Monday, January 28, 2019

Asparagine synthetase deficiency

Gupta N, Tewari VV, Kumar M, Langeh N, Gupta A, Mishra P, Kaur P, Ramprasad V, Murugan S, Kumar R, Jana M, Kabra M. Asparagine Synthetase deficiency-report of a novel mutation and review of literature. Metab Brain Dis. 2017 Dec;32(6):1889-1900.

Asparagine synthetase deficiency is a rare inborn error of metabolism caused by a defect in ASNS, a gene encoding asparagine synthetase. It manifests with a severe neurological phenotype manifesting as severe developmental delay, congenital microcephaly, spasticity and refractory seizures. To date, nineteen patients from twelve unrelated families have been identified. Majority of the mutations are missense and nonsense mutations in homozygous or compound heterozygous state. We add another case from India which harbored a novel homozygous missense variation in exon 11 and compare the current case with previously reported cases.

Ben-Salem S, Gleeson JG, Al-Shamsi AM, Islam B, Hertecant J, Ali BR, Al-Gazali L. Asparagine synthetase deficiency detected by whole exome sequencing causes congenital microcephaly, epileptic encephalopathy and psychomotor delay. Metab Brain Dis. 2015 Jun;30(3):687-94.

Deficiency of Asparagine Synthetase (ASNSD, MIM 615574) is a very rare autosomal recessive disorder presenting with some brain abnormalities. Affected individuals have congenital microcephaly and progressive encephalopathy associated with severe intellectual disability and intractable seizures. The loss of function of the asparagine synthetase (ASNS, EC, particularly in the brain, is the major cause of this particular congenital microcephaly. In this study, we clinically evaluated an affected child from a consanguineous Emirati family presenting with congenital microcephaly and epileptic encephalopathy. In addition, whole-exome sequencing revealed a novel homozygous substitution mutation (c.1193A > C) in the ASNS gene. This mutation resulted in the substitution of highly conserved tyrosine residue by cysteine (p.Y398C). Molecular modeling analysis predicts hypomorphic and damaging effects of this mutation on the protein structure and altering its enzymatic activity. Therefore, we conclude that the loss of ASNS function is most likely the cause of this condition in the studied family. This report brings the number of reported families with this very rare disorder to five and the number of pathogenic mutations in the ASNS gene to four. This finding extends the ASNS pathogenic mutations spectrum and highlights the utility of whole-exome sequencing in elucidation the causes of rare recessive disorders that are heterogeneous and/or overlap with other conditions.

Alrifai MT, Alfadhel M. Worsening of Seizures After Asparagine Supplementation in a Child with Asparagine Synthetase Deficiency. Pediatr Neurol. 2016 May;58:98-100.

Asparagine synthetase deficiency is an autosomal recessive neurometabolic disorder characterized clinically by severe congenital microcephaly, global developmental delay, intractable epilepsy, and motor impairment in the form of spastic quadriparesis. Diagnosis is confirmed by findings of low cerebral spinal fluid or plasma asparagine in addition to a mutation of the subsequently in ASNS gene. There is no documented trial of asparagine as a treatment for this disorder.

We present a child with asparagine synthetase deficiency whose mental status improved slightly from a vegetative state to a minimally conscious state after starting asparagine supplementation. He subsequently became irritable, developed sleep disturbance, and experienced worsening seizures, requiring discontinuation of the asparagine supplements.

Asparagine supplementation may be not effective in controlling the seizures in asparagine synthetase deficiency, and it is likely to make them worse.

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