Gray platelet syndrome: natural history of a large patient cohort and locus assignment to chromosome 3p

Abstract

Gray platelet syndrome (GPS) is an inherited bleeding disorder characterized by macrothrombocytopenia and absence of platelet α-granules resulting in typical gray platelets on peripheral smears. GPS is associated with a bleeding tendency, myelofibrosis, and splenomegaly. Reports on GPS are limited to case presentations. The causative gene and underlying pathophysiology are largely unknown. We present the results of molecular genetic analysis of 116 individuals including 25 GPS patients from 14 independent families as well as novel clinical data on the natural history of the disease. The mode of inheritance was autosomal recessive (AR) in 11 and indeterminate in 3 families. Using genome-wide linkage analysis, we mapped the AR-GPS gene to a 9.4-Mb interval on 3p21.1-3p22.1, containing 197 protein-coding genes. Sequencing of 1423 (69%) of the 2075 exons in the interval did not identify the GPS gene. Long-term follow-up data demonstrated the progressive nature of the thrombocytopenia and myelofibrosis of GPS resulting in fatal hemorrhages in some patients. We identified high serum vitamin B(12) as a consistent, novel finding in GPS. Chromosome 3p21.1-3p22.1 has not been previously linked to a platelet disorder; identification of the GPS gene will likely lead to the discovery of novel components of platelet organelle biogenesis. This study is registered at www.clinicaltrials.gov as NCT00069680 and NCT00369421.

Figure 1

Pedigrees of 14 GPS families included in the study and the microsatellite markers used to establish linkage. The microsatellite markers listed in the top left corner of the figure are the set of markers located within the homozygosity region that is indicated by the small gray bars placed under affected individuals in the pedigrees. These gray bars indicate that, for this segment of chromosome 3, these patients inherited the same set of microsatellite genotypes from their mother and father; hence they are homozygous by descent. *Physical map positions are based on UCSC genome browser version hg18. **Genetic map positions in centiMorgans are based on Marshfield map. Patients in families 12, 13, and 14 did not display a homozygous haplotype in the linked region.

Figure 2

Platelet and neutrophil images of GPS patients in comparison with controls. (A) EM of thin sections of a platelet from patient 1(V-20) showing absence of α-granules and abundant channels of the open canalicular system (labeled as OCS) in comparison with EM of a control platelet (B) showing normal alpha granules (labeled as AG). DTS: Dense tubule system. (C) Light microscopy of the peripheral smear of GPS patient 1(V-20) showing a large pale gray platelet (arrow) without the cytoplasmic color of α-granules, in comparison with a normal smear (D). (E) EM of a neutrophil of GPS patient 11(II-1) showing normal cytoplasmic granules (labeled as G) similar to control neutrophil from a normal volunteer (F); Phillips 301 Electrone microscope.

Figure 3

GPS is a progressive disorder. (A) Platelet counts of 14 GPS patients plotted against their age showing a significant negative correlation (y = -42.04 ln(x) + 174.14, R² = 0.805). Patient 13(II-1), who had splenectomy, is not included. (B) Bone marrow of patient 8 (II-1) at age 10 showing mild (grade 1) reticulin fibrosis (arrows). (C) Bone marrow of patient 8 (II-1) at age 29 showing grade 2–3 reticulin fibrosis (arrows). (D) Bone marrow of patient 13(II-1) at age 47 showing grade 3 reticulin fibrosis (arrows). (E) Bone marrow of patient 4(IV-2) showing grade 3 reticulin fibrosis (arrows). Olympus BX-51 microscope (Olympus America, Melville, NY) equipped with a UPlanFL 20×/0.50 numeric aperture objective. Images were captured using an Olympus DP70 digital camera system. Imaging software was Adobe Photoshop CS3 (Adobe Systems); magnification 200×, all images.