The clinico-radiological findings of MSUD in a group of Egyptian children: Contribution to early diagnosis and outcome.

BACKGROUND: Maple syrup urine disease (MSUD) is an autosomal recessive inborn error of amino acid metabolism, with unique clinico-radiological findings. This study aims to show the benefit of using the clinico-radiological findings for early diagnosis of children with MSUD, and confirming this diagnosis using the tandem mass spectrometry (MS/MS), in order to avoid deleterious outcome. METHODS: A prospective cohort study conducted in the period from August 2016 to December 2020. Twenty-one children were included either by selective screening or by high-risk screening. All children had clinical and neurodevelopmental evaluation, brain magnetic resonance imaging (MRI) assessment, and blood amino acids analysis at diagnosis. Patients were followed clinically. RESULTS: Most children had acute onsets neuro-developmental symptoms, with wide range of brain parenchyma involvement on MRI (hyperintensity). Diagnosis of MSUD was confirmed by detecting high serum levels of leucine/isoleucine (mean value 2085.5 µmol/L) in all patients, and elevated levels of serum valine in (81%) of children. In addition, all children showed elevated leucine: alanine ratio, and leucine: phenylalanine ratio. CONCLUSIONS: The characteristic clinico-radiological features can help in the early diagnosis of MSUD children, thus preventing the delay in laboratory diagnosis and improving their outcomes.

Genotype-phenotype correlation in patients with isovaleric acidaemia: comparative structural modelling and computational analysis of novel variants.

Isovaleric acidaemia (IVA) is an autosomal recessive inborn error of leucine metabolism. It is caused by a deficiency in the mitochondrial isovaleryl-CoA dehydrogenase (IVD) enzyme. In this study, we investigated eight patients with IVA. The patients' diagnoses were confirmed by urinary organic acid analysis and the blood C5-Carnitine value. A molecular genetic analysis of the IVD gene revealed nine different variants: five were missense variants (c.1193G > A; p. R398Q, c.1207T > A; p. Y403N, c.872C > T; p. A291V, c.749G > C; p. G250A, c.1136T > C; p.I379T), one was a frameshift variant (c.ins386 T; p. Y129fs), one was a splicing variant (c.465 + 2T > C), one was a polymorphism (c.732C > T; p. D244D), and one was an intronic benign variant (c.287 + 14T > C). Interestingly, all variants were in homozygous form, and four variants were novel (p. Y403N, p. Y129fs, p. A291V, p. G250A) and absent from 200 normal chromosomes. We performed protein modelling and dynamics analyses, pathogenicity and stability analyses, and a physiochemical properties analysis of the five missense variants (p.Y403N, R398Q, p.A291V, p.G250A, and p.I379T). Variants p.I379T and p.R398Q were found to be the most deleterious and destabilizing compared to variants p.A291V and p.Y403N. However, the four variants were predicted to be severe by the protein dynamic and in silico analysis, which was consistent with the patients' clinical phenotypes. The p.G250A variant was computationally predicted as mild, which was consistent with the severity of the clinical phenotype. This study reveals a potentially meaningful genotype-phenotype correlation for our patient cohort and highlights the development and use of this computational analysis for future assessments of genetic variants in the clinic.

Genotype-phenotype correlation in 18 Egyptian patients with glutaric acidemia type I.

Glutaric acidemia I (GAI) is an autosomal recessive metabolic disease caused by a deficiency of glutaryl-CoA dehydrogenase enzyme (GCDH). Patients with GAI are characterized by macrocephaly, acute encephalitis-like crises, dystonia and frontotemporal atrophy. In this study, we investigated 18 Egyptian patients that were diagnosed with GAI based on their clinical, neuroradiological, and biochemical profiles. Of the 18 patients, 16 had developmental delay and/or regression, dystonia was prominent in 75% of the cases, and three patients died. Molecular genetics analysis identified 14 different mutations in the GCDH gene in the 18 patients, of the 14 mutations, nine were missense, three were in the 3'-Untranslated Region (3'-UTR), one was nonsense, and one was a silent mutation. Four novel mutations were identified (c.148 T > A; p.Trp50Arg, c.158C > A; p.Pro53Gln, c.1284C > G; p.Ile428Met, and c.1189G > T; p.Glu397*) that were all absent in 300 normal chromosomes. The 3'-UTR mutation (c.*165A > G; rs8012), was the most frequent mutation observed (0.5; 18/36), followed by the most common mutation among Caucasian patients (p.Arg402Trp; rs121434369) with allele frequency of 0.36 (13/36), and the 3'-UTR mutation (c.*288G > T; rs9384, 0.22; 8/16). The p.Arg257Gln mutation was found with allele frequency of ~0.17 (6/36). The marked homozygosity observed in our patients is probably due to the high level of consanguinity that is observed in 100% of the cases. We used nine in silico prediction tools to predict the pathogenicity (SIFT, PhD-SNP, SNAP, Meta-SNP, PolyPhen2, and Align GVGD) and protein stability (I-Mutant2.0, Mupro, and istable) of the nine missense mutants. The mutant p.Arg402Trp was predicted to be most deleterious by all the six pathogenicity prediction tools and destabilizing by all the three-stability prediction tools, and highly conserved by the ConSurf server. Using the clinical, biochemical, family history of the 18 patients, and the in silico analysis of the missense mutations, our study showed a mix of conclusive and inconclusive genotype-phenotype correlations among our patient's cohort and suggests the usefulness of using various sophisticated computational analysis to be utilized for future variant classifications in the genetic clinics.

Severe neurological manifestations in an Egyptian patient with a novel frameshift mutation in the Glutaryl-CoA dehydrogenase gene.

To characterize an Egyptian patient with glutaric acidemia type I (GA I) and to identify the causative mutation(s) that may be responsible for the disease phenotype. MRI was performed on the patient using the 1.5 T magnet, biochemical analysis was carried out using gas chromatography/mass spectrometry on the patient's dried blood spot, and the patient's organic acids were measured in dried blood and a urine sample using MS/MS and GC/MS, respectively. Total RNA was isolated from the patient's peripheral blood, and the synthesized cDNA was bi-directionally sequenced. The patient exhibited clinical features and MRI findings compatible with a diagnosis of GA I. The abnormal elevation of organic acids in the urine supported the presence of glutaryl-CoA dehydrogenase deficiency. Gene sequencing revealed a novel homozygous frameshift mutation, c.644_645insCTCG; p.(Pro217Leufs*14), in exon 8 of the GCDH gene. The present study revealed a novel frameshift mutation responsible for a severe GA I phenotype in an Egyptian patient. This novel mutation will ultimately contribute to a better understanding of the molecular pathology of the disease and shed light on the intricacies of the genotype-phenotype correlation of GA I disease.

Two patients with Canavan disease and structural modeling of a novel mutation.

Canavan disease (CD) is a rare fatal childhood neurological autosomal recessive genetic disease caused by mutations in the ASPA gene, which lead to catalytic deficiency of the ASPA enzyme, which catalyzes the hydrolysis of N-acetyl-L-aspartate (NAA) into aspartate and acetate. CD occurs frequently among Ashkenazi Jewish population, however it has been reported in many other ethnic groups with significantly lower frequency. Here, we report on two Egyptian patients diagnosed with CD, the first patient harbors five missense mutations (c.427 A > G; p. I143V, c.502C > T; p. R168C, c.530 T > C; p. I177T, c.557 T > C; p. V186D c.548C > T; p. P183L) and a silent mutation (c.693 C > T; p. Y231Y). The second patient was found to be homozygous for two missense mutations (c.427 A > G; p. I143V and c.557 T > A; p. V186D). Furthermore, molecular modeling of the novel mutation p. P183L provides an instructive explanation of the mutational impact on the protein structure that can affect the function of the ASPA. Here, the clinical, radiological, and biochemical profile of the two patients are reviewed in details.

Novel mutation in an Egyptian patient with infantile Canavan disease.

Canavan disease (CD) is a rare fatal childhood neurological autosomal recessive genetic disease caused by mutations in the ASPA gene, which lead to catalytic deficiency of the ASPA enzyme that catalyzes the deacetylation of NAA. It is a severe progressive leukodystrophy characterized by spongiform degeneration of the white matter of the brain. CD occurs frequently among Ashkenazi Jewish population, however it has been reported in many other ethnic groups with significantly lower frequency. Here, we report on a 2 year-old Egyptian child with severe CD who harbors a novel homozygous missense variant (c.91G > T, p.V31F) in the ASPA gene. The clinical, radiological, and molecular genetic profiles are reviewed in details.