Detection of a significant association between mutations in the ACVRL1 gene and hepatic involvement in German patients with hereditary haemorrhagic telangiectasia.

Hereditary haemorrhagic telangiectasia (HHT) is a heterogeneous multisystemic dysplasia of the vascular tissue. This autosomal dominant inherited disorder shows a wide variation in its phenotypic expression. Between 8 and 78% of the HHT patients show arteriovenous malformations of the liver. The molecular basis for hepatic manifestation is still unknown. Two genes are known to play a major role in the development of HHT: activin A receptor type II-like 1 gene (ACVRL1) and ENG. Previously, we and others showed that hepatic involvement is associated with mutations in the ACVRL1 gene, but rarely caused by ENG mutations. Here, we report about the sequencing analysis of a new cohort of 18 adult HHT patients. In these patients, we identified eight novel (four in ACVRL1 and four in ENG) and eight already known mutations. Statistical analysis of our entire data revealed significant differences in the distribution of ACVRL1 and ENG mutations among HHT patients with and without liver involvement (p = 0.0016). The positive predictive value for type 2 HHT (ACVRL1 positive) patients to develop liver disease until the age of 52 years is 68.4%. We conclude that molecular genetic testing of HHT patients is important for prognosis with respect to liver disease.

Familial thrombocytosis as a recessive, possibly X-linked trait in an Arab family.

Familial thrombocytosis (FT) has previously been described as an autosomal-dominant disorder with manifestations similar to those of sporadic essential thrombocythaemia. We studied an Arab family consisting of four brothers, aged 4-8 years, who had either sustained markedly elevated (> 1000 x 109/l) or moderately elevated (> 500 x 109/l) platelet counts, two healthy sisters and their parents who had normal platelet counts. The four brothers with FT had normal plasma thrombopoietin levels and are currently not presenting with any thrombotic or haemorrhagic complications. Mutation analysis at the thrombopoietin gene (THPO) of the affected family members failed to detect the intron 3 G-->C splice mutation that had been described as causing FT. In addition, segregation analysis using a polymorphic CA marker revealed completely discordant THPO alleles among the affected brothers. We postulate the existence of a new locus for FT whereby the disease is transmitted as a recessive, possibly X-linked trait.

Novel and characteristic CFTR mutations in Saudi Arab children with severe cystic fibrosis.

More than 600 different CFTR (cystic fibrosis transmembrane conductance regulator) gene mutations have been identified so far that are considered to cause the fatal genetic disorder cystic fibrosis (CF). We have investigated 15 Arab children from 12 families, who were diagnosed as having CF, for mutations in the coding region and in the flanking intron sequences of the CFTR gene. Six different CFTR mutations were identified including two novel mutations, 1548delG in exon 10 and 406-2A-->G in intron 3. Prominent mutations were the splice mutation 3120 + 1G-->A (intron 16) followed by N1303K (exon 21) and 1548delG (exon 10). Most CF children were homozygotes who presented with a severe form of the disease including failure to thrive, recurrent chest infections, particularly with Pseudomonas aeruginosa, and frequent hospital admissions. Identification of the CFTR mutations facilitates molecular investigation of the disease and better understanding of its pathophysiology in Arab children, among whom CF is probably an underdiagnosed disease.

The aspirin and heme-binding sites of ovine and murine prostaglandin endoperoxide synthases.

Acetylation of Ser-530 of sheep prostaglandin endoperoxide (PGG/H) synthase by aspirin causes irreversible inactivation of the cyclooxygenase activity of the enzyme. To determine the catalytic function of the hydroxyl group of Ser-530, we used site-directed mutagenesis to replace Ser-530 with an alanine. Cos-1 cells transfected with expression vectors containing the native (Ser-530) or mutant (Ala-530) cDNAs for sheep PGG/H synthase expressed comparable cyclooxygenase and hydroperoxidase activities. Km values for arachidonate (8 microM) and ID50 values for reversible inhibition by the cyclooxygenase inhibitors, flurbiprofen (5 microM), flufenamate (20 microM), and aspirin (20 mM), were also the same for both native and mutant PGG/H synthases; however, only the native enzyme was irreversibly inactivated by aspirin. Thus, the "active site" Ser-530 of PGG/H synthase is not essential for catalysis or substrate binding. Apparently, acetylation of native PGG/H synthase by aspirin introduces a bulky sidechain at position 530 which interferes with arachidonate binding. In related studies, a cDNA for mouse PGG/H synthase was cloned and sequenced. A sequence of 35 residues with Ser-530 at the midpoint was identical in the two proteins. Thus, Ser-530 does lie in a highly conserved region, probably involved in cyclooxygenase catalysis. Sequence comparisons of mouse and sheep PGG/H synthase also provided information about the heme-binding site of the enzyme. The sheep HYPR sequence (residues 274-277), which had been proposed to form a portion of the distal heme-binding site, is not conserved in the mouse PGG/H synthase, suggesting that this region is not the distal heme-binding site. One sequence, TIWLREHNRV (residues 303-312 of the sheep enzyme), is very closely related to the sequence TLW(L)LREHNRL common to thyroid peroxidase and myeloperoxidase. The histidine in this latter sequence is the putative axial heme ligand of these peroxidases. We suggest that the histidine (His-309) of sheep PGG/H synthase sequence is the axial heme ligand of this enzyme.

The biosynthesis and actions of prostaglandins in the renal collecting tubule and thick ascending limb.

PGE2 formed by renal collecting tubules is an important factor in regulating NaCl and water reabsorption in the collecting tubule and medullary thick ascending limb. PGE2 appears to act, depending on its ambient concentration, via several different receptors present in these renal epithelia to modulate cAMP turnover in both positive and negative directions. These putative PGE receptors form a family of receptors, all coupled to G proteins, and this family of PGE receptors is homologous to the adrenergic receptor family.

Nutritional and toxicological properties of some raw and modified starches.

Several food additives, including some raw and chemically modified starches, sorbitol and maltitol, cause caecal enlargement when fed to rodents. The onset of caecal enlargement is rapid and it is reversible when the additive is withdrawn. This poses problems in the safety evaluation of such additives, both in relation to the significance of the caecal enlargement and to the associated effects on food efficiency and nitrogen balance. The mechanisms of causation of caecal enlargement have been studied and will be discussed with particular reference to resistance of starches to enzymic hydrolysis, changes in intestinal microflora, osmotic load in the caecum, cell hyperplasia and rate of turnover of mucosal cells. Where deaths occur, these appear to be due to secondary effects such as impaired resporatory function.