Tryptophanuria with dwarfism.
Incidence
It is a rare autosomal recessive condition.
Clinical Characteristics
Patients may have cutaneous photosensitivity and ataxia in infancy and childhood. The clinical symptoms resemble Harnup disease but the chemical findings are different. Patients tend to have mental retardation and motor retardation in infancy and childhood. Spasticity may be present. Gait disturbance with ataxia is present. There is speech disturbance in childhood. Patients tend to be of small stature or with dwarfism. There may be conjuntival telangiectasia, which together with the ataxia resemble ataxia-telangiectasia. Tryptophan in urine and plasma is elevated. Kynurenine in urine may be normal or decreased. Tryptophan loading increase markedly the plasma levels of tryptophan and remain higher than in normals, and the tryptophanuria is also increased with little increase in kynurenine excretion. It is due to presumed tryptophan-2,3-dioxygenase/kynurenine formylase deficiency present in the liver. It seems to be a defect in tryptophan degradation via the kynurenine pathway. The symptomatology of reported cases with presumed defect in the kynurenine pathway of tryptophan metabolism is caused by nicotinic acid deficiency, one of the products of this pathway. Because of potentially deficient formation of nicotinamide, symptomatic patients should be supplemented with nicotinamide.
Precipitants
no
Provocation Tests
Tryptophan loading increase markedly the plasma levels of tryptophan and remain higher than in normals, and the tryptophanuria is also increased with little increase in kynurenine excretion.
Diagnostic Procedures
EB-L. It is due to presumed tryptophan-2,3-dioxygenase/kynurenine formylase deficiency present in the liver. Tryptophan in urine and plasma is elevated. Kynurenine in urine may be normal or decreased.