High prevalence of Southeast Asian ovalocytosis in Malays with distal renal tubular acidosis

Southeast Asian Ovalocytosis and Hemoglobinopathies in Newborns: Prevalence, Molecular, and Hematologic Analyses

OBJECTIVES

Southeast Asian ovalocytosis (SAO) is an inherited red blood cell (RBC) membrane disorder, whereas hemoglobinopathies are inherited globin gene disorders. In an area where both diseases are prevalent, the interaction between them resulting in variable hematologic parameters can be encountered. However, little is known about the genetic interaction of SAO and thalassemia. We investigated the prevalence of SAO and hemoglobinopathy genotypes among newborns in southern Thailand.

PATIENTS AND METHODS

This study was carried out on 297 newborns recruited consecutively at Naradhiwas Rajanagarindra Hospital in the south of Thailand. The SAO was identified on blood smear examination and polymerase chain reaction analysis. Thalassemia genotypes were defined. Hematologic parameters and hemoglobin (Hb) profiles were recorded and analyzed.

RESULTS

Among 297 newborns, 15 (5.1%) carried SAO, whereas 70 (23.6%) had thalassemia with 15 different thalassemia genotypes. Abnormal Hb including Hb C, Hb Q-Thailand, and Hb D-Punjab were observed in 5 newborns. It was found in the nonthalassemic newborns that RBC count, Hb, and hematocrit of the nonthalassemic newborns with SAO were significantly lower than those without SAO. The same finding was also observed in the thalassemic newborns; RBC count, Hb, and hematocrit of the thalassemic newborns with SAO were significantly lower than those without SAO. However, the mean corpuscular volume, mean corpuscular Hb, and RBC distribution width of the SAO-newborns were significantly higher.

CONCLUSIONS

Both SAO and hemoglobinopathy genotypes are common in southern Thailand. One should take this into consideration when evaluating neonatal anemia and other hematologic abnormalities. Identification of both genetic defects and long-term monitoring on the clinical outcome of this genetic interaction should be essential to understand the pathogenesis of these common genetic disorders in the region.

Coinheritance of Southeast Asian ovalocytosis and the β-thalassemia trait in a Malay family

Background

Southeast Asian ovalocytosis (SAO) is a red blood cell membrane disorder caused by a 27 base pair (bp) deletion in the SLC4A1 that transcribes to a truncated variant of band-3 glycoprotein. β-Thalassemia is another red blood cell disorder, caused by mutant alleles in the β-globin gene that lead to globin chain impairment. Both conditions occur in Southeast Asian countries, including Malaysia.

Objectives

This report describes hematological and molecular features of a patient with both SAO and β-thalassemia and her children.

Methods

A 58-year-old Malay woman presented to our clinic with dizziness, tiredness, and easy fatigability. She was mildly anaemic. Analysis of her complete blood counts and her peripheral blood smear revealed microcytic hypochromic anaemia with large numbers of macro-ovalocytes and stomatocytes.

Results

Hemoglobin and globin gene studies revealed heterozygous β-thalassemia, and further analysis demonstrated a heterozygous 27 bp deletion on the SLC4A1 gene consistent with SAO. Analysis of the patient’s offspring showed co-inheritance of β-thalassemia and SAO in her elder daughter and son, and SAO alone in another daughter.

Conclusions

High frequencies of SAO and different β-thalassemia mutations are present in the Malaysian population, thus coinheritance of SAO and β-thalassemia is not uncommon. However, this coinheritance is rarely reported, possibly because the red blood cell indices are overlooked and peripheral smear examinations are not routine.

Distal renal tubular acidosis in mice lacking the AE1 (band3) Cl-/HCO3- exchanger (slc4a1)

Mutations in the human gene that encodes the AE1 Cl(-)/HCO(3)(-) exchanger (SLC4A1) cause autosomal recessive and dominant forms of distal renal tubular acidosis (dRTA). A mouse model that lacks AE1/slc4a1 (slc4a1-/-) exhibited dRTA characterized by spontaneous hyperchloremic metabolic acidosis with low net acid excretion and, inappropriately, alkaline urine without bicarbonaturia. Basolateral Cl(-)/HCO(3)(-) exchange activity in acid-secretory intercalated cells of isolated superfused slc4a1-/- medullary collecting duct was reduced, but alternate bicarbonate transport pathways were upregulated. Homozygous mice had nephrocalcinosis associated with hypercalciuria, hyperphosphaturia, and hypocitraturia. A severe urinary concentration defect in slc4a1-/- mice was accompanied by dysregulated expression and localization of the aquaporin-2 water channel. Mice that were heterozygous for the AE1-deficient allele had no apparent defect. Thus, the slc4a1-/- mouse is the first genetic model of complete dRTA and demonstrates that the AE1/slc4a1 Cl(-)/HCO(3)(-) exchanger is required for maintenance of normal acid-base homeostasis by distal renal regeneration of bicarbonate in the mouse as well as in humans.