Chronic non-spherocytic hemolytic anemia associated with severe neurological disease due to γ-glutamylcysteine synthetase deficiency in a patient of Moroccan origin

Abstract

A previously undescribed mutation of hereditary γ-glutamylcysteine synthetase (GCS) deficiency was found in a 5 year old boy of Moroccan origin. He presented with chronic haemolytic anaemia, delayed psychomotor development and progressive motor sensitive neuropathy of lower extremities. The parents were third degree relatives. The activity of glycolytic enzymes were found to be normal in the propositus, his parents and a sister, but and a complete lack of GSH was found in the propositus. Accordingly, the measurement of de novo GSH synthetic enzymes was undertaken, and severe GCS deficiency was found in the propositus. Both parents and his sister presented GCS activity ranging from 69% to 90% of normal. GCS gene sequencing showed that the propositus was homozygous for a 1241C>T mutation in exon 11 and both parents and his sister were heterozygous. This mutation predicts a Pro414Leu amino acid substitution. Even though the homology between GCS and crystallographically solved, functionally related proteins is not very high, a three-dimensional model of GCS was derived using Modeller Software. GCS deficiency is a very rare autosomal recessive disorder reported so far in only 8 unrelated probands with severe haemolytic anaemia. In only 3 of these was the anaemia associated with severe neurological dysfunction. We report here the fourth case of GCS deficiency presenting neuropathy, giving further support to the eventual relationship between this enzymopathy and neurological damage

Glutathione (L-γ-glutamyl-L-cysteinyl-glycine;GSH) is an important intracellular antioxidant tripeptide necessary for the protection of cells from damage by oxygen intermediates, free radicals, peroxides, and toxins of both endogenous and exogenous origin.1,2 Two rate-limiting enzymes are involved in de novo ATP-dependent biosynthesis of red blood cell GSSG: γ-glutamylcysteine synthetase, (GCS), also known as glutamate-cysteine ligase (GCL) and glutathione synthetase (GS).

GS is a 118 kD homodimer that catalyses the addition of glycine to the cysteine carboxyl group of GGC to form GSSG. Hereditary deficiency of GS is an autosomal recessive disorder that has been reported in 41 unrelated patients. In its severe form it is characterized by haemolytic anaemia, metabolic acidosis with massive urinary excretion of 5-oxoproline (5-oxoprolinuria) and central nervous system damage.3–5

GCS is a 104 kD heterodimer that consists of a catalytic (-GCSH) and modifier (-GCSL) subunit and catalyzes the amide linkage between cysteine and the γcarboxyl group of glutamate to form the dipeptide γ-glutamylcysteine (GGC). Hereditary deficiency of GCS is a very rare autosomal recessive enzymopathy so far reported in only 8 unrelated families.6–11 The common clinical manifestation of GCS deficiency is recurring bouts of anaemia and jaundice but it has been found to be associated with severe neurological abnormalities in two cases6,12 and mental retardation in one.10 In the two most recently reported cases of GCS deficiency9–11 single-point mutations in the coding sequence of GCS gene have been identified as the underlying molecular cause of the condition.

We report here a novel mutation, a single C>T transversion at cDNA nucleotide 1241 in the γ-GCS gene, found in a patient of Moroccan origin. This is the fourth case of GCS deficiency so far described in which chronic anaemia is associated with both severe neuropathy and mental retardation.