A New and Extensive α0 Deletion in a Brazilian Patient with Hb H Disease

Alpha thalassemias are the commonest group of hereditary hemoglobin disorders in the world, the most common cause being deletions involving the α globin genes on 16p13.3. We found a new α⁰ deletion associated with the -α^3.7 deletion in a 3-month-old brown-skinned female Brazilian patient with Hb H disease. The deletion was identified by Multiplex Ligation-dependent Probe Amplification (MLPA) using the SALSA MLPA P140 C1 HBA kit (MRC Holland, Amsterdam, Holland). An approximately 360 kb-region of DNA extending from the telomeric region of the short arm of chromosome 16 to the DECR2 gene was analyzed, and the fragments generated were compared with Coffalyser.Net. In addition to the α^3.7 deletion, an extensive trans deletion encompassing 70 to 105 kb of DNA and involving the α₂ and α₁ genes and the contiguous LUC7L and ITFG3 genes was detected (Figure 1). The 5' breakpoint of the deletion is located between the ψα₁ and the α₂ gene, while the 3' breakpoint region is between the ITFG3 and RGS11 genes. Familial analysis revealed that while the patient's father was heterozygous for the -α^3.7 deletion, her mother and oldest sister were heterozygous for the α⁰ deletion and her middle sister also had Hb H disease. A polymorphism (C > T) in the 220 probe binding region in the hybrid gene (α₂α₁) (-α^3.7 deletion) was also detected in the patient and her father, causing this probe to have a different pattern from that expected in MLPA. To our knowledge, this deletion does not have any similarities in terms of its breakpoint regions with other deletions previously described in the literature. It was named --^ATB because the family came from the town of Atibaia in the state of São Paulo in southeast Brazil. Molecular characterization of α-thalassemia deletions is essential both for correct diagnosis of carriers of these deletions and for genetic counselling so that new cases of Hb H disease or Hb Bart's Hydrops Fetalis can be prevented. The hematologic and molecular data for the family studied here are shown in Table 1.

Financial Support: FAPESP - 2014/00984-3, CNPq and CAPES / Brazil.

Figure 1. (A) Graph generated by the Coffalyser.Net software with the result for the proband. The x-axis represents the probes, and the y-axis the ratio of the signal intensity of the probes for the proband to the mean signal intensity for the normal controls. A ratio of 1 indicates the presence of both alleles, a ratio of 0.5 a loss of 1 allele and 0 the loss of that region in both alleles. (B) Schematic representation of 16p13.3. The oval represents the telomeric region, the arrows the locations of the probes and the boxes the genes. The blue line corresponds to the deleted fragment, the dotted lines denote the first and last deleted probes and the blank regions show where the breakpoints may be (adapted from MRC-Holland, 2014).

Table 1. Hematologic and molecular data for the family members.

Family	Proband (3 months)	Mother	Father	Sister (2 years)	Sister (3 years)
RBC RV: M:4,5-6,1/F: 4,2-5,4	4.55	5.81	5.39	5.50	5.07
Hb RV: M: 14-18/F: 12-16	7.75	12.1	14.8	7.6	10.4
MCH RV: 27-32	17	20.8	27.4	13.8	20.6
MCV RV: 80-99	54.1	64.2	79.6	41.5	61.4
A2 (%) VR: 1,6-4	0.78	2.13	2.80	2.40	2.80
F (%) RV: < 2	23.70	0.70	0.90	4.70	1
Hb profile	A2, F, A, Bart's + H (10%)	A2, A	A2, A	A2, A, H	A2, A
Genotype	-α3.7/--ATB	αα/--ATB	αα/-α3.7	-α3.7/--ATB	αα/--ATB

 RV: Reference values RBC: red blood cells (10⁶/mm³); Hb: hemoglobin (g/dL); MCH: mean corpuscular hemoglobin (pg); MCV: mean corpuscular   volume (fl).