Detection of clonality in lymphoproliferations using PCR of the antigen receptor genes: does size matter?

A biopsy of a nasal mass that had morphologic and immunostaining features consistent with a B-cell lymphoma was studied for clonality using PCR of the IgH gene. An unexpectedly low molecular weight DNA fragment of approximately 140bp (acceptable size limit: 250-295bp) was obtained using FR2 and JH primers. The sequence of this DNA was consistent with a clonal IgH rearrangement followed by a deletion that removed most of the downstream portion of the V segment. Thus, the biopsy contained a monoclonal population of B-lymphocytes, consistent with a diagnosis of lymphoma. This work illustrates that bands outside of the size range expected from PCR of the antigen receptor genes may still be consistent with a monoclonal result.