Background: Approximately 80% of the a-and 10% of the b-thalassaemias are caused by genomic deletions involving the a-and b-globin gene clusters on chromosomes 16p13.3 and 11p15.5, respectively. Gap-PCR, Southern blot analysis, and fluorescent in situ hybridisation are commonly used to identify these deletions; however, many deletions go undetected using conventional techniques. Methods: Patient samples for which no abnormalities had been found using conventional DNA techniques were analysed by a three colour multiplex ligation-dependent probe amplification assay. Two sets of 35 and 50 probes, covering a region of 700 kb of the a-and 500 kb of the b-globin gene cluster, respectively, were designed to detect rearrangements in the a-and b-globin gene clusters. Results: In 19 out of 38 patient samples, we found 11 different a-thalassaemia deletions, six of which were not previously described. Two novel deletions leaving the a-globin gene cluster intact were found to cause a complete downregulation of the downstream a-genes. Similarly, 31 out of 51 patient samples were found to carry 10 different deletions involving the b-globin gene cluster, three of which were not previously described. One involves the deletion of the locus control region leaving the b-globin gene cluster intact. Conclusions: These deletions, which are not easily detected by conventional techniques, may have clinical implications during pregnancy ranging from mild to life threatening microcytic haemolytic anaemia in neonates. The approach as described here is a rapid and sensitive method for high resolution analysis of the globin gene clusters and for any region of the genome.
Hb Groene Hart [alpha119(H2)Pro-->Ser, CCT-->TCT (alpha1)] has been reported in heterozygotes of Moroccan origin and also in association with the common -alpha(3.7) deletion. In all cases, the mutated protein was not detectable but was apparently associated with a mild alpha-thalassemia (thal) phenotype, presumably due to a modification of the alpha-globin chain domain that is recognized by the a hemoglobin stabilizing protein (AHSP). The present case of Hb Groene Hart homozygosity, confirms that the alpha-thal phenotype is associated with this alpha-globin chain. Hb Groene Hart must be quite frequent not only in Morocco but probably also among the northern African coastal population.
We present a family of North European extraction referred for a refractory non iron depleted microcytic anemia. The proband, a 36 year-old male, presented with chronic borderline anemia and microcytic hypochromic parameters. No abnormal hemoglobin (Hb) fractions were observed on high performance liquid chromatography (HPLC) or on alkaline electrophoresis. Gap-polymerase chain reaction (gap-PCR) excluded the seven common alpha-thalassemia (thal) deletion defects. However, the beta/alpha-globin chain synthesis ratio measured in vitro was unbalanced, indicating a reduced expression of the alpha-globin genes. Direct sequencing of the alpha-globin genes revealed heterozygosity for a T --> A transversion at the IVS-II-2 position of the alpha2 gene. This is the first IVS-II splice donor site mutation described on the alpha2-globin gene.
We have characterized a new abnormal hemoglobin (Hb) at position 32 of the alpha-globin chain. The proband, a 38-year-old woman of Surinamese Black ancestry, was referred to the Academic Hospital in Amsterdam, The Netherlands, after 3 years of Prednisone treatment in Surinam. Kidney failure was diagnosed at the Nephrology Department, Free University Medical Center, Amsterdam, The Netherlands; the cortisone treatment was interrupted and dialysis was started. At this stage, a microcytic hypochromic anemia was observed with high reticulocyte (40%) and ferritin (500 microg/L) levels, and hemoglobinopathy was suspected. No abnormal bands were visible on alkaline electrophoresis and high performance liquid chromatography (HPLC). The Hb A2 level was normal (2.7%) and the erythrocyte count was low (3.59 x 10(12)/L) with a normal haptoglobin level (68 mg/100 mL). None of the common alpha-thalassemia (thal) deletion defects were present. The beta-globin gene sequence was normal but the alpha2-globin gene sequence revealed an ATG-->ATA transition at codon 32, changing the methionine into an isoleucine residue. The mutation, called Hb Amsterdam, was observed in the mother of the proband, who was also heterozygous for the--alpha3.7-thal deletion and affected by a moderate microcytic hypochromic anemia. Both Hb Amsterdam and the--alpha(-3.7) allele were found in association with a new polymorphism, IVS-I-39 (C-->T), previously observed in our laboratory in seven patients of African origin, on both the alpha1 and alpha2 genes. In addition, Hb Amsterdam was also associated with the common African alpha2 polymorphism (G-->CTCGGCCC at position 7238 and T-->G at position 7174). Hb Amsterdam is the first mutation ever described at codon alpha32, a position involved in alpha1/beta1 interaction. The possibility of a contribution of this mutation to the nephropatic state of the proband is discussed.
An abnormal hemoglobin (Hb) fraction was observed during a high performance liquid chromatographic (HPLC) Hb A1c control for diabetes mellitus in a 56-year-old north European woman. Family analyses revealed the abnormal fraction in three of her five siblings and in her son. Elevated Hb and packed cell volume (PCV) values and red blood cell (RBC) counts were present in all carriers. No histories of anemia, hemolytic or circulatory episodes were reported. The abnormal Hb fraction estimated at 40%, migrated just below Hb F on alkaline electrophoresis and overlapped the Hb A2 peak on cation exchange HPLC. Direct sequencing of the beta-globin genes revealed a new GAC --> TAC transversion in heterozygous form at codon 94 of the beta-globin gene. Based on the hematological/biochemical data and the decreased P50 value, we conclude that the new variant is a stable Hb associated with a slightly elevated oxygen affinity.
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