A child presented with severe vomiting, dehydration and fever. History revealed that the child was born normal but was not growing well from the last few months. There was progressive mental retardation. Urine analysis revealed the presence of branched amino acids and their ketoacids in high amount. Preliminary results from the blood amino acid screen showed two elevated amino acids with nonpolar sidechains.
Blood studies showed acidosis with a low bicarbonate concentration. The urine of the patient had a smell of burnt sugar. Urine analysis revealed the presence of branched amino acids and their keto acids in high amount. Preliminary results from the blood amino acid screen showed two elevated amino acids with non polar side chains.
Maple syrup urine disease
Case discussion
The signs and symptoms and the typical smell of urine suggest the presence of Maple Syrup Urine Disease caused by a deficiency of the branched chain alpha keto acid dehydrogenase complex . Fever in this patient suggests that the metabolic imbalance was worsened by an infection. Blood and urine in this disease have elevated levels of branched amino acids and their keto derivatives. The keto derivatives cause acidosis as is evident in this patient, low bicarbonate levels are due to depletion of alkali reserve.
Maple Syrup Urine Disease (MSUD)
It is also called branched chain ketonuria. The incidence is 1 per 1 lakh births. The name originates from the characteristic smell of urine (similar to burnt sugar or maple sugar) due to excretion of branched chain keto acids.
The basic biochemical defect is deficient decarboxylation of branched chain keto acids (BKA)
Clinical findings: Disease starts in the first week of life. It is characterized by convulsions, severe mental retardation, vomiting, acidosis, coma and death within the first year of life.
Laboratory findings: Urine contains branched chain keto acids, valine, leucine and isoleucine. Rothera’s test is positive, but unlike in cases of ketoacidosis, even boiled and cooled urine will give the test. Diagnosis depends on enzyme analysis in cells. Diagnosis should be done prior to 1 week after birth.
Treatment: Giving a diet low in branched chain amino acids. Mild variant is called intermittent branched chain ketonuria. This will respond to high doses of thiamine. This is because the decarboxylation of the BKA requires thiamine. Liver transplantation has been successfully tried in some cases of MSUD.