Bi-allelic Mutations in the Mitochondrial Ribosomal Protein MRPS2 Cause Sensorineural Hearing Loss, Hypoglycemia, and Multiple OXPHOS Complex Deficiencies.

Biogenesis of the mitochondrial oxidative phosphorylation system, which produces the bulk of ATP for almost all eukaryotic cells, depends on the translation of 13 mtDNA-encoded polypeptides by mitochondria-specific ribosomes in the mitochondrial matrix. These mitoribosomes are dual-origin ribonucleoprotein complexes, which contain mtDNA-encoded rRNAs and tRNAs and ∼80 nucleus-encoded proteins. An increasing number of gene mutations that impair mitoribosomal function and result in multiple OXPHOS deficiencies are being linked to human mitochondrial diseases. Using exome sequencing in two unrelated subjects presenting with sensorineural hearing impairment, mild developmental delay, hypoglycemia, and a combined OXPHOS deficiency, we identified mutations in the gene encoding the mitochondrial ribosomal protein S2, which has not previously been implicated in disease. Characterization of subjects' fibroblasts revealed a decrease in the steady-state amounts of mutant MRPS2, and this decrease was shown by complexome profiling to prevent the assembly of the small mitoribosomal subunit. In turn, mitochondrial translation was inhibited, resulting in a combined OXPHOS deficiency detectable in subjects' muscle and liver biopsies as well as in cultured skin fibroblasts. Reintroduction of wild-type MRPS2 restored mitochondrial translation and OXPHOS assembly. The combination of lactic acidemia, hypoglycemia, and sensorineural hearing loss, especially in the presence of a combined OXPHOS deficiency, should raise suspicion for a ribosomal-subunit-related mitochondrial defect, and clinical recognition could allow for a targeted diagnostic approach. The identification of MRPS2 as an additional gene related to mitochondrial disease further expands the genetic and phenotypic spectra of OXPHOS deficiencies caused by impaired mitochondrial translation.

Cutis laxa, fat pads and retinopathy due to ALDH18A1 mutation and review of the literature.

Autosomal recessive cutis laxa (ARCL) is a connective tissue disorder characterized by wrinkled, inelastic skin, frequently associated with a neurologic involvement and multisystem disease. Next generation sequencing was performed in genetically unsolved patients with progeroid features, neurological and eye involvement to assess the underlying etiology. We describe an 6 month old child, diagnosed with a novel, homozygous nonsense mutation c.2339T>C in exon 18 of the ALDH18A1 gene, and reviewed all reported P5CS patients. So far 10 patients were described with mutations in ALDH18A1. Features of our patient that have been described in literature included cutis laxa on hands and feet, visible veins on thorax and abdomen, joint laxity, failure to thrive, short stature, microcephaly, and severe developmental and speech delay. Furthermore, abnormal fat distribution, retinal abnormalities, undescended testis, and retinitis pigmentosa have never been described in ALDH18A1. Some features described as unique in ALDH18A1 have been observed in PYCR1 patients, thus suggesting that the phenotypic overlap is higher than previously shown. In conclusion, the clinical phenotype caused by ALDH18A1 mutations is diverse, with variable degree of progeria in children, but always in association with neurologic disease. We suggest genetic testing for possible ALDH18A1 mutations in all patients with progeroid features, like wrinkled or parchment-like skin, abnormal growth, especially with central nervous system involvement and microcephaly.

Defining the phenotype and diagnostic considerations in adults with congenital disorders of N-linked glycosylation.

Congenital disorders of N-glycosylation (CDG) form a rapidly growing group of more than 20 inborn errors of metabolism. Most patients are identified at the pediatric age with multisystem disease. There is no systematic review on the long-term outcome and clinical presentation in adult patients. Here, we review the adult phenotype in 78 CDG patients diagnosed with 18 different forms of N-glycosylation defects. Characteristics include intellectual disability, speech disorder and abnormal gait. After puberty, symptoms might remain non-progressive and patients may lead a socially functional life. Thrombosis and progressive symptoms, such as peripheral neuropathy, scoliosis and visual demise are specifically common in PMM2-CDG. Especially in adult patients, diagnostic glycosylation screening can be mildly abnormal or near-normal, hampering diagnosis. Features of adult CDG patients significantly differ from the pediatric phenotype. Non-syndromal intellectual disability, or congenital malformations in different types of CDG and decreasing sensitivity of screening might be responsible for the CDG cases remaining undiagnosed until adulthood.

A novel phenotype associated with cutis laxa, abnormal fat distribution, cardiomyopathy and cataract.

Cutis laxa (CL) is a connective tissue disorder, characterized by loose, inelastic, sagging skin. Both acquired and inherited (dominant, recessive, and X-linked) forms exist. Here, we describe a new phenotype, which overlaps with other known CL syndromes. Our patient has a unique combination of features in association with sagging, inelastic, wrinkled skin, including cataract, severe cardiomyopathy, abnormal fat distribution, improvement of skin-wrinkling with age, and white matter abnormalities but no significant histologic collagen or elastin abnormalities. Mutation analysis of known CL genes was negative. We suggest that our patient has a novel syndrome, with the main features of CL, intellectual disability, abnormal fat distribution, cardiomyopathy, and cataract.

Apoptosis and NET formation in the pathogenesis of SLE.

Systemic Lupus Erythematosus is an autoimmune disease characterized by the formation of anti-nuclear autoantibodies, particularly anti-chromatin. Although the aetiology of the disease has not yet been fully elucidated, several mechanisms have been proposed to be involved. Due to an aberrant apoptosis or decreased removal of apoptotic cells, apoptotic blebs containing chromatin are released. During apoptosis, chromatin is modified that increases its immunogenicity. Myeloid dendritic cells (myDC) can take up apoptotic blebs and stimulate autoreactive T helper cells, and subsequently the formation of autoantibodies by autoreactive B cells. Immune complexes formed by anti-chromatin autoantibodies and modified chromatin deposit on basal membranes, and incite a local inflammation, but can also stimulate plasmacytoid dendritic cells to produce IFN-α. In addition to apoptotic blebs, neutrophil extracellular traps released by dying neutrophils, in a process called NETosis, may serve as a source of autoantigens as well. In this review, we describe the role of both apoptosis and NETosis in the pathogenesis of SLE, and show how both processes may interact with each other.