Katri Vuopala

Mutations in the tyrosine phosphatase CD45 gene in a child with severe combined immunodeficiency disease.

The hematopoietic-specific transmembrane protein tyrosine phosphatase CD45 functions to regulate Src kinases required for T- and B-cell antigen receptor signal transduction. So far, there have been no reports to our knowledge of a human deficiency in a tyrosine-specific phosphatase. Here, we identified a male patient with a deficiency in CD45 due to a large deletion at one allele and a point mutation at the other. The point mutation resulted in the alteration of intervening sequence 13 donor splice site. The patient presented at 2 months of age with severe combined immunodeficiency disease. The population of peripheral blood T lymphocytes was greatly diminished and unresponsive to mitogen stimulation. Despite normal B-lymphocyte numbers, serum immunoglobulin levels decreased with age. Thus, CD45 deficiency in humans results in T- and B-lymphocyte dysfunction.

Mutations in mRNA export mediator GLE1 result in a fetal motoneuron disease

The most severe forms of motoneuron disease manifest in utero are characterized by marked atrophy of spinal cord motoneurons and fetal immobility. Here, we report that the defective gene underlying lethal motoneuron syndrome LCCS1 is the mRNA export mediator GLE1. Our finding of mutated GLE1 exposes a common pathway connecting the genes implicated in LCCS1, LCCS2 and LCCS3 and elucidates mRNA processing as a critical molecular mechanism in motoneuron development and maturation.

Childhood Encephalopathies and Myopathies: A Prospective Study in a Defined Population to Assess the Frequency of Mitochondrial Disorders

Objectives. To assess the frequency of mitochondrial abnormalities in muscle histology, defects in respiratory chain enzyme activities, and mutations in mitochondrial DNA (mtDNA) in children with unexplained psychomotor retardation in the population of Northern Finland. Background. The frequency of mitochondrial diseases among patients with childhood encephalopathies and myopathies is not known. Frequencies are difficult to estimate because the clinical presentation of these disorders is variable. Methods. A total of 116 consecutive patients with undefined encephalopathies and myopathies were enrolled during a 7-year period in a hospital serving as the only neurologic unit for a pediatric population of 97 609 and as the only tertiary level neurologic unit for a pediatric population of 48 873. Biochemical and morphologic investigations were performed on muscle biopsy material, including oximetric and spectrophotometric analyses of oxidative phosphorylation, histochemistry, electron microscopy, and molecular analysis of mtDNA. Results. Ultrastructural changes in the mitochondria were the most common finding in the muscle biopsies (71%). Ragged-red fibers were found in 4 cases. An oxidative phosphorylation defect was found in 26 children (28%), complex I (n = 15) and complex IV (n = 13) defects being the most common. Fifteen percent of patients (n = 17/116) with unexplained encephalomyopathy or myopathy had a probable mitochondrial disease. Common pathogenic mutations were found in the mtDNA of only 1 patient (.9%). Conclusions. The common known mutations in mtDNA are rarely causes of childhood encephalomyopathies, which is in contrast to the considerable frequency of the common MELAS mutation observed among adults in the same geographical area. Biochemically and morphologically verified mitochondrial disorders were nevertheless common among the children, making the analysis of a muscle biopsy very important for clinical diagnostic purposes.

Assignment of the disease locus for lethal congenital contracture syndrome to a restricted region of chromosome 9q34, by genome scan using five affected individuals.

Lethal congenital contracture syndrome (LCCS) is an autosomal recessive disease leading to death before the 32d gestational week. It is characterized by the fetal akinesia phenotype, with highly focused degeneration of motoneurons in the spinal cord as the main neuropathological finding. We report here the assignment of the LCCS locus to a defined region of chromosome 9q34, between markers D9S1825 and D9S1830. The initial genome scan was performed with the DNA samples of only five affected individuals from two unrelated LCCS families. The conventional linkage analysis performed with 20 affected individuals and their families was focused on those chromosomal regions in which the affected siblings were identical by descent in the initial scan. One core haplotype of 3 cM was observed in LCCS alleles, supporting the assumption of one major mutation underlying LCCS, and linkage disequilibrium analysis restricted the critical chromosomal region to <100 kb in the vicinity of marker D9S61. Two genes, NGAL (neutrophil gelatinase-associated lipocalin and NOTCH 1, were excluded as causative genes for LCCS

Familial fetal akinesia deformation sequence with a skeletal muscle maturation defect

Two female siblings with the fetal akinesia deformation sequence (FADS) are described. Both showed facial anomalies, arthrogypotic extremities, hypoplastic lungs, and fetal growth retardation. The central nervous system of the second sibling, including the spinal cord, was normal. The skeletal muscle was studied by immunohistochemistry for the expression of several myosin heavy chain isoforms, M-band proteins and intermediate filament proteins. The skeletal muscle was immature and atypical muscle spindles containing up to 31 intrafusal fibers were found. These findings suggest that a lethal FADS phenotype may involve a maturation defect of the skeletal muscle, and, in this family, may be inherited in a recessive fashion.

A homozygous I684T in GLE1 as a novel cause of arthrogryposis and motor neuron loss

Mutations in GLE1, RNA export mediator (GLE1) gene have previously been shown to cause motor neuron diseases such as lethal congenital contracture syndrome 1 (LCCS1) and lethal arthrogryposis with anterior horn cell disease (LAAHD), including arthrogryposis, fetal akinesis and motor neuron loss as common clinical features. The homozygous FinMajor mutation p.T144_E145insPFQ has been described as one of the causes for LCCS1 whereas LAAHD is caused by a heterocompound FinMajor mutation together with p.R569H, p.V617M or p.I684T missense mutation. None of these heterocompound missense mutations have previously been reported as homozygous states. Here we present the clinical features of 2 siblings with a homozygous p.I684T mutation in GLE1. The patients suffered from similar, but milder symptoms than in LCCS1 and LAAHD, surviving up to 6 months before they died due to a progressive disease course including respiratory failure. Arthrogryposis, lack of spontaneous movements, and epilepsy were notable in both cases and lack of anterior horn cells was identified in autopsy samples. Our studies on patient‐derived fibroblasts show that the homozygous p.I684T impairs the nuclear localization of GLE1 further confirming the pathogenic role of this mutation.

Nitrotyrosine (NT) in fatal respiratory failure in infants: influence of inhaled nitric oxide (iNO) treatment

Nitrotyrosine (NT) in fatal respiratory failure in infants: influence of inhaled nitric oxide (iNO) treatment