title: Precision Molecular Diagnosis Defines Specific Therapy in Combined Immunodeficiency with Megaloblastic Anemia Secondary to MTHFD1 Deficiency.
abstract: Methylenetetrahydrofolate dehydrogenase (MTHFD1) deficiency has recently been reported to cause a folate-responsive syndrome displaying a phenotype that includes megaloblastic anemia and severe combined immunodeficiency.
  
  
  
  To describe our investigative approach to the molecular diagnosis and evaluation of immune dysfunction in a family with MTHFD1 deficiency.
  
  
  
  The methods used were exome sequencing and analysis of variants in genes involved in the folate metabolic pathway in a family with 2 affected siblings. Routine laboratory and research data were analyzed to gain an in-depth understanding of innate, humoral, and cell-mediated immune function before and after folinic acid supplementation.
  
  
  
  Interrogation of exome data for concordant variants between the siblings in the genes involved in folate metabolic pathway identified a heterozygous mutation in exon 3 of the MTHFD1 gene that was shared with their mother. In view of highly suggestive phenotype, we extended our bioinformatics interrogation for structural variants in the MTHFD1 gene by manual evaluation of the exome data for sequence depth coverage of all the exons. A deletion involving exon 13 that was shared with their father was identified. Routine laboratory data showed lymphopenia involving all subsets and poor response to vaccines. In vitro analysis of dendritic cell and lymphocyte function was comparable to that in healthy volunteers. Treatment with folinic acid led to immune reconstitution, enabling discontinuation of all prophylactic therapies.
  
  
  
  Exome sequencing demonstrated MTHFD1 deficiency as a novel cause of a combined immunodeficiency. Folinic acid was established as precision therapy to reverse the clinical and laboratory phenotype of this primary immunodeficiency.
authors.affiliation: Academic Unit of Clinical and Experimental Sciences, Faculty of Medicine and Institute for Life Sciences, University of Southampton and National Institute for Health Research (NIHR) Biomedical Respiratory Unit, University Hospital Southampton NHS Foundation Trust, Southampton, United Kingdom.
authors.forename: Kesava A
authors.initials: KA
authors.lastname: Ramakrishnan
authors.affiliation: Academic Unit of Human Development and Health, Human Genetics and Genomic Medicine, Faculty of Medicine, University of Southampton, Southampton, United Kingdom.
authors.forename: Reuben J
authors.initials: RJ
authors.lastname: Pengelly
authors.affiliation: Academic Unit of Cancer Sciences, Faculty of Medicine and Institute for Life Sciences, University of Southampton, and Cancer Research UK (CRUK) National Institute for Health Research (NIHR) Experimental Cancer Medicine Centre, Southampton, United Kingdom.
authors.forename: Yifang
authors.initials: Y
authors.lastname: Gao
authors.affiliation: Southampton National Institute for Health Research (NIHR) Wellcome Trust Clinical Research Facility and Department of Paediatric Medicine, University Hospital Southampton NHS Foundation Trust, Southampton, United Kingdom.
authors.forename: Mary
authors.initials: M
authors.lastname: Morgan
authors.affiliation: Southampton National Institute for Health Research (NIHR) Wellcome Trust Clinical Research Facility and Department of Paediatric Medicine, University Hospital Southampton NHS Foundation Trust, Southampton, United Kingdom.
authors.forename: Sanjay V
authors.initials: SV
authors.lastname: Patel
authors.affiliation: Department of Paediatric Immunology, Great Ormond Street Hospital for Children, NHS Foundation Trust, London, United Kingdom.
authors.forename: E Graham
authors.initials: EG
authors.lastname: Davies
authors.affiliation: Academic Unit of Human Development and Health, Human Genetics and Genomic Medicine, Faculty of Medicine, University of Southampton, Southampton, United Kingdom.
authors.forename: Sarah
authors.initials: S
authors.lastname: Ennis
authors.affiliation: Academic Unit of Clinical and Experimental Sciences, Faculty of Medicine and Institute for Life Sciences, University of Southampton and National Institute for Health Research (NIHR) Biomedical Respiratory Unit, University Hospital Southampton NHS Foundation Trust, Southampton, United Kingdom; Southampton National Institute for Health Research (NIHR) Wellcome Trust Clinical Research Facility and Department of Paediatric Medicine, University Hospital Southampton NHS Foundation Trust, Southampton, United Kingdom. Electronic address: S.Faust@soton.ac.uk.
authors.forename: Saul N
authors.initials: SN
authors.lastname: Faust
authors.affiliation: Academic Unit of Cancer Sciences, Faculty of Medicine and Institute for Life Sciences, University of Southampton, and Cancer Research UK (CRUK) National Institute for Health Research (NIHR) Experimental Cancer Medicine Centre, Southampton, United Kingdom; Department of Allergy, Asthma and Clinical Immunology, University Hospital Southampton NHS Foundation Trust, Southampton, United Kingdom.
authors.forename: Anthony P
authors.initials: AP
authors.lastname: Williams
mesh_terms: D000749:Anemia, Megaloblastic / Q000175:diagnosis* / Q000188:drug therapy / Q000235:genetics / Q000276:immunology; D002648:Child; D002675:Child, Preschool; D059472:Exome; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D002955:Leucovorin / Q000627:therapeutic use; D008297:Male; D008754:Methylenetetrahydrofolate Dehydrogenase (NADP) / Q000172:deficiency / Q000235:genetics*; D015778:Minor Histocompatibility Antigens / Q000235:genetics*; D009154:Mutation; D016511:Severe Combined Immunodeficiency / Q000175:diagnosis* / Q000188:drug therapy / Q000235:genetics / Q000276:immunology
chemical_list: D015778:Minor Histocompatibility Antigens; C539735:MTHFD1 protein, human; D008754:Methylenetetrahydrofolate Dehydrogenase (NADP); D002955:Leucovorin
keywords: C-1-Tetrahydrofolate synthase (C1-THF synthase); Combined immunodeficiency; Folinic acid; Lymphopenia; Megaloblastic anemia