Hypophosphatasia

Hypophosphatasia refers to a rare metabolic disorder characterised by deficient serum alkaline phosphatase activity. The effects of hypophosphatasia are primarily seen in the skeletal system. The condition has marked variation in clinical expression (see subtypes).

The true incidence is uncertain as it is thought many people may live with mild forms of the disease without being diagnosed. Some authors have estimated its prevalence at 1 in 100,000. It can display either autosomal dominant or recessive inheritance, which complicates genetic counselling.

The underlying genetic abnormality is almost exclusively due to a mutation in the ALPL gene that encodes for tissue non-specific alkaline phosphatase (TNSAP) enzyme. This results in defective bone mineralisation and extracellular accumulation of TNSAP substrates. With over 300 different specific mutations recognised, the severity of the resultant clinical disorder depends on the degree to which TNSAP activity is impaired. The severer the impairment, the earlier the presentation.

Subtypes

Hypophosphatasia can be divided into several groups (at least six types 6,8) according to age at presentation 3,6

Skeletal manifestations

Some of the skeletal features are common across subtypes and include 4:

Complications are primarily those of hypercalcaemia.

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Article information

rID: 13871
Tag: cases
Synonyms or Alternate Spellings:
  • Congenital hypophosphatasia
  • Hypophosphatasia: general

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