Deletional mutation of the external domain of the human granulocyte colony-stimulating factor receptor in a patient with severe chronic neutropenia refractory to granulocyte colony-stimulating factor.

Severe chronic neutropenia (SCN) is characterized by a profound neutropenia, which mostly presents during the neonatal period. The precise genetic basis of SCN remains elusive. Acquired somatic mutations involving the carboxy-terminus of the G-CSF receptor (G-CSFR) have been found, often in association with myelodysplastic syndrome. The authors describe a girl with SCN who did not respond to pharmacologic doses of filgrastim. Genetic analysis of bone marrow and germline cells revealed a 182-bp deletion in the extracellular domain of the G-CSFR. Co-precipitation studies showed an association between the wild-type and mutant G-CSFR, confirmed by their co-localization by confocal microscopy. Coexpression of the mutant receptor inhibited the wild-type response in Ba/F3 cells. These findings establish a novel constitutional defect in the G-CSFR that supports a partial dominant negative mechanism for receptor dysfunction in SCN.

Autosomal dominant progressive nephropathy with deafness: linkage to a new locus on chromosome 11q24.

Focal segmental glomerulosclerosis (FSGS) and Alport syndrome (AS) are two major causes of end-stage renal disease (ESRD). A few families with autosomal dominant FSGS have been reported with linkage to chromosome 19q13 or 11q22, while AS is usually linked to mutations in type IV collagen (COL4) subunit genes. A phenotype resembling AS may also be seen with myosin heavy chain-9 (MYH9) gene mutations. This study ascertained a multigeneration family (CHP-177) with clinical aspects of both FSGS and AS where we identified a new locus for the trait. A genome-wide scan was performed with 400 markers, and fine mapping was performed for chromosome 11 markers. Data were analyzed by GENEHUNTER and VITESSE under various models. CHP-177 is a 39-member kindred residing near New Delhi, India, with seven affecteds and showed male-to-male transmission. Two members had ESRD. Renal biopsies showed both FSGS lesions and thin glomerular basement membranes. Five of the affecteds also had sensorineural deafness, which involved both low and high frequency in some members. The AS loci, i.e., COL4A3/COL4A4 and MYH9 (LOD scores: -6.1 and -4.3, respectively) and FSGS loci, on 19q13 and 11q22, were excluded from linkage. A significant evidence of linkage was observed for 11q24 region, with a multipoint LOD (z-score) of 3.2 for marker D11S4464 at theta = 0. The z-1 confidence interval for the linked region spans a genetic distance of 7 cM. This study thus reports an autosomal dominant nephropathy with features of both FSGS and AS in which linkage to currently known loci for such phenotypes was excluded and a new locus on 11q24 was identified. The findings suggest further locus heterogeneity for the autosomal dominant nephropathy phenotype.