Mosaicism of an ELANE Mutation in an Asymptomatic Mother

Case Report: Characterization of known (c.607G>C) and novel (c.416C>G) ELANE mutations in two Mexican families with congenital neutropenia

The most common causes of congenital neutropenia are mutations in the ELANE (Elastase, Neutrophil Expressed) gene (19p13.3), mostly in exon 5 and the distal portion of exon 4, which result in different clinical phenotypes of neutropenia. Here, we report two pathogenic mutations in ELANE, namely, c.607G>C (p.Gly203Arg) and a novel variant c.416C>G (p.Pro139Arg), found in two Mexican families ascertained via patients with congenital neutropenia who responded positively to the granulocyte colony-stimulating factor (G-CSF) treatment. These findings highlight the usefulness of identifying variants in patients with inborn errors of immunity for early clinical management and the need to rule out mosaicism in noncarrier parents with more than one case in the family.

Low frequency of treatable pediatric disease alleles in gnomAD: An opportunity for future genomic screening of newborns

Hematopoietic stem cell transplant (HSCT) can prevent progression of several genetic disorders. Although a subset of these disorders are identified on newborn screening panels, others are not identified until irreversible symptoms develop. Genetic testing is an efficient methodology to ascertain pre-symptomatic children, but the penetrance of risk-associated variants in the general population is not well understood. We developed a list of 127 genes associated with disorders treatable with HSCT. We identified likely pathogenic or pathogenic (LP/P) and loss-of-function (LoF) variants in these genes in the Genome Aggregation Database (gnomAD), a dataset containing exome and genome sequencing data from 141,456 healthy adults. Within gnomAD, we identified 59 individuals with a LP/P or LoF variant in 15 genes. Genes were associated with bone marrow failure syndromes, bleeding disorders, primary immunodeficiencies, osteopetrosis, metabolic disorders, and epidermolysis bullosa. In conclusion, few ostensibly healthy adults had genotypes associated with pediatric disorders treatable with HSCTs. Given that most of these disorders do not have biomarkers that could be cheaply and universally assessed on a standard newborn screen, our data suggest that genetic testing may be a complementary approach to traditional newborn screening methodology that has the potential to improve mortality and is not expected to lead to a high burden of false-positive results.

Congenital neutropenia: disease models guiding new treatment strategies

PURPOSE OF REVIEW

Myeloid diseases are often characterized by a disturbed regulation of myeloid cell proliferation, survival, and maturation. This may either result in a severe paucity of functional neutrophils (neutropenia), an excess production of mature cells (myeloproliferative disorders) or in clonal expansions of dysplastic or immature myeloid cells (myelodysplasia and acute myeloid leukemia). Although these conditions can be regarded as separate entities, caused by the accumulation of distinct sets of somatic gene mutations, it becomes increasingly clear that they may also evolve as the prime consequence of a congenital defect resulting in severe neutropenia. Prominent examples of such conditions include the genetically heterogeneous forms of severe congenital neutropenia (SCN) and Shwachman-Diamond Syndrome. CSF3 treatment is a successful therapy to alleviate neutropenia in the majority of these patients but does not cure the disease nor does it prevent malignant transformation. Allogeneic stem cell transplantation is currently the only therapeutic option to cure SCN, but is relatively cumbersome, e.g., hampered by treatment-related mortality and donor availability. Hence, there is a need for new therapeutic approaches.

RECENT FINDINGS

Developments in disease modeling, amongst others based on induced pluripotent stem cell and CRISPR/Cas9 based gene-editing technologies, have created new insights in disease biology and possibilities for treatment. In addition, they are fueling expectations for advanced disease monitoring to prevent malignant transformation.

SUMMARY

This review highlights the recent progress made in SCN disease modeling and discusses the challenges that are still ahead of us to gain a better understanding of the biological heterogeneity of the disease and its consequences for patient care.