Evaluation of current diagnostic workup for pediatric severe aplastic anemia: Low incidence of cryptic inherited bone marrow failure syndromes

Abstract

Abstract Background:Pediatric severe aplastic anemia (SAA) is a rare diagnosis characterized by pancytopenia with a hypocellular bone marrow. Patients with inherited bone marrow failure syndromes (IBMFS) need to be distinguished from those with idiopathic SAA as the underlying etiology significantly impacts treatment and long-term management decisions. However, awaiting genetic testing results before initiating therapy for idiopathic SAA risks life-threatening complications from prolonged, severe cytopenias. Prior genomic studies have reported a significant incidence of unrecognized IBMFS among patients with SAA; however, these studies did not incorporate the comprehensive clinical and laboratory testing currently used for the diagnostic workup of SAA, which has evolved with our increasing understanding of IBMFS. This study aims to investigate the incidence of cryptic IBMFS among pediatric patients with SAA who have undergone diagnostic evaluation with current standard-of-care clinical and laboratory assessments. Methods: This is a retrospective study of 149 pediatric and young adult patients (age <21 years) who underwent a comprehensive clinical evaluation for SAA from 4 pediatric institutions. All patients met Camitta criteria for SAA diagnosis. Clinical and laboratory testing including Fanconi anemia chromosomal breakage studies, telomere length testing, paroxysmal nocturnal hemagobinuria (PNH) flow cytometry, and bone marrow evaluations were extracted from medical records. Enhanced whole exome sequencing (WES) with added coverage of clinically relevant non-coding sequences was performed for all patients. Analysis focused on variants in 102 IBMFS-associated genes. Results: The median age at diagnosis was 10.15 years (range 1.28 to 20.79 years) with a median length of follow-up of 4.83 years (range 0 – 17.35 years). 98 patients (65.8%) were males. Of the 149 patients in the cohort, 113 patients lacked any clinical/family history or laboratory findings to suggest an IBMFS, and of these, none were identified by enhanced WES to have an underlying genetic IBMFS. Of the remaining 36 patients, at least one clinical feature or family history possibly suggestive of an inherited syndrome was identified. These included a history of cytopenias prior to the diagnosis of SAA, lymphocyte telomere lengths suspicious for a telomere biology disorder, low pancreatic isoamylase, congenital anomalies, short stature, dysmorphic features, recurrent infection, neurologic abnormalities, or a family history of bone marrow failure/chronic cytopenias, hematologic malignancy, or solid tumor diagnosed at an early age. Among these 36 patients with a history possibly suggestive of a germline condition, 1 patient was found to have a heterozygous likely pathogenic variant in SAMD9L (c.1877C>T, p.Ser626Leu) consistent with autosomal dominant SAMD9L syndrome. This patient had a 3-generation paternal family history of a cerebellar degenerative disorder and a personal history of mild cognitive impairment, nystagmus, and ataxia in addition to episodes of severe infection prior to the diagnosis of SAA. Another patient with a history of cytopenias prior to SAA diagnosis was found to have two pathogenic variants in ERCC6L2 (c.1930C>T, p.Arg644Ter and a splicing variant c.950+2T>G) though zygosity could not be determined and therefore affected status could not be ascertained. Conclusion:Among a large cohort of pediatric patients presenting with SAA without features of an IBMFS following a comprehensive clinical history, exam, and laboratory evaluation, none had a IBMFS identified by enhanced WES. Among those with clinical features suggestive of a possible inherited syndrome, one patient was diagnosed with SAMD9L syndrome. Another patient had pathogenic variants in ERCC6L2,but allelic phasing could not be ascertained for diagnosis. Delays in initiating SAA treatment can leave patients vulnerable to complications including infection, particularly fungal infections, from prolonged severe neutropenia or bleeding from severe thrombocytopenia. For patients with a diagnostic evaluation concerning for an IBMFS, germline genetic testing should be considered prior to proceeding with SAA therapy. For patients with a negative comprehensive IBMFS workup utilizing current diagnostic clinical and laboratory evaluations, the low likelihood of benefit gained by awaiting genetic testing results must be weighed against the risks of treatment delay for SAA.