Interpretation of cardiac troponin measurements in neonates--the devil is in the details. Commentary to trevisanuto et Al.: cardiac troponin I in asphyxiated neonates (biol neonate 2006;89:190-193).

Abstract

quences. There are 125 differences between adult fasttwitch skeletal troponin T (sTnT) and cTnT, representing 56.6% sequence homology and 120 differences between adult slow-twitch sTnT and cTnT (58.3% homology). Sequence homology also exists between cTnI and skeletal troponin I (sTnI), with 123 residue differences between cTnI and adult fast-twitch sTnI (41.4% homology) and 113 residue differences between cTnI and adult slowtwitch sTnI (46.2% homology). The majority of the residue differences are located in the N terminus. cTnI has a unique N-terminal region [4] . Life is made more complicated by the expression of the troponins during fetal development. There is simultaneous expression of adult as well as partially homologous fetal isoforms in developing fetal muscle. A fetal isoform of cTnT is transiently expressed in the early development [5] of fetal skeletal muscle but this is then subsequently downregulated to very low levels and is not present in adult skeletal muscle tissue [6] . A fetal isoform of troponin T (TnTf) with sequence homology to cTnT and sTnT is the dominant isoform expressed in fetal skeletal muscle. A fetal exon has been described in the human fast-twitch sTnT gene with a similar sequence to both adult fast-twitch sTnT and cTnT [7] . It is therefore apparent that there is potential for detection of troponins which may not specifi cally relate to cardiac tissue. Measurement of the cardiac troponins, cardiac troponin T (cTnT) and cardiac troponin I (cTnI), is accepted as the ‘gold standard’ test for diagnosis and management of adult acute coronary syndromes [1] . Measurement of cTnT and cTnI has been shown to be prognostic in the adult intensive care unit population [2] . In this issue of Biology of the Neonate , Trevisanuto et al. [3] have examined the value of troponin in asphyxiated neonates and have shown elevated values. What aspects of the molecular biology of troponin might produce pitfalls if it is measured in the neonatal population? Troponin T and troponin I ( fi g. 1 ) are muscle proteins which form part of the contractile apparatus of all striated muscles. In cooperation with troponin C, the complex coordinates muscle contraction in response to voltage changes across the sarcolemmal membrane. The troponin complex is absent from smooth muscle, where contraction is coordinated by calmodulin, a protein synergistic to troponin C. There are three different isoforms of both troponin T and troponin I that are found, respectively, in cardiac muscle, fast-twitch skeletal muscle and slow-twitch skeletal muscle. Each is encoded by different genes (6 genes in total). There are no tissue-specifi c isoforms of troponin C in skeletal muscle. cTnT and cTnI are encoded by genes located at chromosome 1q32 and 19q13.3, respectively. They have unique amino acid sePublished online: November 4, 2005