Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (947 page)

   Spinal muscular atrophy: DNA testing for common mutation

   Sickle cell anemia: presence of sickling; confirmed by Hb electrophoresis

   Tay-Sachs disease: enzyme activity

   α-Thalassemia and β-thalassemia: decreased mean corpuscular volume; confirmed by Hb electrophoresis

   Carrier testing for X-linked disease. Example:

   Fragile X (DNA testing for premutation); not currently offered to general population

   Limitations

   DNA testing for common mutations does not eliminate the possibility that an individual carries a rare mutation not included in the screening panel. Therefore, even if testing is negative, a residual carrier risk remains. Residual risk depends on many factors, including disease prevalence, patient ethnicity, family history, and the number of mutations included in the screen.

GHRELIN

   Definition and Use

   Ghrelin is a 3.5-kDa protein of 28-amino-acid peptide that is the natural ligand for the growth hormone secretagogue receptor. Based on its structure, it is a member of the motilin family of peptides. When administered peripherally or into the CNS, ghrelin stimulates secretion of growth hormone, increases food intake, and produces weight gain. Ghrelin, which is produced by the stomach, increases during periods of fasting or under conditions associated with negative energy balance such as starvation or anorexia. In contrast, ghrelin levels are low after eating or with hyperglycemia and in obesity. Accumulating evidence indicates that ghrelin plays a central role in the neurohormonal regulation of food intake and energy homeostasis.

   
Normal range
(fasting plasma levels): approximately 550–650 pg/mL.

   Interpretation

Increased In

   Fasting