Neurodevelopmental disorders associated variants in ADAT3 disrupt the activity of the ADAT2/ADAT3 tRNA deaminase complex and impair neuronal migration.

The ADAT2/ADAT3 complex catalyzes the adenosine to inosine modification at the wobble position of eukaryotic tRNAs. Mutations in ADAT3 , the catalytically inactive subunit of the ADAT2/ADAT3 complex, have been identified in patients presenting with severe neurodevelopmental disorders (NDDs). Yet, the physiological function of ADAT2/ADAT3 complex during brain development remains totally unknown. Here we showed that maintaining a proper level of ADAT2/ADAT3 catalytic activity is required for correct radial migration of projection neurons in the developing mouse cortex. In addition, we not only reported 7 new NDD patients carrying biallelic variants in ADAT3 but also deeply characterize the impact of those variants on ADAT2/ADAT3 structure, biochemical properties, enzymatic activity and tRNAs editing and abundance. We demonstrated that all the identified variants alter both the expression and the activity of the complex leading to a significant decrease of I 34 with direct consequence on their steady-state. Using in vivo complementation assays, we correlated the severity of the migration phenotype with the degree of the loss of function caused by the variants. Altogether, our results indicate a critical role of ADAT2/ADAT3 during cortical development and provide cellular and molecular insights into the pathogenicity of ADAT3-related neurodevelopmental disorder.

Importance of the biochemical investigations for the functional characterization of a NPC1 variant identified by exome sequencing.

Niemann-Pick disease type C (NPC) is one of the lysosomal storage disorders. It is caused by biallelic pathogenic variants in NPC1 or NPC2, which results in a defective cholesterol trafficking inside the late endosome and lysosome. There is a high clinical variability in the age of presentation and the phenotype of this disorder making the diagnosis challenging. Here, we report a patient with an infantile onset global developmental delay, microcephaly and dysmorphic features, homozygous for c.3560C>T (p.A1187V) variant in NPC1. His plasma oxysterol levels were normal on two occasions. His lyso-sphingomyelin-509 (lyso-SM 509) and urinary bile acid levels were normal. Based on the phenotype and biochemical features, the diagnosis of NPC was excluded in this patient. We emphasize the importance of functional characterization in the classification of novel variants to prevent a misdiagnosis. Matching the phenotype and biochemical evidence with the molecular genomic tests is crucial for the confirmation of genetic diagnoses.

Clinical and biochemical phenotypes, genotypes, and long-term outcomes of individuals with galactosemia type I from a single metabolic genetics center in Alberta.

Background: Galactosemia type I is an autosomal recessive disorder of galactose metabolism due to galactose-1-phosphate uridyltransferase deficiency, encoded by GALT. To investigate the phenotypes, genotypes and long-term outcomes of galactosemia, we performed a retrospective cohort study in our center. Methods: All individuals with galactosemia type I were included. We divided individuals into two groups to compare the outcomes of those treated symptomatically (SymX) and asymptomatically (AsymX). We reviewed electronic patient charts for clinical features, biochemical investigations, molecular genetic investigations, treatments, and outcomes. Results: There were 25 individuals including classic (n = 17), clinical variant (n = 4), and biochemical variant (Duarte) galactosemia (n = 4). Twelve individuals were diagnosed symptomatically (SymX), and 9 individuals were diagnosed asymptomatically (AsymX). We did not include individuals with biochemical variant (Duarte) galactosemia into any of these groups. At the time of the diagnosis, conjugated hyperbilirubinemia was present in 83.3% of SymX group, whereas only 22% of AsymX group. SymX group had hepatomegaly (25%), failure to thrive (33.3%), cataract (16.7%) and sepsis (25%), whereas none of the individuals in the AsymX group had these clinical features. Fourteen variants in GALT were identified including pathogenic/likely pathogenic (n = 12), and likely benign/benign (n = 2) variants. The vast majority of individuals with classic and clinical variant galactosemia were treated with a galactose-lactose-free diet for life (n = 20/21). Intellectual disability was present in 54.5% of the SymX group, and in 37.5% of the AsymX group as a long-term outcome. Tremors were present 50% of the SymX group, and in 22% of the AsymX group as a long-term outcome. Although, intellectual disability and tremors seem to be less common in the AsymX group, there was no statistically significant difference between both groups. Primary ovarian insufficiency was present 50% of the SymX group, whereas in 20% of the AsymX group in post-pubertal females. We report a novel hypomorphic GALT variant (p.Ala303Ser) in one individual with clinical variant galactosemia. We also report an individual with clinical variant galactosemia with normal urine galactitol levels on a normal diet. Conclusion: It seems that newborn screening and early administration of a galactose-lactose-free diet decreases the long-term galactosemia-associated complications but does not prevent them completely. It may be that not all individuals with clinical variant galactosemia may need a galactose-lactose-free diet. It is timely to find new therapeutic strategies that can reduce the frequency of late-onset complications in galactosemia.

Clinical, biochemical, and molecular characterization of mucopolysaccharidosis type III in 34 Egyptian patients.

Mucopolysaccharidosis type III (MPS III) is a rare autosomal recessive lysosomal storage disorder characterized by progressive neurocognitive deterioration. There are four MPS III subtypes (A, B, C, and D) that are clinically indistinguishable with variable rates of progression. A retrospective analysis was carried out on 34 patients with MPS III types at Cairo University Children's Hospital. We described the clinical, biochemical, and molecular spectrum of MPS III patients. Of 34 patients, 22 patients had MPS IIIB, 7/34 had MPS IIIC, 4/34 had MPS IIIA, and only 1 had MPS IIID. All patients presented with developmental delay/intellectual disability, and speech delay. Ataxia was reported in a patient with MPS IIIC, and cerebellar atrophy in a patient with MPS IIIA. We reported 25 variants in the 4 MPS III genes, 11 of which were not previously reported. This is the first study to analyze the clinical and genetic spectrum of MPS III patients in Egypt. This study explores the genetic map of MPS III in the Egyptian population. It will pave the way for a national registry for rare diseases in Egypt, a country with a high rate of consanguineous marriage and consequently a high rate of autosomal recessive disorders.

Clinical and biochemical spectrum of metabolic cardiomyopathy in Egyptian children.

Background: Inborn errors of metabolism (IEMs) commonly present with pediatric cardiomyopathy. Identification of the underlying cause is necessary as it may lead to improved outcomes. Objectives: We aimed to investigate the diagnostic rate, the clinical, and biochemical spectra of IEMs among Egyptian pediatric patients presenting with cardiomyopathy, and their outcome measures. Methods: We retrospectively analyzed the clinical, biochemical, and radiological data of 1512 children diagnosed with cardiomyopathy at Cairo University Children's Hospital over a 5-year duration. Results: Two hundred twenty-nine children were clinically suspected as IEMs and underwent metabolic workup. Nineteen different IEMs were confirmed in 57 (24.4%) of the suspected children. Their median age at presentation was 2.6 years and the majority had extra-cardiac manifestations. Hypertrophic cardiomyopathy represented 43/57 (75.4%) of confirmed cases, while dilated cardiomyopathy represented 13/57 (22.8%), and one patient presented with a mixed phenotype. Twenty- six patients (45.6%) survived, while 31 patients (54%) either died or were lost to follow up and assumed deceased. Conclusions: We developed for the first time a database and a diagnostic scheme for metabolic cardiomyopathies in Egyptian children. With the recent introduction of enzyme replacement therapy, many metabolic disorders became treatable, thus establishing an early and accurate diagnosis is extremely important.

Clinical and genetic spectrum of mitochondrial DNA depletion syndromes: A report of 6 cases with 4 novel variants.

Mitochondrial DNA (mtDNA) depletion syndromes (MDS) are a heterogeneous group of rare autosomal recessive genetic disorders characterized by a decrease in the number of mtDNA copies inside the organ involved. There are three distinct forms of MDS including the hepatocerebral, the myopathic and the encephalomyopathic forms. The diversity in the clinical and genetic spectrum of these disorders makes the diagnosis challenging. Here, we describe the clinical phenotype and the genetic spectrum of 6 patients with MDS including 4 novel variants and compare them with previously reported cases. SUBJECT AND METHODS: Six patients from six unrelated families were included in this study. All the patients were subjected to a detailed history, thorough general and neurologic examination, basic laboratory investigations including lactic acid and ammonia, amino acids, acylcarnitine profiles and brain MRI. Whole-exome sequencing was performed for all of them to confirm the suspicion of mitochondrial disorder. RESULTS: In our series, four patients presented with the hepatocerebral form of MDS with the major presenting manifestation of progressive liver cell failure with severe hypotonia and global developmental delay. Four variants in the DGUOK gene and the MPV17 have been identified including 2 novel variants. One patient was identified in the myopathic form presenting with myopathy associated with two novel variants in the TK2 gene. One patient was diagnosed with encephalomyopathic form presenting with persistent lactic acidosis and global delay due to a homozygous variant in the FBXL4 gene. CONCLUSION: MDS has a wide spectrum of heterogeneous clinical presentations and about nine different genes involved. Whole exome sequencing (WES) has resulted in faster diagnosis of these challenging cases as the phenotype overlap with many other disorders. This should be considered the first-tier diagnostic test obviating the need for more invasive testing like muscle biopsies.