Blood, Vol. 92 No. 7 (October 1), 1998:
pp. 2593-2594
CORRESPONDENCE
Genetic Heterogeneity of Congenital Dyserythropoietic Anemia Type
II
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LETTER |
To the Editor:
Congenital dyserythropoietic anemia type II (CDA-II, CDAN2, or HEMPAS)
(MIM224100) is an autosomal recessive trait and it represents the
most frequent form of congenital dyserythropoiesis.1 It is
characterized by normocytic anemia, variable jaundice, and hepatosplenomegaly. Gallbladder disease and secondary hemochromatosis are frequent complications. Bone marrow histology shows binucleated and
multinucleated (10% to 40%) erythroblasts with karyorrehexis. Electron microscopy of these cells shows the presence of the so-called double membrane, ie, peripheral cisternae running parallel to and
beneath the plasma membrane.2 The diagnosis could be
confirmed by Positive Acidified Serum test (Ham test) and by presence
of enhanced agglutination with anti-i antibodies. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of red blood cell
membrane proteins shows a narrower aspect and a faster migration of
band 3 (anion exchange transporter), and Western blot of membrane proteins shows the presence of reticulum-endotelial proteins
(calreticulin, glucose regulated protein 78, protein disulphide
isomerase).3
Recently we have recruited a panel of well-characterized CDA II
families and used them to search for CDA II gene by linkage analysis.
We first excluded three candidate genes (
-Mannosidase II,
-Mannosidase x, and N-Acetylglucosaminyltransferase II) (MANA, MANAx, Gnt-II),4 and obtained conclusive evidence for
linkage of CDA II to microsatellite markers on the long arm of
chromosome 20 (20q11.2).5 Strong evidence of allelic
association with the disease was also detected with marker D20S863.
Here we describe two unrelated families in which CDA-II disease was not
linked with the CDAN2 locus, demonstrating for the first time the
presence of genetic heterogeneity.
The first family comes from a little town on the Ionian sea (southern
Italy). The parents could be related because three of the grandparents
had the same family name. The propositus was born in 1982; at 3 days of
age a severe icterus demanded an exchange transfusion. A
severe thrombocytopenia was observed. During the next years anemia
(range, 61 to 92 g/L) seldom required transfusions and the platelet
count was always low (15 to 50 × 109/L). Bone marrow
observation and electronic microscopy showed the characteristic feature
of CDA-II associated with severe reduction of megakaryocytes, which did
not show double membranes. Analysis of SDS-PAGE of red blood cell
membrane protein and the Western blot showed the characteristic feature
of CDA-II.3
The second family comes from Lecce province (southern Italy) and it
consisted of two affected and one unaffected sibs (Fig 1). The mother and the sons (II-2 and II-3)
had 
-thalassemic trait. The probands' (II-1 and II-2) anemia was
documented since the newborn period when jaundice required
exchange-transfusion. During infancy and childhood the patients
received an unknown number of red blood cell transfusions, until
splenectomy. Physical examination showed moderate hepatomegaly. After
splenectomy the affected brothers had a very mild anemia requiring one
transfusion only during an episode of infection. Bone marrow
observation showed characteristic pattern of CDA-II as well as SDS-PAGE
and Western blotting.
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| Fig 1.
Allele segregation for microsatellite markers in two
CDA-II families (1 and 2): the solid squares indicate the affected
individuals. The microsatellite markers are tightly linked to the
following genes: MANA, mapping on chromosome 5 (5q2.1-2.2); MANAx
isozyme, mapping on chromosome 15q25; Gnt-II mapping on chromosome
14q21 and CDAN2 mapping on chromosome 20q11.2.
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Linkage analysis by means of microsatellite markers localized at long
arm of chromosome 20 performed in these families showed that the CDA-II
locus was not linked to chromosome 20 (Fig 1). As a matter of fact,
there is no segregation of alleles of each marker with the disease.
Furthermore, in literature a reduced activity of Gnt-II has been shown
in two cases and of MANA in another CDA-II case.6,7 Since it was suggested that these alterations could be directly involved in CDA-II, we performed a linkage analysis with these genes.
For this purpose, highly informative markers located at the same
chromosomal region where MANA-II and Gnt-II genes mapped were used as previously described.4 Negative results
obtained indicated that none of the investigate regions contains
the gene involved in determining CDA-II in these families (Fig
1).
The CDA-II anemia is often mild to moderate but may be severe and,
rarely, causes fetal distress. Approximately 300 cases are present in
the literature, but the prevalence of this disorder is almost certainly
higher because it is likely that many asymptomatic cases with little or
no anemia are underdiagnosed.1 The clinical heterogeneity
could be caused by genetic heterogeneity or by the association with
another red blood cell disorder (ie, -talassemia). The presented
clinical cases are severe forms. In one case -thalassemia could
account for the increased clinical feature; in the other case no other
red blood cell abnormality was demonstrated, but the coinheritance of
thrombocytopenia in a consanguineous tree suggested the presence of two
hematopoietic defects. CDA-II diagnosis was confirmed by bone marrow
observation, electron microscopy, and laboratory data. From the
biochemical point of view the disease appears very homogeneous. All the
subjects showed the characteristic pattern of SDS-PAGE and the presence
of reticulum endotelial proteins exposed on the surface. These two new
families demonstrated for the first time that in these severe cases,
although in the presence of an identical biochemical pattern, the
disease is caused by a different gene and, thus, that
genetic heterogeneity is present. Moreover, the biochemical defect most
likely could present into a different step of the same pathway. A
complementation assay could confirm this data.
Achille Iolascon
Domenico De Mattia
Dipartimento di Biomedicina
dell'Età Evolutiva
Università di
Bari
Bari, Italy
Silverio Perrotta
Dipartimento di
Pediatria
II Università Napoli
Napoli, Italy
Massimo Carella
Paolo Gasparini
Servizio di Genetica
Medica
IRCCS-CSS
San Giovanni Rotondo (Fg),
Italy
Giorgio Lambertenghi Deliliers
Istituto di
Scienze Mediche
Università di Milano
Milano, Italy
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ACKNOWLEDGMENT |
We thank the families who collaborated in this work. This work is
supported in part by Ministero Italiano della Sanita' (to P.G.) and by
Telethon (to A.I.) project E-645.
| |
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