Neuroimaging findings in Menkes disease: a rare neurodegenerative disorder

Deep intronic variant causes aberrant splicing of ATP7A in a family with a variable occipital horn syndrome phenotype

Genetic variants in ATP7A are associated with a spectrum of X-linked disorders. In descending order of severity, these are Menkes disease, occipital horn syndrome, and X-linked distal spinal muscular atrophy. After 30 years of diagnostic investigation, we identified a deep intronic ATP7A variant in four males from a family affected to variable degrees by a predominantly skeletal phenotype, featuring bowing of long bones, elbow joints with restricted mobility which dislocate frequently, coarse curly hair, chronic diarrhoea, and motor coordination difficulties. Analysis of whole genome sequencing data from the Genomics England 100,000 Genomes Project following clinical re-evaluation identified a deep intronic ATP7A variant, which was predicted by SpliceAI to have a modest splicing effect. Using a mini-gene splicing assay, we determined that the intronic variant results in aberrant splicing. Sanger sequencing of patient cDNA revealed ATP7A transcripts with exon 5 skipping, or inclusion of a novel intron 4 pseudoexon. In both instances, frameshift leading to premature termination are predicted. Quantification of ATP7A mRNA transcripts using a qPCR assay indicated that the majority of transcripts (86.1 %) have non-canonical splicing, with 68.0 % featuring exon 5 skipping, and 18.1 % featuring the novel pseudoexon. We suggest that the variability of the phenotypes within the affected males results from the stochastic effects of splicing. This deep intronic variant, resulting in aberrant ATP7A splicing, expands the understanding of intronic variation on the ATP7A-related disease spectrum.

Fatal congenital copper transport defect caused by a homozygous likely pathogenic variant of SLC31A1

Known hereditary human diseases featuring impaired copper trafficking across cellular membranes involve ATP7A (Menkes disease, occipital horn disease, X-linked spinal muscular atrophy type 3) and ATP7B (Wilson disease). Herein, we report a newborn infant of consanguineous parents with a homozygous pathogenic variant in a highly conserved sequence of SLC31A1, coding for the copper influx transporter 1, CTR1. This missense variant, c.236T > C, was detected by whole exome sequencing. The infant was born with pulmonary hypoplasia and suffered from severe respiratory distress immediately after birth, necessitating aggressive mechanical ventilation. At 2 weeks of age, multifocal brain hemorrhages were diagnosed by cerebral ultrasound and magnetic resonance imaging, together with increased tortuosity of cerebral arteries. Ensuing seizures were only partly controlled by antiepileptic drugs, and the infant became progressively comatose. Laboratory investigations revealed very low serum concentrations of copper and ceruloplasmin. No hair shaft abnormalities were detected by dermatoscopy or light microscopic analyses of embedded hair shafts obtained at 4 weeks of life. The infant died after redirection of care and elective cessation of invasive mechanical ventilation at 1 month of age. This case adds SLC31A1 to the genes implicated in severe hereditary disorders of copper transport in humans.

Microcephaly in Neurometabolic Diseases

Neurometabolic disorders are an important group of diseases that mostly occur in neonates and infants. They are mainly due to the lack or dysfunction of an enzyme or cofactors necessary for a specific biochemical reaction, which leads to a deficiency of essential metabolites in the brain. This, in turn, can cause certain neurometabolic diseases. Disruption of metabolic pathways, and the inhibition at earlier stages, may lead to the storage of reaction intermediates, which are often toxic to the developing brain. Symptoms are caused by the progressive deterioration of mental, motor, and perceptual functions. The authors review the diseases with microcephaly, which may be one of the most visible signs of neurometabolic disorders.

Cu Homeostasis in Bacteria: The Ins and Outs

Copper (Cu) is an essential trace element for all living organisms and used as cofactor in key enzymes of important biological processes, such as aerobic respiration or superoxide dismutation. However, due to its toxicity, cells have developed elaborate mechanisms for Cu homeostasis, which balance Cu supply for cuproprotein biogenesis with the need to remove excess Cu. This review summarizes our current knowledge on bacterial Cu homeostasis with a focus on Gram-negative bacteria and describes the multiple strategies that bacteria use for uptake, storage and export of Cu. We furthermore describe general mechanistic principles that aid the bacterial response to toxic Cu concentrations and illustrate dedicated Cu relay systems that facilitate Cu delivery for cuproenzyme biogenesis. Progress in understanding how bacteria avoid Cu poisoning while maintaining a certain Cu quota for cell proliferation is of particular importance for microbial pathogens because Cu is utilized by the host immune system for attenuating pathogen survival in host cells.

Sorting nexin 27 (SNX27) variants associated with seizures, developmental delay, behavioral disturbance, and subcortical brain abnormalities

Sorting nexin 27 (SNX27) influences the composition of the cellular membrane via regulation of selective endosomal recycling. Molecular analysis indicates that SNX27 regulates numerous cellular processes through promiscuous interactions with its receptor cargos. SNX27 deficient (Snx27 ^-/- ) mice exhibit reduced embryonic survival, marked postnatal growth restriction and lethality. Haploinsufficient mice (Snx27 ^+/- ) show a less severe phenotype, with deficits in learning, memory, synaptic transmission and neuronal plasticity. One family previously reported with a homozygous SNX27 frameshift variant (c.515_516del;p.His172Argfs*6), exhibited infantile intractable myoclonic epilepsy, axial hypotonia, startle-like movements, cardiac septal defects, global developmental delay, failure to thrive, recurrent chest infections, persistent hypoxemia and early death secondary to respiratory failure. Here, we report two additional patients with compound heterozygous SNX27 variants, that are predicted to be damaging: (a) c.510C>G;p.Tyr170* and c.1295G>A;p.Cys432Tyr, and (b) c.782dupT;p.Leu262Profs*6 and c.989G>A;p.Arg330His. They exhibit global developmental delay, behavioral disturbance, epilepsy, some dysmorphic features and subcortical white matter abnormalities. In addition, possible connective tissue involvement was noted. Epilepsy, developmental delays and subcortical white matter abnormalities appear to be core features of SNX27-related disorders. We correlate the observed phenotype with available in vitro, in vivo and proteomic data and suggest additional possible molecular mediators of SNX27-related pathology.