Liver tissue analysis may help ID, distinguish PFIC types: Study
Process, called immunohistochemistry, an option when genetic testing isn't
Analyzing the presence of different proteins in liver tissue under a microscope can be used to help diagnose progressive familial intrahepatic cholestasis (PFIC) and distinguish between its different types, according to a study done in India.
The findings indicate that this type of relatively cheap and accessible analysis, called immunohistochemistry, could be used to aid in identifying and discriminating PFIC types when standard — but more expensive — genetic testing isn’t an option.
“Immunohistochemical examination [and other tissue testing processes] are simple, cost-effective diagnostic modalities for determining or narrowing the … diagnosis,” the researchers wrote.
Their study, “Immunohistochemistry in progressive familial intrahepatic cholestasis (PFIC): Bridging gap between morphology and genetics,” was published in the Journal of Clinical and Experimental Hepatology.
Costly genetic testing often not available in ‘resource-constrained’ regions
PFIC refers to a group of genetic disorders marked by cholestasis, in which the flow of the digestive fluid bile out of the liver is stalled or blocked. Left untreated, cholestasis can lead to a number of symptoms that reflect liver problems, which can eventually progress to liver failure.
Identified as the cause of cholestasis in up to 13% of pediatric cases, PFIC can be divided into several types — each due to mutations in different genes. The gold standard for diagnosing PFIC and differentiating between its types is genetic testing to identify the disease-causing mutation in each case.
“However, this approach has always been challenging given the costly nature of the technique and lack of availability, especially in resource-constrained countries such as India,” the researchers wrote.
Immunohistochemistry is a well-established technique that uses labeled antibodies to detect and localize specific proteins in tissues. The antibody-protein bond can then be visualized under the microscope with specific staining. Immunohistochemistry is much more widely available than genetic testing, and it can usually be done fairly inexpensively.
In this study, a team led by researchers at the Sanjay Gandhi Postgraduate Institute of Medical Sciences sought to determine if immunohistochemistry can reliably be used to identify PFIC types and differentiate them from other causes of pediatric cholestasis.
The technique was used to analyze liver tissue samples from 39 children with genetically confirmed PFIC and 20 children with other types of cholestatic diseases.
In the PFIC group, eight children had type 1, and 11 had been diagnosed with type 2. A total of 13 had type 3, six were diagnosed with type 4, and one had type 6. The team evaluated whether the specific proteins that are affected by each PFIC type were present or absent in the liver tissue of each patient based on the percentage of stained cells.
Liver tissue testing generally over 90% accurate, per analysis
The results showed that all but one of the children with PFIC type 2 — which is caused by mutations in the gene that provides instructions to make the BSEP protein — showed complete BSEP absence. The remaining child (9.1%) showed moderately reduced BSEP levels.
Among PFIC type 3 patients, who carry mutations in the gene that encodes the MDR3 protein, 84.6% lacked MDR3, while 15.4% had moderately low levels of the protein. All children with PFIC type 4, which is caused by mutations in the gene that encodes TJP2, had a complete or marked decrease in TJP2 levels.
In contrast, PFIC type 1 patients — who have mutations in the gene coding for the FIC 1 protein, which was not assessed in this study — were positive for BSEP, MDR3, and TJP2 on immunohistochemistry testing.
PFIC type 6 is caused by mutations in a gene that encodes the MYO5B protein. The single child diagnosed with this type of PFIC had no MYO5B protein on immunohistochemistry staining. However, given that the study included only one PFIC type 6 patient, caution is needed in interpreting these results, the team noted.
The team also found that negative immunohistochemistry for some of these proteins, including BSEP and MDR3, was not exclusive to PFIC patients. For example, although BSEP was absent in samples from most children with PFIC type 2, it was also absent in a liver sample from a child with biliary atresia.
Still, statistical tests based on the available data indicated that immunohistochemistry can distinguish PFIC patients from those with other cholestatic diseases with a level of accuracy that was generally higher than 90%.
Genetic analysis is the gold standard for diagnosis. However, immunohistochemistry [liver tissue analysis] can be an alternative.
“This study demonstrated that immunostaining for BSEP, MDR3, TJP2, and MYO5B can identify PFIC subtypes,” the researchers wrote, noting it also can be used to “distinguish PFIC patients from non-PFIC patients.”
Overall, these findings support immunohistochemistry as a method for diagnosing PFIC and discriminating its types, especially when genetic testing isn’t an option.
“Genetic analysis is the gold standard for diagnosis. However, immunohistochemistry can be an alternative,” the team wrote.
Still, larger studies are needed to confirm these findings, the researchers noted.
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