Christo Shalish

The early-onset torsion dystonia gene (DYT1) encodes an ATP-binding protein

Early-onset torsion dystonia is a movement disorder, characterized by twisting muscle contractures, that begins in childhood. Symptoms are believed to result from altered neuronal communication in the basal ganglia. This study identifies the DYT1 gene on human chromosome 9q34 as being responsible for this dominant disease. Almost all cases of early-onset dystonia have a unique 3-bp deletion that appears to have arisen independently in different ethnic populations. This deletion results in loss of one of a pair of glutamic-acid residues in a conserved region of a novel ATP-binding protein, termed torsinA. This protein has homologues in nematode, rat, mouse and humans, with some resemblance to the family of heat-shock proteins and Clp proteases.

Relationship Between Platelet Monoamine Oxidase B Activity and Alleles at the MAOB Locus

Abstract: Genetic variations in monoamine oxidase (MAO)‐B activity have been proposed to have a contributory role in several neurologic and psychiatric diseases. Variations in activity could affect rates of degradation of exogenous amines, including toxins, precursors of toxins (like 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine), or false transmitters, and of endogenous amines, such as neurotransmitters. In this study a highly polymorphic (GT)n repeat element was used to mark alleles at the MAOB locus. The MAOB allele status and levels of platelet MAO‐B activity were determined for 41 control males. No correlation was noted between specific alleles and levels of MAO‐B activity in this sample set. This suggests that the structural gene for MAOB is not usually the primary determinant of activity levels in platelets.

Mutational analysis of the human MAOA gene

The monoamine oxidases (MAO-A and MAO-B) are the enzymes primarily responsible for the degradation of amine neurotransmitters, such as dopamine, norepinephrine, and serotonin. Wide variations in activity of these isozymes have been reported in control humans. The MAOA and MAOB genes are located next to each other in the p11.3-11.4 region of the human X chromosome. Our recent documentation of an MAO-A-deficiency state, apparently associated with impulsive aggressive behavior in males, has focused attention of genetic variations in the MAOA gene. In the present study variations in the coding sequence of the MAOA gene were evaluated by RT-PCR, SSCP, and sequencing a mRNA or genomic DNA in 40 control males with > 100-fold variations of MAO-A activity, as measured in cultured skin fibroblasts. Remarkable conservation of the coding sequence was found with only 5 polymorphisms observed. All but one of these were in the third codon position and thus did not alter the deduced amino acid sequence. The one amino acid alteration observed, lys --> arg, was neutral and should not affect the structure of the protein. This study demonstrates high conservation of coding sequence in the human MAOA gene in control males, and provides primer sets which can be used to search genomic DNA for mutations in this gene in males with neuropsychiatric conditions.

β-Galactosidase Gene Mutations in Patients With Slowly Progressive GM1 Gangliosidosis

Three unrelated North American cases with slowly progressive forms of GM1 gangliosidosis were found to have two unique point mutations and a 9 bp insertion in the coding region of the gene encoding β-galactosidase. Case 1 was noted to have a 9 bp insertion {CAGAATTTT} on one allele between nucleotides 730 and 731 with no other mutations identified in the other allele. In case 2, two point mutations were found: a unique G→A transition at nucleotide 602 causing an Arg→His substitution in codon 201 (mutation R201H); and a previously identified G→T transition at nucleotide 1527 causing a Trp→Cys substitution in codon 509 (mutation W509C), which has been noted in adult and chronic forms of GM1 gangliosidosis. Case 3 had a unique point mutation (A→G transition at nucleotide 797) resulting in a Asn→Ser amino acid substitution in codon 266 (mutation N266S), with no other mutations found in the same or the other allele. Single-strand conformation polymorphism performed on over 100 controls did not demonstrate the presence of the point mutations R201H or N266S. Also, the mutant proteins coded by the two point mutations did not show enzymatic activity in the Cos-1 cell expression system confirming that these mutations are associated with low enzyme activity. ( J Child Neurol 1997;12:242—247).

Molecular cloning and expression of rat torsinA in the normal and genetically dystonic (dt) rat.

Deletions within the TOR1A gene cause early-onset (DYT1) torsion dystonia. We have cloned and sequenced the rat cDNA homologue of TOR1A and found a 91% identity with the human sequence. Northern blot analysis detects a single transcript of approximately 1.5 kb. In situ hybridization reveals a widespread distribution of torsinA mRNA within brain. No mutations were identified in the coding region of the gene in the genetically dystonic (dt) rat.

Exclusion of p75NGFR and other candidate genes in a family with hereditary sensory neuropathy Type II

&NA; Hereditary sensory neuropathy Type II (HSN II) is an autosomal recessive disorder characterized by the loss of peripheral sensory modalities in individuals with otherwise normal development. Patients with HSN II often have chronic ulceration of the fingers and toes, autoamputation of the distal phalanges, and neuropathic joint degeneration associated with loss of pain sensation. Recent descriptions of a similar phenotype in mice carrying a targeted mutation in the low affinity nerve growth factor receptor, p75NGFR, suggested the possibility that mutations in this gene or other members of the nerve growth factor (NGF) family of genes and their receptors might be responsible for this human disorder. In this study candidate genes were evaluated by their inheritance pattern in two sisters affected with HSN II, their unaffected sister and mother in a consanguineous family. The segregation of polymorphic alleles at and around loci for p75NGFR, TRKA, TRKB, BDNF, and familial dysautonomia (another hereditary sensory neuropathy having features in common with HSN II) virtually excluded these genes as the cause of HSN II in this family. Further evaluation of loci for other neurotrophic factors and their receptors, which will be possible when mapping information on their loci becomes available, may permit the identification of the gene responsible for HSN II.

Analysis of MAOA mutations in humans.

Publisher Summary This chapter presents an analysis of monoamine oxidase (MAO) A mutations in humans. A direct correlation between an MAOA mutation and a phenotype has been provided by recent studies of a pedigree in the Netherlands. Eight males in the pedigree, who are mildly retarded and show episodic aggressive behavior, including attempted murder, attempted rape, exhibitionism, attempted suicide, and arson, were found to carry a point mutation that converts a glutamine codon into a stop codon in the eighth exon. This mutation completely disrupts MAO-A activity. The common feature shared by these males of an apparent episodic loss of impulse control suggests the involvement of physiological changes resulting from MAO-A deficiency, but could also be related to mild retardation. The correlations of sequence variations with disease phenotypes, as in the MAO-A-deficient patients, may begin to emerge by the use of methods based on polymerase chain reaction (PCR) and single-strand conformational polymorphisms (SSCP). In addition, the allelic-association approach will continue to provide an efficient means for evaluating the role of MAO genes in different disease states.

Chromosomal Effects on Peptidase Activities in Drosophila melanogaster

The peptidase system inDrosophila melanogaster (dipeptidase-A, -B, and -C and leucine aminopeptidases G and P) was used as a model to study the effects of modifier genes on activity of enzymes with similar functions. A screen of X, second, and third chromosome substitution isogenic lines revealed the presence of activity modifiers for peptidases on all three chromosomes. Correlation analyses indicated that covariation between some of the peptidase activities is independent of genetic background, while others are associated with variable second chromosomes. Chromosome-specific effects onKm,Vmax, and specific activity of partially purified peptidases were also detected. Moreover, a repeatable technique using anion-exchange column chromatography allowed the characterization of possibly two putative peptidic enzymes, glycyl-l-isoleucine-ase andl-leucyl-l-proline-ase, whose kinetic properties differ from the dipeptidases and the leucine aminopeptidases. These findings confirm the existence of activity modifiers for peptidases, much like other enzymes inDrosophila melanogaster.