Autosomal dominant late-onset spinal motor neuronopathy is linked to a new locus on chromosome 22q11.2-q13.2

Neuromuscular Research Unit, University of Tampere, Tampere, Finland.
European journal of human genetics: EJHG (Impact Factor: 4.35). 04/2012; 20(11):1193-6. DOI: 10.1038/ejhg.2012.76
Source: PubMed


Spinal muscular atrophies (SMAs) are hereditary disorders characterized by degeneration of lower motor neurons. Different SMA types are clinically and genetically heterogeneous and many of them show significant phenotypic overlap. We recently described the clinical phenotype of a new disease in two Finnish families with a unique autosomal dominant late-onset lower motor neuronopathy. The studied families did not show linkage to any known locus of hereditary motor neuron disease and thus seemed to represent a new disease entity. For this study, we recruited two more family members and performed a more thorough genome-wide scan. We obtained significant linkage on chromosome 22q, maximum LOD score being 3.43 at marker D22S315. The linked area is defined by flanking markers D22S686 and D22S276, comprising 18.9 Mb. The region harbours 402 genes, none of which is previously known to be associated with SMAs. This study confirms that the disease in these two families is a genetically distinct entity and also provides evidence for a founder mutation segregating in both pedigrees.

Download full-text


Available from: Sini Penttilä, Mar 09, 2015
  • [Show abstract] [Hide abstract]
    ABSTRACT: We previously described two Finnish families with a new autosomal dominant late-onset spinal motor neuronopathy that was mapped to chromosome 22q11.2-q13.2. In the current screening study of 43 lower motor neuron disease patients from Finland and Sweden, we identified 26 new late-onset spinal motor neuronopathy patients sharing the founder haplotype. In addition to the main symptoms and signs: painful cramps, fasciculations, areflexia and slowly evolving muscle weakness, new features such as mild bulbar findings, were identified. The disease is relatively benign in terms of life expectancy and rate of disability progression, and it is therefore noteworthy that three patients were initially misdiagnosed with ALS. Significant recombinants in this new patient cohort restricted the disease locus by 90% to 1.8 Mb. Late-onset spinal motor neuronopathy seems not to be very rare, at least not in Finland, with 38 patients identified in a preliminary ascertainment.
    No preview · Article · Jan 2013 · Neuromuscular Disorders
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The most common form of spinal muscular atrophy (SMA) is a recessive disorder caused by deleterious SMN1 mutations in 5q13, whereas the genetic etiologies of non-5q SMA are very heterogeneous and largely remain to be elucidated. In a Bulgarian family affected by autosomal-dominant proximal SMA, we performed genome-wide linkage analysis and whole-exome sequencing and found a heterozygous de novo c.320C>T (p.Ser107Leu) mutation in bicaudal D homolog 2 (Drosophila) (BICD2). Further analysis of BICD2 in a cohort of 119 individuals with non-5q SMA identified a second de novo BICD2 mutation, c.2321A>G (p.Glu774Gly), in a simplex case. Detailed clinical and electrophysiological investigations revealed that both families are affected by a very similar disease course, characterized by early childhood onset, predominant involvement of lower extremities, and very slow disease progression. The amino acid substitutions are located in two interaction domains of BICD2, an adaptor protein linking the dynein molecular motor with its cargo. Our immunoprecipitation and localization experiments in HeLa and SH-SY5Y cells and affected individuals' lymphoblasts demonstrated that p.Ser107Leu causes increased dynein binding and thus leads to accumulation of BICD2 at the microtubule-organizing complex and Golgi fragmentation. In addition, the altered protein had a reduced colocalization with RAB6A, a regulator of vesicle trafficking between the Golgi and the endoplasmic reticulum. The interaction between p.Glu744Gly altered BICD2 and RAB6A was impaired, which also led to their reduced colocalization. Our study identifies BICD2 mutations as a cause of non-5q linked SMA and highlights the importance of dynein-mediated motility in motor neuron function in humans.
    Full-text · Article · May 2013 · The American Journal of Human Genetics
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Hereditary spinal muscular atrophy is a motor neuron disorder characterized by muscle weakness and atrophy due to degeneration of the anterior horn cells of the spinal cord. Initially, the disease was considered purely as an autosomal recessive condition caused by loss-of-function SMN1 mutations on 5q13. Recent developments in next generation sequencing technologies, however, have unveiled a growing number of clinical conditions designated as non-5q forms of spinal muscular atrophy. At present, 16 different genes and one unresolved locus are associated with proximal non-5q forms, having high phenotypic variability and diverse inheritance patterns. This review provides an overview of the current knowledge regarding the phenotypes, causative genes, and disease mechanisms associated with proximal SMN1-negative spinal muscular atrophies. We describe the molecular and cellular functions enriched among causative genes, and discuss the challenges in the post-genomics era of spinal muscular atrophy research.
    Full-text · Article · Jun 2014 · Brain
Show more