Precision Molecular Diagnosis Defines Specific Therapy in Combined Immunodeficiency with Megaloblastic Anemia Secondary to MTHFD1 Deficiency

Abstract

Background: 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 (SCID). Objective: To describe our investigative approach to the molecular diagnosis and evaluation of immune dysfunction in a family with MTHFD1 deficiency. Methods: Exome sequencing and analysis of variants in genes involved in the folate metabolic pathway in a family with two 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. Results: 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 were comparable to healthy volunteers. We will email all CoI forms as soon as we have them from all authors but have not delayed this resubmission. Responses to Comments

The clinical presentation of cobalamin‐related disorders: From acquired deficiencies to inborn errors of absorption and intracellular pathways

“…Some patients presented with pancytopenia, aHUS, mental retardation, retinopathy, and epilepsy; others with severe combined immunodeficiency with lymphopenia, defective cell mediated and humoral immunity causing severe or even lethal infections. THcy was moderately elevated only in some patients (maximum 50 μmol/L); serum Cbl and folate levels were normal and MMA was minimally elevated in a single patient, probably due to unrelated reasons.…”

Cerebral folate deficiency: Analytical tests and differential diagnosis

“…In MTHFD1 deficiency, impaired nuclear de novo dTMP biosynthesis is thought to underlie both the megaloblastic anaemia and the SCID . Treatment of affected individuals with folinic acid supplementation (in addition to intramuscular hydroxocobalamin, betaine and prophylactic antibiotics) was associated with clinical improvement, including resolution of anaemia and improved lymphocyte function in two cases …”

“…Methylenetetrahydrofolate dehydrogenase (MTHFD1) deficiency (OMIM #617780) is a rare inborn error of folate metabolism that has been reported in seven individuals from four families to date. 55,65,66 Clinical features include megaloblastic anaemia, atypical hemolytic uraemic syndrome and severe combined immune deficiency (SCID), with seizures, intellectual impairment and abnormal brain imaging in some cases. Biochemical features include elevated blood levels of homocysteine and methylmalonic acid 65 , with low CSF 5-MTHF levels documented in some affected individuals.…”

“…67 Treatment of affected individuals with folinic acid supplementation (in addition to intramuscular hydroxocobalamin, betaine and prophylactic antibiotics) was associated with clinical improvement, including resolution of anaemia and improved lymphocyte function in two cases. 55,66 3.3 | Genetic diseases associated with CFD…”

Primary Immunodeficiency: New Insights and Practical Clinical Approaches

“…The third original article concerns the diagnosis of methylenetetrahydrofolate dehydrogenase deficiency made in 2 brothers who had lymphopenia, opportunistic and bacterial infections, and macrocytosis. Ramakrishnan et al 12 report that with a mixed picture of immune deficiency, but no molecular diagnosis, the boys were managed on immune globulin and antibiotic treatment for some time. However, with the application of whole-exome sequencing, they were found to have a missense methylenetetrahydrofolate dehydrogenase mutation inherited from one parent and a large deletion from the other, which in combination led to the loss of gene function.…”