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A 1-week-old newborn has had poor feeding, vomiting, and progressive lethargy over the past 4 days. She was born at term; pregnancy, labor, and delivery were uncomplicated, and she had no congenital anomalies. She is being breast-fed. She has a healthy 2-year-old brother; a sister died at 10 days of age after a full-term birth. Examination shows decreased muscle tone and poor responsiveness; reflexes are normal. Serum bicarbonate level is 8 mEq/L, pH is 7.15, and plasma ammonia level is 10 times the upper limit of normal. Which of the following is the most likely cause?
A) Mitochondrial disorder
B) Mucopolysaccharidoses disorder
C) Organic acid metabolism disorder
D) Renal tubular acidosis
E) X-linked leukodystrophy
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Raised ammonia is most commonly seen in 2 problems
1. Urea cycle defects- Ammonia raised in 1000's
2.Organic acidemia's- raised in 100's
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The only doubt I have is A?? How do you rule out A?
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Motochondrial disorders -1. We dont see raised Ammonia
2. The affected males die inutero and females survive and usually present with developmental regression staerting at few months of age
Sister died -is of no significance in this scenario
Here we have a picture of acute presentation suggesting metabolic disorder.#
Other views welcome
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Uptodate
Hyperammonemia ” Hyperammonemia is a characteristic feature of the urea cycle defects and propionic and methylmalonic acidemias. It also may occur in other amino acid disorders (such as lysinuric protein intolerance) and fatty acid oxidation defects, and rarely in mitochondrial disorders or with hepatic dysfunction. Ammonia concentrations tend to be highest in urea cycle disorders (300 to 1000 micromol/L [5.1 to 17 microgram/mL]) and only moderately elevated or normal in organic acidemias. However ammonia can be normal in urea cycle disorders when the patient is not acutely ill and can be well over 1000 micromol/L (17 microgram/mL) in organic acidemias. Modest elevations occur rarely in mitochondrial disorders or with hepatic dysfunction. The ammonia concentration is usually normal in disorders of carbohydrate metabolism, lysosomal storage disorders, or peroxisomal disorders [11].
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The other categories of IEM (amino acid disorders, organic acidemias, urea cycle disorders, disorders of carbohydrate metabolism, fatty acid oxidation disorders, and mitochondrial disorders) may be considered in two broad categories [14]:
* Disorders of acute or progressive intoxication or encephalopathy ” Signs and symptoms in these disorders are caused by accumulation of toxic compounds proximal to the metabolic block. Patients typically present with a symptom free-interval followed by clinical signs of acute or chronic intoxication with progressive or recurrent metabolic disturbances. This category includes amino acid disorders, most organic acidemias, urea cycle disorders, and disorders of carbohydrate intolerance (eg, galactosemia, hereditary fructose intolerance).
Presentation of the case kind of fits the above.
* Disorders associated with energy deficiency ” Signs and symptoms in these disorders are caused at least partly by a deficiency in energy production or utilization in the liver, myocardium, skeletal muscle, or brain. Disorders in this category also may have signs or symptoms related to accumulation of toxic compounds. This category includes disorders of glycogenolysis and gluconeogenesis, fatty acid oxidation defects, disorders of ketogenesis, and mitochondrial disorders.
