Frans W. Verheijen

A new gene, encoding an anion transporter, is mutated in sialic acid storage diseases.

Sialic acid storage diseases (SASD, MIM 269920) are autosomal recessive neurodegenerative disorders that may present as a severe infantile form (ISSD) or a slowly progressive adult form, which is prevalent in Finland (Salla disease). The main symptoms are hypotonia, cerebellar ataxia and mental retardation; visceromegaly and coarse features are also present in infantile cases. Progressive cerebellar atrophy and dysmyelination have been documented by magnetic resonance imaging (ref. 4). Enlarged lysosomes are seen on electron microscopic studies and patients excrete large amounts of free sialic acid in urine. A H+/anionic sugar symporter mechanism for sialic acid and glucuronic acid is impaired in lysosomal membranes from Salla and ISSD patients. The locus for Salla disease was assigned to a region of approximately 200 kb on chromosome 6q14–q15 in a linkage study using Finnish families. Salla disease and ISSD were further shown to be allelic disorders. A physical map with P1 and PAC clones was constructed to cover the 200-kb area flanked by the loci D6S280 and D6S1622, providing the basis for precise physical positioning of the gene. Here we describe a new gene, SLC17A5 (also known as AST), encoding a protein (sialin) with a predicted transport function that belongs to a family of anion/cation symporters (ACS). We found a homozygous SLC17A5 mutation (R39C) in five Finnish patients with Salla disease and six different SLC17A5 mutations in six ISSD patients of different ethnic origins. Our observations suggest that mutations in SLC17A5 are the primary cause of lysosomal sialic acid storage diseases.

Mutations in a TGF-β Ligand, TGFB3, Cause Syndromic Aortic Aneurysms and Dissections

Background Aneurysms affecting the aorta are a common condition associated with high mortality as a result of aortic dissection or rupture. Investigations of the pathogenic mechanisms involved in syndromic types of thoracic aortic aneurysms, such as Marfan and Loeys-Dietz syndromes, have revealed an important contribution of disturbed transforming growth factor (TGF)-β signaling. Objectives This study sought to discover a novel gene causing syndromic aortic aneurysms in order to unravel the underlying pathogenesis. Methods We combined genome-wide linkage analysis, exome sequencing, and candidate gene Sanger sequencing in a total of 470 index cases with thoracic aortic aneurysms. Extensive cardiological examination, including physical examination, electrocardiography, and transthoracic echocardiography was performed. In adults, imaging of the entire aorta using computed tomography or magnetic resonance imaging was done. Results Here, we report on 43 patients from 11 families with syndromic presentations of aortic aneurysms caused by TGFB3 mutations. We demonstrate that TGFB3 mutations are associated with significant cardiovascular involvement, including thoracic/abdominal aortic aneurysm and dissection, and mitral valve disease. Other systemic features overlap clinically with Loeys-Dietz, Shprintzen-Goldberg, and Marfan syndromes, including cleft palate, bifid uvula, skeletal overgrowth, cervical spine instability and clubfoot deformity. In line with previous observations in aortic wall tissues of patients with mutations in effectors of TGF-β signaling (TGFBR1/2, SMAD3, and TGFB2), we confirm a paradoxical up-regulation of both canonical and noncanonical TGF-β signaling in association with up-regulation of the expression of TGF-β ligands. Conclusions Our findings emphasize the broad clinical variability associated with TGFB3 mutations and highlight the importance of early recognition of the disease because of high cardiovascular risk.

The spectrum of SLC17A5-gene mutations resulting in free sialic acid-storage diseases indicates some genotype-phenotype correlation.

Lysosomal free sialic acid-storage diseases include the allelic disorders Salla disease (SD) and infantile sialic acid-storage disease (ISSD). The defective gene, SLC17A5, coding for the lysosomal free sialic acid transporter was recently isolated by positional cloning. In the present study, we have identified a large number of mutations in SLC17A5 in patients presenting with either Salla disease or the ISSD phenotype. We also report for the first time the exon-intron boundaries of SLC17A5. All Finnish patients with SD (n=80) had a missense mutation changing a highly conserved arginine to cysteine (R39C); 91% of them were homozygotes for this old founder mutation. The compound-heterozygote patients, with the founder mutation in only one allele, presented with a more severe phenotype than did the homozygote patients. The same R39C mutation was also found both in most of the Swedish patients with SD and in a heterozygous form in five patients from central Europe who presented with an unusually severe (intermediate) SD phenotype. Ten different mutations, including deletions, insertions, and missense and nonsense mutations, were identified in patients with the most severe ISSD phenotype, most of whom were compound heterozygotes. Our results indicate some genotype-phenotype correlation in free sialic acid-storage diseases, suggesting that the phenotype associated with the homozygote R39C mutation is milder than that associated with other mutations.

COL4A1 mutation in two preterm siblings with antenatal onset of parenchymal hemorrhage.

To report the presence of intracerebral hemorrhage and porencephaly, both present at birth, in two preterm infants with a mutation in the collagen 4 A1 gene.

Mutation in the AP4M1 Gene Provides a Model for Neuroaxonal Injury in Cerebral Palsy

Cerebral palsy due to perinatal injury to cerebral white matter is usually not caused by genetic mutations, but by ischemia and/or inflammation. Here, we describe an autosomal-recessive type of tetraplegic cerebral palsy with mental retardation, reduction of cerebral white matter, and atrophy of the cerebellum in an inbred sibship. The phenotype was recorded and evolution followed for over 20 years. Brain lesions were studied by diffusion tensor MR tractography. Homozygosity mapping with SNPs was performed for identification of the chromosomal locus for the disease. In the 14 Mb candidate region on chromosome 7q22, RNA expression profiling was used for selecting among the 203 genes in the area. In postmortem brain tissue available from one patient, histology and immunohistochemistry were performed. Disease course and imaging were mostly reminiscent of hypoxic-ischemic tetraplegic cerebral palsy, with neuroaxonal degeneration and white matter loss. In all five patients, a donor splice site pathogenic mutation in intron 14 of the AP4M1 gene (c.1137+1G-->T), was identified. AP4M1, encoding for the mu subunit of the adaptor protein complex-4, is involved in intracellular trafficking of glutamate receptors. Aberrant GluRdelta2 glutamate receptor localization and dendritic spine morphology were observed in the postmortem brain specimen. This disease entity, which we refer to as congenital spastic tetraplegia (CST), is therefore a genetic model for congenital cerebral palsy with evidence for neuroaxonal damage and glutamate receptor abnormality, mimicking perinatally acquired hypoxic-ischemic white matter injury.

Purification of acid β-galactosidase and acid neuraminidase from bovine testis: Evidence for an enzyme complex

Abstract The isolation of an acid neuraminidase from bovine testis is described. Under all experimental conditions this neuraminidase copurifies with acid β-galactosidase, but not with other lysosomal hydrolases. Immunotitration with an antiserum raised against purified human placental β-galactosidase results in the coprecipitation of both enzyme activities. Our data indicate that acid neuraminidase and β-galactosidase are present as an enzyme complex. The possible physiological relevance is discussed.

Presence of ATM protein and residual kinase activity correlates with the phenotype in ataxia-telangiectasia: a genotype-phenotype study.

Ataxia‐telangiectasia (A‐T) is an autosomal recessive neurodegenerative disorder with multisystem involvement and cancer predisposition, caused by mutations in the A‐T mutated (ATM) gene. To study genotype–phenotype correlations, we evaluated the clinical and laboratory data of 51 genetically proven A‐T patients, and additionally measured ATM protein expression and kinase activity. Patients without ATM kinase activity showed the classical phenotype. The presence of ATM protein, correlated with slightly better immunological function. Residual kinase activity correlated with a milder and essentially different neurological phenotype, absence of telangiectasia, normal endocrine and pulmonary function, normal immunoglobulins, significantly lower X‐ray hypersensitivity in lymphocytes, and extended lifespan. In these patients, cancer occurred later in life and generally consisted of solid instead of lymphoid malignancies. The genotypes of severely affected patients generally included truncating mutations resulting in total absence of ATM kinase activity, while patients with milder phenotypes harbored at least one missense or splice site mutation resulting in expression of ATM with some kinase activity. Overall, the phenotypic manifestations in A‐T show a continuous spectrum from severe classical childhood‐onset A‐T to a relatively mild adult‐onset disorder, depending on the presence of ATM protein and kinase activity. Each patient is left with a tremendously increased cancer risk. Hum Mutat 33:561–571, 2012.

Human USP18 deficiency underlies type 1 interferonopathy leading to severe pseudo-TORCH syndrome

Meuwissen and collaborators define a novel genetic cause of pseudo-TORCH syndrome, which resembles the sequelae of congenital infection and represents a novel type I interferonopathy.

The use of dried blood spot samples in the diagnosis of lysosomal storage disorders — Current status and perspectives

Dried blood spot (DBS) methods are currently available for identification of a range of lysosomal storage disorders (LSDs). These disorders are generally characterized by a deficiency of activity of a lysosomal enzyme and by a broad spectrum of phenotypes. Diagnosis of LSD patients is often delayed, which is of particular concern as therapeutic outcomes (e.g. enzyme replacement therapy) are generally more favorable in early disease stages. Experts in the field of LSDs diagnostics and screening programs convened and reviewed experiences with the use of DBS methods, and discuss the diagnostic challenges, possible applications and quality programs in this paper. Given the easy sampling and shipping and stability of samples, DBS has evident advantages over other laboratory methods and can be particularly helpful in the early identification of affected LSD patients through neonatal screening, high-risk population screening or family screening.

Prenatal diagnosis of sialidosis with combined neuraminidase and ø-galactosidase deficiency

Recently a combined deficiency of neuraminidase and P-galactosidase was reported in two patients (Wenger et al. 1978, O’Brien 1978), who had earlier been described as having variant types of Gq-gangliosidosis (Justice et al. 1977, Koster et al. 1976). We have found similar deficiencies in the second of two children who both died at birth with severe hydrops fetalis (Niermeijer et al. unpublished). The parents are consanguineous, of Turkish origin, and living in The Netherlands. Cultured skin fibroblasts and liver, obtained at autopsy, showed a deficiency of p-galactosidase with a residual activity of 5-10 % of normal. In addition, we found an almost complete deficiency of neuraminidase activity in the fibroblasts and an increased level of sialic acid in both fibroblasts and liver (3 and 23 times the normal levels, respectively). We now wish to report the results of the prenatal diagnosis which was offered to the parents during the third pregnancy. Amniocentesis was done in the 17th week (Dr. R. Vosters, University Hospital, Rotterdam). After 18 days of growth, the amniotic fluid cells were harvested in their first passage for enzyme assays. P-galactosidase and neuraminidase activities were determined using the fluorogenic 4-methyl-umbelliferyl substrates and micromethods, as described earlier for p-galactosidase in the prenatal analysis for GM1-gangliosidosis (Kleijer et al. 1976). The results are shown in Table 1. Both B-galactosidase and neuraminidase activity are strongly reduced in the amniotic fluid cells from the pregnancy at risk, as was the case in fibroblasts of the index patient. These results indicated that the fetus was affected with the variant type of sialidosis. Further evidence was obtained 1 week later by the demonstration of a 2-fold elevated sialic acid content of the amniotic fluid cells (44.3 nmol/mg protein, control: 22.1 nmoYmg). The parents decided on termination of the pregnancy, which was done by prostaglandin induction in the 21st week of pregnancy. The prenatal diagnosis was confirmed by the demonstration of reduced activities in the freshly obtained fetal liver and brain for P-galactosidase (5-10 % of normal activity) and neuraminidase (undetectable). The sialic acid content was 20-fold