Mutations in more than 70 genes cause hereditary anemias (HA), a highly heterogeneous group of rare/low frequency disorders in which we included: hyporegenerative anemias, as congenital dyserythropoietic anemia (CDA) and Diamond-Blackfan anemia; hemolytic anemias due to erythrocyte membrane defects, as hereditary spherocytosis and stomatocytosis; hemolytic anemias due to enzymatic defects. The study describes the diagnostic workflow for HA, based on the development of two consecutive versions of a targeted-NGS panel, including 34 and 71 genes, respectively. Seventy-four probands from 62 unrelated families were investigated. Our study includes the most comprehensive gene set for these anemias and the largest cohort of patients described so far. We obtained an overall diagnostic yield of 64.9%. Despite 54.2% of cases showed conclusive diagnosis fitting well to the clinical suspicion, the multi-gene analysis modified the original clinical diagnosis in 45.8% of patients (nonmatched phenotype-genotype). Of note, 81.8% of nonmatched patients were clinically suspected to suffer from CDA. Particularly, 45.5% of the probands originally classified as CDA exhibited a conclusive diagnosis of chronic anemia due to enzymatic defects, mainly due to mutations in PKLR gene. Interestingly, we also identified a syndromic CDA patient with mild anemia and epilepsy, showing a homozygous mutation in CAD gene, recently associated to early infantile epileptic encephalopathy-50 and CDA-like anemia. Finally, we described a patient showing marked iron overload due to the coinheritance of PIEZO1 and SEC23B mutations, demonstrating that the multi-gene approach is valuable not only for achieving a correct and definitive diagnosis, but also for guiding treatment.

Shwachman-Diamond syndrome (SDS) (OMIM #260400) is a rare inherited bone marrow failure syndrome (IBMFS) that is primarily characterized by neutropenia and exocrine pancreatic insufficiency. Seventy-five to ninety percent of patients have compound heterozygous loss-of-function mutations in the Shwachman-Bodian-Diamond syndrome (SBDS) gene. Using trio whole-exome sequencing (WES) in an SBDS-negative SDS family and candidate gene sequencing in additional SBDS-negative SDS cases or molecularly undiagnosed IBMFS cases, we identified 3 independent patients, each of whom carried a de novo missense variant in SRP54 (encoding signal recognition particle 54 kDa). These 3 patients shared congenital neutropenia linked with various other SDS phenotypes. 3D protein modeling revealed that the 3 variants affect highly conserved amino acids within the GTPase domain of the protein that are critical for GTP and receptor binding. Indeed, we observed that the GTPase activity of the mutated proteins was impaired. The level of SRP54 mRNA in the bone marrow was 3.6-fold lower in patients with SRP54-mutations than in healthy controls. Profound reductions in neutrophil counts and chemotaxis as well as a diminished exocrine pancreas size in a SRP54-knockdown zebrafish model faithfully recapitulated the human phenotype. In conclusion, autosomal dominant mutations in SRP54, a key member of the cotranslation protein-targeting pathway, lead to syndromic neutropenia with a Shwachman-Diamond-like phenotype.

Leukocyte adhesion deficiency-1/variant (LAD1v) syndrome presents early in life and manifests by infections without pus formation in the presence of a leukocytosis combined with a Glanzmann-type bleeding disorder, resulting from a hematopoietic defect in integrin activation. In 7 consanguineous families, we previously established that this defect was not the result of defective Rap1 activation, as proposed by other investigators. In search of the genetic defect, we carried out homozygosity mapping in 3 of these patients, and a 13-Mb region on chromosome 11 was identified. All 7 LAD1v families share the same haplotype, in which 3 disease-associated sequence variants were identified: a putative splice site mutation in CALDAGGEF1 (encoding an exchange factor for Rap1), an intronic 1.

Key Points Germ line mutations in MECOM cause a heterogeneous bone marrow failure syndrome with congenital hypomegakaryocytic thrombocytopenia. MECOM-associated syndrome includes various organ malformations with variable penetrance, including radioulnar synostosis.

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