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Condition report · Metabolic

Homocystinuria and Cobalamin Disorders

Inherited disorders that raise homocysteine levels or prevent the body from absorbing, transporting or using vitamin B12 (cobalamin) and folate, including classic homocystinuria, cblC disease and Imerslund-Gräsbeck syndrome. Many are treatable with vitamins, betaine or diet. Common MTHFR variants such as C677T are not part of this report.

A condition report looks for rare variants known to cause the conditions it covers.

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The 5 conditions we analyse

Homocystinuria

Autosomal recessive

Includes classic homocystinuria due to CBS deficiency, severe MTHFR deficiency and the combined and remethylation cobalamin disorders, which can cause lens dislocation, blood clots, skeletal changes, anaemia and developmental problems.

What a diagnosis changes

Knowing allows treatment with vitamin B6, B12, folate, betaine and diet as appropriate, which can prevent lens dislocation, thrombosis and other complications.

Genes analysed

Also known as

CBS deficiency; cystathionine beta synthase deficiency; cystathionine synthase deficiency; homocystinuria (disease)

Includes 15 related subtypes ↓
  • classic homocystinuria
  • homocystinuria due to methylene tetrahydrofolate reductase deficiency
  • homocystinuria without methylmalonic aciduria
  • homocystinuria-megaloblastic anemia cblD type
  • hyperhomocysteinemia
  • methylcobalamin deficiency type cblDv1
  • methylcobalamin deficiency type cblE
  • methylcobalamin deficiency type cblG
  • methylmalonic acidemia with homocystinuria, type cblJ
  • methylmalonic acidemia with homocystinuria, type cblX
  • methylmalonic aciduria and homocystinuria
  • methylmalonic aciduria and homocystinuria type cblC
  • methylmalonic aciduria and homocystinuria type cblD
  • methylmalonic aciduria and homocystinuria type cblF
  • methylmalonic aciduria and homocystinuria, cb1L type
MONDO:0004737MedGen 42485

Inborn Disorders of Cobalamin Metabolism and Transport

Autosomal recessive

Includes defects in vitamin B12 absorption and transport such as Imerslund-Gräsbeck syndrome (CUBN, AMN), intrinsic factor deficiency (CBLIF) and transcobalamin II deficiency (TCN2), as well as intracellular cobalamin processing defects, which can cause megaloblastic anaemia, nerve damage and failure to thrive.

What a diagnosis changes

Knowing allows lifelong vitamin B12 injections or other cobalamin treatment, which can prevent anaemia and neurological damage.

Genes analysed

Also known as

cobalamin deficiency; hypocobalaminemia; inborn error of cobalamin metabolic process; inborn vitamin B12 deficiency (disease); rare inborn error of cobalamin metabolic process

Includes 25 related subtypes ↓
  • hereditary intrinsic factor deficiency
  • homocystinuria without methylmalonic aciduria
  • homocystinuria-megaloblastic anemia cblD type
  • Imerslund-Grasbeck syndrome
  • Imerslund-Grasbeck syndrome type 1
  • Imerslund-Grasbeck syndrome type 2
  • intrinsic factor and r binder, combined congenital deficiency of
  • methylcobalamin deficiency type cblDv1
  • methylcobalamin deficiency type cblE
  • methylcobalamin deficiency type cblG
  • methylmalonic acidemia due to transcobalamin receptor defect
  • methylmalonic acidemia with homocystinuria, type cblJ
  • methylmalonic acidemia with homocystinuria, type cblX
  • methylmalonic aciduria and homocystinuria
  • methylmalonic aciduria and homocystinuria type cblC
  • methylmalonic aciduria and homocystinuria type cblD
  • methylmalonic aciduria and homocystinuria type cblF
  • methylmalonic aciduria and homocystinuria, cb1L type
  • methylmalonic aciduria and/or homocystinuria, cblD type
  • methylmalonic aciduria, cblA type
  • methylmalonic aciduria, cblB type
  • transcobalamin I deficiency
  • transcobalamin II deficiency
  • vitamin B12-responsive methylmalonic acidemia
  • vitamin B12-responsive methylmalonic acidemia, type cblDv2
MONDO:0019220Orphanet 79171MedGen 1826150

Methionine Adenosyltransferase Deficiency

Caused by variants in MAT1A, which raise blood methionine levels; most people have no symptoms, but severe forms can affect the brain.

What a diagnosis changes

Knowing explains a raised methionine result and supports monitoring in the rare severe forms.

Genes analysed

Also known as

brain demyelination due to methionine adenosyltransferase deficiency; hypermethioninemia, persistent, autosomal dominant, due to methionine adenosyltransferase I/III deficiency; isolated persistent hypermethioninemia; MAT deficiency; MAT I/III deficiency; methionine adenosyltransferase deficiency, autosomal recessive

MONDO:0009607OMIM 250850Orphanet 168598MedGen 75700

S-Adenosylhomocysteine Hydrolase Deficiency

Autosomal recessive

Caused by variants in AHCY, which can cause muscle weakness, developmental delay and liver problems.

What a diagnosis changes

Knowing allows a methionine-restricted diet and supplements, which can improve some features.

Genes analysed

MONDO:0013404OMIM 613752Orphanet 88618MedGen 462408

Cerebral Folate Transport Deficiency

Autosomal recessive

Caused by variants in FOLR1, which prevent folate from reaching the brain and can cause developmental regression, movement problems and seizures in early childhood.

What a diagnosis changes

Knowing allows treatment with folinic acid, which can improve or prevent neurological symptoms when started early.

Genes analysed

Also known as

cerebral folate deficiency syndrome

MONDO:0013110OMIM 613068Orphanet 217382MedGen 442763

Limitations

  • FOLR1 lies in a region of near-identical gene copies (FOLR1, FOLR2, FOLR3), and some exons of AMN have low sequencing coverage, so variants in these genes may be missed or need confirmation.

Other metabolic conditions

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