The Finnish disease heritage database (FinDis) update-a database for the genes mutated in the Finnish disease heritage brought to the next-generation sequencing era.

The Finnish Disease Heritage Database (FinDis) (http://findis.org) was originally published in 2004 as a centralized information resource for rare monogenic diseases enriched in the Finnish population. The FinDis database originally contained 405 causative variants for 30 diseases. At the time, the FinDis database was a comprehensive collection of data, but since 1994, a large amount of new information has emerged, making the necessity to update the database evident. We collected information and updated the database to contain genes and causative variants for 35 diseases, including six more genes and more than 1,400 additional disease-causing variants. Information for causative variants for each gene is collected under the LOVD 3.0 platform, enabling easy updating. The FinDis portal provides a centralized resource and user interface to link information on each disease and gene with variant data in the LOVD 3.0 platform. The software written to achieve this has been open-sourced and made available on GitHub (http://github.com/findis-db), allowing biomedical institutions in other countries to present their national data in a similar way, and to both contribute to, and benefit from, standardized variation data. The updated FinDis portal provides a unique resource to assist patient diagnosis, research, and the development of new cures.

Prenatal diagnosis of free sialic acid storage disorders (SASD).

Free sialic acid storage disorders, Salla disease (SD) and Infantile sialic acid storage disease (ISSD), are lysosomal storage diseases due to impaired function of a sialic acid transporter, sialin, at the lysosomal membrane. Several mutations of the sialin gene, SLC17A5, are known, leading either to the severe neonatal/infantile disease or to the milder, adult-type developmental disorder, Salla disease. Free sialic acid accumulation in lysosomes causes increased tissue concentration and consequently elevated urinary excretion. Prenatal diagnosis of SASD is possible either by determination of free sialic acid concentration or by mutation analysis of the SLC17A5 gene in fetal specimen, in chorionic villus biopsy particularly. Both techniques have been successfully applied in several cases, sialic acid assay more often in ISSD cases but mutation analysis preferentially in SD. Sialic acid assay of amniotic fluid supernatant or cultured amniotic fluid cells may give erroneous results and should not be used for prenatal diagnosis of these disorders. The present comments are mainly based on our experience of prenatal diagnosis of SD in Finnish families. A founder mutation in SLC17A5 gene, 115C-> T, represents 95% of the disease alleles in the Finnish SD patients, which provides a unique possibility to apply mutation analysis. Therefore, molecular studies have successfully been used in 17 families since the identification of the gene and the characterization of the SD mutations. Earlier, eight prenatal studies were performed by measuring the free sialic acid concentration in chorionic villus samples.

Neurocognitive profiles in Salla disease.

Salla disease, a free sialic acid storage disorder, is one of the 36 currently known disorders in Finland that form the Finnish disease heritage. Salla disease leads to learning disability* with a wide clinical variation. Two main categories of the disease have been classified: a conventional subtype and a severe subtype with more severe defects. We present detailed neurocognitive profiles of 41 Finnish patients with Salla disease (19 females, 22 males; age range 11mo to 63y, median 19y). The neurocognitive development of patients with Salla disease was assessed by psychological and neuropsychological testing. All patients were also examined by a paediatric neurologist and a speech therapist. The characteristic cognitive profile consisted of a lower non-verbal performance (mean developmental age 13mo) compared with linguistic skills (mean developmental age 17mo). In particular, spatial and visual-constructive impairments were typical of these patients. Tactile and visual discrimination of forms was poor. Tasks demanding hand-eye coordination, maintenance of visual attention, and those requiring short-term visual memory and executive skills were performed better. Receptive language skills were notably better compared with expressive speech. The patients' interactive and non-verbal communication skills were quite strong. Another typical pattern with Salla disease was severe motor disability. After the second decade of life, the decline in these skills was more pronounced than patients' cognitive deterioration. Our results indicate that even though there is a considerable variation in the clinical findings of patients with Salla disease, the characteristic neurocognitive profile of the disease can be outlined.

Promoter analysis of the human SLC7A7 gene encoding y+L amino acid transporter-1 (y+LAT-1).

The human SLC7A7 gene on chromosome 14q11.2 encodes the y+L amino acid transporter-1 (y+LAT-1) protein that transports, together with the 4F2hc cell surface antigen, cationic amino acids through the basolateral membrane of epithelial cells in the small intestine and kidney. The SLC7A7 gene comprises 11 exons, but the first two are not translated. Mutations in the coding region of the SLC7A7 gene cause a rare autosomal disorder, lysinuric protein intolerance (LPI). We have now investigated the expression levels and putative 5' promoter elements of the SLC7A7. The 5' region of the first untranslated exon contains no TATA-box, Inr elements nor other classical promoter elements, but has instead other putative transcription factor binding sequences. The E-box and AP-2 elements were able to bind proteins in HEK293 cells and adult kidney tissue extracts, but not in fibroblasts. Using transient transfection and luciferase reporter gene studies, we showed that the first two introns located in the untranslated region contained transcriptional enhancer elements. Northern blot analysis showed low and equal SLC7A7 mRNA levels in the control and LPI patient fibroblastoid and lymphoblast cells.

Unraveling the molecular pathogenesis of free sialic acid storage disorders: altered targeting of mutant sialin.

Salla disease (SD) and infantile sialic acid storage disease (ISSD) are recessively inherited, neuro-degenerative disorders caused by mutations in the SLC17A5 gene. The gene product, sialin, is a lysosomal membrane protein which transports free sialic acid across the membrane. Although the function of sialin is basically known, the details of biosynthesis and intracellular trafficking as well as functional consequences of disease mutations in the SLC17A5 gene are not characterized. Here we studied for the first time the expression, localization, and targeting of the wild-type sialin as well as two mutant polypeptides; one mimicking the Finnish founder mutation, R39C (Salla(FIN)), and the other a deletion (del268-272) found in ISSD patients using in vitro expression of the corresponding cDNA constructs. The wild-type sialin was targeted to lysosomes whereas a significant fraction of the Salla(FIN) polypeptides and the majority of the ISSD polypeptides remained in the Golgi compartment. Further, using a temperature block of intracellular transport, we observed that the rate of the trafficking of the mutant polypeptides to lysosomes is significantly slower than that of their wild-type counterpart. These findings are in line with the phenotypic differences between SD and ISSD, the former presenting mental retardation with long life span in contrast to the latter being an early fatal disorder.

Phenotypic spectrum of Salla disease, a free sialic acid storage disorder.

Salla disease (MIM 269920) represents the mildest phenotype among recessively inherited lysosomal-free sialic acid storage disorders. Although the vast majority of Salla disease patients in Finland share the same founder mutation, R39C in the SLC17A5 gene, there still is a wide clinical variation among mentally retarded, ataxic patients. We evaluated neurologic and neurocognitive findings of Salla disease in a cross-sectional study of 41 Finnish patients who were 11 months to 63 years of age (median = 19.5 years). The phenotype of Salla disease could be classified into two main categories. The majority of patients (90%) had so-called conventional phenotype, including a subgroup of seven patients with relatively mild symptoms. All but two patients with conventional phenotype were homozygous for the Finnish founder mutation. Four severely disabled, profoundly mentally retarded patients, 15-28 years of age, clearly could be clinically delineated as a separate group, likely reflecting the underlying compound heterozygous genotype. A typical developmental pattern could be outlined in the conventional type of the disease, emphasizing a strong motor handicap in Salla disease. The cognitive profile consisted of better verbal ability, especially speech comprehension, compared with nonverbal functioning in all patients. Our results indicate a partial genotype-phenotype correlation, although factors other than the molecular background are also involved in the phenotypic manifestation of Salla disease.

Expression of normal and mutant GFP-tagged y(+)L amino acid transporter-1 in mammalian cells.

Lysinuric protein intolerance (LPI; MIM 222700) is an autosomal recessive disorder characterized by defective transport of cationic amino acids lysine, arginine and ornithine. The defect is localized in the basolateral membrane of polar epithelial cells of the renal tubules and intestine. The SLC7A7 (solute carrier family 7, member 7) gene that encodes y(+)LAT-1 (y(+)L amino acid transporter-1) is mutated in LPI, and leads to the malfunction of the heterodimer composed of y(+)LAT-1 and 4F2hc (4F2 heavy chain) responsible for the system y(+)L amino acid transport activity at the membrane. In this study, the intracellular trafficking and membrane expression of wild type and four mutant y(+)LAT-1 proteins (LPI(Fin), G54V, 1548delC, W242X) was studied in two human cell lines by expressing green fluorescent protein (GFP) tagged proteins. Different SLC7A7 mutations influenced the trafficking of y(+)LAT-1 in the cells differently, as the wild type and missense mutant fusion proteins localized to the plasma membrane, while the frameshift and nonsense mutants sequestered to the cytoplasmic membranes, never reaching the target areas of the cell.

Database for the mutations of the Finnish disease heritage.

The Finnish disease heritage refers to a group of monogenic diseases that are enriched in the Finnish population due to founder effect and genetic isolation. The molecular genetics of these diseases has recently been intensely studied, and several founder and private mutations have been identified. The purpose of the present study was to create a database of the presently known mutations of the Finnish disease heritage.