Congenital dyserythropoietic anemias (CDAs) constitute a rare group of inherited red-blood-cell disorders associated with dysplastic changes in late erythroid precursors. CDA type I (CDAI [MIM 224120], gene symbol CDAN1) is characterized by erythroid pathological features such as internuclear chromatin bridges, spongy heterochromatin, and invagination of the nuclear membrane, carrying cytoplasmic organelles into the nucleus. A cluster of 45 highly inbred Israeli Bedouin with CDAI enabled the mapping of the CDAN1 disease gene to a 2-Mb interval, now refined to 1.2 Mb, containing 15 candidate genes on human chromosome 15q15 (Tamary et al. 1998). After the characterization and exclusion of 13 of these genes, we identified the CDAN1 gene through 12 different mutations in 9 families with CDAI. This 28-exon gene, which is transcribed ubiquitously into 4738 nt mRNA, was reconstructed on the basis of gene prediction and homology searches. It encodes codanin-1, a putative o-glycosylated protein of 1,226 amino acids, with no obvious transmembrane domains. Codanin-1 has a 150-residue amino-terminal domain with sequence similarity to collagens and two shorter segments that show weak similarities to the microtubule-associated proteins, MAP1B (neuraxin) and synapsin. These findings, and the cellular phenotype, suggest that codanin-1 may be involved in nuclear envelope integrity, conceivably related to microtubule attachments. The specific mechanisms by which codanin-1 underlies normal erythropoiesis remain to be elucidated.

No abstract

No abstract

Key Points Germ line biallelic loss-of-function THPO mutations cause BMF. Marrow failure due to THPO mutations is characterized by poor graft function after transplantation but responds to THPO receptor agonists.

SummaryCongenital dyserythropoietic anaemia (CDA) type I is a rare, inherited disorder characterised by ineffective erythropoiesis and macrocytic anaemia. Complex bone disease has only occasionally been associated with this disease. CDA I is caused by mutations in the CDAN1 gene encoding for codanin-1. Our aim was to characterise the CDAN1 mutation in eight unrelated patients with sporadic CDA I, three of whom had complex bone disease. Six novel mutations in the CDAN1 gene were identified. In two patients, one mutation and in another, both mutations were elusive. No patient was homozygous for a null-type mutation. However, one patient with complex bone disease was homozygous for a splice-site mutation (IVS-12+5G > A). Western blotting revealed that codanin-1 synthesis was 65% less than the control. Five single nucleotide polymorphisms (SNPs) previously unreported in the literature or the SNP database were also identified. Although the absence of codanin-1 is probably lethal, the presence of 35% of the protein was compatible with life but was associated with severe clinical manifestations. However, in most patients studied, no correlation could be established between the expected levels of codanin-1 or the nature of the mutation and the severity of the clinical manifestations.

Although a relatively small number of previous studies suggest a modest response to hydroxyurea (HU) therapy in b-thalassemia, more recent investigations have revealed that some transfusion-dependent patients can become transfusion-independent following HU therapy. Patients with Gc XmnI polymorphism, several b-globin mutations, and a-thalassemia deletions were inconsistently reported to have significant responses to HU therapy. To better predict who may respond, we retrospectively evaluated the clinical response and the molecular background of 18 b-thalassemia patients treated with HU for a mean of 46 months. The majority of transfusion-dependent patients responded to HU therapy with 9 out of 11 (82%) becoming transfusion-independent. Five thalassemia intermedia (TI) patients receiving occasional blood transfusion did not require any additional transfusions following therapy and two TI patients who had never received transfusions had a 2 g/dl increase in their hemoglobin level. The majority of b-thalassemia major patients who became transfusion-independent (7/9) were either homozygous (5) or heterozygous (2) for the XmnI polymorphism. No correlation was identified between response to therapy and the presence of specific b-thalassemia mutations or a-globin deletions. We conclude that further analysis of the degree of response of transfusion-dependent b-thalassemia patients to HU therapy, as well as, the impact of their genetic background on this response is required to identify patients likely to have significant response. Am. J. Hematol. 83:366-370, 2008. V

Severe thrombocytopenia, characterized by dysplastic megakaryocytes and intracranial bleeding, was diagnosed in six individuals from a consanguineous kindred. Three of the individuals were successfully treated by bone marrow transplant. Whole-exome sequencing and homozygosity mapping of multiple family members, coupled with whole-genome sequencing to reveal shared non-coding variants, revealed one potentially functional variant segregating with thrombocytopenia under a recessive model: GALE p.R51W (c.C151T, NM_001127621). The mutation is extremely rare (allele frequency = 2.5 × 10−05), and the likelihood of the observed co-segregation occurring by chance is 1.2 × 10−06. GALE encodes UDP-galactose-4-epimerase, an enzyme of galactose metabolism and glycosylation responsible for two reversible reactions: interconversion of UDP-galactose with UDP-glucose and interconversion of UDP-N-acetylgalactosamine with UDP-N-acetylglucosamine. The mutation alters an amino acid residue that is conserved from yeast to humans. The variant protein has both significantly lower enzymatic activity for both interconversion reactions and highly significant thermal instability. Proper glycosylation is critical to normal hematopoiesis, in particular to megakaryocyte and platelet development, as reflected in the presence of thrombocytopenia in the context of congenital disorders of glycosylation. Mutations in GALE have not previously been associated with thrombocytopenia. Our results suggest that GALE p.R51W is inadequate for normal glycosylation and thereby may impair megakaryocyte and platelet development. If other mutations in GALE are shown to have similar consequences, this gene may be proven to play a critical role in hematopoiesis.

Congenital dyserythropoietic anemia (CDA) type I is an inherited disorder characterized by macrocytic anemia with pathognomonic morphologic ultrastructural features of the erythroid precursors. The authors recently cloned the CDAN1 gene and identified one founder missense mutation in all of their Bedouin patients. In a previous study, the authors found that the majority of their 31 Bedouin patients had anemia and jaundice during the first month of life and required blood transfusions; some had persistent pulmonary hypertension. In the present retrospective evaluation of 70 Bedouin patients with CDA type I, the authors more than doubled the number. Forty-five (64%) patients were symptomatic in the neonatal period, 29 (65%) had hepatomegaly, 24 (53%) had early jaundice, 11 (27%) were born small for gestational age, 7 (15%) had persistent pulmonary hypertension, and 6 (13%) had direct hyperbilirubinemia and another 6 (13%) had transient thrombocytopenia. Thirty-six of the symptomatic neonates (80%) required at least one blood transfusion. These results confirm the authors' previous findings and add neonatal manifestations not previously described, particularly hyperbilirubinemia and thrombocytopenia. Early diagnosis of CDA type I may be beneficial in light of the potential efficacy of alpha-interferon in avoiding transfusions in some patients.