Myelodysplasia and deficiency of uridine diphosphate-galactose 4-epimerase

GALE variants associated with syndromic manifestations, macrothrombocytopenia, bleeding, and platelet dysfunction

GALE gene encodes the uridine diphosphate [UDP]-galactose-4-epimerase, which catalyzes the bidirectional interconversion of UDP-glucose to UDP-galactose, and UDP-N-acetyl-glucosamine to UDP-N-acetyl-galactosamine. In that way, GALE balances, through reversible epimerization, the pool of four sugars that are essential during the biosynthesis of glycoproteins and glycolipids. GALE-related disorder presents an autosomal recessive inheritance pattern, and it is commonly associated with galactosemia. Peripheral galactosemia generally associates with non-generalized forms or even asymptomatic presentations, while classical galactosemia may be related to complications such as learning difficulties, developmental delay, cardiac failure, or dysmorphic features. Recently, GALE variants have been related to severe thrombocytopenia, pancytopenia, and in one patient, to myelodysplastic syndrome.

Inherited Thrombocytopenia Caused by Variants in Crucial Genes for Glycosylation

Protein glycosylation, including sialylation, involves complex and frequent post-translational modifications, which play a critical role in different biological processes. The conjugation of carbohydrate residues to specific molecules and receptors is critical for normal hematopoiesis, as it favors the proliferation and clearance of hematopoietic precursors. Through this mechanism, the circulating platelet count is controlled by the appropriate platelet production by megakaryocytes, and the kinetics of platelet clearance. Platelets have a half-life in blood ranging from 8 to 11 days, after which they lose the final sialic acid and are recognized by receptors in the liver and eliminated from the bloodstream. This favors the transduction of thrombopoietin, which induces megakaryopoiesis to produce new platelets. More than two hundred enzymes are responsible for proper glycosylation and sialylation. In recent years, novel disorders of glycosylation caused by molecular variants in multiple genes have been described. The phenotype of the patients with genetic alterations in GNE, SLC35A1, GALE and B4GALT is consistent with syndromic manifestations, severe inherited thrombocytopenia, and hemorrhagic complications.

Expansion of the clinical phenotype of GALE deficiency

Congenital disorders of glycosylation are a group of rare monogenic inborn errors of metabolism caused by defective glycoprotein and glycolipid glycan synthesis and attachment. Here, we present a patient with galactose epimerase deficiency, also known as GALE deficiency, accompanied by pancytopenia and immune dysregulation. She was first identified by an abnormal newborn screen for galactosemia with subsequent genetic evaluation due to pancytopenia and immune dysregulation. The evaluation ultimately revealed that her known diagnosis of GALE deficiency was the cause of her hematologic and immune abnormalities. These findings further expand the clinical spectrum of disease of congenital disorders of glycosylation.

Inherited thrombocytopenia associated with mutation of UDP-galactose-4-epimerase (GALE)

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.

Dysplasia and disorder of cell membrane entirety in iron-deficiency anemia

Peripheral blood smears of 43 patients (26 males, median age 18 months, range: 6-180 months) with nutritional iron-deficiency anemia (IDA) were examined for the presence of trilineage hematological dysplasia. Twelve patients were reexamined for dysplastic findings after achieving a normal Hb and hematocrit level for age by the end of 2-3 months of iron treatment. A control group of 17 age-matched healthy children were also included. Neutrophils with loss of membrane entirety and protrusions were remarkable in 34/43 (79%) in the IDA group versus 1/12 (8%) after iron treatment and none of the control group. Microspherocytes were seen in 9/43 (21%) of IDA patients. Additionally, trilienage dysplasia was observed in the bone marrow samples available in 3 of the patients. It has been shown that iron-deficiency results in cellular DNA and RNA alterations, cell-cycle G1/S phase arrest, and apoptosis. Rac GTPases have been shown to control actin cytoskeleton, influencing cell polarity, microtubule dynamics, and the cytoskeletal organization of hematopoietic cells. Thus, the findings described above in neutrophils and red cells suggest a plausible link between iron and the Rac GTPase gene family. It may be a new avenue for iron waiting for proof.

[Myelodysplastic syndromes in children, Groupe d'étude des myélodysplasies de l'enfant de la Société d'hématologie et d'immunologie pédiatrique (SHIP)]

Myelodysplastic syndromes (MDS) in children constitute a heterogeneous disorder, including 'primary' MDS and MDS associated with constitutional abnormalities. The Franco-American-British (FAB) cytological classification for adults can be applied for childhood in 50 to 100% of the cases. The transformation into acute myeloblastic leukemia often occurs, but stabilisation or spontaneous regression of the disease may also be observed. The therapeutic decision is difficult because there is no predictive factor of the course of the disease. Allogenic bone marrow transplantation is the best curative option when treatment is necessary.