The hereditary spastic paraplegias (HSPs; Strümpell-Lorrain syndrome, MIM number 18260) are a diverse class of disorders characterized by insidiously progressive lower-extremity spastic weakness (reviewed in refs. 1-3). Eight autosomal dominant HSP (ADHSP) loci have been identified, the most frequent of which is that linked to the SPG4 locus on chromosome 2p22 (found in approximately 42%), followed by that linked to the SPG3A locus on chromosome 14q11-q21 (in approximately 9%). Only SPG4 has been identified as a causative gene in ADHSP. Its protein (spastin) is predicted to participate in the assembly or function of nuclear protein complexes. Here we report the identification of mutations in a newly identified GTPase gene, SPG3A, in ADHSP affected individuals.

Recent work in human glioblastoma (GBM) has documented recurrent mutations in the histone chaperone protein ATRX. We developed an animal model of ATRX-deficient GBM and show that loss of ATRX reduces median survival and increases genetic instability. Further, analysis of genome-wide data for human gliomas showed that ATRX mutation is associated with increased mutation rate at the single nucleotide variant (SNV) level. In mouse tumors, ATRX deficiency impairs non-homologous end joining (NHEJ) and increases sensitivity to DNA-damaging agents that induce double-stranded DNA breaks. We propose that ATRX loss results in a genetically unstable tumor, which is more aggressive when left untreated, but is more responsive to double-stranded DNA-damaging agents, resulting in improved overall survival.

Nephropathic cystinosis is an autosomal recessive lysosomal storage disease characterized by renal failure at 10 years of age and other systemic complications. The gene for cystinosis, CTNS, has 12 exons. Its 2.6-kb mRNA codes for a 367-amino-acid putative cystine transporter with seven transmembrane domains. Previously reported mutations include a 65-kb "European" deletion involving marker D17S829 and 11 small mutations. Mutation analysis of 108 American-based nephropathic cystinosis patients revealed that 48 patients (44%) were homozygous for the 65-kb deletion, 2 had a smaller major deletion, 11 were homozygous and 3 were heterozygous for 753G-->A (W138X), and 24 had 21 other mutations. In 20 patients (19%), no mutations were found. Of 82 alleles bearing the 65-kb deletion, 38 derived from Germany, 28 from the British Isles, and 4 from Iceland. Eighteen new mutations were identified, including the first reported missense mutations, two in-frame deletions, and mutations in patients of African American, Mexican, and Indian ancestry. CTNS mutations are spread throughout the leader sequence, transmembrane, and nontransmembrane regions. According to a cystinosis clinical severity score, homozygotes for the 65-kb deletion and for W138X have average disease, whereas mutations involving the first amino acids prior to transmembrane domains are associated with mild disease. By northern blot analysis, CTNS was not expressed in patients homozygous for the 65-kb deletion but was expressed in all 15 other patients tested. These data demonstrate the origins of CTNS mutations in America and provide a basis for possible molecular diagnosis in this population.

Background: Paroxysmal dystonic choreoathetosis (PDC) is characterized by attacks of involuntary movements that occur spontaneously while at rest and following caffeine or alcohol consumption. Previously, we and others identified a locus for autosomal dominant PDC on chromosome 2q33-2q35. Objective: To identify the PDC gene. Design: Analysis of PDC positional candidate genes by exon sequencing and reverse transcription-polymerase chain reaction. Setting: Outpatient clinical and molecular genetic laboratory at a university hospital. Patients: Affected (n = 12) and unaffected (n =26) subjects from 2 unrelated families with PDC and 105 unrelated control subjects. Results: We identified missense mutations in the myofibrillogenesis regulator gene (MR-1) in affected subjects in 2 unrelated PDC kindreds. These mutations were absent in control subjects and caused substitutions of valine for alanine at amino acid positions 7 and 9. The substitutions disturb interspecies conserved residues and are predicted to alter the MR-1 gene's aminoterminal ␣ helix. The MR-1 exon containing these mutations (exon 1) was expressed only in the brain, a finding that explains the brain-specific symptoms of subjects with these mutations. Conclusions: Although MR-1 gene function is unknown, the precedence of ion channel disturbance in other episodic neurologic disorders suggests that the pathophysiologic features of PDC also involve abnormal ion localization. The discovery that MR-1 mutations underlie PDC provides opportunities to explore this condition's pathophysiologic characteristics and may provide insight into the causes of other paroxysmal neurologic disorders as well as the neurophysiologic mechanisms of alcohol and caffeine, which frequently precipitate PDC attacks.

Abstract. Lysosomes constitute only 4% of the intracellular volume of a normal human fibroblast. When human fibroblasts are incubated for 2-5 min with 20 t~M [asS]cystine in Krebs-Ringer phosphate solution at pH 7.4, a minimum of 50-60% of the total radioactivity taken up by the cells is found sequestered into the lysosomal compartment in the form of cysteine. A lysosomal transport system, highly specific for cysteine, appears to facilitate this rapid lysosomal cysteine sequestration. Time courses of [35S]cysteine uptake into isolated, Percoll-purified fibroblast lysosomes at pH 7.0 and 37°C are linear for the first 4-5 min and attain a steady state by 10 min. Lysosomal cysteine uptake displays a Km of 0.05 mM at pH 7.0 and an activation energy of 21 kcal/mol, corresponding to a Qt0 of 3.2. The role of this transport system in delivering cysteine into lysosomes is supported by its pH curve showing a slow rate of cysteine transport at the acidic pHs between 5 and 6, but then increasing sevenfold between pH 6 and 7.5 to be maximally active near the cytosolic pH of 7. Carrier mediation by this lysosomal transport route demonstrates a high specificity for cysteine as indicated by the inability of the following amino acids to significantly inhibit at 5 mM the lysosomal uptake of 0.035 mM [3sS]e-cysteine: ala, ser, pro, val, gly, homocysteine, D-or e-penicillamine, arg, asp, or leu. Similarly, D-cysteine and 3-mercaptopropionate were poor inhibitors, suggesting that both the L-isomer and a-amino group of cysteine appear to be required for recognition by the cysteine-specific transport system. In contrast, cysteamine, which lacks an a-carboxyl group, was able to strongly inhibit lysosomal cysteine uptake. The physiological importance of this cysteinespecific lysosomal transport system may be to aid lysosomal proteolysis by delivering cysteine into the lysosomal compartment to (a) maintain the catalytic activity of the thiol-dependent lysosomal enzymes and (b) break protein disulfide bridges at susceptible linkages, thereby allowing proteins to unfold, facilitating their degradation.VSOSOMES are a major intracellular site for the degradation of a wide variety of macromolecules which are delivered to this organelle by receptor-mediated endocytosis, pinocytosis, or autophagy. Many of the metabolites formed in the lysosome as a consequence of the breakdown of macromolecules appear to egress from the lysosomal compartment by way of carrier-mediated transport systems. Specific lysosomal transport systems for cystine (13)(14)(15)19), the cationic amino acids (29, 31), small neutral amino acids (30), large neutral amino acids (6, 47), nucleosides (28), acidic monosaccharides (24, 32), and the sugars N-acetyl galactosamine and N-acetyl glucosamine (20) have been described. The importance of transport systems in mediating the escape of metabolites from the lysosomal compartment becomes especially obvious in the lethal genetic disease, nephropathic cystinosis. In this disorder, defective A preliminary report of this work has appe...