Whole exome sequencing for diagnosis of hereditary thrombocytopenia

Abstract

Hereditary thrombocytopenia comprises extremely diverse diseases that are difficult to diagnose by phenotypes alone. Definite diagnoses are helpful for patient (Pt) management. To evaluate the role of whole exome sequencing (WES) in these Pts. Cases with unexplained long-standing thrombocytopenia and/or suggestive features were enrolled to the observational study. Bleeding scores and blood smear were evaluated. The variant pathogenicity from WES was determined by bioinformatics combined with all other information including platelet aggregometry, flow cytometry, and electron microscopy (EM). Seven unrelated Pts were recruited. All were female with macrothrombocytopenia. Clinical bleeding was presented in four Pts; extra-hematological features were minimal and family history was negative in every Pt. WES successfully identified all the 11 responsible mutant alleles; of these, four have never been previously reported. Pt 1 with GNE-related thrombocytopenia showed reduced lectin binding by flow cytometry, increased glycogen granules by EM and a novel homozygous mutation in GNE. Pts 2 and 3 had phenotypic diagnoses of Bernard Soulier syndrome and novel homozygous mutations in GP1BB and GP1BA, respectively. Pt 4 had impaired microtubule structures, concomitant delta storage pool disease by EM and a novel heterozygous TUBB1 mutation. Pt 5 had sitosterolemia showing platelets with reduced ristocetin responses and a dilated membrane system on EM with compound heterozygous ABCG5 mutations. Pts 6 and 7 had MYH9 disorders with heterozygous mutations in MYH9. This study substantiates the benefits of WES in identifying underlying mutations of macrothrombocytopenia, expands mutational spectra of four genes, and provides detailed clinical features for further phenotype-genotype correlations.

GNE-related thrombocytopenia: evidence for a mutational hotspot in the ADP/substrate domain of the GNE bifunctional enzyme

“…At least to our knowledge, 20 patients from 9 unrelated families of the nearly one thousand individuals with alterations of this gene have been reported to have thrombocytopenia (Table 3S). [2][3][4]10,11 Of the 15 different variants identified in these patients, including P1 and P2, seven have been previously reported in patients with GNE myopathy (Figure 3). Except for p.His188Tyr, which is in cis with a known mutation (p.Asn550Ser) associated with myopathy, 4 the others (p.Asp444Tyr, p.Gly447Arg, p.Gly506Phe, p.Val516Arg, p.Leu517Pro, p.Thr575Arg, and p.Gly578Ser) were regarded as specific variants associated with isolated thrombocytopenia.…”

Severe Congenital Thrombocytopenia Characterized by Decreased Platelet Sialylation and Moderate Complement Activation Caused by Novel Compound Heterozygous Variants in GNE

“…Although not a hallmark symptom, congenital thrombocytopenia in patients suffering from GNE myopathy has previously been described in three unrelated families (15)(16)(17). Interestingly, isolated macrothrombocytopenia attributed to homozygous or compound heterozygous variants in GNE has just recently been reported in the literature (18)(19)(20)(21)(22). In addition, platelet sialylation was investigated in two of the reports, showing reduced expression of sialic acid on platelet surfaces (19,20).…”

“…Interestingly, isolated macrothrombocytopenia attributed to homozygous or compound heterozygous variants in GNE has just recently been reported in the literature (18)(19)(20)(21)(22). In addition, platelet sialylation was investigated in two of the reports, showing reduced expression of sialic acid on platelet surfaces (19,20).…”

“CHildren with Inherited Platelet disorders Surveillance” (CHIPS) retrospective and prospective observational cohort study by Italian Association of Pediatric Hematology and Oncology (AIEOP)

“…Furthermore, some of ITs (i.e., MYH9 and Bernard–Soulier syndrome) may present platelets that, due to their increased size, are unrecognized by the electronic counter, which therefore underestimates the MPV ( 54 ). In the last few years, new genes and de novo mutations responsible for inherited thrombocytopenia are continuously detected, and the classification of hereditary thrombocytopenias is updated constantly ( 55 , 56 ). Therefore, pathogenicity could be due to different predisposing genetic variants in a polygenic setting.…”