WHIM Syndrome Caused by Waldenström’s Macroglobulinemia-Associated Mutation CXCR4 L329fs

Abstract

WHIM syndrome is an autosomal dominant immunodeficiency disease caused by mutations affecting the carboxy-terminus of CXCR4. To characterize novel genetic causes of the syndrome, we recruited a pediatric patient with possible WHIM syndrome, performed CXCR4 gene sequencing and compared his clinical phenotype and CXCR4 tail amino acid sequences with other patients with WHIM syndrome carrying CXCR4 (R334X) mutations. We identified and biochemically characterized a heterozygous 5 base pair deletion (nucleotides 986-990) located in the portion of the open reading frame (ORF) of CXCR4 that encodes the carboxy-terminal domain of the receptor. This CXCR4 (L329fs) mutation causes a frame-shift at codon 329 resulting in replacement of the final 24 predicted amino acids of the receptor with 12 missense amino acids. Like previously reported WHIM mutations, this frame-shift mutation CXCR4 (L329fs) decreased receptor downregulation in response to the CXCR4 agonist CXCL12 in patient PBMCs as well as in transfected K562 and HEK 293 cells, but increased calcium flux responses in K562 cells to CXCL12 stimulation. Thus, CXCR4 (L329fs) appears to be a de novo autosomal dominant frame-shift gain-of-function mutation that like other carboxy-terminus mutations causes WHIM syndrome. The same CXCR4 (L329fs) frame-shift variant has been reported to occur in tumor cells from a patient with Waldenström's Macroglobulemia (WM), but is caused by a distinct genetic mechanism: insertion of a single nucleotide in the L329 codon, providing additional evidence that the carboxy-terminus of CXCR4 is a genetic hotspot for mutation.

CXCR4 signaling in health and disease

“…After the interaction with the CD4 molecules, the envelope glycoprotein gp120 of the T-tropic leads to the impairment of the CXCL12-induced receptor desensitization and to the enhancement of ligand-induced receptor signaling [97]. Studies conducted in leukocytes isolated from WHIM patients provided the evidence that CXCR4 dimerization emphasize β-arrestin2 signaling which, through ERK1/2 activity, results in an enhanced chemotaxis to CXCL12 [98].…”

“…The genetic basis of the disease has been discovered by identifying heterozygous mutations of chemokine receptor CXCR4 co−segregated with the disease in most of the reported pedigrees[96]. Most of the 50 WHIM patients reported so far have one of four mutations causing a 10-19 amino acid truncation of the C-terminal domain of CXCR4 (R334X, G336X, S338X, E343X), which is crucial for ligand-induced internalization and receptor desensitization[97]. Very recently,McDermott and colleagues described a de novo case of WHIM Syndrome caused by a 5 base pair deletion of CXCR4 open reading frame nucleotides 986-990, causing a frame shift at the codon L329 (identified as CXCR4 L329fs ).…”

Pathogenesis, diagnosis and therapeutic strategies in WHIM syndrome immunodeficiency

“…It has been reported in two cases that IgG was normal despite selective IgM deficiency [20] or combined IgA and IgM deficiency [13]. B lymphopenia, including reduced memory B cells, is a common feature in WHIM patients [3,10,21–24]; however, a precise pathophysiologic mechanism linking this with a particular immunoglobulin subtype deficiency is lacking.…”

“…Additionally, sequelae associated with repeated infections may significantly affect quality of life. For example, bronchiectasis may cause WHIM patients to be dependent on supplemental oxygen [3,7], and repeated ear infections can lead to hearing loss and delayed speech development in children [23,24]. …”

How I treat warts, hypogammaglobulinemia, infections, and myelokathexis syndrome

“…The treatment with granulocyte colony-stimulating factor (G-CSF) results in the downregulation of CXCR4 and a decreased cell responsiveness to CXCL12, promoting neutrophil mobilization from the bone marrow to the peripheral blood. in a WHIM patient 21 (Table 2). Interestingly, mutations affecting the intracellular tail of CXCR4 can occur as somatic mutations, which is shown in patients with Waldenström macroglobulinemia, suggesting that the C-tail of CXCR4 has an important regulatory function for Bcell lymphomagenesis.…”