Protein-tyrosine kinases (PTKs) play an essential role in the intracellular mitogenic signaling mechanism. In fact, many growth factor receptors themselves have intrinsic PTK activity, as evidenced by the cases of epidermal growth factor (EGF), nerve growth factor (NGF) and stem cell factor (SCF) receptors. In contrast to these receptor-type PTKs, many PTKs do not have a transmembrane domain in their structure. These are designated as non-receptor-type PTKs or cytoplasmic PTKs. Non-receptor PTKs can be further subdivided into a number of sub- families, one of which is the Tec family. The Tec family consists of five members, namely Tec, Btk, Itk/Emt/Tsk, Bmx and Txk/Rlk. Many members of this family are abundantly expressed in hematopoietic tissues, where they are presumed to function in the growth, differentiation or both processes of blood cells. This hypothesis is strengthened by the fact that the Btk kinase molecule is responsible for X chromosome-linked agammaglobulinemia (XLA) in humans and X chromosome-linked immunodeficiency (Xid) in mice.

Accurate interpretation of the organic acid chromatographs obtained from the gas chromatography/mass spectrometry requires a significant amount of practice. Pattern recognition is an important factor and a skill that is gained through time and effort. A Quick Guide to Metabolic Disease Testing Interpretation, Second Edition, provides these example chromatographs demonstrating specific disease-related metabolites for the inborn error of metabolism diagnosed via this method. One or more representative chromatographs from each of the common disorders is presented, with the important compounds noted on the chromatographs. This is a must-have for laboratory and medical professionals who interpret testing for the diagnosis and monitoring of IEM.