Dehydrated hereditary stomatocytosis (DHS) (MIM#194380) is a rare autosomal dominant disorder of red blood cell permeability, characterized by a partially or fully compensated nonimmune hemolytic anemia. PIEZO1 is the major gene involved with hundreds of families described, some of which present transient perinatal edema of varying severity. A smaller subset of individuals harbors pathogenic variants in KCNN4, sometimes referred as \"Gardos channelopathy.\" Up to now, only six pathogenic variants in KCNN4 have been reported in 13 unrelated families. Unlike PIEZO1-DHS, neither perinatal edema nor fetal loss has ever been observed linked to KCNN4-DHS. We report the first fetal loss due to non-immune hydrops fetalis related to a pathogenic 28 bp deletion (NM_002250.2: c.1109_1119+17del) in KCNN4. This observation underlies the need for very close monitoring of pregnancies when one parent is affected by DHS regardless of genotype (PIEZO1 or KCNN4).

Congenital hemolytic anemia (CHA) develops not only in the neonatal period but in all age groups, from fetuses to adults. In this study, we summarized the differential diagnoses of hemolytic anemia cases with undetermined etiology in the past 5 years. In total, 319 patients with CHA were included. For cases in which autoimmune hemolytic anemia and paroxysmal nocturnal hemoglobinuria were ruled out, we performed CHA-related laboratory tests. For cases in which a definitive diagnosis of membrane and enzyme abnormalities was required, and for cases in which it was difficult to diagnose the disease type based on biochemical and cell biological tests, we used a gene panel analyzing 68 hemolytic anemia-related genes. The incidence of dehydrated hereditary stomatocytosis (DHSt) has increased since definitive diagnosis by genetic analysis became available. DHSt is now the second most frequent type of CHA. Target-captured sequencing (TCS) analysis is useful for the diagnosis of DHSt, but is a time-consuming and labor-intensive process involving the analysis of a large amount of data generated by the next-generation sequencer. In order to overcome this limitation, simpler and faster laboratory testing should be developed.

Hereditary hemolytic anemias present a unique diagnostic challenge due to their wide phenotypic and genotypic spectrum. Accurate diagnosis is essential to ensure appropriate treatment. We report two cases, which presented as hemolytic anemias, but initial workup was inconclusive and they were finally diagnosed with the help of Next Generation Sequencing (Dehydrated Hereditary Stomatocytosis and Kӧln Hemoglobinopathy). The introduction of gene sequencing to aid diagnosis of these disorders is a revolutionary step forward and should be incorporated earlier in the workup of such patients.

BACKGROUND: Dehydrated hereditary stomatocytosis (DHS) or hereditary xerocytosis is a rare, autosomal dominant hemolytic anemia characterized by macrocytosis, presence of stomatocytes and dehydration of red blood cells (RBCs). The dehydration is caused by a defect in cellular cation content. The most frequent expression of the pathology is hemolytic well-compensated anemia with high reticulocyte count, a tendency to macrocytosis, increased mean corpuscular hemoglobin concentration (MCHC) and mild jaundice. We here describe a new mutation of PIEZO1 gene, the most frequent mutated gene in DHS, in a family affected by hereditary hemolytic anemia.
METHODS: We describe the case of a 12-years-old girl with well-compensated chronic hemolysis, increased MCHC and a father who had the same hematological characteristics. After excluding secondary causes of chronic hemolysis and enzymatic defects of the RBCs, microscopic observation of the peripheral blood smear, tests of RBC lysis, ektacytometry, SDS-PAGE and in last instance genetic analysis has been performed. This complex diagnostic workup identified a new variant in the PIEZO1 gene, never described in literature, causative of DHS. This pathogenetic variant was also detected in the father.
CONCLUSIONS: This case report highlights the importance of a correct and exhaustive diagnostic-workup in patients with clinical suspicious for hemolytic anemia in order to make a differential diagnosis. This is relevant for the management of these patients because splenectomy is contraindicated in DHS due to high thrombotic risk.

Severe iron overload is frequent in dehydrated hereditary stomatocytosis (DHSt) despite well-compensated hemolysis and no or little transfusion requirement. We investigated 4 patients with proven DHSt, in whom the degree of hemolysis was closely related to iron status. Genetic modifiers increasing iron stores (HFE:pCys282Tyr, HAMP:c-153C>T mutations) were accompanied with high liver iron concentrations and increased hemolysis, whereas therapeutic phlebotomies alleviated the hemolytic phenotype. There were no manifestations of hemolysis in one patient with low iron stores. Hemolysis reappeared when iron supplementation was given. The search for genetic or acquired modifiers of iron status and the modulation of iron stores may help in the management of these patients.

PIEZO1 is a large mechanosensitive ion channel protein. Diseases associated with PIEZO1 include autosomal recessive generalised lymphatic dysplasia of Fotiou (GLDF) and autosomal dominant dehydrated hereditary stomatocytosis with or without pseudohyperkalemia and/or perinatal oedema (DHS). The two disorders show overlapping features, fetal hydrops/perinatal oedema have been reported in both. Electrophysiological studies suggest opposite mechanisms of action: the mutations identified in GLDF patients cause a loss-of-function mechanism of disease and mutations in DHS patients cause gain of function. This raises the question: Is the pathogenic disease mechanism behind the fetal oedema the same in the two phenotypes? In this Symposium Review, we will discuss the two conditions and highlight key questions that remain to be answered. For instance, the perinatal oedema often resolves soon after birth and we are still at a loss to understand why. Are there any mechanisms which could compensate for the faulty PIEZO1 in these patients? Are there physiological changes at birth that are less reliant on the function of PIEZO1? Thus, there is a clear need for further studies into the two disorders, in order to fully understand the role of PIEZO1 in health and disease.