Contributions
Abstract: EP688
Type: E-Poster Presentation
Session title: Enzymopathies, membranopathies and other anemias
Background
Hereditary anemias are a heterogeneous group of conditions that are characterized by complex genotype-phenotype correlations. Based on clinical manifestations and morphological red blood cell (RBC) alterations, hereditary anemias can be broadly classified into four different subtypes: (i) disorders of hemoglobin synthesis, such as thalassemia and hemoglobinopathies; (ii) hypo-regenerative and hypo-productive anemias, such as Diamond-Blackfan anemia and congenital dyserythropoietic anemias; (iii) RBC membrane defects that are due to either alterations to the structural organization of the membranes, such as hereditary spherocytosis and hereditary elliptocytosis, or to alterations to membrane transport functions, such as hereditary stomatocytosis; and (iv) nonspherocytic hemolytic anemias, due to RBC enzyme defects.
Next-generation sequencing (NGS) has revolutionized the framework of the diagnosis of hereditary anemias by reducing both time and cost. Nevertheless, it remains a challenge to diagnose many hereditary anemia phenotypes according to phenotypic features and conventional diagnostic testing.
Aims
To identify complex modes of inheritance in hereditary red blood cell disorders by NGS analysis.
Methods
In this study, we evaluated a large case series of 155 consecutive patients with different of forms hereditary erythrocyte defects who were referred to the Medical Genetics Unit (‘Federico II’ University Hospital, Naples, Italy) from January 2018 to September 2020. All of the cases followed a diagnostic workflow based on a targeted-NGS panel of 86 genes known to be causative of hereditary RBC defects.
Results
We obtained an overall diagnostic yield of 83% of tested patients. Monogenic inheritance was seen for 67% (104/155), and multi-locus inheritance for 17% (26/155). PIEZO1 and SPTA1 were the most mutated loci among the other causative genes identified. The high frequencies of mutations in both of these genes were mainly related to their low genic intolerance, as suggested by the high values of the Residual Variation Intolerance Score percentiles for both genes. Accordingly, 18/26 patients with multi-locus inheritance showed dual molecular diagnosis of hereditary stomatocytosis (mainly dehydrated hereditary stomatocytosis type 1) and hereditary spherocytosis. These dual inheritance cases were characterized by analysis of their inheritance patterns, hematological indices, iron balance parameters, and hemolytic markers. Of note, dual inheritance patients were clinically indistinguishable from patients with hereditary spherocytosis. Additionally, their Osmoscan profiles were analyzed, which highlighted alterations of the ektacytometry curve of dual inheritance patients compared to both dehydrated hereditary stomatocytosis and hereditary spherocytosis.
Conclusion
One of the major advantages of the NGS approach is the identification of both polygenic conditions and modifier variants associated with causative mutations. Studies of Mendelian conditions have revealed the extent to which many rare diseases can be characterized by complex modes of inheritance, such as digenic inheritance and dual molecular diagnoses. Our findings expand the genotypic spectrum of red blood cell disorders and indicate that multi-locus inheritance should be considered for analysis and counseling of these patients. Of note, the genetic testing was crucial for diagnosis of patients with a complex mode of inheritance.
Keyword(s): Anemia, Diagnosis, Genetic, Red blood cell
Abstract: EP688
Type: E-Poster Presentation
Session title: Enzymopathies, membranopathies and other anemias
Background
Hereditary anemias are a heterogeneous group of conditions that are characterized by complex genotype-phenotype correlations. Based on clinical manifestations and morphological red blood cell (RBC) alterations, hereditary anemias can be broadly classified into four different subtypes: (i) disorders of hemoglobin synthesis, such as thalassemia and hemoglobinopathies; (ii) hypo-regenerative and hypo-productive anemias, such as Diamond-Blackfan anemia and congenital dyserythropoietic anemias; (iii) RBC membrane defects that are due to either alterations to the structural organization of the membranes, such as hereditary spherocytosis and hereditary elliptocytosis, or to alterations to membrane transport functions, such as hereditary stomatocytosis; and (iv) nonspherocytic hemolytic anemias, due to RBC enzyme defects.
Next-generation sequencing (NGS) has revolutionized the framework of the diagnosis of hereditary anemias by reducing both time and cost. Nevertheless, it remains a challenge to diagnose many hereditary anemia phenotypes according to phenotypic features and conventional diagnostic testing.
Aims
To identify complex modes of inheritance in hereditary red blood cell disorders by NGS analysis.
Methods
In this study, we evaluated a large case series of 155 consecutive patients with different of forms hereditary erythrocyte defects who were referred to the Medical Genetics Unit (‘Federico II’ University Hospital, Naples, Italy) from January 2018 to September 2020. All of the cases followed a diagnostic workflow based on a targeted-NGS panel of 86 genes known to be causative of hereditary RBC defects.
Results
We obtained an overall diagnostic yield of 83% of tested patients. Monogenic inheritance was seen for 67% (104/155), and multi-locus inheritance for 17% (26/155). PIEZO1 and SPTA1 were the most mutated loci among the other causative genes identified. The high frequencies of mutations in both of these genes were mainly related to their low genic intolerance, as suggested by the high values of the Residual Variation Intolerance Score percentiles for both genes. Accordingly, 18/26 patients with multi-locus inheritance showed dual molecular diagnosis of hereditary stomatocytosis (mainly dehydrated hereditary stomatocytosis type 1) and hereditary spherocytosis. These dual inheritance cases were characterized by analysis of their inheritance patterns, hematological indices, iron balance parameters, and hemolytic markers. Of note, dual inheritance patients were clinically indistinguishable from patients with hereditary spherocytosis. Additionally, their Osmoscan profiles were analyzed, which highlighted alterations of the ektacytometry curve of dual inheritance patients compared to both dehydrated hereditary stomatocytosis and hereditary spherocytosis.
Conclusion
One of the major advantages of the NGS approach is the identification of both polygenic conditions and modifier variants associated with causative mutations. Studies of Mendelian conditions have revealed the extent to which many rare diseases can be characterized by complex modes of inheritance, such as digenic inheritance and dual molecular diagnoses. Our findings expand the genotypic spectrum of red blood cell disorders and indicate that multi-locus inheritance should be considered for analysis and counseling of these patients. Of note, the genetic testing was crucial for diagnosis of patients with a complex mode of inheritance.
Keyword(s): Anemia, Diagnosis, Genetic, Red blood cell