Complex Modes of Inheritance in Hereditary Red Blood Cell Disorders: A Case Series Study of 155 Patients

Abstract

Hereditary erythrocytes disorders include a large group of conditions with heterogeneous molecular bases and phenotypes. We analyzed here a case series of 155 consecutive patients with clinical suspicion of hereditary erythrocyte defects referred to the Medical Genetics Unit from 2018 to 2020. All of the cases followed a diagnostic workflow based on a targeted next-generation sequencing panel of 86 genes causative of hereditary red blood cell defects. We obtained an overall diagnostic yield of 84% of the tested patients. Monogenic inheritance was seen for 69% (107/155), and multi-locus inheritance for 15% (23/155). PIEZO1 and SPTA1 were the most mutated loci. Accordingly, 16/23 patients with multi-locus inheritance showed dual molecular diagnosis of dehydrated hereditary stomatocytosis/xerocytosis and hereditary spherocytosis. These dual inheritance cases were fully characterized and were clinically indistinguishable from patients with hereditary spherocytosis. Additionally, their ektacytometry curves highlighted alterations of dual inheritance patients compared to both dehydrated hereditary stomatocytosis and hereditary spherocytosis. 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.

Keywords: PIEZO1; SPTA1; multi-locus inheritance; red blood cell defects; targeted next-generation sequencing.

Figure 1

Molecular features of patients with hereditary red blood cell disorders. (A) Pie chart showing the proportions of patients diagnosed as monogenic (single gene condition) and multi-locus diseases. The undiagnosed cases evaluated by extended targeted next-generation sequencing for hereditary anemias are also shown. (B) Bubble chart defining the lengths of the coding sequences of each hereditary anemia causative gene and their relative Residual Variation Intolerance Score (RVIS) percentiles. Low RVIS percentiles identify increased constraints (intolerance to variation). The size of each bubble represents the frequency of the mutations in each gene, as calculated by the ratio of the number of mutated alleles for each gene and the overall count of disease alleles (n = 207).

Figure 2

Hematological features and Osmoscan indices of digenic/oligogenic patients. (A) Hemoglobin (Hb) (n = 16), mean corpuscular volume (MCV) (n = 16), mean corpuscular hemoglobin (MCH) (n = 16), and ferritin/age levels in patients with dual inheritance (n = 16, patients indicated in bold in Table 2), dehydrated hereditary stomatocytosis type 1 (DHS1; n = 37), and hereditary spherocytosis (HS; n = 21). Data are medians and whiskers for 10-90 percentiles. (B). O min, EI max, and O hyper values from Osmoscan profiles of patients with dual inheritance (n = 11), DHS1 (n = 18), and HS (n = 16). Data are medians and interquartile range. °, p <0.05 (dual inheritance vs. DHS1, Student’s t test). *, p < 0.05; ***, p < 0.0001 (dual inheritance vs. DHS1). +++, p < 0.0001 (HS vs. DHS1). §§, p < 0.001 (dual inheritance vs. HS). §§§, p < 0.0001 (dual inheritance vs. HS) (Kruskal–Wallis tests, with post-hoc correction for internal comparisons by Dunn’s multiple comparison tests).