Pathophysiology
Congenital dysfibrinogenemia is most often caused by a single autosomal dominant missense mutation in the Aα, Bβ, or γ gene; rarely, it is caused by a homozygous or compound heterozygous missense mutation, a deletion, frameshift mutation, insert mutation, or splice site mutation in one of these genes. The most frequent sites for these mutations code for the N-terminus of the Aα chain or the C-terminus of the γ chain that lead to defective assembly of fibrin in early clot formation and thereby a bleeding predisposition. Two particular missense mutations represent the majority (74% in one study of 101 individuals) of all mutations associated with dysfibrinogenemia and therefore represent prime sites to examine in the initial testing of individuals having a congenital dysfibrinogenmia bleeding disorder. These mutations alter the codon coded for the amino acid arginine at either the 35th position of FGA (termed Arg35; see fibrinogen Metz1 and fibrinogen Bicetre in the Table below) and or the 301st position of FGG (termed Arg301; see fibrinogen Baltimore IV in the Table below).The following Table lists examples of mutations causing congenital dysfibrinogenemias. It gives: a) the mutated proteins trivial name; b) the gene mutated (i.e. FGA, FGB, or FGG), its mutation site (i.e. numbered nucleotide in the cloned gene), and the names of the nucleotides (i.e.
So the patient can in fact have his or her medication with food as long as the meal does not contain fat or oils (e.g., a cup of black coffee or toast with jam and no butter). Taking the medicines with food also helps ease the nausea that many patients feel when taking the medicines on an empty stomach. The effect of food on the absorption of INH is not clear: two studies have shown reduced absorption with food but one study showed no difference. There is a small effect of food on the absorption of PZA and of EMB that is probably not clinically important.It is possible to test urine for isoniazid and rifampicin levels to check for compliance. The interpretation of urine analysis is based on the fact that isoniazid has a longer half-life than rifampicin:
urine positive for isoniazid and rifampicin – patient probably fully compliant
urine positive for isoniazid only – patient has taken his medication in the last few days preceding the clinic appointment, but had not yet taken a dose that day. urine positive for rifampicin only – patient has omitted to take his medication the preceding few days, but did take it just before coming to clinic. urine negative for both isoniazid and rifampicin – patient has not taken either medicine for a number of daysIn countries where doctors are unable to compel patients to take their treatment (e.g., the UK), some say that urine testing only results in unhelpful confrontations with patients and does not help increase compliance.