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A case report of a rare type of skeletal dysplasia diagnosed by a common blood test
  1. S I Aslam,
  2. S Sivakumar
  1. Neonates, Birmingham City Hospital, Birmingham, UK

Abstract

We report a rare case of enzyme defect affecting the skeleton. Antenatal scans gave suspicion of skeletal dysplasia (micromelia affecting all four limbs with bone echogenicity). This baby girl was born preterm at 33 weeks of gestation with birth weight of 2.18 kg. She had short proximal limbs, small mandible with excessive subcutaneous tissue and large anterior fontanelle. Skeletal survey showed poorly ossified cranial vault, absence of posterior vertebral elements from L3 caudally including the sacrum, narrow chest with thin wavy ribs and gross metaphyseal rachitic changes in all x-rayed bones. Blood tests revealed low levels of alkaline phosphatise (ALP) (<5 IU) which along with high level of urinary phosphoethanolamine (PEA) confirmed the diagnosis of Hypophosphatasia. She initially required incubator O2 or Continuous Positive Airway Pressure. She became ventilatory dependent from day 5. She also developed seizures treated with phenobarbitone. On day 14, she died of respiratory failure.

Hypophosphatasia is a rare metabolic disorder with incidence of 1 in 100 000 births. This is due to low activity of the tissue-nonspecific isoenzyme of alkaline phosphatase (TNSALP). Alterations in TNSALP gene lead to rickets or osteomalacia, which characterise this disorder. Clinical presentation widely varies, from death in utero to cases in which pathologic fractures first present only in adulthood. The reported forms include perinatal (lethal), infantile, childhood, adult, odontohypophosphatasia and pseudohypophosphatasia. Our case was a lethal perinatal type. Workup for hypophosphatasia includes performing a skeletal survey (fractures and deficient skeletal mineralisation). This condition is picked up by bone profile which shows low level of ALP in blood and diagnosis further confirmed by high levels of PEA in serum or urine. Life threatening complications include respiratory compromise (due to skeletal deformities) and craniosynostosis which can lead to increased intracranial pressure. Management is mainly supportive. Replacement therapy with recombinant Alkaline Phosphatase is available as a part of research trial in very few centres.

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