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Zorluk: ZorPediatric Genetic and Metabolic Disorders

A 3-year-old boy is brought to the pediatrician by his parents due to worsening behavioral outbursts and a decline in his communication skills. Over the past year, he has stopped using two-word phrases and has become increasingly hyperactive and aggressive. The parents also report that he has "noisy breathing," chronic nasal discharge, and recurrent wheezing that has not improved with multiple trials of inhaled albuterol. His medical history is notable for bilateral inguinal hernia repairs at age 1. Vital signs are within normal limits. Physical examination reveals a macrocephalic child with prominent supraorbital ridges, a broad nose, and a large tongue. Abdominal examination demonstrates a firm liver edge 4 cm below the right costal margin and a palpable splenic tip. Skin examination reveals distinct, grouped, ivory-colored papules over the scapular region. Slit-lamp examination of the eyes shows perfectly clear corneas. Laboratory studies show a serum thyroid-stimulating hormone (TSH) of 2.1 µU/mL (normal: 0.5–5.0 µU/mL). Which of the following is the most likely underlying etiology of this patient's condition?

  1. A
    Deficiency of alpha-L-iduronidase
  2. B
    Bronchial smooth muscle hyperreactivity
  3. Deficiency of iduronate-2-sulfataseCevap
  4. D
    Thyroid gland dysgenesis
  5. E
    Disseminated cutaneous viral infection

Cevap

Deficiency of iduronate-2-sulfatase
The patient's presentation of developmental regression, severe hyperactivity, coarse facial features, hepatosplenomegaly, hernias, and clear corneas is classic for Hunter syndrome (Mucopolysaccharidosis type II). The ivory-colored, grouped papules over the scapular region are known as 'Hunter papules' and are a rare but pathognomonic finding for this disease. Hunter syndrome is an X-linked recessive disorder caused by a deficiency of iduronate-2-sulfatase, which leads to the toxic accumulation of heparan sulfate and dermatan sulfate in various tissues. The tissue accumulation in the airways also accounts for his noisy breathing and unresponsiveness to asthma medications.

Adım Adım Çözüm

1
Analyze the patient's physical and developmental findings.
The patient has a syndromic presentation consisting of developmental regression, coarse facial features, macroglossia, hepatosplenomegaly, hernias, and specific skin papules.
Synthesizing these multi-system findings is required to narrow the differential diagnosis to a metabolic storage disorder, specifically a mucopolysaccharidosis (MPS).
2
Differentiate between the distinct types of mucopolysaccharidoses.
The presence of perfectly clear corneas and grouped, ivory-colored scapular papules (Hunter papules) distinguishes this condition from MPS I (Hurler syndrome).
Corneal clouding is a critical physical exam discriminator that is present in Hurler syndrome but characteristically absent in Hunter syndrome.
3
Identify the specific biochemical defect responsible for the identified syndrome.
Hunter syndrome is caused by a deficiency in iduronate-2-sulfatase.
This specific enzyme deficiency leads to the tissue accumulation of heparan sulfate and dermatan sulfate, directly causing the unique clinical phenotype.

Anahtar Kavram

Hunter syndrome (Mucopolysaccharidosis Type II) is an X-linked recessive lysosomal storage disease caused by iduronate-2-sulfatase deficiency. It is distinguished from Hurler syndrome by the absence of corneal clouding and the presence of pathognomonic grouped, ivory-colored skin papules.
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Pediatric Genetic and Metabolic Disorders

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