A 10-year-old male child who presented with nephrolithiasis due to distal renal tubular acidosis (dRTA) was found to have red blood cell (RBC) membrane defect as well. On review of literature, we found that both the conditions are caused by mutations in anion exchanger gene 1 (AE1) on chromosome 17 which is expressed on the RBC membrane and on the membrane of renal tubule alfa intercalated cell. It has now been shown that some AE1 mutations are responsible for causing autosomal-recessive dRTA. These patients should be either homozygous or double heterozygous with other AE1 mutations, one of which is the SAO (Southeast Asian ovalocytosis) mutation. In the latter situation, both the phenotypes, that is, dRTA and RBC membrane defect will coexist in the same patient.

1. A case of red cell membrane defect with distal renal tubular acidosis
presenting as recurrent nephrolithiasis

2. Apollo Medicine 2011 December
Case Report
Volume 8, Number 4; pp. 317–318
© 2011, Indraprastha Medical Corporation Ltd
A case of red cell membrane defect with distal renal tubular acidosis
presenting as recurrent nephrolithiasis
Sanjay Bafna*, Vibha Bafna**, Manoj Matnani†
, Mayur Choudhari‡
, Shweta Agarwal‡
*Senior Consultant, Paediatrician and Head of the Department, **Senior Consultant, Paediatrician and Paediatrics Hematologist-Oncologist,
†
IPNA Fellow, Paediatric Nephrology (London), Consultant Paediatric Nephrologist, ‡
Senior Regisrar and DNB Resident, Jehangir Apollo
Hospital, Pune – 411001, India.
ABSTRACT
A 10-year-old male child who presented with nephrolithiasis due to distal renal tubular acidosis (dRTA) was found to
have red blood cell (RBC) membrane defect as well. On review of literature, we found that both the conditions are
caused by mutations in anion exchanger gene 1 (AE1) on chromosome 17 which is expressed on the RBC mem-
brane and on the membrane of renal tubule alfa intercalated cell. It has now been shown that some AE1 mutations
are responsible for causing autosomal-recessive dRTA. These patients should be either homozygous or double het-
erozygous with other AE1 mutations, one of which is the SAO (Southeast Asian ovalocytosis) mutation. In the latter
situation, both the phenotypes, that is, dRTA and RBC membrane defect will coexist in the same patient.
Keywords: Anion exchanger 1 gene family, distal renal tubular acidosis (dRTA), hemolytic anemia, nephrolithiasis,
Southeast Asian ovalocytosis (SAO)
Correspondence: Dr. Sanjay Bafna, E-mail: sanjaybafna16@gmail.com; nirmitee@vsnl.com
doi: 10.1016/S0976-0016(11)60019-7
CASE HISTORY
A 10-year-old male child, born out of nonconsanguinous
marriage, from Sindhi community was brought to the casu-
alty with severe pain in abdomen and vomiting. His vitals
and all other system were normal. He also had a mild icterus
and a just palpable spleen. On past history, as a newborn, he
had indirect hyperbilirubinemia for which he required two
exchange transfusions and phototherapy. Mother and baby
were both B-positive and his G6PD levels were normal. No
cause for his hyperbilirubinemia could be ascertained. After
that he was admitted twice at the age of 7 and 8 years with
renal colic. He was found to have a left ureterovesical (UV)
junction calculus first time and right UV junction calculus
second time. He was treated conservatively and the calculus
disappeared. Mild icterus and a just palpable spleen were
noted during the second admission also.
During the present episode too, he had a renal colic and
was found to have an obstructive right calculus and multiple
bilateral nonobstructive calculi on ultrasonography (USG).
He was investigated thoroughly for the cause of repeated epi-
sodes of nephrolithiasis. His venous blood gas (VBG) had a
normal anion gap acidosis. Hence, he was diagnosed to have
a distal renal tubular acidosis. Meanwhile, his complete blood
count (CBC) showed evidence of mild hemolytic anemia with
anisopoikilocytosis and microcytic hypochromia. He had a
high reticulocyte-count and a mild indirect hyperbiliruben-
emia. He had a just palpable spleen clinically and a splenom-
egaly on USG. All this along with a history of severe neonatal
jaundice, we worked him up for hemolytic anemia. His
hemoglobin electrophoresis incidentally showed evidence
of thalassemia trait. His G6PD levels were normal. Though
his peripheral smear did not show any spherocytes or any
other abnormal shaped red blood cell (RBC) and osmotic
fragility was normal, we considered the possibility of a
RBC membrane defect. Flow cytometric analysis for RBC
membrane defect done at the National Institute of Immuno-
hematology, ICMR, Mumbai, was positive for the patient
and his father whereas the mother had thalassemia trait but
had no membrane disorder. All his other investigations for
nephrolithiasis, i.e., 24h urine for oxalate, calcium, phos-
phorus, uric acid, were normal. There was no evidence of
rickets. Serum parathyroid hormone levels were normal.
DISCUSSION
Therefore, we had a child with convincing evidence of distal
RTA with nephrolithiasis and hemolytic anemia, most
probably due to RBC membrane disorder. We reviewed litera-
turetoseeiftheseconditionscouldco-existinapatient.SLC4A1

3. 318 Apollo Medicine 2011 December; Vol. 8, No. 4 Bafna et al
© 2011, Indraprastha Medical Corporation Ltd
(solute carrier family 4 anion exchanger membrane 1) gene
on chromosome 17-q 21–22,1
codes for chloride–bicarbo-
nate anion exchanger 1 family of glycoprotein in the band 3
of the RBC membrane (eAE1). It also codes for the chloride
bicarbonate exchanger on the basolateral membrane of the
renal collecting tubules alpha intercalated cells (kAE1). The
eAE1 defect results in the morphologic changes of the RBC
while the kAE1 defect leads to distal RTA.2,3
AE1 mutations
expressed in these two different cells have distinct and
seemingly unrelated phenotypes, hereditary spherocytosis
(HS) or other forms of erythrocyte membrane defects and
dRTA.2
The largest group of mutations in human AE1 is
associated with autosomal-dominant red cell dysmorphol-
ogy (hereditary spherocytosis [HS], Southeast Asian ovalo-
cytosis [SAO]). Southeast Asian ovalocytosis is an RBC
membrane defect, seen in Southeast Asian countries such as
Philippines, Malay, Indonesia, and Thailand. RBCs in this
condition are rigid and probably protect against malaria para-
site invasion.2
It is a heterozygous condition and manifests as
neonatal hyperbilirubinemia and subsequently as a mild
hemolytic anemia. We may find the characteristic theta cells
on the peripheral smear.4
The homozygous form of SAO is not
seen, most probably because it is lethal in the fetal state itself.2
We could not find theta cells in our patient, most prob-
ably the presence of thalassemia minor may be distorting
the characteristic morphology. Southeast Asian ovalocyto-
sis is caused by the deletion of 27bp in codon 400–408
leading to a lack of nine amino acids in the protein which is
hence inactive for anion transport.2,3
The AE1 gene also codes for the protein responsible for
chloride bicarbonate exchange on the basolateral mem-
brane of the renal alpha intercalated cell. Mutations in this
gene are responsible for dRTA.2,3
Dominant HS-associatedAE1 mutations are generally not
associated with dRTA, conversely dRTA associatedAE1 muta-
tions are also not associated with HS. How can we explain this
when both disorders are caused by mutations in the same gene?3
Recent genetic studies have shown that some of the
AE1 mutations are responsible for autosomal-recessive dRTA
in countries of Southeast Asia. These patients are either
homozygous for the mutation or compound heterozygotes
of two different AE1 mutations, one of which is the SAO
mutations. AE1G701D mutation is one of the dRTA muta-
tions which when present in the compound heterozygous
form with the SAO mutation can present with both pheno-
types in the same patient. Other mutations which cause
hemolytic anemia with dRTA are V850/SAO, A858D/SAO
and ⌬V850/A858D. The mutation in the same gene that is
the AE1 gene is responsible for both these conditions but
they can co-exist in the same patient only if they are com-
pound heterozygotes for both mutations causing these
different disorders.3,7
There are case reports from Malaysia,
Papua New Guinea, Thailand, and Philippines describing
patients with recessive dRTA and red cell dysmorphology.5,6,8
We could find only one case report from our country describ-
ing two unrelated patients from Maratha Kunbi families.9
We would like to do a mutation analysis of our patient to
conclusively prove that he has indeed a dRTA and hemolytic
anemia due to RBC membrane defect phenotypes together.
ACKNOWLEDGMENTS
We express our thanks to Dr. Prasad Muglikar, Director of
Medical Services, Jehangir Hospital, Pune, for permitting
us to publish this case. We are grateful to the National
Institute of Immunohematology for doing flow cytometry
analysis for RBC membrane defect of our patient.
REFERENCES
1. SLC4A1-Genetics Home Reference. A service of the US
National Library of Medicine.
2. Wrong O, Bruce LJ, Unwin RJ, Toye AM, Tanner MJ. Band 3
mutations, distal renal tubular acidosis and Southeast Asian
ovalocytosis. Kidney Int 2002;62:10–9.
3. Pereira PC, Miranda DM, Oliveira EA, Silva AC. Molecular
pathophysiology of renal tubular acidosis. Curr Genom 2009;
10:51–9.
4. Nathan DG, Orkin SH. In: Hematology of Infancy and
Childhood 7th ed. Saunders, Elsevier.
5. Bruce LJ, Wrong O, Toye AM, et al. Band 3 mutations, renal
tubular acidosis and Southeast Asian ovalocytosis in Malaysia
and Papua New Guinea—loss of up to 95% band 3 transport
in red cell. Biochem J 2000;350:41–51.
6. Sritippayawan S, Sumboonnanonda A, Vasuvattakul S, et al.
Novel compound heterozygous SLC4A1 mutations in Thai
patients with autosomal recessive distal RTA (renal tubular
acidosis). Am J Kidney Dis 2004;44:64–70.
7. Khositseth S, Sirikanaerat A, Khoprasert S, et al. Hematological
abnormalities in patients with distal renal tubular acidosis and
hemoglobinopathies. Am J Hematol 2008;83:465–71.
8. Anacleto FE, Bruce LJ, Clayton P, et al. Distal renal tubular
acidosis in Filipino children, caused by mutations of anion-
exchanger SLC4A1 (AE Band 3) gene. Nephron Physiol
2010;114:19–24.
9. Boris E Shmuckler, Prabhakar S Kedar, et al. Hemolytic ane-
mia and distal renal tubular acidosis in two Indian patients
homozygous for SLC4A1/AE1 mutation A858D. Wileyonline
library. DOI: 10. 1002/ajh 21836. Am J Hematol 2010 [Letter
published online on 23rd July].

4. Apollohospitals:http://www.apollohospitals.com/
Twitter:https://twitter.com/HospitalsApollo
Youtube:http://www.youtube.com/apollohospitalsindia
Facebook:http://www.facebook.com/TheApolloHospitals
Slideshare:http://www.slideshare.net/Apollo_Hospitals
Linkedin:http://www.linkedin.com/company/apollo-hospitals
Blog:Blog:http://www.letstalkhealth.in/