Biallelic GRM7 variants cause epilepsy, microcephaly, and cerebral atrophy

Objective: Defects in ion channels and neurotransmitter receptors are implicated in developmental and epileptic encephalopathy (DEE). Metabotropic glutamate receptor 7 (mGluR7), encoded by GRM7, is a presynaptic G-protein-coupled glutamate receptor critical for synaptic transmission. We previously proposed GRM7 as a candidate disease gene in two families with neurodevelopmental disorders (NDDs). One additional family has been published since. Here, we describe three additional families with GRM7 biallelic variants and deeply characterize the associated clinical neurological and electrophysiological phenotype and molecular data in 11 affected individuals from six unrelated families. Methods: Exome sequencing and family-based rare variant analyses on a cohort of 220 consanguineous families with NDDs revealed three families with GRM7 biallelic variants; three additional families were identified through literature search and collaboration with a clinical molecular laboratory. Results: We compared the observed clinical features and variants of 11 affected individuals from the six unrelated families. Identified novel deleterious variants included two homozygous missense variants (c.2671G>A:p.Glu891Lys and c.1973G>A:p.Arg685Gln) and one homozygous stop-gain variant (c.1975C>T:p.Arg659Ter). Developmental delay, neonatal- or infantile-onset epilepsy, and microcephaly were universal. Three individuals had hypothalamic–pituitary–axis dysfunction without pituitary structural abnormality. Neuroimaging showed cerebral atrophy and hypomyelination in a majority of cases. Two siblings demonstrated progressive loss of myelination by 2 years in both and an acquired microcephaly pattern in one. Five individuals died in early or late childhood. Conclusion: Detailed clinical characterization of 11 individuals from six unrelated families demonstrates that rare biallelic GRM7 pathogenic variants can cause DEEs, microcephaly, hypomyelination, and cerebral atrophy. © 2020 The Authors. Annals of Clinical and Translational Neurology published by Wiley Periodicals, Inc on behalf of American Neurological Association

SLC35A2â CDG: Functional characterization, expanded molecular, clinical, and biochemical phenotypes of 30 unreported Individuals

Pathogenic de novo variants in the Xâ linked gene SLC35A2 encoding the major Golgiâ localized UDPâ galactose transporter required for proper protein and lipid glycosylation cause a rare type of congenital disorder of glycosylation known as SLC35A2â congenital disorders of glycosylation (CDG; formerly CDGâ IIm). To date, 29 unique de novo variants from 32 unrelated individuals have been described in the literature. The majority of affected individuals are primarily characterized by varying degrees of neurological impairments with or without skeletal abnormalities. Surprisingly, most affected individuals do not show abnormalities in serum transferrin Nâ glycosylation, a common biomarker for most types of CDG. Here we present data characterizing 30 individuals and add 26 new variants, the single largest study involving SLC35A2â CDG. The great majority of these individuals had normal transferrin glycosylation. In addition, expanding the molecular and clinical spectrum of this rare disorder, we developed a robust and reliable biochemical assay to assess SLC35A2â dependent UDPâ galactose transport activity in primary fibroblasts. Finally, we show that transport activity is directly correlated to the ratio of wildâ type to mutant alleles in fibroblasts from affected individuals.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/150498/1/humu23731_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/150498/2/humu23731-sup-0001-Supp_Mat__2019.2.10_.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/150498/3/humu23731.pd

Tyrosinemia type I: an unusual case presentation

Background: Hereditary tyrosinemia type 1 (HT1) is an autosomal recessive inherited metabolic disorder caused by the fumerylacetoacetate hydrolase enzyme deficiency. It is characterized by liver dysfunction and/ or failure, renal tubular dysfunction. If left untreated it may lead to Fanconi syndrome and neurological crisis (porphyria-like crisis). Nitisinone is the recommended therapy for HT1 in combination with tyrosine and phenylalanine restricted diet. Case Presentation: In this report, we present 3 years and 8-months-old boy who was referred to the Metabolic Clinic after his cousin was diagnosed with HT1. His history was significant for pleural effusion at 8 months of age which contributed to pulmonary tuberculosis. His alpha-fetoprotein was checked (for no apparent reason) at one and a half years of age and was elevated. Upon evaluation at 3 years and 8 months at our facility, his succinylacetone was significantly elevated. Liver function tests and coagulation results were also mildly elevated. Liver ultrasound was routine apart from gallstones. Targeted mutation testing revealed a fumarylacetoacetate hydrolase gene's homozygous pathogenic variant (c.982C>T; p. Gln328*). Conclusion: In conclusion, we presented a patient with an unusual, late presentation of HT1, to highlight the clinical variability in this rare, treatable metabolic disease. [JBCGenetics 2022; 5(1.000): 17-19

Opsismodysplasia and Dilated Cardiomyopathy: a case report

Background: Opsismodysplasia (OPSMD) is an extremely rare and severe autosomal recessive skeletal dysplasia that is under the category of severe spondylodysplastic dysplasia. It is characterized by delayed bone maturation, and affected patients are identified by a peculiar craniofacioskeletal dysmorphism in the form of wide anterior fontanelle, depressed nasal bridge, anteverted nares, and short limbs and feet. Radiologically, they are characterized by severe platyspondyly, squared metacarpals, delayed skeletal ossification, and metaphyseal cupping. Case Presentation: We present the clinical and radiological features of a 14-month-old boy with a homozygous, likely pathogenic variant in INPPL1 gene c.2627dup (p.Pro977Thrfs*7) consistent with the diagnosis of OPSMD. He also has dilated cardiomyopathy. Conclusion: OPSMD is an uncommon form of skeletal dysplasia that should be suspected in the context of short stature with characteristic radiological features. Up to now, no definitive therapeutic measures are available, and hence preventive measures are essential in the management of families with affected members. [JBCGenetics 2020; 3(2.000): 100-103

A case report of de novo 11q triplication, duplication, and segmental area of absence of heterozygosity in an infant with dysmorphic features, failure to thrive, and developmental delay.

Background With recent advances in array comparative genomic hybridization (aCGH) methods, several, previously unrecognized pathogenic copy number variants (CNVs) have been recognized. Intrachromosomal triplications are rare and have been reported in a few genomic regions. In this report, we describe an infant with complex chromosomal rearrangement involving the long arm of chromosome 11 with concomitant triplication, duplication, and segmental area of absence of heterozygosity (AOH). Case Presentation: We report an infant who was presented with dysmorphic features, severe failure to thrive, developmental delay, dysgenesis of the corpus callosum, and intestinal obstruction. The aCGHshowed 19,930 megabases (Mb) triplication at 11q13.3q14.3, 346 kilobases(Kb) duplication at 11q14.3 and an area of AOH at 11q14.3-qter. Conclusion The occurrence of triplication along with AOH (most likely as a result of segmental uniparental isodisomy) is a rare, complex genomic rearrangement. It is suggested that these complex genomic rearrangements coupled with segmental uniparental isodisomy arise as a result of one-ended DNA break repair coupled with microhomology-mediated break-induced replication (MMBIR). [JBCGenetics 2019; 2(1.000): 70-73

Carnitine Inborn Errors of Metabolism

Carnitine plays essential roles in intermediary metabolism. In non-vegetarians, most of carnitine sources (~75%) are obtained from diet whereas endogenous synthesis accounts for around 25%. Renal carnitine reabsorption along with dietary intake and endogenous production maintain carnitine homeostasis. The precursors for carnitine biosynthesis are lysine and methionine. The biosynthetic pathway involves four enzymes: 6-N-trimethyllysine dioxygenase (TMLD), 3-hydroxy-6-N-trimethyllysine aldolase (HTMLA), 4-N-trimethylaminobutyraldehyde dehydrogenase (TMABADH), and γ-butyrobetaine dioxygenase (BBD). OCTN2 (organic cation/carnitine transporter novel type 2) transports carnitine into the cells. One of the major functions of carnitine is shuttling long-chain fatty acids across the mitochondrial membrane from the cytosol into the mitochondrial matrix for β-oxidation. This transport is achieved by mitochondrial carnitine–acylcarnitine cycle, which consists of three enzymes: carnitine palmitoyltransferase I (CPT I), carnitine-acylcarnitine translocase (CACT), and carnitine palmitoyltransferase II (CPT II). Carnitine inborn errors of metabolism could result from defects in carnitine biosynthesis, carnitine transport, or mitochondrial carnitine–acylcarnitine cycle. The presentation of these disorders is variable but common findings include hypoketotic hypoglycemia, cardio(myopathy), and liver disease. In this review, the metabolism and homeostasis of carnitine are discussed. Then we present details of different inborn errors of carnitine metabolism, including clinical presentation, diagnosis, and treatment options. At the end, we discuss some of the causes of secondary carnitine deficiency

Mitochondrial Membranes and Mitochondrial Genome: Interactions and Clinical Syndromes

Mitochondria are surrounded by two membranes; the outer mitochondrial membrane and the inner mitochondrial membrane. They are unique organelles since they have their own DNA, the mitochondrial DNA (mtDNA), which is replicated continuously. Mitochondrial membranes have direct interaction with mtDNA and are therefore involved in organization of the mitochondrial genome. They also play essential roles in mitochondrial dynamics and the supply of nucleotides for mtDNA synthesis. In this review, we will discuss how the mitochondrial membranes interact with mtDNA and how this interaction is essential for mtDNA maintenance. We will review different mtDNA maintenance disorders that result from defects in this crucial interaction. Finally, we will review therapeutic approaches relevant to defects in mitochondrial membranes

Harel-Yoon syndrome: the first case report from Saudi Arabia

Background: Harel-Yoon syndrome (HAYOS) is a recently described, rare neurodevelopmental disorder characterized by developmental delay, hypotonia, appendicular hypertonia, axonal neuropathy, and other variable features, such as spasticity and optic atrophy. With only a few reports in the literature, both heterozygous and homozygous mutations have been reported in ATPase Family AAA Domain Containing 3A (ATAD3A). Case Presentation: Herein, we present the first case of HAYOS in Saudi Arabia. A 3-month-old girl presented with global developmental delay, hypotonia, bilateral severe sensorineural hearing loss, and vision impairment. Brain magnetic resonance imaging showed mild brain atrophy and delayed myelination. Laboratory tests showed high serum lactate and increased urinary excretion of 3-hydroxy methyl glutaconic acid. Whole exome sequencing revealed a pathogenic heterozygous variant in ATAD3A gene (c.1726C>T; p. R576W: NM_018188.4 or c.1582C>T; p. R528W: NM_001170535.1) which is the same recurrent variant reported in patients with the dominant form of HAYOS. Conclusion: Our report provides further evidence of the clinical relevance of ATAD3A gene variant (c. 1726C>T; p. R576W) in the pathogenesis of HAYOS. The therapeutic options for HAYOS are limited to supportive measures as in other mitochondrial diseases. [JBCGenetics 2020; 3(1.000): 22-27

Arginine and Citrulline for the Treatment of MELAS Syndrome

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome is a maternally inherited mitochondrial disease with a broad spectrum of manifestations. In addition to impaired energy production, nitric oxide (NO) deficiency occurs in MELAS syndrome and leads to impaired blood perfusion in microvasculature that can contribute to several complications including stroke-like episodes, myopathy, and lactic acidosis. The supplementation of NO precursors, L-arginine and L-citrulline, increases NO production and hence can potentially have therapeutic utility in MELAS syndrome. L-citrulline raises NO production to a greater extent than L-arginine; therefore, L-citrulline may have a better therapeutic effect. The clinical effect of L-citrulline has not yet been studied and clinical studies on L-arginine, which are limited, only evaluated the stroke-like episodes’ aspects of the disease. Controlled studies are still needed to assess the clinical effects of L-arginine and L-citrulline on different aspects of MELAS syndrome