Novel mutations in mitochondrial carrier family gene SLC25A38, causing congenital sideroblastic anemia in Iranian families, identified by whole exome sequencing.

Sideroblastic anemias are heterogeneous rare hematological disorders, representing diverse phenotypes. In this study, the genetic cause of congenital, transfusion dependent anemia in four unrelated families consisting of eighteen individuals, with one affected member was investigated. Probands were suspected to rare anemias, including sideroblastic anemia. Whole exome sequencing in probands followed by segregation analysis in families was performed. Two novel frame shift mutations and one previously reported missense mutation in SLC25A38 gene was identified in these families. Mutations and their recessive mood of inheritance in each family were confirmed by PCR and Sanger sequencing. These findings suggest that sideroblastic anemia must be considered a possible etiology in cases with unexplained hemolytic anemia. Furthermore, mutations in SLC25A38 gene could be a prevalent cause of congenital sideroblastic anemia (CSA) in the Iranian population. Considering that parents of all affected individuals had consanguineous marriage and belong to sub populations, where consanguineous marriage is prevalent, it is important to perform carrier screening and genetic counseling in these families and their close relatives as prevention strategy in populations at risk.

SF3B1 mutation identifies a distinct subset of myelodysplastic syndrome with ring sideroblasts.

Refractory anemia with ring sideroblasts (RARS) is a myelodysplastic syndrome (MDS) characterized by isolated erythroid dysplasia and 15% or more bone marrow ring sideroblasts. Ring sideroblasts are found also in other MDS subtypes, such as refractory cytopenia with multilineage dysplasia and ring sideroblasts (RCMD-RS). A high prevalence of somatic mutations of SF3B1 was reported in these conditions. To identify mutation patterns that affect disease phenotype and clinical outcome, we performed a comprehensive mutation analysis in 293 patients with myeloid neoplasm and 1% or more ring sideroblasts. SF3B1 mutations were detected in 129 of 159 cases (81%) of RARS or RCMD-RS. Among other patients with ring sideroblasts, lower prevalence of SF3B1 mutations and higher prevalence of mutations in other splicing factor genes were observed (P < .001). In multivariable analyses, patients with SF3B1 mutations showed significantly better overall survival (hazard ratio [HR], .37; P = .003) and lower cumulative incidence of disease progression (HR = 0.31; P = .018) compared with SF3B1-unmutated cases. The independent prognostic value of SF3B1 mutation was retained in MDS without excess blasts, as well as in sideroblastic categories (RARS and RCMD-RS). Among SF3B1-mutated patients, coexisting mutations in DNA methylation genes were associated with multilineage dysplasia (P = .015) but had no effect on clinical outcome. TP53 mutations were frequently detected in patients without SF3B1 mutation, and were associated with poor outcome. Thus, SF3B1 mutation identifies a distinct MDS subtype that is unlikely to develop detrimental subclonal mutations and is characterized by indolent clinical course and favorable outcome.

Biology of sideroblastic anemia.

Sideroblastic anemia is characterized by anemia with ring sideroblasts produced by the bone marrow. Sideroblasts are formed by disutilization and deposit of iron in the mitochondoria. There are two forms of sideroblastic anemia: congenital and acquired. Congenital sideroblastic anemia is caused by mutations in genes involved in heme biosynthesis, iron-sulfur (Fe-S) cluster biogenesis, or mitochondrial metabolism. Although there is a variation in the mutated genes among races, the most common congenital sideroblastic anemia is X-linked sideroblastic anemia caused by mutations in the erythroid-specific δ-aminolevulinate synthase gene, which is the first enzyme of heme biosynthesis in erythroid cells. The most commonly acquired sideroblastic anemia is myelodysplastic syndrome with ring sideroblasts (MDS-RS). It has been shown that the splicing factor 3b subunit 1 (SF3B1) gene, which is a core component of the RNA splicing complex, is highly mutated in MDS-RS, although the underlying mechanism of the onset of the disease by the mutation of the SF3B1 gene remains unclear. Molecular analysis will contribute to the development of effective treatment for congenital and acquired sideroblastic anemia, which are intractable diseases.

SF3B1 mutations are prevalent in myelodysplastic syndromes with ring sideroblasts but do not hold independent prognostic value.

SF3B1 mutations were recently reported in myelodysplastic syndromes (MDSs), especially in the presence of ring sideroblasts (RSs). We sought to define the interaction between SF3B1 mutations, morphology, karyotype, and prognosis in MDS with more than or equal to 15% RS (MDS-RS). We studied 107 patients with MDS-RS, including 48 with refractory anemia with RS (RARS), 43 with refractory cytopenia with multilineage dysplasia (RCMD)-RS, 11 with refractory anemia with excess blasts-1 (RAEB1)-RS, and 5 with RAEB2-RS. SF3B1 mutations were detected in 53 (∼ 50%) patients: 35 RARS (73%), 16 RCMD-RS (37%), and 2 RAEB1-RS (18%). In univariate analysis, the presence of SF3B1 mutations was associated with better overall (P < .01) and leukemia-free (P < .01) survival; however, in both instances, significance was completely accounted for by World Health Organization morphologic risk categorization. In other words, when RARS and RCMD-RS were analyzed separately, there was no additional prognostic value from the presence or absence of SF3B1 mutations.

Clinical significance of SF3B1 mutations in Korean patients with myelodysplastic syndromes and myelodysplasia/myeloproliferative neoplasms with ring sideroblasts.

Somatic mutations in the SF3B1 gene, a gene encoding the splicing factor 3B subunit 1, were recently reported in myelodysplastic syndromes (MDS), particularly in the presence of ring sideroblasts (RS). The authors investigated the prevalence and clinical significance of SF3B1 mutations in Korean patients with myeloid neoplasms with RS. The study subjects were 43 Korean patients with myeloid neoplasms. Twenty-nine patients (67 %) had 15 % or more RS (high-count RS [HC-RS]), and 14 (33 %) had RS less than 15 % (low-count RS [LC-RS]). Molecular genetic tests were performed to detect SF3B1 mutations by direct sequencing on bone marrow samples of the patients. SF3B1 mutations were detected in 55 % (16/29) of the HC-RS group: 3 RARS (3/3), 8 RCMD (8/16), 3 RARS-t (3/4), 1 RAEB (1/4), and 1 MDS-U (1/1). All mutations were previously reported mutations with K700E being the most common (63 % of mutation-positive cases). On the other hand, none (0 %) of the LC-RS group had SF3B1 mutation. The patients with SF3B1 mutations had higher platelet counts (p = 0.023), higher proportions of RS (p = 0.003), and lower proportions of bone marrow blasts (p = 0.026) than those without SF3B1 mutations. SF3B1 mutations showed a favorable survival implication (p = 0.025), but not in multivariate analysis (p = 0.178). This study confirmed that SF3B1 mutation is highly specific to the HC-RS phenotype in Korean patients with myeloid neoplasms with similar frequencies and distributions in previous findings and is associated with distinct hematologic features.

Comprehensive Genomic Analysis Identifies a Diverse Landscape of Sideroblastic and Nonsideroblastic Iron-Related Anemias with Novel and Pathogenic Variants in an Iron-Deficient Endemic Setting.

Inherited iron metabolism defects are possibly missed or underdiagnosed in iron-deficient endemic settings because of a lack of awareness or a methodical screening approach. Hence, we systematically evaluated anemia cases (2019 to 2021) based on clinical phenotype, normal screening tests (high-performance liquid chromatography, α gene sequencing, erythrocyte sedimentation rate, C-reactive protein, and tissue transglutaminase), and abnormal iron profile by targeted next-generation sequencing (26-gene panel) supplemented with whole-exome sequencing, multiplex ligation probe amplification/mitochondrial DNA sequencing, and chromosomal microarray. Novel variants in ALAS2, STEAP3, and HSPA9 genes were functionally validated. A total of 290 anemia cases were screened, and 41 (14%) enrolled for genomic testing as per inclusion criteria. Comprehensive genomic testing revealed pathogenic variants in 23 of 41 cases (56%). Congenital sideroblastic anemia was the most common diagnosis (14/23; 61%), with pathogenic variations in ALAS2 (n = 6), SLC25A38 (n = 3), HSPA9 (n = 2) and HSCB, SLC19A2, and mitochondrial DNA deletion (n = 1 each). Nonsideroblastic iron defects included STEAP3-related microcytic anemia (2/23; 8.7%) and hypotransferrenemia (1/23; 4.3%). A total of 6 of 22 cases (27%) revealed a non-iron metabolism gene defect on whole-exome sequencing. Eleven novel variants (including variants of uncertain significance) were noted in 13 cases. Genotype-phenotype correlation revealed a significant association of frameshift/nonsense/splice variants with lower presentation age (0.8 months versus 9 years; P < 0.01) compared with missense variants. The systematic evaluation helped uncover an inherited iron defect in 41% (17/41) of cases, suggesting the need for active screening and awareness for these rare diseases in an iron-deficient endemic population.

Clinical and genetic characteristics of congenital sideroblastic anemia: comparison with myelodysplastic syndrome with ring sideroblast (MDS-RS).

Sideroblastic anemia is characterized by anemia with the emergence of ring sideroblasts in the bone marrow. There are two forms of sideroblastic anemia, i.e., congenital sideroblastic anemia (CSA) and acquired sideroblastic anemia. In order to clarify the pathophysiology of sideroblastic anemia, a nationwide survey consisting of clinical and molecular genetic analysis was performed in Japan. As of January 31, 2012, data of 137 cases of sideroblastic anemia, including 72 cases of myelodysplastic syndrome (MDS)-refractory cytopenia with multilineage dysplasia (RCMD), 47 cases of MDS-refractory anemia with ring sideroblasts (RARS), and 18 cases of CSA, have been collected. Hemoglobin and MCV level in CSA are significantly lower than those of MDS, whereas serum iron level in CSA is significantly higher than those of MDS. Of 14 CSA for which DNA was available for genetic analysis, 10 cases were diagnosed as X-linked sideroblastic anemia due to ALAS2 gene mutation. The mutation of SF3B1 gene, which was frequently mutated in MDS-RS, was not detected in CSA patients. Together with the difference of clinical data, it is suggested that genetic background, which is responsible for the development of CSA, is different from that of MDS-RS.

Systematic molecular genetic analysis of congenital sideroblastic anemia: evidence for genetic heterogeneity and identification of novel mutations.

BACKGROUND: Sideroblastic anemias are heterogeneous congenital and acquired bone marrow disorders characterized by pathologic iron deposits in mitochondria of erythroid precursors. Among the congenital sideroblastic anemias (CSAs), the most common form is X-linked sideroblastic anemia, due to mutations in 5-aminolevulinate synthase (ALAS2). A novel autosomal recessive CSA, caused by mutations in the erythroid specific mitochondrial transporter SLC25A38, was recently defined. Other known etiologies include mutations in genes encoding the thiamine transporter SLC19A2, the RNA-modifying enzyme pseudouridine synthase 1 (PUS1), a mitochondrial ATP-binding cassette transporter (ABCB7), glutaredoxin 5 (GLRX5), as well as mitochondrial DNA deletions. Despite these known diverse causes, in a substantial portion of CSA cases a presumed genetic defect remains unknown. PROCEDURE: In the context of the recent discovery of SLC25A38 as a major novel cause, we systematically analyzed a large cohort of previously unreported CSA patients. Sixty CSA probands (28 females, 32 males) were examined for ALAS2, SLC25A38, PUS1, GLRX5, and ABCB7 mutations. SLC19A2 and mitochondrial DNA were only analyzed if characteristic syndromic features were apparent. RESULTS: Twelve probands had biallelic mutations in SLC25A38. Seven ALAS2 mutations were detected in eight sporadic CSA cases, two being novel. We also identified a novel homozygous null PUS1 mutation and novel mitochondrial DNA deletions in two patients with Pearson syndrome. No mutations were encountered in GLRX5, ABCB7, or SLC19A2. CONCLUSIONS: The remaining undefined probands (43%) can be grouped according to gender, family, and clinical characteristics, suggesting novel X-linked and autosomal recessive forms of CSA.

Clinico-haematological characteristics in Pakistani patients of primary myelodysplastic syndrome according to World Health Organization classification.

OBJECTIVE: To assess the applicability of WHO classification on a cohort of Pakistani myelodysplastic syndrome (MDS) patients, and determine their epidemiological and clinico-pathological features. STUDY DESIGN: Case series. PLACE AND DURATION OF STUDY: Haematology Department, Shaikh Zayed Hospital, Lahore, from April 2004 to March 2006. METHODOLOGY: Forty six patients of primary MDS diagnosed by World Health Organization (WHO) criteria were included in the study by nonprobability purposive sampling. The cohort was classified accordingly and the epidemiological, clinical and haematological parametres were assessed. Descriptive statistics were used to describe the data. RESULTS: Forty six patients (28 males and 18 females) of primary MDS were included in the study. The mean age was 46.21 years. According to the WHO classification, 12 cases of refractory anaemia, 24 cases of refractory cytopenia with multi lineage dysplasia, 1 case of refractory cytopenia with multi lineage dysplasia and ring sideroblasts, 3 cases of MDS unclassified and 3 cases each of refractory anaemia with excess of blasts I and II were diagnosed. Symptomatic anaemia was seen in 37 cases and pancytopenia was documented in 33 cases. Dyserythropoiesis affected 41 cases. Grade III reticulosis was seen in 7 cases. ALIP was present in 13 cases. CONCLUSION: MDS presented at a young age. Refractory cytopenia with multi lineage dysplasia was the dominant disease category. Further studies are suggested for identifying the cytogenetic abnormalities and del 5q- category.

Primary myelodysplastic syndrome in Jordan: a single-centre experience.

OBJECTIVE: Study of the disease patterns and clinical evaluation of myelodysplastic syndrome (MDS). SUBJECTS AND METHODS: A retrospective analysis was carried out on 85 patients, with MDS who were followed up over a period of 23 years at Jordan University Hospital, Amman, Jordan. Cases were analyzed according to the French, American and British Classification. RESULTS: Of the 85 patients, 42 (49.4%) were females and 43 (50%) males; mean age was 59 +/- 19 years (range 18-88). Most subtypes found in patients were refractory anemia (RA) in 27 (31.8%) and RA with excess blasts (RAEB) in 28 (32.9%). Adverse prognostic indicators were RAEB subtype and requirement for blood transfusion. CONCLUSION: Our findings showed that MDSs appeared at a younger age and tended to be of the aggressive subtype. Chronic myelomonocytic leukemia subtype seemed to appear dominantly in men.

Onset of X-linked sideroblastic anemia in the fourth decade.

We report the case of a 40-year female who manifested late onset, pyridoxine-refractory X-linked sideroblastic anemia, heterozygous for the first described frameshift ALAS2 mutation, CD506-507 (-C). On presentation she had macrocytic anemia with severe iron overload.

X-linked sideroblastic anaemia due to ALAS2 mutations in the Netherlands: a disease in disguise.

BACKGROUND: X-linked sideroblastic anaemia (XLSA; OMIM#300751) is the most common inherited form of sideroblastic anaemia and is associated with several mutations in the erythroid specific 5-aminolevulinate synthase gene (ALAS2). This gene encodes for aminolevulinic acid synthase 2 (ALAS2), the catalytic enzyme involved in the first en rate-limiting step of haem biosynthesis.1-3 The disorder is characterised by mostly mild hypochromic microcytic anaemia with bone marrow ring sideroblasts. Even untransfused patients with mild or no anaemia are at risk for severe systemic iron overload due to ineffective erythropoiesis. To date, 61 different ALAS2 mutations have been reported in 120 families with XLSA. Descriptions of molecularly confirmed case series from the Netherlands, however, are lacking. METHODS: We reviewed age of presentation, clinical and biochemical features, ALAS₋2 defects and treatment characteristics of 15 Dutch patients from 11 unrelated families diagnosed with XLSA. RESULTS AND CONCLUSIONS: In one family a novel pathogenic c.1412G>A (p.Cys471Tyr) mutation was found. All other families shared the previously described c.1355G>A (p.Arg452His) mutation. Haplotype analysis in seven probands with the p.Arg452His mutation strongly suggests that six of them were ancestrally related. Nevertheless, their phenotype was very different. Our patients illustrate the phenotypical heterogeneity in the presentation of XLSA patients, the effectiveness of treatment regimens and the various pitfalls associated with the diagnosis, follow-up and treatment of the disease. A timely diagnosis avoids unnecessary investigations and allows adequate treatment that can prevent systemic iron load with subsequent severe life-threatening complications. Therefore, we suggest considering XLSA in both male and female patients with unexplained iron overload and÷or (mild) microcytic anaemia, also at older age.

[Myelodysplastic syndrome classification]. / La classification des syndromes myélodysplasiques.

Myelodysplastic syndromes (MDS) are myeloid disorders with various clinical and biological presentations. The French-American-British (FAB-1982) classification included five categories basing on morphology and bone marrow blast count. Three criteria are taken into account: 1) the percentage of blasts in peripheral blood and bone marrow, 2) the percentage of ringed sideroblasts, and 3) the number of monocytes in peripheral blood. The World Health Organization classification (WHO 2001, 2008) modifies the FAB system by also taking cytogenetic characteristics and molecular biology into consideration. The last classification (WHO-2008) takes into account: 1) the number of peripheral cytopenia, 2) the percentage of blasts in peripheral blood and bone marrow, 3) the percentage of ringed sideroblasts, 4) the possible presence of Auer Rods, and 5) the detection of a cytogenetic abnormality (the isolated 5q deletion). The following subgroups are defined: refractory cytopenia with unilineage dysplasia, refractory anemia with ringed sideroblasts, refractory cytopenia with multilineage dysplasia, refractory anemia with excess blasts, myelodysplastic syndrome unclassifiable and myelodysplastic syndrome with isolated del(5q).

Prognoses of MDS subtypes RARS, RCMD and RCMD-RS are comparable but cytogenetics separates a subgroup with inferior clinical course.

In 2008, the WHO combined the former categories RCMD (refractory cytopenia with multilineage dysplasia) and RCMD-RS (ring sideroblasts ≥ 15%). We studied the clinical impact and genetic background of RARS, RCMD, and RCMD-RS in 1082 patients. Good karyotypes (IPSS) were similarly frequent in RARS, RCMD, and RCMD-RS. 2-year overall survival (OS) rates were similar in RARS, RCMD, and RCMD-RS (85.9%/89.0%/91.7%; n.s.). The 2-year OS rate was better in good than intermediate or poor karyotypes (p<0.001). These results support to combine RCMD and RCMD-RS as performed by WHO and emphasize the prognostic power of cytogenetic criteria for these MDS subtypes.