Search

Sandhoff disease, one of the GM2 gangliosidoses, is a lysosomal storage disorder characterized by the absence of β-hexosaminidase A and B activity and the concomitant lysosomal accumulation of its substrate, GM2 ganglioside. It features catastrophic neurodegeneration and death in early childhood. How the lysosomal accumulation of ganglioside might affect the early development of the nervous system is not understood. Recently, cerebral organoids derived from induced pluripotent stem (iPS) cells have illuminated early developmental events altered by disease processes. To develop an early neurodevelopmental model of Sandhoff disease, we first generated iPS cells from the fibroblasts of an infantile Sandhoff disease patient, then corrected one of the mutant HEXB alleles in those iPS cells using CRISPR/Cas9 genome-editing technology, thereby creating isogenic controls. Next, we used the parental Sandhoff disease iPS cells and isogenic HEXB-corrected iPS cell clones to generate cerebral organoids that modeled the first trimester of neurodevelopment. The Sandhoff disease organoids, but not the HEXB-corrected organoids, accumulated GM2 ganglioside and exhibited increased size and cellular proliferation compared with the HEXB-corrected organoids. Whole-transcriptome analysis demonstrated that development was impaired in the Sandhoff disease organoids, suggesting that alterations in neuronal differentiation may occur during early development in the GM2 gangliosidoses.

Intellectual disability (ID) is a heterogeneous condition arising from a variety of environmental and genetic factors. Among these causes are defects in transcriptional regulators. Herein, we report on two brothers in a nonconsanguineous family with novel compound heterozygous, disease-segregating mutations (NM_015979.3: [3656A > G];[4006C > T], NP_057063.2: [H1219R];[R1336X]) in MED23. This gene encodes a subunit of the Mediator complex that modulates the expression of RNA polymerase II-dependent genes. These brothers, who had profound ID, spasticity, congenital heart disease, brain abnormalities, and atypical electroencephalography, represent the first case of MED23-associated ID in a non-consanguineous family. They also expand upon the clinical features previously reported for mutations in this gene. © 2015 Wiley Periodicals, Inc.

With recent advances in anabolic steroids, it is easy to see the gender- bending aspects of a professional bodybuilder’s body. The shaven and pumped-up pecs of male bodybuilders can grow droopy with gyne- comastia, a condition in which the body produces unwanted oestro- gen, inflating the pectoral area into protuberant lumps. Besides his developing “bitch tits,” as they are called in gym vernacular, a male bodybuilder’s testicles might shrink — in the words of one former Mr Universe,1 “to the size of cocktail peanuts” — even as his body elsewhere swells with giant balls of muscle. Similarly, a female bodybuilder, who in using steroids actually ingests male hormones, might lose the hair on her head, only to find it growing in patches on her face. Beyond the obvious development of her “manly” muscular body and the noticeable deepening of her voice, her menstruation might stop and her clitoris can elongate to the size of a small penis.

Inborn errors of metabolism (IEMs) that manifest primarily as psychiatric and behavioural symptoms in childhood are often mistaken for idiopathic primary psychiatric disorders. The pathophysiological basis of these symptoms may be overlooked until later in the disease course when neurological deficits become dominant; this results in a significant delay in establishing a proper diagnosis. To illustrate this, we describe two siblings who presented with behavioural issues and mild learning disabilities in childhood, and were consequently given multiple psychiatric diagnoses. In early adulthood, however, they manifested a rapid cognitive decline. Subsequent cranial MRI imaging revealed progressive brain iron accumulation in deep brain nuclei. Whole exome sequencing and biochemical investigation confirmed the diagnosis of mucopolysaccharidosis type IIIB. Their long diagnostic odyssey illustrates the importance of considering IEMs when assessing individuals with behavioural abnormalities and cognitive impairment.

The covalent attachment of adenosine monophosphate (AMP) to proteins, a process called AMPylation (adenylylation), has recently emerged as a novel theme in microbial pathogenesis. Although several AMPylating enzymes have been characterized, the only known virulence protein with de-AMPylation activity is SidD from the human pathogen Legionella pneumophila. SidD de-AMPylates mammalian Rab1, a small GTPase involved in secretory vesicle transport, thereby targeting the host protein for inactivation. The molecular mechanisms underlying Rab1 recognition and de-AMPylation by SidD are unclear. Here, we report the crystal structure of the catalytic region of SidD at 1.6 Å resolution. The structure reveals a phosphatase-like fold with additional structural elements not present in generic PP2C-type phosphatases. The catalytic pocket contains a binuclear metal-binding site characteristic of hydrolytic metalloenzymes, with strong dependency on magnesium ions. Subsequent docking and molecular dynamics simulations between SidD and Rab1 revealed the interface contacts and the energetic contribution of key residues to the interaction. In conjunction with an extensive structure-based mutational analysis, we provide in vivo and in vitro evidence for a remarkable adaptation of SidD to its host cell target Rab1 which explains how this effector confers specificity to the reaction it catalyses., Author Summary The covalent attachment of adenosine monophosphate (AMP) to proteins, a process called AMPylation (adenylylation), has recently emerged as a novel theme in microbial pathogenesis. While AMPylases from various pathogenic microorganisms have recently been characterized, the only virulence protein with de-AMPylation activity known to date is the Legionella pneumophila effector SidD which catalyzes AMP removal from the host GTPase Rab1. Thus, both AMPylation and de-AMPylation constitute a novel catalytic mechanism to precisely control the function and membrane dynamics of a host Rab GTPase. In spite of this pivotal role, the molecular mechanism of AMP removal and the structural determinants for Rab1 recognition by SidD have remained largely unexplored. Here, we present the crystal structure of the de-adenylylation domain of SidD and reveal the catalytic mechanism of Rab1 de-adenylylation. Surprisingly, the structure of SidD is not related to the other known enzyme with de-AMPylation activity, the Escherichia coli GS-ATase. Instead, the catalitic domain of SidD is remarkably similar to that of the metal-dependent protein phosphatases (PPMs), however with distinctive structural features to distinguish AMPylated Rab1 from similarly modified substrates. Importantly, we provide a model for the SidD-Rab1 complex which sheds light into the specific details of substrate recognition and catalysis by this virulence factor.

Lysosomal storage diseases (LSD) are a heterogeneous group of approximately 60 disorders caused by lysosomal dysfunction. The significant variability in the age of onset, rate of progression, and symptomatology of these disorders can make diagnosis difficult, particularly for those LSD with later onset and delayed progression. We report a 25-year-old female who exhibited profound behavioral issues andmild learning disabilities in childhood. As a result, shewas diagnosed with multiple psychiatric disorders, and treated to attain acceptable behavior. In her mid-twenties, she manifested a rapid cognitive decline. Brain imaging studies showed moderate cortical atrophy and significant deposition of metal in several regions. Her family history was notable for an older sister with a very similar phenotype. In the absence of signs pathognomonic for their disease, we pursued whole exome sequencing of the family. This identified compound heterozygous mutations in NAGLU,which encodesN-acetyl-D-glucosaminidase. Biochemical studies confirmed enzyme deficiency diagnostic of mucopolysaccharidosis IIIB (Sanfilippo syndrome). Both the initial behavioral presentation and late onset of cognitive decline contributed to the 22-year diagnostic odyssey of this patient. This case demonstrates the importance of considering late-onset metabolic disorders, such as Sanfilippo syndrome, when evaluating individuals in a mental-health setting who exhibit behavioral abnormalities and learning disabilities.