely in this family.

Neurochemical findings in neuroacanthocytosis

We performed a neurochemical study of the brain of two unrelated patients, living in different continents, with neuroacanthocytosis. The levels of monoamines and their metabolites, gamma-aminobutyric acid and substance P, were measured in several brain areas and the monoamine metabolites in cerebrospinal fluid. The binding of 3H-spiperone to striatal membranes and to lymphocytes was also measured. Both patients had a progressive neurological disorder with onset in the third decade of life and characterized by a complex movement disorder, epilepsy, muscular wasting, and changes in behavior. The movement disorder initially manifested with oromandibular dystonia and limb chorea, but at the time of death was characterized by a severe dystonic syndrome. The chemical changes were similar in the two patients. The most important neurochemical findings were a depletion of dopamine and its metabolites in most brain areas, most notably in the striatum, and elevation of norepinephrine levels in the putamen and globus pallidus. Substance P was markedly reduced in the striatum and substantia nigra. Our findings may provide clues to the neurochemical mechanisms underlying dystonia.