LC-MS/MS measurements of urinary guanidinoacetic acid and creatine: Method optimization by deleting derivatization step

Creatine Deficiency Syndromes: Comparison of Screening Methods and Characterization of Four Novel Intronic Variants

BACKGROUND

Cerebral creatine deficiency syndromes (CCDS) are disorders affecting creatine synthesis or transport. Several methods have been developed to measure creatine and guanidinoacetate (GAA) in different body fluids including methods based on gas chromatography-mass spectrometry (GC-MS) and High-pressure liquid chromatography mass spectrometry (HPLC-MS). The diagnosis of CCDS is then confirmed by sequencing of creatine biosynthesis genes guanidinoacetate methyltransferase (GAMT) and Arginine: glycine amidinotransferase (GATM) and creatine transporter gene solute carrier family 6 member 8 (SLC6A8) or by functional enzymatic assay. The aim of the current study was to find the most reliable and accurate screening method for CCDS by comparing methods using Nuclear Magnetic Resonance spectroscopy (NMR), GC-MS and HPLC-MS. Additionally, this study was performed to estimate the prevalence of CCDS in a cohort of Egyptian patients and potentially to discover novel variants.

SUBJECTS AND METHODS

The study was conducted on 150 subjects with clinical signs and symptoms consistent with CCDS. Metabolic profiling of urine samples was performed using three techniques: 1) GC-MS 2) Ultra high-pressure (or performance) liquid chromatography - Tandem Mass Spectrometry (UHPLC- MS/MS) and 3) NMR.

RESULTS

The linearity of peak areas for creatine and GAA by UHPLC-MS/MS and NMR covered and exceeded the ranges normally found in urine. The limit of quantification and the inter-day precision results for creatine and GAA were more robust by UHPLC-MS/MS than NMR. Ten cases were identified as being positive for CCDS by our analytical approaches and underwent next generation sequencing (NGS) for GAMT, GATM and SLC6A8 genes. NGS was performed and confirmed one patient with one likely Pathogenic variant in GAMT gene: (NC_000019.10:g.1401317C > G, NP_000147.1:p.Ala54Pro). Additionally, we describe four novel intronic variants in the GATM gene: c.1043-357del and c.1043-357_1043-356insT, and were predicted to activate cryptic acceptor site with potential alteration of splicing, c.979-227G > A was found to significantly alter the Exon Splice Enhancer (ESE) xon Splice Silencer (ESS) motifs ratio and c.1042 + 262del which was found to have no implications on splicing.

CONCLUSIONS

Both UHPLC-MS/MS and NMR spectroscopy are comparable to GC-MS in screening for CCDS. Nonetheless, the UHPLC-MS/MS method had better performance than NMR spectroscopy. Additionally, Sequencing of the full length of GATM, GAMT, and SLC6A8 genes is needed to identify intronic variants that could cause CCDS via affecting splice sites.

Laboratory Diagnosis of Cerebral Creatine Deficiency Syndromes by Determining Creatine and Guanidinoacetate in Plasma and Urine

Cerebral creatine deficiency syndromes are caused by the dysfunctional creatine biosynthesis or transport and comprise three hereditary neurodevelopmental defects including arginine-glycine amidinotransferase (AGAT), guanidinoacetate methyltransferase (GAMT), and creatine transporter deficiencies. All conditions are characterized by seizures, intellectual disability, and behavioral abnormalities. Laboratory diagnosis of these disorders relies on the determination of creatine and guanidinoacetate concentrations in both plasma and urine. Here we describe a rapid quantitative UPLC/MS/MS method for the simultaneous determination of these analytes using a normal-phase HILIC column after analyte derivatization. The approach is suitable for neonatal screening follow-ups and monitoring of the treatment for creatine deficiency syndromes.

Adult GAMT deficiency: A literature review and report of two siblings

Guanidinoacetate methyltransferase (GAMT) deficiency is a creatine deficiency disorder and an inborn error of metabolism presenting with progressive intellectual and neurological deterioration. As most cases are identified and treated in early childhood, adult phenotypes that can help in understanding the natural history of the disorder are rare. We describe two adult cases of GAMT deficiency from a consanguineous family in Pakistan that presented with a history of global developmental delay, cognitive impairments, excessive drooling, behavioral abnormalities, contractures and apparent bone deformities initially presumed to be the reason for abnormal gait. Exome sequencing identified a homozygous nonsense variant in GAMT: NM_000156.5:c.134G>A (p.Trp45*). We also performed a literature review and compiled the genetic and clinical characteristics of all adult cases of GAMT deficiency reported to date. When compared to the adult cases previously reported, the musculoskeletal phenotype and the rapidly progressive nature of neurological and motor decline seen in our patients is striking. This study presents an opportunity to gain insights into the adult presentation of GAMT deficiency and highlights the need for in-depth evaluation and reporting of clinical features to expand our understanding of the phenotypic spectrum.