Neurodegeneration associated with genetic defects in phospholipase A(2).

OBJECTIVE: Mutations in the gene encoding phospholipase A(2) group VI (PLA2G6) are associated with two childhood neurologic disorders: infantile neuroaxonal dystrophy (INAD) and idiopathic neurodegeneration with brain iron accumulation (NBIA). INAD is a severe progressive psychomotor disorder in which axonal spheroids are found in brain, spinal cord, and peripheral nerves. High globus pallidus iron is an inconsistent feature of INAD; however, it is a diagnostic criterion of NBIA, which describes a clinically and genetically heterogeneous group of disorders that share this hallmark feature. We sought to delineate the clinical, radiographic, pathologic, and genetic features of disease resulting from defective phospholipase A(2). METHODS: We identified 56 patients clinically diagnosed with INAD and 23 with idiopathic NBIA and screened their DNA for PLA2G6 mutations. RESULTS: Eighty percent of patients with INAD had mutations in PLA2G6, whereas mutations were found in only 20% of those with idiopathic NBIA. All patients with two null mutations had a more severe phenotype. On MRI, nearly all mutation-positive patients had cerebellar atrophy, and half showed brain iron accumulation. We observed Lewy bodies and neurofibrillary tangles in association with PLA2G6 mutations. CONCLUSION: Defects in phospholipase A(2) lead to a range of phenotypes. PLA2G6 mutations are associated with nearly all cases of classic infantile neuroaxonal dystrophy but a minority of cases of idiopathic neurodegeneration with brain iron accumulation, and genotype correlates with phenotype. Cerebellar atrophy predicts which patients are likely to be mutation-positive. The neuropathologic changes that are caused by defective phospholipase A(2) suggest a shared pathogenesis with both Parkinson and Alzheimer diseases.

Deprivation of pantothenic acid elicits a movement disorder and azoospermia in a mouse model of pantothenate kinase-associated neurodegeneration.

We asked whether a movement disorder could be elicited by deprivation of pantothenic acid (PA; vitamin B5), the substrate for the enzyme pantothenate kinase 2 (PANK2), which is deficient in the inherited neurological disorder PKAN (pantothenate kinase-associated neurodegeneration formerly called Hallervorden-Spatz syndrome). This study was undertaken because mice made null for Pank2 failed to show the neurological manifestations of the human disease. Wild-type and Pank2 mutant mice were fed pantothenic acid-deficient diets and were monitored for general health, fertility and movement compared with animals on control diets over time. Mice of both genotypes on PA-deficient diets exhibited poor grooming, greying of fur and decreased body weight. With PA deprivation, wild-type mice manifested azoospermia (a phenotype also seen in Pank2 mice) as well as a movement disorder with a low-lying pelvis and slow steps. Rear limbs appeared to drag and occasionally extended into unnatural postures for 16-17 s duration, possibly indicative of dystonia. Movement disruption probably also occurs in PA-deprived Pank2 mutant mice, but they died precipitously before undergoing detailed analysis. Remarkably, restoration of dietary PA led to recovery of general health and grooming, weight gain, reversal of the movement disorder, and reappearance of mature sperm within 4 weeks. This study confirms the primacy of PA metabolism in the mechanism of disease in PKAN. PA deprivation provides a useful phenocopy for PKAN and allows us to test pharmacological and other interventional strategies in the treatment of this devastating disease.

Brain MRI in neurodegeneration with brain iron accumulation with and without PANK2 mutations.

BACKGROUND AND OBJECTIVE: Patients with a clinical diagnosis of neurodegeneration with brain iron accumulation (NBIA, formerly called Hallervorden-Spatz syndrome) often have mutations in PANK2, the gene encoding pantothenate kinase 2. We investigated correlations between brain MR imaging changes, mutation status, and clinical disease features. METHODS: Brain MRIs from patients with NBIA were reviewed by 2 neuroradiologists for technical factors, including signal intensity abnormalities in specific brain regions, presence and location of atrophy, presence of white matter abnormality, contrast enhancement, and other comments. PANK2 genotyping was performed by polymerase chain reaction amplification of patient genomic DNA followed by automated nucleotide sequencing. RESULTS: Sixty-six MR imaging examinations from 49 NBIA patients were analyzed, including those from 29 patients with mutations in PANK2. All patients with mutations had the specific pattern of globus pallidus central hyperintensity with surrounding hypointensity on T2-weighted images, known as the eye-of-the-tiger sign. This sign was not seen in any studies from patients without mutations. Even before the globus pallidus hypointensity developed, patients with mutations could be distinguished by the presence of isolated globus pallidus hyperintensity on T2-weighted images. Radiographic evidence for iron deposition in the substantia nigra was absent early in disease associated with PANK2 mutations. MR imaging abnormalities outside the globus pallidus, including cerebral or cerebellar atrophy, were more common and more severe in mutation-negative patients. No specific MR imaging changes could be distinguished among the mutation-negative patients. CONCLUSION: MR imaging signal intensity abnormalities in the globus pallidus can distinguish patients with mutations in PANK2 from those lacking a mutation, even in the early stages of disease.

Mislocalisation of hephaestin, a multicopper ferroxidase involved in basolateral intestinal iron transport, in the sex linked anaemia mouse.

BACKGROUND: Hephaestin is a multicopper ferroxidase required for basolateral transport of iron from enterocytes. Sex linked anaemia (sla) mice have a defect in the release of iron from intestinal enterocytes into the circulation due to an interstitial deletion in the hephaestin gene (heph). RESULTS: We have demonstrated that hephaestin is primarily localised to a supranuclear compartment in both intestinal enterocytes and in cultured cells. In normal intestinal enterocytes, hephaestin was also present on the basolateral surface. In sla mice, hephaestin was present only in the supranuclear compartment. In contrast, the iron permease Ireg1 localised to the basolateral membrane in both control and sla mice. CONCLUSION: We suggest that mislocalisation of hephaestin likely contributes to the functional defect in sla intestinal epithelium.

HARP syndrome is allelic with pantothenate kinase-associated neurodegeneration.

HARP (hypoprebetalipoproteinemia, acanthocytosis, retinitis pigmentosa, and pallidal degeneration) is a rare syndrome with many clinical similarities to pantothenate kinase-associated neurodegeneration (PKAN, formerly Hallervorden-Spatz syndrome). Despite these common features, lipoprotein abnormalities have not been reported in PKAN. After the recent discovery of the genetic defect in PKAN, we report a homozygous nonsense mutation in exon 5 of the PANK2 gene that creates a stop codon at amino acid 371 (R371X) in the original HARP patient. This finding establishes that HARP is part of the PKAN disease spectrum.

hGFRalpha-4: a new member of the GDNF receptor family and a candidate for NBIA.

Hallervorden-Spatz syndrome (neurodegeneration with brain iron accumulation type 1; OMIM entry 234200) is a rare inherited neurodegenerative disease. In this article, evidence for a newly identified gene as a candidate for Hallervorden-Spatz syndrome is given. Previously Hallervorden-Spatz syndrome was mapped to a 4-cm region in 20p12.3-13. During positional cloning efforts a new member of the glial-derived neurotrophic factor receptor family was discovered in this region. Like other members of this receptor family, this new gene is predicted to be secreted and glycosyl-phosphatidylinositol linked, and it maintains conserved cysteine residues. However, cDNA and genomic studies in both humans and mice indicate that this gene lacks the sequence corresponding to exons 2 and 3 in other family members. In situ hybridization reveals that it is expressed primarily in the brain and bladder in the embryonic mouse. Mutation analysis of patients with Hallervorden-Spatz syndrome revealed two potentially significant amino acid changes in two patients but failed to identify mutations in the remaining 10 subjects. The implication of these findings for the relationship between this gene and Hallervorden-Spatz syndrome is discussed.

A novel pantothenate kinase gene (PANK2) is defective in Hallervorden-Spatz syndrome.

Hallervorden-Spatz syndrome (HSS) is an autosomal recessive neurodegenerative disorder associated with iron accumulation in the brain. Clinical features include extrapyramidal dysfunction, onset in childhood, and a relentlessly progressive course. Histologic study reveals iron deposits in the basal ganglia. In this respect, HSS may serve as a model for complex neurodegenerative diseases, such as Parkinson disease, Alzheimer disease, Huntington disease and human immunodeficiency virus (HIV) encephalopathy, in which pathologic accumulation of iron in the brain is also observed. Thus, understanding the biochemical defect in HSS may provide key insights into the regulation of iron metabolism and its perturbation in this and other neurodegenerative diseases. Here we show that HSS is caused by a defect in a novel pantothenate kinase gene and propose a mechanism for oxidative stress in the pathophysiology of the disease.

The copper transporter CTR1 provides an essential function in mammalian embryonic development.

Copper serves as an essential cofactor for a variety of proteins in all living organisms. Previously, we described a human gene (CTR1;SLC31A1) that encodes a high-affinity copper-uptake protein and hypothesized that this protein is required for copper delivery to mammalian cells. Here, we test this hypothesis by inactivating the Ctr1 gene in mice by targeted mutagenesis. We observe early embryonic lethality in homozygous mutant embryos and a deficiency in copper uptake in the brains of heterozygous animals. Ctr1(-/-) embryos can be recovered at E8.5 but are severely developmentally retarded and morphologically abnormal. Histological analysis reveals discontinuities and variable thickness in the basement membrane of the embryonic region and an imperfect Reichert's membrane, features that are likely due to lack of activity in the collagen cross-linking cupro-enzyme lysyl oxidase. A collapsed embryonic cavity, the absence of an allantois, retarded mesodermal migration, and increased cell death are also apparent. In the brains of heterozygous adult mice, which at 16 months are phenotypically normal, copper is reduced to approximately half compared with control littermates, implicating CTR1 as the required port for copper entry into at least this organ. A study of the spatial and temporal expression pattern of Ctr1 during mouse development and adulthood further shows that CTR1 is ubiquitously transcribed with highest expression observed in the specialized epithelia of the choroid plexus and renal tubules and in connective tissues of the eye, ovary, and testes. We conclude that CTR1 is the primary avenue for copper uptake in mammalian cells.

Homozygosity mapping places the acrodermatitis enteropathica gene on chromosomal region 8q24.3.

Acrodermatitis enteropathica (AE) is a rare autosomal recessive pediatric disease characterized by dermatitis, diarrhea, alopecia, and growth failure. The disease results from insufficient uptake of zinc by the intestine and can be fatal unless the diet is supplemented with zinc. To map the gene responsible for AE, a genomewide screen was performed on 17 individuals, including 4 affected individuals, in a consanguineous Jordanian family. Three markers-D8S373, D10S212, and D6S1021-had a pattern consistent with tight linkage to a recessive disease: one allele in the affected sibs and multiple alleles in unaffected sibs and parents. Two-point parametric linkage analysis using FASTLINK identified one region, D8S373, with a maximum LOD score >1.5 (1.94 at D8S373: recombination fraction.001). Twelve additional markers flanking D8S373 were used to genotype the extended family, to fine-map the AE gene. All five affected individuals-including one who was not genotyped in the genomewide screen-were found to be homozygous for a common haplotype, spanning approximately 3.5 cM, defined by markers D8S1713 and D8S2334 on chromosomal region 8q24.3. To support these mapping data, seven consanguineous Egyptian families with eight patients with AE were genotyped using these markers, and six patients from five families were found to be homozygous in this region. Multipoint analysis with all consanguineous families, by Mapmaker/Homoz, resulted in a maximum LOD score of 3.89 between D8S1713 and D8S373. Sliding three-point analysis resulted in a maximum LOD score of 5.16 between markers D8S1727 and D8S1744.

Familial aggregation of absolute pitch.

Absolute pitch (AP) is a behavioral trait that is defined as the ability to identify the pitch of tones in the absence of a reference pitch. AP is an ideal phenotype for investigation of gene and environment interactions in the development of complex human behaviors. Individuals who score exceptionally well on formalized auditory tests of pitch perception are designated as "AP-1." As described in this report, auditory testing of siblings of AP-1 probands and of a control sample indicates that AP-1 aggregates in families. The implications of this finding for the mapping of loci for AP-1 predisposition are discussed.

The pallid gene encodes a novel, syntaxin 13-interacting protein involved in platelet storage pool deficiency.

Pallid (pa) is 1 of 13 platelet storage pool deficiency (SPD) mouse mutants. pa animals suffer from prolonged bleeding time, pigment dilution, kidney lysosomal enzyme elevation, serum alpha1-antitrypsin activity deficiency and abnormal otolith formation. As with other mouse mutants of this class, characterization of pa mice suggests a defect in organelle biosynthesis. Here we describe the physical mapping, positional cloning, and mutational and functional analysis of the gene that is defective in pa mice. It encodes a ubiquitously expressed, highly charged 172-amino-acid protein (termed pallidin) with no homology to known proteins. We detected a nonsense mutation at codon 69 of this gene in the pallid mutant. In a yeast two-hybrid screen, we discovered that pallidin interacts with syntaxin 13, a t-SNARE protein that mediates vesicle-docking and fusion. We confirmed this interaction by co-immunoprecipitation assay. Immunofluorescence studies corroborate that the cellular distribution of pallidin overlaps that of syntaxin 13. Whereas the mocha and pearl SPD mutants have defects in Ap-3, our findings suggest that pa SPD mutants are defective in a more downstream event of vesicle-trafficking: namely, vesicle-docking and fusion.

Hephaestin, a ceruloplasmin homologue implicated in intestinal iron transport, is defective in the sla mouse.

Iron is essential for many cellular functions; consequently, disturbances of iron homeostasis, leading to either iron deficiency or iron overload, can have significant clinical consequences. Despite the clinical prevalence of these disorders, the mechanism by which dietary iron is absorbed into the body is poorly understood. We have identified a key component in intestinal iron transport by study of the sex-linked anaemia (sla) mouse, which has a block in intestinal iron transport. Mice carrying the sla mutation develop moderate to severe microcytic hypochromic anaemia. Although these mice take up iron from the intestinal lumen into mature epithelial cells normally, the subsequent exit of iron into the circulation is diminished. As a result, iron accumulates in enterocytes and is lost during turnover of the intestinal epithelium. Biochemical studies have failed to identify the underlying difference between sla and normal mice, therefore, we used a genetic approach to identify the gene mutant in sla mice. We describe here a novel gene, Heph, encoding a transmembrane-bound ceruloplasmin homologue that is mutant in the sla mouse and highly expressed in intestine. We suggest that the hephaestin protein is a multicopper ferroxidase necessary for iron egress from intestinal enterocytes into the circulation and that it is an important link between copper and iron metabolism in mammals.

Absolute pitch: an approach for identification of genetic and nongenetic components.

Absolute pitch (AP) is the ability to recognize a pitch, without an external reference. By surveying more than 600 musicians in music conservatories, training programs, and orchestras, we have attempted to dissect the influences of early musical training and genetics on the development of this ability. Early musical training appears to be necessary but not sufficient for the development of AP. Forty percent of musicians who had begun training at <=4 years of age reported AP, whereas only 3% of those who had initiated training at >=9 years of age did so. Self-reported AP possessors were four times more likely to report another AP possessor in their families than were non-AP possessors. These data suggest that both early musical training and genetic predisposition are needed for the development of AP. We developed a simple computer-based acoustical test that has allowed us to subdivide AP possessors into distinct groups, on the basis of their performance. Investigation of individuals who performed extremely well on this test has already led us to identify several families that will be suitable for studies of the genetic basis of AP.

Solution structure of the fourth metal-binding domain from the Menkes copper-transporting ATPase.

Menkes disease is an X-linked disorder in copper transport that results in death during early childhood. The solution structures of both apo and Ag(I)-bound forms of the fourth metal-binding domain (mbd4) from the Menkes copper-transporting ATPase have been solved. The 72-residue mbd4 has a ferredoxin-like beta alpha beta beta alpha beta fold. Structural differences between the two forms are limited to the metal-binding loop, which is disordered in the apo structure but well ordered in the Ag(I)-bound structure. Ag(I) binds in a linear bicoordinate manner to the two Cys residues of the conserved GMTCxxC motif; Cu(I) likely coordinates in a similar manner. Menkes mbd4 is thus the first bicoordinate copper-binding protein to be characterized structurally. Sequence comparisons with other heavy-metal-binding domains reveal a conserved hydrophobic core and metal-binding motif.

A novel gene involved in zinc transport is deficient in the lethal milk mouse.

We have identified the gene responsible for the inherited zinc deficiency in the lethal milk (lm) mouse. The gene, here designated Znt4, encodes a 430-amino-acid protein that is homologous to two proteins, ZnT2 and ZnT3, responsible for sequestration of zinc into endosomal/lysosomal compartments and synaptic vesicles, respectively. We show that the Znt4 gene confers zinc resistance to a zinc-sensitive yeast strain and that it is abundantly expressed in the mammary epithelia and brain. The lethal milk mutant has a nonsense mutation at arginine codon 297 in the Znt4 gene.