Katherine B. Sims

Exome sequencing in amyotrophic lateral sclerosis identifies risk genes and pathways

New players in Lou Gehrigs disease Amyotrophic lateral sclerosis (ALS), often referred to as “Lou Gehrigs disease,” is a progressive neurodegenerative disease that affects nerve cells in the brain and the spinal cord. Cirulli et al. sequenced the expressed genes of nearly 3000 ALS patients and compared them with those of more than 6000 controls (see the Perspective by Singleton and Traynor). They identified several proteins that were linked to disease in patients. One such protein, TBK1, is implicated in innate immunity and autophagy and may represent a therapeutic target. Science, this issue p. 1436; see also p. 1422 Analysis of the expressed genes of nearly 2900 patients with amyotrophic lateral sclerosis and about 6400 controls reveals a disease predisposition–associated gene. [Also see Perspective by Singleton and Traynor] Amyotrophic lateral sclerosis (ALS) is a devastating neurological disease with no effective treatment. We report the results of a moderate-scale sequencing study aimed at increasing the number of genes known to contribute to predisposition for ALS. We performed whole-exome sequencing of 2869 ALS patients and 6405 controls. Several known ALS genes were found to be associated, and TBK1 (the gene encoding TANK-binding kinase 1) was identified as an ALS gene. TBK1 is known to bind to and phosphorylate a number of proteins involved in innate immunity and autophagy, including optineurin (OPTN) and p62 (SQSTM1/sequestosome), both of which have also been implicated in ALS. These observations reveal a key role of the autophagic pathway in ALS and suggest specific targets for therapeutic intervention.

Fabry disease: Guidelines for the evaluation and management of multi-organ system involvement

Fabry disease is an X-linked metabolic storage disorder due to the deficiency of lysosomal α-galactosidase A, and the subsequent accumulation of glycosphingolipids, primarily globotriaosylceramide, throughout the body. Males with classical Fabry disease develop early symptoms including pain and hypohidrosis by the second decade of life reflecting disease progression in the peripheral and autonomic nervous systems. An insidious cascade of disease processes ultimately results in severe renal, cardiac, and central nervous system complications in adulthood. The late complications are the main cause of late morbidity, as well as premature mortality. Disease presentation in female heterozygotes may be as severe as in males although women may also remain asymptomatic. The recent introduction of enzyme replacement therapy to address the underlying pathophysiology of Fabry disease has focused attention on the need for comprehensive, multidisciplinary evaluation and management of the multi-organ system involvement. In anticipation of evidence-based recommendations, an international panel of physicians with expertise in Fabry disease has proposed guidelines for the recognition, evaluation, and surveillance of disease-associated morbidities, as well as therapeutic strategies, including enzyme replacement and other adjunctive therapies, to optimize patient outcomes.

Strikingly Different Clinicopathological Phenotypes Determined by Progranulin-Mutation Dosage

We performed hypothesis-free linkage analysis and exome sequencing in a family with two siblings who had neuronal ceroid lipofuscinosis (NCL). Two linkage peaks with maximum LOD scores of 3.07 and 2.97 were found on chromosomes 7 and 17, respectively. Unexpectedly, we found these siblings to be homozygous for a c.813_816del (p.Thr272Serfs∗10) mutation in the progranulin gene (GRN, granulin precursor) in the latter peak. Heterozygous mutations in GRN are a major cause of frontotemporal lobar degeneration with TDP-43 inclusions (FTLD-TDP), the second most common early-onset dementia. Reexamination of progranulin-deficient mice revealed rectilinear profiles typical of NCL. The age-at-onset and neuropathology of FTLD-TDP and NCL are markedly different. Our findings reveal an unanticipated link between a rare and a common neurological disorder and illustrate pleiotropic effects of a mutation in the heterozygous or homozygous states.

Stroke in Fabry disease frequently occurs before diagnosis and in the absence of other clinical events: natural history data from the Fabry Registry.

Background and Purpose— Stroke is a common and serious clinical manifestation of Fabry disease, an X-linked lysosomal storage disorder caused by deficiency of &agr;-galactosidase A activity. This study was undertaken to better understand the natural history of cerebrovascular manifestations of Fabry disease. Methods— Data from 2446 patients in the Fabry Registry were analyzed to identify clinical characteristics of patients experiencing stroke during the natural history period (ie, before enzyme replacement therapy). Results— A total of 138 patients (86 of 1243 males [6.9%] and 52 of 1203 females [4.3%]) experienced strokes. Median age at first stroke was 39.0 years in males and 45.7 years in females. Most patients (70.9% of males and 76.9% of females) had not experienced renal or cardiac events before their first stroke. Fifty percent of males and 38.3% of females experienced their first stroke before being diagnosed with Fabry disease. Thirty patients (21 males and 9 females) had strokes at age <30 years. Most patients (86.8%) had ischemic strokes, but 16.9% of males and 6.9% of females had hemorrhagic strokes, among those for whom stroke type was reported. At the most recently available follow-up examination after their first stroke, 60% of males and 25.5% of females exhibited stage 3 to 5 chronic kidney disease and 66.1% of males and 59.5% of females had left ventricular hypertrophy. Conclusions— All patients with Fabry disease, regardless of age or gender, should be monitored for possible cerebrovascular complications, as stroke can occur in the absence of other key signs of the disease.

Survey of Somatic Mutations in Tuberous Sclerosis Complex (TSC) Hamartomas Suggests Different Genetic Mechanisms for Pathogenesis of TSC Lesions

Tuberous sclerosis complex (TSC), an autosomal dominant disease caused by mutations in either TSC1 or TSC2, is characterized by the development of hamartomas in a variety of organs. Concordant with the tumor-suppressor model, loss of heterozygosity (LOH) is known to occur in these hamartomas at loci of both TSC1 and TSC2. LOH has been documented in renal angiomyolipomas (AMLs), but loss of the wild-type allele in cortical tubers appears to be very uncommon. Analysis of second, somatic events in tumors for which the status of both TSC1 and TSC2 is known is essential for exploration of the pathogenesis of TSC-lesion development. We analyzed 24 hamartomas from 10 patients for second-hit mutations, by several methods, including LOH, scanning of all exons of both TSC1 and TSC2, promoter methylation of TSC2, and clonality analysis. Our results document loss of the wild-type allele in six of seven AMLs, without evidence of the inactivation of the second allele in many of the other lesions, including tumors that appear to be clonally derived. Laser-capture microdissection further demonstrated loss of the second allele in all three cellular components of an AML. This study thus provides evidence that, in both TSC1 and TSC2, somatic mutations resulting in the loss of wild-type alleles may not be necessary in some tumor types-and that other mechanisms may contribute to tumorigenesis in this setting.

Angiogenin loss-of-function mutations in amyotrophic lateral sclerosis

Heterozygous missense mutations in the coding region of angiogenin (ANG), an angiogenic ribonuclease, have been reported in amyotrophic lateral sclerosis (ALS) patients. However, the role of ANG in motor neuron physiology and the functional consequences of these mutations are unknown. We searched for new mutations and sought to define the functional consequences of these mutations.

Analysis of both TSC1 and TSC2 for germline mutations in 126 unrelated patients with tuberous sclerosis

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder characterized by the development of multiple hamartomas involving many organs. About two‐thirds of the cases are sporadic and appear to represent new mutations. With the cloning of two causative genes, TSC1 and TSC2 it is now possible to analyze both genes in TSC patients and identify germline mutations. Here we report the mutational analysis of the entire coding region of both TSC1 and TSC2 genes in 126 unrelated TSC patients, including 40 familial and 86 sporadic cases, by single‐stranded conformational polymorphism (SSCP) analysis followed by direct sequencing. Mutations were identified in a total of 74 (59%) cases, including 16 TSC1 mutations (5 sporadic and 11 familial cases) and 58 TSC2 mutations (42 sporadic and 16 familial cases). Overall, significantly more TSC2 mutations were found in our population, with a relatively equal distribution of mutations between TSC1 and TSC2 among the familial cases, but a marked underrepresentation of TSC1 mutations among the sporadic cases (P = 0.0035, Fishers exact test). All TSC1 mutations were predicted to be protein truncating. However, in TSC2 13 missense mutations were found, five clustering in the GAP‐related domain and three others occurring in exon 16. Upon comparison of clinical manifestations, including the incidence of intellectual disability, we could not find any observable differences between TSC1 and TSC2 patients. Our data help define the distribution and spectrum of mutations associated with the TSC loci and will be useful for both understanding the function of these genes as well as genetic counseling in patients with the disease. Hum Mutat 14:412–422, 1999.

Structural features of human monoamine oxidase A elucidated from cDNA and peptide sequences

Abstract: Monoamine oxidase (MAO), an important enzyme for the degradation of amine neurotransmitters, has been implicated in neu‐ropsychiatric illness. The amino acid sequence for one form of the enzyme, MAO‐A, has been deduced from human cDNA clones and verified against proteolytic peptides. The covalent binding site for the flavin adenine dinucleotide (FAD) cofactor is near the C‐terminal region. The presence of features characteristic of the ADP‐binding fold suggests that the N‐terminal region is also involved in the binding of FAD. These cDNAs should facilitate the study of the structure, function, and intracellular targeting of MAO, as well as the analysis of its expression in normal and pathological states.

Monoamine oxidase deficiency in males with an X chromosome deletion.

Mapping of the human MAOA gene to chromosomal region Xp21-p11 prompted our study of two affected males in a family previously reported to have Norrie disease resulting from a submicroscopic deletion in this chromosomal region. In this investigation we demonstrate in these cousins deletion of the MAOA gene, undetectable levels of MAO-A and MAO-B activities in their fibroblasts and platelets, respectively, loss of mRNA for MAO-A in fibroblasts, and substantial alterations in urinary catecholamine metabolites. The present study documents that a marked deficiency of MAO activity is compatible with life and that genes for MAO-A and MAO-B are near each other in this Xp chromosomal region. Some of the clinical features of these MAO deletion patients may help to identify X-linked MAO deficiency diseases in humans.

Diagnosis and management of mitochondrial disease: a consensus statement from the Mitochondrial Medicine Society.

Purpose:The purpose of this statement is to review the literature regarding mitochondrial disease and to provide recommendations for optimal diagnosis and treatment. This statement is intended for physicians who are engaged in diagnosing and treating these patients. Methods:The Writing Group members were appointed by the Mitochondrial Medicine Society. The panel included members with expertise in several different areas. The panel members utilized a comprehensive review of the literature, surveys, and the Delphi method to reach consensus. We anticipate that this statement will need to be updated as the field continues to evolve. Results:Consensus-based recommendations are provided for the diagnosis and treatment of mitochondrial disease.Conclusion:The Delphi process enabled the formation of consensus-based recommendations. We hope that these recommendations will help standardize the evaluation, diagnosis, and care of patients with suspected or demonstrated mitochondrial disease.Genet Med 17 9, 689–701.