Development and clinical implementation of a combination deletion PCR and multiplex ligation-dependent probe amplification assay for detecting deletions involving the human α-globin gene cluster

Detection of α-thalassemia South-East Asian deletion based on a fully integrated digital polymerase chain reaction system DropXpert S6

OBJECTIVES

This study aimed to establish a droplet digital polymerase chain reaction (ddPCR) assay for South-East Asian (SEA) deletion based on a fully integrated digital PCR system DropXpert S6.

METHODS

A total of 151 whole blood samples, 10 chorionic villus samples, and 17 amniotic fluid samples were collected, including 106 SEA heterozygotes, 43 normal individuals, 10 Hb Bart's hydrops details, and 19 SEA deletions combined with other genotypes.Genotypes of these samples were determined by the Gap-PCR method. We perform a series of optimizations of the ddPCR system to ensure the performance of the entire ddPCR reaction, such as droplet stability, fluorescence clustering, sensitivity, and accuracy.

RESULTS

Our assay exhibited 99.4% (177/178) accuracy compared with the Gap-PCR method, and the minimum detection limit of DNA was 0.1 ng/μL.Both targets have reliable linearity, R2 = 0.9999 for the α-thalassemia SEA deletion allele and R2 = 1 for the wild-type allele. The coefficient of variation for α-thalassemia SEA deletion allele detection at 2 and 10 ng/μL concentrations was 5.42% and 1.91%, respectively. In contrast, the coefficient of variation for wild-type allele detection was 4.06% and 1.83%, demonstrating its high quantitative accuracy. In addition, the DropXpert S6 PCR system showed some advantages over other ddPCR instruments, such as reducing testing costs, simplifying and automating the workflow.

CONCLUSIONS

The DropXpert S6 PCR system provided a highly accurate diagnosis for α-thalassemia SEA deletion and can be used to detect α-thalassemia as an alternative method.

Newborn Screening for Sickle Cell Disease in Catalonia between 2015 and 2022-Epidemiology and Impact on Clinical Events

In 2015, Catalonia introduced sickle cell disease (SCD) screening in its newborn screening (NBS) program along with standard-of-care treatments like penicillin, hydroxyurea, and anti-pneumococcal vaccination. Few studies have assessed the clinical impact of introducing NBS programs on SCD patients. We analyzed the incidence of SCD and related hemoglobinopathies in Catalonia and the change in clinical events occurring after introducing NBS. Screening 506,996 newborns from 2015 to 2022, we conducted a retrospective multicenter study including 100 screened (SG) and 95 unscreened (UG) SCD patients and analyzed SCD-related clinical events over the first six years of life. We diagnosed 160 cases of SCD, with an incidence of 1 in 3169 newborns. The SG had a significantly lower median age at diagnosis (0.1 y vs. 1.68 y, p < 0.0001), and initiated penicillin prophylaxis (0.12 y vs. 1.86 y, p < 0.0001) and hydroxyurea treatment earlier (1.42 y vs. 4.5 y, p < 0.0001). The SG experienced fewer median SCD-related clinical events (vaso-occlusive crisis, acute chest syndrome, infections of probable bacterial origin, acute anemia requiring transfusion, acute splenic sequestration, and pathological transcranial Doppler echography) per year of follow-up (0.19 vs. 0.77, p < 0.0001), a reduced number of annual emergency department visits (0.37 vs. 0.76, p < 0.0001), and fewer hospitalizations (0.33 vs. 0.72, p < 0.0001). SCD screening in Catalonia's NBS program has effectively reduced morbidity and improved affected children's quality of life.

Diagnosis and screening of abnormal hemoglobins

Hemoglobin (Hb) abnormalities, such as thalassemia and structural Hb variants, are among the most prevalent inherited diseases and are associated with significant mortality and morbidity worldwide. However, there were not comprehensive reviews focusing on different clinical analytical techniques, research methods and artificial intelligence (AI) used in clinical screening and research on hemoglobinopathies. Hence the review offers a comprehensive summary of recent advancements and breakthroughs in the detection of aberrant Hbs, research methods and AI uses as well as the present restrictions anddifficulties in hemoglobinopathies. Recent advances in cation exchange high performance liquid chromatography (HPLC), capillary zone electrophoresis (CZE), isoelectric focusing (IEF), flow cytometry, mass spectrometry (MS) and polymerase chain reaction (PCR) etc have allowed for the definitive detection by using advanced AIand portable point of care tests (POCT) integrating with smartphone microscopic classification, machine learning (ML) model, complete blood counts (CBC), imaging-based method, speedy immunoassay, and electrochemical-, microfluidic- and sensing-related platforms. In addition, to confirm and validate unidentified and novel Hbs, highly specialized genetic based techniques like PCR, reverse transcribed (RT)-PCR, DNA microarray, sequencing of genomic DNA, and sequencing of RT-PCR amplified globin cDNA of the gene of interest have been used. Hence, adequate utilization and improvement of available diagnostic and screening technologies are important for the control and management of hemoglobinopathies.

The role of molecular diagnostic testing for hemoglobinopathies and thalassemias

Hemoglobin disorders are among the most common genetic diseases worldwide. Molecular diagnosis is helpful in cases where the diagnosis is uncertain and for genetic counseling. Protein-based diagnostic techniques are frequently adequate for initial diagnosis. Molecular genetic testing is pursued in some cases, particularly when a definitive diagnosis is not possible and especially for the purpose of assessing genetic risk for couples wanting to have children. The expertise available in the clinical hematology laboratory is essential for the diagnosis of patients with hemoglobin abnormalities. Initial diagnoses are made using protein-based techniques such as electrophoresis and chromatography. Based on these findings, genetic risk to an individual's offspring can be assessed. In the setting of β-thalassemia and other β-globin disorders, coincident α-thalassemia may be difficult to diagnose, which can have potentially serious consequences. In addition, unusual forms of β-thalassemia caused by deletions in the β-globin locus cannot be definitively characterized using standard techniques. Molecular diagnostic testing has an important role in the diagnosis of hemoglobin disorders and is important in the setting of genetic counseling. Molecular testing also has a role in prenatal diagnosis to identify fetuses affected by severe hemoglobinopathies and thalassemias.

εγ-Thalassemia, a New Hemoglobinopathy Category

BACKGROUND

Large β-globin gene cluster deletions (hereditary persistence of fetal hemoglobin [Hb] or β-, δβ-, γδβ-, and ϵγδβ-thalassemia), are associated with widely disparate phenotypes, including variable degrees of microcytic anemia and Hb F levels. When present, increased Hb A2 is used as a surrogate marker for β-thalassemia. Notably, ϵγδβ-thalassemias lack the essential regulatory locus control region (LCR) and cause severe transient perinatal anemia but normal newborn screen (NBS) results and Hb A2 levels. Herein, we report a novel deletion of the ϵ, Aγ, Gγ, and ψβ loci with intact LCR, δ-, and β-regions in 2 women and newborn twins.

METHODS

Capillary electrophoresis (CE), high-performance liquid chromatography (HPLC), DNA sequencing, multiplex ligation-dependent probe amplification (MLPA), gap-polymerase chain reaction (gap-PCR), and long-read sequencing (LRS) were performed.

RESULTS

NBS showed an Hb A > Hb F pattern for both twins. At 20 months, Hb A2 was increased similarly to that in the mother and an unrelated woman. Unexplained microcytosis was absent and the twins lacked severe neonatal anemia. MLPA, LRS, and gap-PCR confirmed a 32 599 base pair deletion of ϵ (HBE1) through ψβ (HBBP1) loci.

CONCLUSIONS

This deletion represents a hemoglobinopathy category with a distinct phenotype that has not been previously described, an ϵγ-thalassemia. Both the NBS Hb A > F pattern and the subsequent increased Hb A2 without microcytosis are unusual. A similar deletion should be considered when this pattern is encountered and appropriate test methods selected for detection. Knowledge of the clinical impact of this new category will improve genetic counselling, with distinction from the severe transient anemia associated with ϵγδβ-thalassemia.

The need to perform α-thalassemia genetic testing in Italian patients with β-thalassemia trait: A case report

Here, we describe a case report of a Sardinian woman diagnosed as pure beta-thalassemia carrier for her anemia who underwent to alpha-thalassemia genetic testing that revealed she was heterozygous for both thalssemias. This allowed to reach a conclusive diagnosis useful for family counseling and for assess the reproductive risk.

Improved Characterization of Complex β-Globin Gene Cluster Structural Variants Using Long-Read Sequencing

Complex insertion-deletion (indel) events in the globin genes manifest in widely variable clinical phenotypes. Many are incompletely characterized because of a historic lack of efficient methods. A more complete assessment enables improved prediction of clinical impact, which guides emerging therapeutic choices. Current methods have limited capacity for breakpoint assignment and accurate assessment of mutation extent, especially in cases containing duplications or multiple deletions and insertions. Technology, such as long-read sequencing, holds promise for significant impact in the characterization of indel events because of read lengths that span large regions, resulting in improved resolution. Four known complex β-globin gene cluster indel types were assessed using single-molecule, real-time sequencing technology and showed high correlation with previous reports, including the Caribbean locus control deletion (g.5,305,478_5,310,336del), a large β-gene duplication containing the Hb S mutation (g.4,640,335_5,290,171dup with g.5,248,232T>A, c.20A>T; variant allele fraction, 64%), and two nested variants (double deletions with intervening inversion): the Indian ^Gγ(^Aγδβ)⁰-thalassemia (g.5,246,804-5,254,275del, g.5,254,276_5,269,600inv, and g.5,269,601_5,270,442del) and the Turkish/Macedonian (δβ)⁰ thalassemia (g.5,235,064_5,236,652del, g.5,236,653_5,244,280inv, and g.5,244,281_5,255,766del). Our data confirm long-read sequencing as an efficient and accurate method to identify these clinically significant complex events. Limitations include high-complexity sample preparation requirements, which hinder routine use in clinical laboratories. Continued improvements in sample and data workflow processes are needed to accommodate volumes in a tertiary clinical laboratory.

Analysis of rare thalassemia caused by HS-40 regulatory site deletion

ABSTRACT Objectives: To investigate the effect of HS-40 regulatory site deletion on α-globin gene expression and its clinical significance. Methods: Venous blood samples of subjects were analyzed using a hematology analyzer and high- performance liquid chromatography; fetal cord blood was analyzed by a capillary electrophoresis analyzer. Gap-polymerase chain reaction (PCR), reverse dot blot (RDB), and multiple-link-dependent probe amplification (MLPA) were used for genotyping of thalassemia. Results: The proband was POLR3 K, HS-40 heterozygous deletion; the proband's wife was -SEA/αα; the fetus was POLR3 K, HS-40 heterozygous deletion combined with -SEA deletion; all of them had microcytic hypochromic anemia. Fetal umbilical cord blood electrophoresis revealed a suspected Hb Bart's band to be 88.4%, and the fetus was, thus, diagnosed as Hb Bart's fetus. The red blood cell parameters of the sporadic case showed that he had microcytic hypochromic anemia. Hemoglobin (Hb) electrophoresis analysis showed Hb H to be 5.3%, leading to a diagnosis of Hb H disease. Gap-PCR and RDB identified the genotype to be -α3.7/αα, β^A/β^A. MLPA detected heterozygous deletion or -α3.7 deletion on one allele and deletion of the HS-40 regulatory site on the other allele. Conclusion: The deletion of HS-40 regulatory site reduced expression of α-globin. HS-40 heterozygous deletion manifested as mild anemia, which was of microcytic hypochromic type. When compounded with -α3.7/αα, it manifested as Hb H disease; and when compounded with -SEA/αɑ, it manifested as Hb Bart's fetus.

Further Characterization of Hb Bronovo [α103(G10)His→Leu; HBA2: c.311A>T] and First Report of the Homozygous State

Hb Bronovo [α103(G10)His→Leu, HBA2: c.311A>T] is an α-globin variant that interferes with and decreases binding efficiency to α hemoglobin (Hb) stabilizing protein (AHSP), a chaperone molecule. The histidine residue at position 103 is integral to the AHSP hydrogen bond formation where disruption results in an increased quantity of cytotoxic free α-globin chains, thereby creating a similar pathophysiology as β-thalassemia (β-thal). We report a family with Hb Bronovo, including a homozygous proband, which resulted from maternal uniparental disomy (UPD). Although not detected by routine studies in previous reports, the variant protein is visible by intact mass spectrometry (MS).

Characterization of two novel Alu element-mediated α-globin gene cluster deletions causing α0-thalassemia by targeted next-generation sequencing

α-thalassemia is an inherited blood disorder commonly caused by deletions or point mutations involving one or both α-globin genes. Recent studies shed new light on the critical role of upstream enhancers multi-species conserved sequences (MCSs) in the ordered regulation of α-globin gene expression. Herein, we reported two unrelated probands with deletions in α-globin genes and MCSs, respectively. The proband from Family A is a compound heterozygote carrying a known α⁺ mutation (-α^3.7) and a novel 60.2 kb deletion causing the absence of both α-globin genes. The proband from Family B, on the other hand, is a compound heterozygote with a known α⁰ mutation (--^SEA) and a novel deletion involving only upstream regulatory elements MCS-R1, R2 and R3, while the α-globin genes remain intact. Notably, both these two patients suffered varied extent of anemia, indicating that the loss of enhancer elements could equally lead to reduced synthesis of α-globin. Upon these observations, we then confirmed the exact breakpoints of these two novel deletions using a targeted next-generation sequencing (NGS) previously established by our group, which may enable further elucidation of the rearrangement mechanisms on these deletions and functional dissection of MCSs. Taken together, our study reports a reliable NGS-based molecular screening approach for accurate identification of copy number variations (CNVs) in the α-globin cluster and the genetic diagnosis of these two probands may help to extend the spectrum of α-thalassemia mutations in Chinese population.

A novel perspective on MOL-PCR optimization and MAGPIX analysis of in-house multiplex foodborne pathogens detection assay

Multiplex oligonucleotide ligation-PCR (MOL-PCR) is a rapid method for simultaneous detection of multiple molecular markers within a single reaction. MOL-PCR is increasingly employed in microbial detection assays, where its ability to facilitate identification and further characterization via simple analysis is of great benefit and significantly simplifies routine diagnostics. When adapted to microsphere suspension arrays on a MAGPIX reader, MOL-PCR has the potential to outperform standard nucleic acid-based diagnostic assays. This study represents the guideline towards in-house MOL-PCR assay optimization using the example of foodborne pathogens (bacteria and parasites) with an emphasis on the appropriate choice of crucial parameters. The optimized protocol focused on specific sequence detection utilizes the fluorescent reporter BODIPY-TMRX and self-coupled magnetic microspheres and allows for a smooth and brisk workflow which should serve as a guide for the development of MOL-PCR assays intended for pathogen detection.

Molecular Diagnosis of Thalassemias and Hemoglobinopathies: An ACLPS Critical Review

OBJECTIVES

To describe the use of molecular diagnostic techniques for patients with hemoglobin disorders.

METHODS

A clinical scenario is presented in which molecular diagnosis is important for genetic counseling. Globin disorders, techniques for their diagnosis, and the role of molecular genetic testing in managing patients with these disorders are described in detail.

RESULTS

Hemoglobin disorders, including thalassemias and hemoglobinopathies, are among the commonest genetic diseases, and the clinical laboratory is essential for the diagnosis of patients with these abnormalities. Most disorders can be diagnosed with protein-based techniques such as electrophoresis and chromatography. Since severe syndromes can result due to inheritance of combinations of globin genetic disorders, genetic counseling is important to prevent adverse outcomes. Protein-based methods cannot always detect potentially serious thalassemia disorders; in particular, α-thalassemia may be masked in the presence of β-thalassemia. Deletional forms of β-thalassemia are also sometimes difficult to diagnose definitively with standard methods.

CONCLUSIONS

Molecular genetic testing serves an important role in identifying individuals carrying thalassemia traits that can cause adverse outcomes in offspring. Furthermore, prenatal genetic testing can identify fetuses with severe globin phenotypes.

Diagnostic approaches for inherited hemolytic anemia in the genetic era

Inherited hemolytic anemias (IHAs) are genetic diseases that present with anemia due to the increased destruction of circulating abnormal RBCs. The RBC abnormalities are classified into the three major disorders of membranopathies, hemoglobinopathies, and enzymopathies. Traditional diagnosis of IHA has been performed via a step-wise process combining clinical and laboratory findings. Nowadays, the etiology of IHA accounts for germline mutations of the responsible genes coding for the structural components of RBCs. Recent advances in molecular technologies, including next-generation sequencing, inspire us to apply these technologies as a first-line approach for the identification of potential mutations and to determine the novel causative genes in patients with IHAs. We herein review the concept and strategy for the genetic diagnosis of IHAs and provide an overview of the preparations for clinical applications of the new molecular technologies.

Invasive prenatal diagnosis of fetal thalassemia

Thalassemia is the most common monogenic inherited disease worldwide, affecting individuals originating from many countries to various extents. As the disease requires long-term care, prevention of the homozygous state presents a substantial global disease burden. The comprehensively preventive programs involve carrier detections, molecular diagnostics, genetic counseling, and prenatal diagnosis. Invasive prenatal diagnosis refers to obtaining fetal material by chorionic villus sampling (CVS) at the first trimester, and by amniocentesis or cordocentesis at the second trimester. Molecular diagnosis, which includes multiple techniques that are aimed at the detection of mutations in the α- or β-globin genes, facilitates prenatal diagnosis and definitive diagnosis of the fetus. These are valuable procedures for couples at risk, so that they can be offered options to have healthy offspring. According to local practices and legislation, genetic counseling should accompany the invasive diagnostic procedures, DNA testing, and disclosure of the results. The most critical issue in any type of prenatal molecular testing is maternal cell contamination (MCC), especially when a fetus is found to inherit a particular mutation from the mother. The best practice is to perform MCC studies on all prenatal samples. The recent successful studies of fetal DNA in maternal plasma may allow future prenatal testing that is non-invasive for the fetus and result in significant reduction of invasive diagnostic procedures.

Characterization of Deletions of the HBA and HBB Loci by Array Comparative Genomic Hybridization

Thalassemia is among the most common genetic diseases worldwide. α-Thalassemia is usually caused by deletion of one or more of the duplicated HBA genes on chromosome 16. In contrast, most β-thalassemia results from point mutations that decrease or eliminate expression of the HBB gene on chromosome 11. Deletions within the HBB locus result in thalassemia or hereditary persistence of fetal Hb. Although routine diagnostic testing cannot distinguish thalassemia deletions from point mutations, deletional hereditary persistence of fetal Hb is notable for having an elevated HbF level with a normal mean corpuscular volume. A small number of deletions accounts for most α-thalassemias; in contrast, there are no predominant HBB deletions causing β-thalassemia. To facilitate the identification and characterization of deletions of the HBA and HBB globin loci, we performed array-based comparative genomic hybridization using a custom oligonucleotide microarray. We accurately mapped the breakpoints of known and previously uncharacterized HBB deletions defining previously uncharacterized deletion breakpoints by PCR amplification and sequencing. The array also successfully identified the common HBA deletions --(SEA) and --(FIL). In summary, comparative genomic hybridization can be used to characterize deletions of the HBA and HBB loci, allowing high-resolution characterization of novel deletions that are not readily detected by PCR-based methods.

Detection of α-Thalassemia by Using Multiplex Ligation-Dependent Probe Amplification as an Additional Method for Rare Mutations in Southern Turkey

α-thalassemia is the most common single gene disorder in the Cukurova Region in Turkey. It is therefore routinely screened, including premaritally, in our region. The heterogeneous molecular basis of the disease makes α-thalassemia mutation detection difficult and complex. Besides well established methods, multiplex ligation dependent probe amplification (MLPA) is known as an effective, simple and specific method for the detection and characterization of deletions and duplications. We employed MLPA testing to 30 patients with hematological parameters suggestive of α-thalassemia carrier status but was negative for α-thalassemia with conventional reverse dot blot hybridization (RDB). We found α-globin gene deletions in 3 out of 30 (10 %) patients with MLPA. We propose that MLPA can be used as a second tier test in addition to other techniques such as RDB to identify α-thalassemia carriers in high prevalence regions such as ours, thereby allowing clinicians to provide accurate genetic counselling.

Guidelines for optimisation of a multiplex oligonucleotide ligation-PCR for characterisation of microbial pathogens in a microsphere suspension array

With multiplex oligonucleotide ligation-PCR (MOL-PCR) different molecular markers can be simultaneously analysed in a single assay and high levels of multiplexing can be achieved in high-throughput format. As such, MOL-PCR is a convenient solution for microbial detection and identification assays where many markers should be analysed, including for routine further characterisation of an identified microbial pathogenic isolate. For an assay aimed at routine use, optimisation in terms of differentiation between positive and negative results and of cost and effort is indispensable. As MOL-PCR includes a multiplex ligation step, followed by a singleplex PCR and analysis with microspheres on a Luminex device, several parameters are accessible for optimisation. Although MOL-PCR performance may be influenced by the markers used in the assay and the targeted bacterial species, evaluation of the method of DNA isolation, the probe concentration, the amount of microspheres, and the concentration of reporter dye is advisable in the development of any MOL-PCR assay. Therefore, we here describe our observations made during the optimisation of a 20-plex MOL-PCR assay for subtyping of Salmonella Typhimurium with the aim to provide a possible workflow as guidance for the development and optimisation of a MOL-PCR assay for the characterisation of other microbial pathogens.

Rapid and reliable detection of α-globin copy number variations by quantitative real-time PCR

BACKGROUND

Alpha-thalassemia is the most common human genetic disease worldwide. Copy number variations in the form of deletions of α-globin genes lead to α-thalassemia while duplications of α-globin genes can cause a severe phenotype in β-thalassemia carriers due to accentuation of globin chain imbalance. It is important to have simple and reliable methods to identify unknown or rare deletions and duplications in cases in which thalassemia is suspected but cannot be confirmed by multiplex gap-PCR. Here we describe a copy number variation assay to detect deletions and duplications in the α-globin gene cluster (HBA-CNV).

RESULTS

Quantitative real-time PCR was performed using four TaqMan® assays which specifically amplify target sequences representing both the α-globin genes, the -α3.7 deletion and the HS-40 region. The copy number for each target was determined by the 2-ΔΔCq method. To validate our method, we compared the HBA-CNV method with traditional gap-PCR in 108 samples from patients referred to our laboratory for hemoglobinopathy evaluation. To determine the robustness of the four assays, we analyzed samples with and without deletions diluted to obtain different DNA concentrations. The HBA-CNV method identified the correct copy numbers in all 108 samples. All four assays showed the correct copy number within a wide range of DNA concentrations (3.2-100 ng/μL), showing that it is a robust and reliable method. By using the method in routine diagnostics of hemoglobinopathies we have also identified several deletions and duplications that are not detected with conventional gap-PCR.

CONCLUSIONS

HBA-CNV is able to detect all known large deletions and duplications affecting the α-globin genes, providing a flexible and simple workflow with rapid and reliable results.

Hb Grand Junction (HBB: c.348_349delinsG; p.His117IlefsX42): a new hyperunstable hemoglobin variant

Hyperunstable hemoglobinopathy (HUH) [dominantly inherited β-thalassemia (β-thal)] is a relatively rare form of congenital hemolytic anemia in which mutations occur in the genes encoding for α and β chains, or both chains of the hemoglobin (Hb) molecule. We describe two Hispanic adolescents with a new unstable Hb variant (HBB: c.348_349delinsG; p.His117IlefsX42), resulting from a frameshift mutation at codons 115/116 of the β-globin gene. Both patients also have a 3.7 kb deletion on one α gene, leading to a decreased imbalance between α and β chain formation, and subsequently a milder phenotype than that seen in other hyperunstable Hb variants.

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.

Use of the MLPA assay in the molecular diagnosis of gene copy number alterations in human genetic diseases

Multiplex Ligation-dependent Probe Amplification (MLPA) assay is a recently developed technique able to evidence variations in the copy number of several human genes. Due to this ability, MLPA can be used in the molecular diagnosis of several genetic diseases whose pathogenesis is related to the presence of deletions or duplications of specific genes. Moreover, MLPA assay can also be used in the molecular diagnosis of genetic diseases characterized by the presence of abnormal DNA methylation. Due to the large number of genes that can be analyzed by a single technique, MLPA assay represents the gold standard for molecular analysis of all pathologies derived from the presence of gene copy number variation. In this review, the main applications of the MLPA technique for the molecular diagnosis of human diseases are described.