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Serum and urinary amino acid levels in sickle cell disease
D J VanderJagt1, G J Kanellis, C Isichei
1Department of Biochemistry, School of Medicine, University of New Mexico Albuquerque, NM 87131, USA.
Insights
Children with sickle cell disease (SCD) experience growth delays due to increased urinary amino acid loss. This study found lower serum amino acids and higher urinary excretion in SCD patients, suggesting a link to impaired growth.
Area of Science:
- Pediatric Hematology
- Nephrology
- Biochemistry
Background:
- Neonates with sickle cell disease (SCD) exhibit normal birth size but lag in growth by six months.
- Proximal tubule abnormalities in SCD may affect amino acid reabsorption.
- Growth retardation in SCD is a significant clinical concern.
Purpose of the Study:
- To investigate the hypothesis that increased urinary amino acid excretion contributes to growth retardation in children with SCD.
- To compare serum and urinary amino acid levels in children with SCD and healthy controls.
Main Methods:
- Serum and urine samples were collected from 13 children with SCD and 17 age-matched controls.
- Analysis of free amino acids and creatinine in serum and urine.
- Comparison of nutrient status using serum prealbumin levels.
Main Results:
- SCD patients showed significantly lower serum prealbumin levels, indicating poorer nutrition.
- Essential amino acid concentrations were significantly reduced in SCD patients' serum.
- Increased urinary excretion of seven essential amino acids, notably methionine, was observed in SCD children.
Conclusions:
- Reduced serum amino acid levels, caused by increased urinary loss, may contribute to growth deficits in children with SCD.
- Abnormalities in renal amino acid handling are implicated in the pathophysiology of SCD-related growth failure.
Abstract:
Neonates with sickle cell disease (SCD) are of normal size at birth in terms of height and weight. However, by the sixth month of life their growth begins to lag significantly behind that of non-sicklers. We hypothesize that such growth retardation could be explained, at least in part, by the increased excretion of free amino acids in the urine of children with SCD. It is well established that in SCD there are abnormalities in the proximal tubules where amino acids are reabsorbed. We collected serum and urine samples from 13 patients with SCD (age range, 10 months to 14 years), and 17 age-and gender-matched controls, and analysed these specimens for free amino acids and creatinine. The SCD population was less well nourished than the controls, as evidenced by the lower serum prealbumin levels in the former group (91.3 v. 127 mg/l, P = 0.01). The serum concentrations of all of the essential amino acids were significantly reduced (21-47 per cent, P < 0.01) in the SCD subjects, as were those of most of the non-essential amino acids (exceptions: alanine, glutamic acid, proline). The urine concentrations of seven of the essential amino acids (indexed to creatinine) were increased in the SCD children. The greatest difference in urinary amino acid excretion was seen with methionine; the SCD subjects excreted 3.6-fold more methionine than the controls. These data indicate that reduced levels of serum amino acids resulting from increased urinary loss of these amino acids in children with SCD could contribute to the decreased growth rates one sees in children with this genetically inherited hematologic disorder.