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Zorluk: OrtaPediatric Genetic and Metabolic Disorders

An 11-month-old girl is brought to the pediatric emergency department by her adoptive parents after experiencing a generalized tonic-clonic seizure that lasted 3 minutes. She was adopted internationally at age 4 months, and her neonatal medical records and newborn screening results are unavailable. The parents report that over the past several months, she has become increasingly lethargic and hypotonic, and she has not started crawling or babbling. On physical examination, her temperature is 37.1∘C37.1^\circ\text{C} (98.8∘F98.8^\circ\text{F}), heart rate is 120/min120/\text{min}, and respiratory rate is 32/min32/\text{min}. The patient is lethargic with absent deep tendon reflexes. She has diffuse thinning of her scalp hair and an erythematous, scaly eruption around her mouth and diaper area.

Laboratory studies show:
Serum sodium: 140 mEq/L140\text{ mEq/L}
Serum chloride: 104 mEq/L104\text{ mEq/L}
Serum bicarbonate: 14 mEq/L14\text{ mEq/L}

Arterial blood gas on room air reveals:
pH: 7.287.28
pCO2\text{pCO}_2: 29 mmHg29\text{ mmHg}

Which of the following is the most appropriate next step in the management of this patient?

  1. Administration of oral biotinCevap
  2. B
    Endotracheal intubation and mechanical ventilation
  3. C
    Initiation of a phenylalanine-restricted diet
  4. D
    Intravenous ceftriaxone and vancomycin
  5. E
    Reassurance and referral for early intervention physical therapy

Cevap

Administration of oral biotin
The clinical vignette describes a classic presentation of biotinidase deficiency, an autosomal recessive metabolic disorder. Without newborn screening (which typically detects this disorder early), patients present in late infancy with neurologic abnormalities (seizures, hypotonia, developmental delay), cutaneous findings (alopecia, eczematous/seborrheic rash), and a high anion gap metabolic acidosis (due to lactic and organic acid accumulation). The treatment is immediate and lifelong administration of oral biotin, which provides the essential cofactor directly and bypasses the recycling defect, rapidly reversing the clinical symptoms.

Adım Adım Çözüm

1
Interpret the clinical presentation (developmental delay, hypotonia, seizures, alopecia, and an erythematous scaly rash).
These findings are highly characteristic of late-onset or untreated biotinidase deficiency (a multiple carboxylase deficiency).
Without newborn screening, biotinidase deficiency typically presents in late infancy with neurologic and cutaneous abnormalities due to the inability to recycle biotin.
2
Analyze the patient's laboratory values and acid-base status.
The patient has a high anion gap metabolic acidosis (AG = 22) with an appropriately compensated respiratory response (expected pCO2 = 29 mmHg).
A high anion gap is expected due to lactic acidosis and organic acid accumulation resulting from carboxylase dysfunction. Winter's formula confirms the respiratory rate is a normal compensatory mechanism.
3
Determine the appropriate management based on the diagnosis and stable respiratory status.
The next best step is oral biotin supplementation.
Biotin bypasses the enzymatic defect and resolves the metabolic and clinical abnormalities.

Anahtar Kavram

Biotinidase deficiency classically presents in unscreened infants with developmental delay, seizures, hypotonia, alopecia, a seborrheic dermatitis-like rash, and high anion gap metabolic acidosis; it is treated definitively with lifelong oral biotin.
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Pediatric Genetic and Metabolic Disorders

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