Hypophosphatasia is clinically divided into three types, all caused by defects in the ALPL gene.

Hypophosphatasia is clinically divided into three types, all caused by defects in the ALPL gene.

Hypophosphatasia, infantile (MIM 241500), is a severe form with onset in utero or before 6 months of age. Inheritance is autosomal recessive. Patients may have blue sclera, bowed short limbs, metaphyseal cupping, bone spurs of the ulna and fibula, poorly formed teeth, small thoracic cage with rachitic ribs, lack of skeletal ossification with fractures, craniosynostosis, skin dimples over the apex of long bone angulations and platyspondyly. Mental retardation or development delay may also be a feature. This disorder overlaps with osteogenesis imperfecta and achondrogenesis type IA. Laboratory abnormalities include: hypercalcemia, hypercalciuria, phosphoethanolaminuria, decreased tissue and serum alkaline phosphatase and mildly elevated phosphoethanolamine. Plasma and urine inorganic pyrophosphate may be elevated.

Hypophosphatasia, childhood (MIM 241510), has a more gradual and later onset. Inheritance is also autosomal recessive. Patients share many features with the infantile form including short stature, rachitic ribs, bowed legs, skin dimples and premature loss of teeth. They may also display craniostenosis, dolichocephaly, frontal bossing, proptosis and characteristic metaphyseal radiolucency. Presentation occurs beyond 6 months of age and there may be delayed onset of walking. Laboratory abnormalities include: low alkaline phosphatase, phosphoethanolaminuria and elevated plasma and urine inorganic pyrophosphate.

Hypophosphatasia, adult type (MIM 146300) presents in middle age and may actually be asymptomatic. Inheritance can be autosomal dominant or recessive with compound heterozygosity. Patients may suffer premature tooth loss, skeletal abnormalities, osteoporosis, recurrent fractures or long bone pseudofractures, with bowed legs, bone pain or arthropathy and chondrocalcinosis. Laboratory abnormalities are similar to those described under the childhood variant.

Gene(s)

ALPL

MIM

241500

Methodology

Billing

CPT Code(s)
81479 x 1

Ordering

Test Code
1565

Additional Test Codes
1169 — Deletion / Duplication Only
1168 — Sanger

Turnaround Time
Typically 2 to 4 weeks from receipt of a sample in the laboratory. All cases involving ongoing pregnancies will be expedited.

Prenatal Specimens
Cultured cells: 2 confluent T-25 flasks derived from amnio or CVS samples
Genomic DNA: minimum of 3 µg (at a concentration of at least 30 ng/µl)

Non-Prenatal Specimens
Whole blood: purple-top (EDTA) tube, minimum of 3 ml
Genomic DNA: a minimum of 3 µg (at a concentration of at least 30 ng/µl)
Fibroblasts: 2 confluent T-25 flasks
Saliva: only samples collected in Oragene DNA Self-Collection Kit or Oragene Saliva Collection Kit for Young Children are accepted

Shipping
Ship all specimen types at room temperature by overnight courier. Do not freeze.

The American Medical Association (AMA) Current Procedural Terminology (CPT) codes published by HNL Lab Medicine are guidelines and are intended for informational purposes only. CPT coding is the exclusive responsibility of the billing entity. HNL Lab Medicine strongly recommends confirmation of CPT codes with third-party payors and/or the AMA. We assume no responsibility for billing errors due to reliance upon CPT codes provided by HNL Lab Medicine.

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