Hb Dartmouth (HBA2: c.200T>C): An α2-Globin Gene Associated with Hb H Disease in One Homozygous Patient.

Hb H (ß4) disease is caused by deletion or inactivation of three out of four α-globin genes. A high incidence of Hb H disease has been reported all over the world. There is a wide spectrum of phenotypic presentations, from clinically asymptomatic to having significant hepatosplenomegaly and requiring occasional or even regular blood transfusions, even more severe anemia, Hb Bart's (γ4) hydrops fetalis syndrome that can cause death in the affected fetuses late in gestation. We here present a case who was diagnosed with Hb H disease that represents a new genotype for this hereditary disorder. Hb Dartmouth is a variant caused by a missense mutation at codon 66 of the α2-globin gene (HBA2: c.200T>C), resulting in the substitution of leucine by proline. We here emphasize the importance of this point mutation involving Hb H disease and also the necessity for prenatal diagnosis (PND) for those who carry this point mutation in the heterozygous state.

A 21 Nucleotide Duplication on the α1- and α2-Globin Genes Involves a Variety of Hypochromic Microcytic Anemias, From Mild to Hb H Disease.

α-Thalassemia (α-thal) is a common genetic disorder in Iran and many parts of the world. Genetic defects in the α-globin gene cluster can result in α-thal that may develop into a clinical phenotype varying from almost asymptomatic to a lethal hemolytic anemia. Loss of one functional α gene, indicated as heterozygous α(+)-thal, shows minor hematological abnormalities. Homozygosity for α(+)- or heterozygosity for α(0)-thal have more severe hematological abnormalities due to a markedly reduced α chain output. At the molecular level, the absence of three α-globin genes resulting from the compound heterozygous state for α(0)- and α(+)-thal, lead to Hb H disease. Here we present a 21 nucleotide (nt) duplication consisting of six amino acids and 3 bp of intronic sequence at the exon-intron boundary, in both the α-globin genes, detected by direct DNA sequencing. This duplication was identified in three patients originating from two different Iranian ethnic groups and one Arab during more than 12 years. The clinical presentation of these individuals varies widely from a mild asymptomatic anemia (heterozygote in α1-globin gene) to a severely anemic state, diagnosed as an Hb H individual requiring blood transfusion (duplication on the α2-globin gene in combination with the - -(MED) double α-globin gene deletion). The third individual, who was homozygous for this nt duplication on the α1-globin gene, showed severe hypochromic microcytic anemia and splenomegaly. In the last decade, numerous α-globin mutations have demonstrated the necessity of prenatal diagnosis (PND) for α-thal, and this study has contributed another mutation as important enough that needs to be considered.

Interaction of an α-Globin Gene Triplication with ß-Globin Gene Mutations in Iranian Patients with ß-Thalassemia Intermedia.

The 3.7 kb triplicated α-globin gene (ααα(anti 3.7)) mutation has been found in most populations. It results from an unequal crossover between misaligned homologous segments in the α-globin gene cluster during meiosis. The pathophysiology and clinical severity of ß-thalassemia (ß-thal) are associated with the degree of α chain imbalance. The excess of α-globin chains plays an important role in the pathophysiology of ß-thal. When heterozygous/homozygous ß-thal coexists with an α gene numerical alteration, the clinical and hematological phenotype of thalassemia could change to mild anemia in case of an α deletion (-α/αα) or severe anemia in the case of an α triplication (αα/ααα). The coexistence of an ααα(anti 3.7) triplication is considered an important factor in the severity of ß-thal, exacerbating the phenotypic severity of ß-thal by causing more globin chain imbalance. This study shows that the ααα(anti 3.7) triplication is an important factor in the causation of ß-thal intermedia (ß-TI) in heterozygous ß-thal. This type of phenotype modification has rarely been observed and reported in the Iranian population. Here we report the coinheritance of a triplicated α-globin gene arrangement and heterozygous/homozygous ß-thal in 23 cases, presenting with a ß-TI or ß-thal major (ß-TM) phenotype. Some of these patients were considered to have a mild ß-TI phenotype as they needed no blood transfusions; some occasionally received blood transfusions in their lifetime (for example on delivery) but some are dependent on regular blood transfusions (every 20 to 40 days). Our study was focused on the importance of detecting the α-globin gene triplication in genotype/phenotype prediction in Iranian thalassemia patients.

Chromosomal aberrations in pregnancy and fetal loss: Insight on the effect of consanguinity, review of 1625 cases.

BACKGROUND: Pregnancy loss affects 10%-15% of pregnancies and is caused by several factors, maternal and fetal. Most common cause is chromosomal aneuploidy and has traditionally been detected by karyotyping product of conception and/or fetal tissue. In recent years, array comparative genomic hybridization (a-CGH) has been used because of its higher detection and lower failure rates. METHODS: DNA was extracted from 1625 products of abortion or fetal tissue. In 1,104 cases both quantitative fluorescent-polymerase chain reaction (QF-PCR) and a-CGH, and in 521 cases only a-CGH, was performed. RESULTS: The detection rate using QF-PCR and a-CGH is 20% compared to 12.7%, overall, and 15.7%, excluding failed samples, by karyotypes in our center. QF-PCR and a-CGH failed in 1.9% of cases, while the failure rate for karyotypes was 20.1%. The difference of detection and failure rates is significant (p-value < 0.001 and p-value < 0.001 respectively). Unexpectedly we also found a significant difference in frequency of imbalances in related versus unrelated couples. (χ2  = 11.4926, p-value < 0.001). CONCLUSION: It is highly likely that the pregnancy loss in consanguineous couples is caused by other genetic and immune mechanisms. It is plausible that, through the same mechanism by which single gene disorders have a higher prevalence of manifesting disease in consanguineous couples, they can cause lethal genetic disorders leading to pregnancy loss and intra-uterine fetal death (IUFD) in these couples. Our findings suggest that this is a matter for further study as it will greatly influence the approach to counseling and managing consanguineous couples with pregnancy loss.

Point mutations which should not be overlooked in Hb H disease.

BACKGROUND: Hb H disease is an alpha-thalassemia (α-thal) syndrome characterized by chronic hemolytic anemia that occurs when three of total four α-globin genes lost their function due to completely deletions or different kind of mutations. OBJECTIVE: We here described 66 patients who have been diagnosed for Hb H disease during the last five years in our center. The genotypes involving point mutations present more severe phenotype than deletional forms that make them of primary important to health management. STUDY DESIGN: Hb H subjects carry different α-globin genotypes including deletional and non-deletional mutations showing heterogenous clinical manifestations. RESULTS: The Hb H patients presenting a wide range of phenotype carried different deletional, non-deletional mutations or compound heterozygosity of them. CONCLUSION: We emphasize the importance of some point mutations responsible for more severe form of Hb H disease in Iranian population and the necessity for consideration of prenatal diagnosis (PND) in high-risk couples.

Copy number variations of six and seven α-globin genes in a family with intermedia and major thalassemia phenotypes.

BACKGROUND: Copy number variations in α-globin genes are results of unequal crossover between homologous segments in the α-globin gene cluster that misalign during the meiosis phase of the gametogenesis process. Reduction or augmentation of α-globin genes leads to imbalance of α/ß chains in hemoglobin tetramer and consequently attenuate or worsen the ß-thal clinical symptoms, respectively. OBJECTIVE: Multiplications in α-globin genes have been found in some populations, justifying unexpected severe phenotype of ß-thal carriers. STUDY DESIGN: Unexpected severe phenotype in the family members may result from coexistence of extra α-globin genes, which is an important factor in the causation of thalassemia intermedia and major in heterozygous ß-thalassemia. RESULTS: We described different multiplications in α-globin locus in an Iranian family with one, two or three extra α-globin genes (ααα/αα, αααα/αα and αααα/ααα). CONCLUSION: The excess α-globin gene/genes cause increment in ß/α chain imbalance and leads to worsening pathophysiology and clinical severity of ß-thalassemia carriers.