A major transport function of the human intestine involves the absorption of chloride in exchange for bicarbonate. We have studied a recessively inherited defect of this exchange, congenital chloride diarrhoea (CLD; MIM 214700). The clinical presentation of CLD is a lifetime, potentially fatal diarrhoea with a high chloride content. The CLD locus was previously mapped to 7q3 adjacent to the cystic fibrosis gene (CFTR). By refined genetic and physical mapping, a cloned gene having anion transport function, Down-regulated in adenoma (DRA), was implicated as a positional and functional candidate for CLD. In this study, we report segregation of two missense mutations, delta V317 and H124L, and one frameshift mutation, 344delT, of DRA in 32 Finnish and four Polish CLD patients. The disease-causing nature of delta V317 is supported by genetic data in relation to the population history of Finland. By mRNA in situ hybridization, we demonstrate that the expression of DRA occurs preferentially in highly differentiated colonic epithelial cells, is unchanged in Finnish CLD patients with delta V317, and is low in undifferentiated (including neoplastic) cells. We conclude that DRA is an intestinal anion transport molecule that causes chloride diarrhoea when mutated.

The mechanism by which germline mutations of DNA mismatch repair genes cause susceptibility to tumour formation is not yet understood. Studies in vitro indicate that heterozygosity for these mutations, unlike homozygosity, does not affect mismatch repair. Surprisingly, no loss of heterozygosity at the predisposing loci has so far been described in hereditary nonpolyposis colorectal cancers. Here, we show that loss of heterozygosity (LOH) of markers within or adjacent to the MLH1 gene on chromosome 3p occurs nonrandomly in tumours from members of families in which the disease phenotype cosegregates with MLH1. In every informative case, the loss affects the wild type allele. These results suggest that DNA mismatch repair genes resemble tumour suppressor genes in that two hits are required to cause a phenotypic effect.

An association between DiGeorge's syndrome and an unbalanced chromosomal rearrangement leading to trisomy 20pter leads to 20q11 and monosomy 22pter leads to 22q11 was found in four individuals belongings to one family. These and other data from the literature are interpreted to suggest that DiGeorge's syndrome can be caused by deletion of a gene located in chromosome 22, probably in band 22q11.

Dominantly inherited familial amyloidosis, Finnish type (FAF) is caused by the accumulation of a 71-amino acid amyloidogenic fragment of mutant gelsolin (GSN). FAF is common in Finland but is very rare elsewhere. In Finland and in two American families, the mutation is a G654A transition leading to an Asp to Asn substitution at residue 187. We found the same mutation in a Dutch family but a Danish FAF family had a G654T mutation, predicting Asp to Tyr at residue 187. We also found the G654T transversion in a Czech family. Using GSN polymorphisms, different haplotypes were found in the Danish and Czech families. We conclude that substitution of the uncharged Asn or Tyr for the acidic Asp at residue 187 creates a conformation that may be preferentially amyloidogenic for GSN.

Usher syndrome (USH) refers to genetically and clinically heterogeneous autosomal recessive disorders with combined visual and hearing loss. Type I (USH1) is characterized by a congenital, severe to profound hearing loss and absent vestibular function; in type II (USH2) the hearing loss is congenital and moderate to severe, and the vestibular function is normal. Progressive pigmentary retinopathy (PPR) is present in both types. A third type (USH3) differing from USH2 by the progressive nature of its hearing loss has been suggested. USH3 has previously been estimated to comprise 2% of all USH. However, based on clinical criteria, in Finland 42% of USH patients have progressive hearing loss suggesting enrichment of an USH3 gene. We excluded the four previously mapped USH regions as the site of the USH3 disease locus. Systematic search for USH3 by genetic linkage analyses in 10 multiple affected families using polymorphic microsatellite markers revealed significant linkage with markers mapping to chromosome 3q. Pairwise lod scores at zero recombination distance were 7.87 for D3S1308, and 11.29 for D3S1299, incorporating the observed linkage disequilibrium. Conventional multipoint linkage analysis gave a maximum lod score of 9.88 at D3S1299 assigning USH3 to the 5 cM interval between markers D3S1555 and D3S1279 in 3q21-25.(ABSTRACT TRUNCATED AT 250 WORDS)

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Diastrophic dysplasia (DTD) is especially prevalent in Finland and the existence of a founder mutation has been previously inferred from the fact that 95% of Finnish DTD chromosomes have a rare ancestral haplotype found in only 4% of Finnish control chromosomes. Here we report the identification of the Finnish founder mutation as a GT-> GC transition (c.-26 + 2T > C) in the splice donor site of a previously undescribed 5'-untranslated exon of the diastrophic dysplasia sulfate transporter gene (DTDST); the mutation acts by severely reducing mRNA levels. Among 84 DTD families in Finland, patients carried two copies of the mutation in 69 families, one copy in 14 families, and no copies in one family. Roughly 90% of Finnish DTD chromosomes thus carry the splice-site mutation, which we have designated DTDST Fin . Unexpectedly, we found that nine of the DTD chromosomes having the apparently ancestral haplotype did not carry DTDST Fin , but rather two other mutations. Eight such chromosomes had an R279W mutation and one had a V340del deletion. We consider the possible implications of presence of multiple DTD mutations on this rare haplotype.

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