Kawasaki Disease Diagnosed by Urine Proteins?

Diedtra Henderson

December 26, 2012

Of thousands of protein molecules found within urine, researchers using recently developed technologies have identified 2 proteins that hold promise as biomarkers of Kawasaki disease (KD), a rare disease that is the most common cause of acquired pediatric heart disease in the developed world.

Alex Kentsis, MD, PhD, from the Division of Hematology/Oncology, Department of Pediatric Oncology, Dana-Farber Cancer Institute, Boston Children's Hospital, and Harvard Medical School, Boston, Massachusetts, and coauthors report their findings in an article published online December 20 in EMBO Molecular Medicine.

KD, thought to be an exaggerated immune system response to an infectious trigger, occurs in 1 of 10,000 US and European children, and 1 in 100 Japanese children, younger than 5 years. Diagnosing KD is difficult because the symptoms, which include prolonged fever, nonexudative conjunctivitis, rash, swollen and red hands and feet, and enlarged lymph nodes, mimic other childhood febrile illnesses. Diagnosis of KD has been improved through the use of clinical algorithms and echocardiography, but if diagnosis and treatment are delayed, as many as 25% of patients may go on to develop coronary artery dilation or aneurysms.

Incomplete understanding of KD's molecular underpinnings, however, has complicated identification of therapeutic targets. Dr. Kentsis and colleagues used high-accuracy mass spectrometry to discover and validate more accurate diagnostic markers of KD in children's urine.

They enrolled 107 patients over the course of 39 months who had fever and who were suspected of having KD. Fifty-three patients ultimately were diagnosed with the disease, 33 were found to have nonspecific viral syndrome, and the remainder had an assortment of conditions, such as adenovirus and serum sickness, that mimic KD. The researchers identified KD candidate markers by analyzing 15 urine specimens (6 from children with KD, 6 from children found to have other illnesses, and 3 samples taken from children convalescing from KD a month after treatment). Of thousands of protein molecules they analyzed, more than 190 proteins appeared only in children with KD, including proteins associated with endothelial and myocardial cell injury, such as filamin C, and such immune regulators as meprin A.

When they tested the KD diagnostic ability of these 2 proteins, the research team found that either urine meprin A or filamin C "was superior" (area under the curve value, 0.98; 95% confidence interval, 0.97 - 1 and 0.95 - 1, respectively) when compared with erythrocyte sedimentation rate or blood C–reactive protein.

"Taken together, the identified proteomes, including both raw and processed data, available openly at Peptide Atlas...and containing 190 novel candidate KD markers...provide a molecular physiological profile of Kawasaki disease," the authors write.

"[E]levated levels of filamin C in patients with KD who did not respond to initial therapy as compared to those with complete response suggest that filamin C is a marker of Kawasaki disease activity. Meprin A and filamin C were also elevated in patients with incomplete presentations of KD, suggesting that these markers may be used to improve the diagnosis of incomplete presentations of KD," the researchers continue.

Study limitations include the possibility that the discovered molecular pathophysiological profile of KD may omit important proteins and include insignificant ones, but the authors note that they attempted to "mitigate the stochastic effects of instrumental sampling." In addition, development of clinical-grade assays for meprin A and filamin C will require normalization for potential variations in total urine protein concentrations.

"[T]he work presented here opens many potential approaches for improving the diagnosis of Kawasaki disease, elucidating its pathophysiology and directing therapy," the authors conclude. "In particular, validation of meprin A and filamin C as specific and sensitive markers of Kawasaki disease using commonly available [enzyme-linked immunosorbent assays] enables their clinical use to improve the accuracy and timeliness of diagnosis of KD."

The study was supported by the Boston Children's Hospital Division of Immunology and translational research programs, Harvard Catalyst, and the National Institutes of Health. The lead author is supported by a grant from the National Institutes of Health. The authors have disclosed no relevant financial relationships.

EMBO Mol Med. Published online December 20, 2012. Full text