NORD gratefully acknowledges Jess G. Thoene, MD, Director, Biochemical Genetics Laboratory, Active Professor Emeritus of Pediatrics, University of Michigan, for assistance in the preparation of this report.
Citrullinemia type I (CTLN1) is a rare autosomal recessive genetic disorder that includes a neonatal acute (classic) form, a milder late-onset form, a form that begins during or after pregnancy, and an asymptomatic form.
CTLN1 is caused by deficiency or absence of the enzyme argininosuccinate synthetase (ASS). ASS is one of six enzymes that play a role in the removal of nitrogen from the body, a process known as the urea cycle. The lack of this enzyme results in excessive accumulation of nitrogen, in the form of ammonia (hyperammonemia), in the blood and all body fluids.
Infants with the classic form may experience vomiting, refusal to eat, progressive lethargy, and show signs of increased intracranial pressure. Prompt treatment can prolong survival, but neurologic deficits are usually present. The course of the late-onset form is sometimes milder but episodes of hyperammonemia are similar to the classic form.
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