The Clinical and Molecular Characteristics of Molybdenum Cofactor Deficiency Due to MOCS2 Mutations

Consensus guidelines for the diagnosis and management of isolated sulfite oxidase deficiency and molybdenum cofactor deficiencies

Sulfite intoxication is the hallmark of four ultrarare disorders that are caused by impaired sulfite oxidase activity due to genetic defects in the synthesis of the molybdenum cofactor or of the apoenzyme sulfite oxidase. Delays on the diagnosis of these disorders are common and have been caused by their unspecific presentation of acute neonatal encephalopathy with high early mortality, followed by the evolution of dystonic cerebral palsy and also by the lack of easily available and reliable diagnostic tests. There is significant variation in survival and in the quality of symptomatic management of affected children. One of the four disorders, molybdenum cofactor deficiency type A (MoCD-A) has recently become amenable to causal treatment with synthetic cPMP (fosdenopterin). The evidence base for the rational use of cPMP is very limited. This prompted the formulation of these clinical guidelines to facilitate diagnosis and support the management of patients. The guidelines were developed by experts in diagnosis and treatment of sulfite intoxication disorders. It reflects expert consensus opinion and evidence from a systematic literature search.

A case report of molybdenum cofactor deficiency type A: the first case diagnosed in Syria

Introduction

Molybdenum cofactor deficiency (MoCD) type A, a rare mitochondrial disorder with characteristic clinical presentation and imaging findings, is one of the forms of molybdenum cofactor deficiency. It presents with seizures, psychomotor delay, and breastfeeding difficulties. Seizures are especially prominent in patients with MoCD.

Case presentation

A 3-month-old girl presented with refractory generalized tonic-clonic seizures since the third day of life. Her parents were third-degree relatives. On physical examination, she demonstrated psychomotor delay, breastfeeding difficulties, seizures, doll-like facial features, and other neurological abnormalities. Her brain MRI scan revealed cortical and white matter atrophy of the cerebral hemispheres. Metabolic workup revealed elevated levels of liver enzymes, lactic acid, and ammonia. These results were inconclusive. She received anticonvulsants and vitamin therapy to manage her seizures. Based on a suspicion of mitochondrial disease, genetic analysis was performed, revealing a homozygous variant of uncertain significance in the MOCS1 gene associated with autosomal recessive molybdenum cofactor deficiency type A.

Conclusion

MoCD is a rare disease. Early diagnosis should be considered based on the patient's medical history and MRI findings, after excluding other possible diagnoses. The definitive diagnosis relies on genetic testing results.

Epilepsy in sulfite oxidase deficiency and related disorders: insights from neuroimaging and genetics

Sulfite oxidase deficiency (SOD) and related disorders, especially molybdenum cofactor deficiency (MoCD), are a group of rare and severe neurometabolic disorders caused by gene mutations that affect the sulfur-containing amino acid catabolic pathway. These disorders are characterized by distinctive neuroimaging features such as diffuse cerebral atrophy, multicystic encephalomalacia, and ventriculomegaly in early infancy. These features are essential for early diagnosis and treatment. Moreover, the genetics of these disorders are complex but have been increasingly elucidated in the era of molecular medicine. Therefore, we reviewed 28 articles (published from January 1967 until October 2021) on SOD and MoCD, focusing on their neuroimaging and genetic aspects. We highlighted the differences between SOD and MoCD and other conditions that may mimic them, such as common neonatal hypoxic-ischemic encephalopathy and uncommon neonatal metabolic disorder (Leigh syndrome). We also summarized the current knowledge on the genetic mechanisms and the manifestation of seizure disorders of SOD and MoCD. In conclusion, if clinical, neuroimaging, and neuropathological findings suggest a possible SOD or related disorder; extensive molecular diagnostics should be performed to confirm the diagnosis.

Molybdenum Cofactor Deficiency in Humans

Molybdenum cofactor (Moco) deficiency (MoCD) is characterized by neonatal-onset myoclonic epileptic encephalopathy and dystonia with cerebral MRI changes similar to hypoxic-ischemic lesions. The molecular cause of the disease is the loss of sulfite oxidase (SOX) activity, one of four Moco-dependent enzymes in men. Accumulating toxic sulfite causes a secondary increase of metabolites such as S-sulfocysteine and thiosulfate as well as a decrease in cysteine and its oxidized form, cystine. Moco is synthesized by a three-step biosynthetic pathway that involves the gene products of MOCS1, MOCS2, MOCS3, and GPHN. Depending on which synthetic step is impaired, MoCD is classified as type A, B, or C. This distinction is relevant for patient management because the metabolic block in MoCD type A can be circumvented by administering cyclic pyranopterin monophosphate (cPMP). Substitution therapy with cPMP is highly effective in reducing sulfite toxicity and restoring biochemical homeostasis, while the clinical outcome critically depends on the degree of brain injury prior to the start of treatment. In the absence of a specific treatment for MoCD type B/C and SOX deficiency, we summarize recent progress in our understanding of the underlying metabolic changes in cysteine homeostasis and propose novel therapeutic interventions to circumvent those pathological changes.

Ocular characteristics of a 6-year-Old boy with molybdenum cofactor deficiency type B

Purpose

To report a rare case of Molybdenum Cofactor Deficiency with novel ocular manifestations.

Observations

This is a case study of a 6-year-old boy who initially presented with conjunctival hyperemia and ocular pain of the left eye. Medical history revealed refractory convulsion, global developmental delay, microcephaly, feeding difficulties, aphasia, and spastic quadriplegia, as well as pathogenic MOCS2 mutations, indicating the diagnosis of molybdenum cofactor deficiency (MoCD). This case report highlights detailed ocular manifestations of late-onset MoCD-B, ectopia lentis of bilateral eyes, spherophakia, hyperemia, secondary glaucoma, cyclodialysis, and retinal detachment of the left eye, which will help further understanding of MoCD.

Conclusions and importance

MoCD as a rare genetic disease is tend to be easily neglected. The ophthalmic examination could provide important evidence for early diagnosis.

Congenital Brain Malformations: An Integrated Diagnostic Approach

Congenital brain malformations are abnormalities present at birth that can result from developmental disruptions at various embryonic or fetal stages. The clinical presentation is nonspecific and can include developmental delay, hypotonia, and/or epilepsy. An informed combination of imaging and genetic testing enables early and accurate diagnosis and management planning. In this article, we provide a streamlined approach to radiologic phenotyping and genetic evaluation of brain malformations. We will review the clinical workflow for brain imaging and genetic testing with up-to-date ontologies and literature references. The organization of this article introduces a streamlined approach for imaging-based etiologic classification into malformative, destructive, and migrational abnormalities. Specific radiologic ontologies are then discussed in detail, with correlation of key neuroimaging features to embryology and molecular pathogenesis.

Genotype-Phenotype Dissociation in Two Taiwanese Children with Molybdenum Cofactor Deficiency Caused by MOCS2 Mutation

BACKGROUND

To describe the genotype-phenotype dissociation in two Taiwanese patients with molybdenum cofactor deficiency (MoCoD) caused by MOCS2 gene mutations.

PATIENT DESCRIPTION

Patient 1 exhibited early-onset neurological symptoms soon after birth, followed by subsequent myoclonic seizures and movement disorder. The brain magnetic resonance imaging (MRI) showed diffuse brain injury with cystic encephalomalacia along with bilateral globus pallidi involvement, hypoplasia of corpus callosum, and cerebellar atrophy. Patient 2 had a mild phenotype with prominent movement disorder after intercurrent illness, and the brain MRI showed selective injury of the bilateral globus pallidi and the cerebellum. Both patients had markedly low levels of plasma uric acid and harbored the same MOCS2 homozygous c.16C > T mutation. Patient 1 showed chronic regression of developmental milestones and died of respiratory failure at the age of 8 years, whereas patient 2 demonstrated improvement in motor function.

CONCLUSION

Genotype-phenotype dissociation could be noted in patients with MoCoD due to MOCS2 mutation. Patients with neonatal seizures, developmental delay, movement disorder, and motor regression after an illness, as well as focal or bilateral involvement of the globus pallidi on the neuroimages, should undergo biochemical testing of plasma uric acid. A pronounced plasma uric acid level is a good indicator of MoCoD. Early diagnosis can allow early provision of adequate genetic counseling.

Case Report: Compound Heterozygous Variants in MOCS3 Identified in a Chinese Infant With Molybdenum Cofactor Deficiency

Background: The molybdenum cofactor (Moco) deficiency in humans results in the inactivity of molybdenum-dependent enzymes and is caused by pathogenic variants in MOCS1 (Molybdenum cofactor synthesis 1), MOCS2 (Molybdenum cofactor synthesis 2), and GPHN (Gephyrin). These genes along with MOCS3 (Molybdenum cofactor synthesis 3) are involved in Moco biosynthesis and providing cofactors to Moco-dependent enzymes. Until now, there was no study to confirm that MOCS3 is a causative gene of Moco deficiency. Methods: Detailed clinical information was collected in the pedigree. The Whole-exome sequencing (WES) accompanied with Sanger sequencing validation were performed. Results: We described the clinical presentations of an infant, born to a non-consanguineous healthy family, diagnosed as having MOCS3 variants caused Moco deficiency and showing typical features of Moco deficiency including severe neurologic symptoms and cystic encephalomalacia in the brain MRI, resulting in neonatal death. Compound heterozygous variants in the MOCS3 gene were identified by WES. Positive sulfite and decreased levels of uric acid in plasma and urine were detected. Conclusion: To our knowledge, this is the first case of MOCS3 variants causing Moco deficiency. Our study may contribute to genetic diagnosis of Moco deficiency and future genetic counseling.

Adolescent-Onset and Adult-Onset Vitamin-Responsive Neurogenetic Diseases: A Review

Importance

Vitamin-responsive inherited diseases are among the rare genetic disorders with a specific pharmacological treatment. Many of these conditions have a prominent neurological phenotype that is mainly reported in children. Being rare and often strikingly different in adult-onset forms, they are still poorly known in the medical fields specific to adults.

Observation

This article reviews all articles reporting cases of patients with a genetically confirmed inherited vitamin-responsive neurological disease and neurological onset after the age of 10 years. On this basis, 24 different diseases are described, involving vitamins A, B1, B2, B3, B6, B8, B9, B12, E, and tetrahydrobiopterin (BH4). Information such as clinical symptoms, disease course, imaging studies, biochemical alterations, and response to treatment present an overall picture of these patients.

Conclusions and Relevance

Vitamin-responsive neurogenetic diseases represent a group of rare conditions that are probably underdiagnosed in adults and may have a dramatic response to treatment when started early in the course of the disease. In this review, main features of the adult-onset forms are defined and simple key messages are provided to help identify clinical situations when specific diagnostic tests should be performed and/or vitamins should be promptly administered.

A neonate with molybdenum cofactor deficiency type B

Molybdenum cofactor deficiency (MoCD) is an autosomal recessive disease which leads to a combined deficiency of molybdenum cofactor dependent enzymes. There are four different genes in molybdenum cofactor biosynthesis, MOCS1, MOCS2, MOCS3, GEPH. The patients with MOCS2 homozygous mutation who onset in the neonatal period always have severe seizures, feeding difficulties, progressive neurological deterioration. The incidence of the disease is low, and certain types have never been reported in China. Here, we present a Chinese term infant with MOCS2 who presented seizure, intolerance to feed and hypotonia on the third day after birth. Treatment included intravenous nutrition, antibiotic, and anticonvulsant therapy. The seizure can't be controlled and her encephalopathy progressed. A homozygous mutation in exon 4 in MOSC2 gene was found and the mutation of the patient has not been reported before. In conclusion, the patients with MOCS2 who onset in neonatal period often shows uncontrolled seizure, feeding difficulties, hypotonia and early death. And the MRI of them shows severe encephalomalacia. There is no treatment for the disease by now, but early diagnosis and genetic detection can give the family genetic counseling.

Fosdenopterin: a First-in-class Synthetic Cyclic Pyranopterin Monophosphate for the Treatment of Molybdenum Cofactor Deficiency Type A

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Proteins Structure Models in the Evaluation of Novel Variant (C.472_477del) in the MOCS2 Gene

(1) Background: Molybdenum cofactor deficiency type B (MOCODB, #252160) is a rare autosomal recessive metabolic disorder characterized by intractable seizures of neonatal-onset, muscular spasticity, accompanying with hypouricemia, elevated urinary sulfite levels and craniofacial dysmorphism. Thirty-five patients were reported to date. (2) Methods: Our paper aimed to delineate the disease genotype by presenting another patient, in whom a novel, in-frame variant within the MOCS2 gene was identified. (3) Results: Exome sequencing led to the identification of a novel variant in the MOCS2 gene-c.472_477del of unknown significance (VUS). (4) Conclusions: To prove the clinical significance of the mentioned variant, analysis of the possible mutation consequences on molecular level with the use of the available crystal structure of the human molybdopterin synthase complex was of great importance. Moreover, a potential pathomechanism resulting from a molecular defect was presented, giving original insight into the current knowledge on this rare disease, including treatment options.