Caroline Garcia

Rapid and reliable β-globin gene cluster haplotyping of sickle cell disease patients by FRET Light Cycler and HRM assays

BACKGROUND β-Globin haplotypes are important to predict the clinical development of patients suffering from sickle cell disease (SCD). Five main haplotypes (Benin, Bantu, Senegal, Cameroon and Arabic-Indian) are defined for β(S) chromosomes and their determination usually requires the genotyping by restriction fragment length polymorphism (RFLP) of six to eight single nucleotide polymorphisms (SNPs). However, RFLP is time-consuming and can lead to a misdiagnosis in case of a supplementary SNP on the restriction sequence. We propose a rapid β-globin haplotyping method using fluorescence resonance transfer (FRET) and high resolution melting (HRM) assays. METHODS We have settled a fluorescence resonance energy transfer (FRET) assay for HincII ε, XmnI, HindIII (G)γ, HindIII (A)γ, HincII δ and a high resolution melting (HRM) assay for HincII ψβ. These six SNPs are sufficient in most cases to determine the β(S) haplotype. RESULTS Our methodology allowed us to successfully determine the β-globin haplotypes of 139 patients suffering from sickle cell disease. For some β(S) / β(0)-patients, a supplementary SNP has been identified on the HindIII (G)γ restriction sequence leading to a false-negative RFLP result. CONCLUSION Combination of FRET and HRM assays is a rapid and reliable method for the β-globin gene cluster haplotyping.

A Novel Deletion/Insertion Caused by a Replication Error in the β-Globin Gene Locus Control Region

Deletions in the β-globin locus control region (β-LCR) lead to (εγδβ)0-thalassemia [(εγδβ)0-thal]. In patients suffering from these rare deletions, a normal hemoglobin (Hb), phenotype is found, contrasting with a hematological thalassemic phenotype. Multiplex-ligation probe amplification (MLPA) is an efficient tool to detect β-LCR deletions combined with long-range polymerase chain reaction (PCR) and DNA sequencing to pinpoint deletion breakpoints. We present here a novel 11,155 bp β-LCR deletion found in a French Caucasian patient which removes DNase I hypersensitive site 2 (HS2) to HS4 of the β-LCR. Interestingly, a 197 bp insertion of two inverted sequences issued from the HS2-HS3 inter-region is present and suggests a complex rearrangement during replication. Carriers of this type of thalassemia can be misdiagnosed as an α-thal trait. Consequently, a complete α- and β-globin gene cluster analysis is required to prevent a potentially damaging misdiagnosis in genetic counselling.

Characterization of three new deletions in the β-globin gene cluster during a screening survey in two French urban areas.

BACKGROUND Deletions represent about 5% of the mutations in the β-globin gene cluster. We report here the screening for such deletions in the two French urban areas of Paris and Lyon between 2003 and 2010. METHODS Semi-quantitative PCR methods were used for the first screening of deletions. Thereafter, a specific gap-PCR, eventually followed by DNA sequencing, was used for precise identification. RESULTS 285 patients bore a deletion or recombination event in the β-globin gene cluster. Hbs Lepore or anti-Lepore were detected in 99 patients. Among the remaining 186 patients, 132 bore a deletion that could be fully identified. The most prevalent deletions were the Ghanaian HPFH-2 (n=46), the Sicilian (δβ)(0)-thal (n=22) and the Spanish (δβ)(0)-thal (n=12). The other characterized deletions were the: HPFH-3, HPFH-1, Filipino, Senegalese, Corfu, Kabilian, -1.39 kb, Indian -619 bp and -468 bp. Interestingly, three new deletions were fully characterized: a -7719 bp deletion, a -27,825 bp deletion with a 25 bp insertion and a -125 bp deletion. CONCLUSIONS The present study emphasizes the importance to detect deletions in the β-globin gene cluster, particularly for at risk couples. The new -27,825 bp deletion illustrates the complexity to understand the transcriptional regulation of fetal to adult hemoglobin switch.

Protein characterization by LC–MS/MS may be required for the DNA identification of a fusion hemoglobin: The example of Hb P-Nilotic

DNA analysis is currently the easiest way to identify a hemoglobin variant in most cases. Nevertheless, in case of complex gene rearrangements, mass spectrometry studies may be required to orientate the DNA diagnosis. The present report shows the use of mass spectrometry techniques prior to DNA analysis for the identification of the rare P-Nilotic fusion hemoglobin. Complete protein analysis is performed by liquid chromatography-tandem mass spectrometry on the abnormal globin chain isolated by reversed-phase liquid chromatography.

Two New δ-Globin Gene Variants: Hb A2-Saint-Etienne [δ14(A11)Leu→Pro (HBD: c.44T>C)] and Hb A2-Marseille [δ22(B4) Ala→Lys (HBD: c.67G>A;68C>A)]

We report two new variants of the δ-globin gene: Hb A2-Saint-Etienne [δ14(A11)Leu→Pro] and Hb A2-Marseille [δ22(B4)Ala→Lys]. The first variant has a low rate of expression, the second results from a double nucleotide mutation on the same codon.

Two new hemoglobin variants: Hb Aix-Les-Bains [β5(A2)Pro→Leu; HBB:c.17 C>T] and Hb Dubai [α122(H5)His→Leu (α2); HBA2:c.368 A>T].

We report two new hemoglobin (Hb) variants; one causing an impairment of the N-terminal glycation of the β-globin chain and the other a hematological phenotype of α-thalassemia (α-thal). The first variant is Hb Aix-les-Bains [β5(A2)Pro→Leu] and the second Hb Dubai [α122(H5)His→Leu (α2)]. These two new Hb variants were detected by chromatographic and electrophoretic methods and characterized by molecular studies. Hb Dubai gives an α-thalassemic phenotype and should be routinely detected for preventing severe Hb H disease in couples at-risk for α-thal.

Two New α-Thalassemia Point Mutations that are Undetectable by Biochemical Techniques

We report two new point mutations causing α-thalassemia (α-thal) that could not be characterized by conventional biochemical studies. The first mutation is a single base substitution at codon 123 of the α1-globin gene [α123(H6)Ala→Pro, GCC>CCC (α1)] and leads to the substitution of a proline residue in the H helix. The resulting unstable hemoglobin (Hb) variant has been named Hb Voreppe. The second is a frameshift of the α2 gene due to a deletion (−C), either of the third base of codon 112 or of the first base of codon 113, that causes a premature stop codon at position 132.

A New Hemoglobin Variant: Hb Meylan [β73(E17)Asp → Phe; HBB: c.220G>T; c.221A>T] with a Double Base Mutation at the Same Codon

Abstract We report a new β-globin chain variant: Hb Meylan [β73(E17)Asp → Phe; HBB: c.220G>T; c.221A>T]. The new variant results from a double nucleotide mutation at the same codon. The possible molecular mechanisms are discussed.

Two Complex Associations of an HBD Mutation and a Rare α Hemoglobinopathy

We present two case reports in which an HBD mutation is present with a rare α hemoglobinopathy that substantially complicates the associated phenotype. In the first case, a new δ-globin variant, Hb A2-Pierre-Bénite [δ83(EF7)Gly→Arg; HBD: c.250G>C] is associated with Hb Groene Hart [α119(H2)Pro→Ser (α1); HBA1: c.358C>T], an α-thalassemic variant. In the second case, a δ+-thalassemic variant, δ4(A1)Thr→Ile; HBD: c.14C>T, is associated with a newly described deletion of the hypersensitive site 40 (HS-40) region on the α-globin gene cluster. In both patients, a δ-globin mutation was suspected because of an abnormally low Hb A2 level, whereas the α hemoglobinopathy was sought to explain the slight microcytosis and hypochromia presented by the probands.

A new Frameshift mutation on the α2-globin gene causing α⁺-thalassemia: codon 43 (TTC>-TC or TTC>T-C).

We report a new mutation on the α2-globin gene causing α+-thalassemia (α+-thal) with a deletion of a single nucleotide (T) at amino acid residue 43 [HBA2:c.130delT or HBA2:c.131delT]. This frameshift deletion gives rise to a premature termination codon at codon 47.