l-arginine:glycine amidinotransferase (AGAT) deficiency: clinical presentation and response to treatment in two patients with a novel mutation.

Creatine and creatine phosphate provide storage and transmission of phosphate-bound energy in muscle and brain. Of the three inborn errors of creatine metabolism causing brain creatine depletion, l-arginine:glycine amidinotransferase (AGAT) deficiency has been described in only two families. We describe clinical and biochemical features, magnetic resonance spectroscopy (MRS) findings and response to creatine supplementation in two siblings with a novel mutation in the AGAT-encoding GATM gene. The sister and brother were evaluated at age 12 and 18years, respectively, because of mild mental retardation, muscle weakness and low weight. Extensive work-up had previously yielded negative results. Electron microscopy of the muscle revealed tubular aggregates and the activity of respiratory chain complexes was decreased in the muscle. Urine organic acid concentrations normalized to urine creatinine concentration were all increased, suggesting a creatine metabolism disorder. Brain MRS was remarkable for absence of creatine. Urine guanidinoacetate levels by tandem mass spectrometry were low, suggesting AGAT deficiency. GATM sequencing revealed a homozygous single nucleotide insertion 1111_1112insA, producing a frame-shift at Met-371 and premature termination at codon 376. Eleven months after commencing treatment with oral creatine monohydrate 100mg/kg/day, repeat MRI/MRS showed significantly increased brain creatine in the sister and a slight increase in the older brother. The parents' impression of improved strength and stamina was substantiated by increased post-treatment versus pre-treatment scores in the Vineland Adaptive Behavior Scale, straight-arm raising and timed up-and-go tests. Similarly, there was an apparent improvement in cognitive function, with significantly increased IQ-scores in the sister and marginal improvement in the brother.

A novel SLC25A20 splicing mutation in patients of different ethnic origin with neonatally lethal carnitine-acylcarnitine translocase (CACT) deficiency.

Carnitine-acylcarnitine translocase (CACT) deficiency is a rare disorder of fatty acid oxidation associated with high mortality. Two female newborns of different ethnic origin (the first Anglo-Celtic and the second Palestinian Arab) both died after sudden collapse on day 2 of life. Both had elevated bloodspot long-chain acylcarnitines consistent with either CACT or carnitine palmitoyltransferase II (CPT2) deficiency; the latter was excluded by demonstrating normal CPT2 activity in fibroblasts. Direct sequencing of all SLC25A20 (CACT) gene exons and exon-intron boundaries revealed that Patient 1 was compound heterozygous for a novel c.609-3c>g (IVS6-3c>g) mutation on the paternal allele and a previously described c.326delG mutation on the maternal allele. Patient 2 was homozygous for the same, novel c.609-3c>g mutation. Previously reported SLC25A20 mutations have been almost exclusively confined to a single family or ethnic group. Analysis of fibroblast cDNA by RT-PCR, agarose gel electrophoresis and sequencing of extracted bands showed that both mutations produce aberrant splicing. c.609-3C>G results in exon 7 skipping leading to a frameshift with premature termination seven amino acids downstream. c.326delG was confirmed to produce skipping of exons 3 or 3 plus 4. CACT activity in both patients' fibroblasts was near-zero. For both families, prenatal diagnosis of an unaffected fetus was performed by mutation analysis on CVS tissue in a subsequent pregnancy. Due to the urgency of prenatal diagnosis in the second family, molecular diagnosis was performed prior to demonstration of CACT enzyme deficiency, illustrating that mutation analysis is a rapid and reliable approach to first-line diagnosis of CACT deficiency.