Non-invasive Biomarkers of Fibrosis in Pediatric Liver Diseases

Abnormal liver biochemical and function tests are frequently detected in symptomatic patients since many screening blood test panels routinely include them. A population-based survey in the United States conducted between 1999 and 2002 estimated that an abnormal alanine aminotransferase (ALT) was present in 8.9 percent of respondents. These patients are often referred to hepatology to elucidate the cause of these abnormal liver tests and potential liver disease. Identifying the cause of specific pediatric liver diseases is critical to the management and treatment. Liver biopsy provides histological information often needed to make a conclusive diagnosis and has historically been accepted as the best way to measure liver fibrosis. Given that the current gold standard for assessing for liver fibrosis is via liver biopsy, there are several reasons why the field is looking for a non-invasive method that correlates highly with liver histology. Hemorrhage, infection, the need to often be observed overnight, anxiety, and need for sedation are the accepted risks for all liver biopsies. The histologic grade on liver biopsy (grades 0-4) is used to grade the severity of hepatic fibrosis and make clinical decisions such as initiating treatment with antiviral or immunomodulator therapy. Ultrasound imaging (sonography) uses high-frequency sound waves to view soft tissues such as muscles and internal organs, limited primarily by non-sound transmitting tissues such as air and bone. Ultrasound is an excellent modality for the pediatric population and provides far ranging diagnostic possibilities, limiting the use of radiation whenever possible. Sheerwave elastography is a complimentary noninvasive, real-time sonographic technique that has been shown to have a wide range of clinical applications, including the ability to assess the degree of liver fibrosis in chronic liver disease. Tissue has an inherent elasticity which may be altered by pathologic processes such as inflammation, fibrosis, and tumors. Elastography has been used extensively in breast imaging showing much promise in detecting non-compressible masses associated with an increased risk of malignancy. Elastography has the ability to assess small changes in pliability of liver tissue across the entire liver. Elasticity of tissue in the context of elastography is the ratio of tension (stress) needed to produce a relative change in length (strain), and quantifies how much pressure must be placed on tissue in order to cause elastic deformation. Ultrasonic elastography has been performed to detect hepatic fibrosis in patients with fatty liver disease in adults, but not yet in children with viral hepatitis B or C. Performance compression ultrasound require no more than 5-10 additional minutes of imaging and have no known associated risks. Serum fibrosis markers are promising non-invasive indicators of fibrosis and progression to cirrhosis in adult liver diseases: e.g. the commercially available Fibrotest® is used to detect hepatic fibrosis in hepatitis C and in non-alcoholic fatty liver disease (NAFLD). However, marker patterns appear to be disease and development (age) specific, making some of the adult markers of doubtful value in children. As proof of principle, in a biopsy study of another pediatric fibrosing liver entity, cystic fibrosis liver disease, specific marker patterns derived from mechanistic studies were found to highly correlate with F3/4 fibrosis vs F0/1. The rapid onset of liver disease in some children (i.e. HBV, genotype C) indicates a need to identify early markers of liver fibrosis to help facilitate early intervention. Serum chemistries used to assess hepatic inflammation and injury are not reliable. Empirically identified markers identified by genomic, proteomic, and metabolomic technologies, as well as targeted serum marker analysis, offer new strategies with which to diagnose and predict outcomes in pediatric liver diseases. Preliminary studies in children with fibrotic liver diseases have identified specific markers reflecting matrix re-modeling, hepatic stellate cell activation and chemoattractant expression in this age group.