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Condition report · Neurological

Asparagine Synthetase Deficiency

Whole genome sequencing reads the ASNS gene for inherited changes that cause asparagine synthetase deficiency, a condition with a small head at birth, severe developmental delay and seizures.

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

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About this condition

A rare inherited neurological condition with a small head at birth, severe developmental delay, seizures and progressive loss of brain tissue. It is caused by changes in both copies of ASNS, the gene for the enzyme that makes the amino acid asparagine.

Asparagine synthetase deficiency is a rare inherited neurological condition. Most affected babies have a small head at birth that becomes smaller over time as brain tissue is lost. Severe developmental delay and seizures are common, and most people with the condition do not survive past childhood.

The condition is caused by changes in both copies of ASNS, the gene for an enzyme that converts aspartic acid into asparagine. Asparagine cannot cross from the blood into the brain, so brain cells rely on this enzyme to make their own supply. Without enough of the enzyme, brain cells cannot make sufficient asparagine, which they depend on during development.

Muscle tone is low at first and later becomes stiff, and feeding difficulties are common. Care is supportive, with seizure treatment, nutrition and feeding support, physiotherapy and palliative care where needed.

The condition is inherited in an autosomal recessive way. Genetic counselling explains this pattern, and carrier and prenatal testing are available to families once the changes in the family are known.

The condition we analyse

Congenital Microcephaly - Severe Encephalopathy - Progressive Cerebral Atrophy Syndrome

Autosomal recessive

Caused by changes in both copies of ASNS, which makes asparagine synthetase. Without enough of this enzyme, brain cells cannot make sufficient asparagine, which they depend on during development.

Signs and symptoms

Microcephaly present at birth that becomes more marked with time, severe developmental delay and seizures that are often difficult to control. Muscle tone is low at first, later becoming stiff with spasticity. Exaggerated startle responses and feeding difficulties are common. Brain imaging may show generalised loss of brain tissue.

What a diagnosis changes

Care is supportive, with seizure treatment, nutrition and feeding support, physiotherapy and palliative care where needed. Genetic counselling explains the recessive inheritance, and carrier and prenatal testing are available for families.

Genes analysed

Also known as

ASNSD; asparagine synthetase deficiency

MONDO:0014258OMIM 615574Orphanet 391376MedGen 816301Sources: [1][2][3]

Why whole genome sequencing

Asparagine synthetase deficiency is inherited in a recessive way, so the family's changes matter for relatives and future pregnancies. Whole genome sequencing reads the ASNS gene in one test.

Low asparagine helps tell it apart

Low asparagine concentration in the cerebrospinal fluid can help clinicians tell this condition apart from others with similar features. Molecular genetic testing of ASNS then confirms the diagnosis when two changes are found.

Carrier and prenatal testing

In recessive inheritance both parents are carriers, and each child of two carriers has a 1 in 4 chance of being affected. Once the ASNS changes in a family are known, carrier testing for relatives and prenatal testing in future pregnancies are available.

References

  1. Alfadhel M, El-Hattab AW, 2018. Asparagine Synthetase Deficiency. GeneReviews
  2. Asparagine synthetase deficiency. MedlinePlus Genetics
  3. ASNS gene. MedlinePlus Genetics

Other neurological conditions

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