Mutations in MYLPF Cause a Novel Segmental Amyoplasia that Manifests as Distal Arthrogryposis.

We identified ten persons in six consanguineous families with distal arthrogryposis (DA) who had congenital contractures, scoliosis, and short stature. Exome sequencing revealed that each affected person was homozygous for one of two different rare variants (c.470G>T [p.Cys157Phe] or c.469T>C [p.Cys157Arg]) affecting the same residue of myosin light chain, phosphorylatable, fast skeletal muscle (MYLPF). In a seventh family, a c.487G>A (p.Gly163Ser) variant in MYLPF arose de novo in a father, who transmitted it to his son. In an eighth family comprised of seven individuals with dominantly inherited DA, a c.98C>T (p.Ala33Val) variant segregated in all four persons tested. Variants in MYLPF underlie both dominant and recessively inherited DA. Mylpf protein models suggest that the residues associated with dominant DA interact with myosin whereas the residues altered in families with recessive DA only indirectly impair this interaction. Pathological and histological exam of a foot amputated from an affected child revealed complete absence of skeletal muscle (i.e., segmental amyoplasia). To investigate the mechanism for this finding, we generated an animal model for partial MYLPF impairment by knocking out zebrafish mylpfa. The mylpfa mutant had reduced trunk contractile force and complete pectoral fin paralysis, demonstrating that mylpf impairment most severely affects limb movement. mylpfa mutant muscle weakness was most pronounced in an appendicular muscle and was explained by reduced myosin activity and fiber degeneration. Collectively, our findings demonstrate that partial loss of MYLPF function can lead to congenital contractures, likely as a result of degeneration of skeletal muscle in the distal limb.

Molecular autopsy in maternal-fetal medicine.

PurposeThe application of genomic sequencing to investigate unexplained death during early human development, a form of lethality likely enriched for severe Mendelian disorders, has been limited.MethodsIn this study, we employed exome sequencing as a molecular autopsy tool in a cohort of 44 families with at least one death or lethal fetal malformation at any stage of in utero development. Where no DNA was available from the fetus, we performed molecular autopsy by proxy, i.e., through parental testing.ResultsPathogenic or likely pathogenic variants were identified in 22 families (50%), and variants of unknown significance were identified in further 15 families (34%). These variants were in genes known to cause embryonic or perinatal lethality (ALPL, GUSB, SLC17A5, MRPS16, THSD1, PIEZO1, and CTSA), genes known to cause Mendelian phenotypes that do not typically include embryonic lethality (INVS, FKTN, MYBPC3, COL11A2, KRIT1, ASCC1, NEB, LZTR1, TTC21B, AGT, KLHL41, GFPT1, and WDR81) and genes with no established links to human disease that we propose as novel candidates supported by embryonic lethality of their orthologs or other lines of evidence (MS4A7, SERPINA11, FCRL4, MYBPHL, PRPF19, VPS13D, KIAA1109, MOCS3, SVOPL, FEN1, HSPB11, KIF19, and EXOC3L2).ConclusionOur results suggest that molecular autopsy in pregnancy losses is a practical and high-yield alternative to traditional autopsy, and an opportunity for bringing precision medicine to the clinical practice of perinatology.

Clinical and molecular characterization of 6 children with glutamate-cysteine ligase deficiency causing hemolytic anemia.

Glutathione (gamma-glutamylcysteinylglycine) has diverse functions including free radicals scavenging and modulating many critical cellular processes. Glutathione is synthesized by the consecutive action of the enzymes glutamate-cysteine ligase (GCL) and glutathione synthetase. GCL is composed of a catalytic subunit encoded by the GCLC gene and a regulatory subunit encoded by the GCLM gene. GCL deficiency due to homozygous mutations in GCLC has been reported in 6 individuals from 4 independent families. All presented with hemolytic anemia and 4 had additional neurological manifestations including cognitive impairment, neuropathy, ataxia, and myopathy. In this report, we present additional 6 children from 2 independent consanguineous families with GCL deficiency. All the children presented with neonatal hemolytic anemia. Beyond the neonatal period, they did not have jaundice or hemolysis, but continued to have mild anemia. They all had normal development and neurological examination. The affected children from the first family had the homozygous mutation c.1772G>A (p.S591N) and the second family had the homozygous mutation c.514T>A (p.S172T) in GCLC. GCL deficiency can have a mild non-neurological phenotype or a more severe phenotype with neurological manifestations. GCL deficiency can be an underdiagnosed cause of hemolytic anemia, thus awareness may aid in early diagnosis, appropriate genetic counseling, and management.

Activating de novo mutations in NFE2L2 encoding NRF2 cause a multisystem disorder.

Transcription factor NRF2, encoded by NFE2L2, is the master regulator of defense against stress in mammalian cells. Somatic mutations of NFE2L2 leading to NRF2 accumulation promote cell survival and drug resistance in cancer cells. Here we show that the same mutations as inborn de novo mutations cause an early onset multisystem disorder with failure to thrive, immunodeficiency and neurological symptoms. NRF2 accumulation leads to widespread misregulation of gene expression and an imbalance in cytosolic redox balance. The unique combination of white matter lesions, hypohomocysteinaemia and increased G-6-P-dehydrogenase activity will facilitate early diagnosis and therapeutic intervention of this novel disorder.The NRF2 transcription factor regulates the response to stress in mammalian cells. Here, the authors show that activating mutations in NRF2, commonly found in cancer cells, are found in four patients with a multisystem disorder characterized by immunodeficiency and neurological symptoms.