A large kindred with X-linked neutropenia with an I294T mutation of the Wiskott-Aldrich syndrome gene

Abstract

X-linked neutropenia (XLN, OMIM #300299) is a rare form of severe congenital neutropenia. It was originally described in a three-generation family with five affected members that had an L270P mutation in the GTP-ase binding domain (GBD) of the Wiskott-Aldrich syndrome protein (WASP) [Devriendt et al (2001) Nature Genetics, Vol. 27, 313-317]. Here, we report and describe a large three-generation family with XLN, with 10 affected males and eight female carriers. A c.882T>C mutation was identified in the WAS gene, resulting in an I294T mutation. The infectious course is variable and mild in view of the profound neutropenia. In addition to the original description, low-normal IgA levels, low to low-normal platelet counts and reduced natural killer (NK)-cell counts also appear as consistent XLN features. However, inverted CD4/CD8 ratios were not found in this family, nor were cases identified with myelodysplastic syndrome or acute myeloid leukaemia. Female carriers exhibited a variable attenuated phenotype. Like L270P WASP, I294T WASP is constitutively active towards actin polymerization. In conclusion, this largest XLN kindred identified to date provides new independent genetic evidence that mutations disrupting the auto-inhibitory GBD of WASP are the cause of XLN. Reduced NK cells, low to low normal platelet counts and low to low-normal IgA levels are also features of XLN.

Figure 1

Pedigree showing all 60 screened individuals, from I.1 till III.26: affected males (black squares), carrier females (filled circles) and unaffected family members (unfilled symbols).

Figure 2

Mean IgA levels in g/L for male XLN patients (n=10), I294T carriers (n=8) and unaffected family members (n=23). P-value for IgA is 0.002 as calculated by the Mann-Whitney test comparing adult affected cases with unaffected family members.

Figure 3

Thermal denaturation of wild type GBD-VCA and GBD-VCA I294T by circular dichroism (CD) spectroscopy. CD measurements (222 nm) were obtained on 10 μM samples in 25 mM phosphate (pH 7), 150 mM NaCl, and 1 mM DTT, as described in Materials and Methods.

Figure 4

Pyrene actin polymerization assays show that GBD-VCA I294T display Cdc42-independent activation. Pyrene fluorescence at 407 nm (excitation wavelength 365 nm) was monitored over time, as described in Materials and Methods. Control : 4 μM actin (6% pyrene), 10 nM bovine Arp2/3 complex. 500 nM VCA, 500nM GBD-VCA or 500 nM GBD-VCA I294T were added as indicated.