Hyperphosphatasia with Mental Retardation Syndrome 6

Background and History: 

This is an extremely rare multisystem hereditary disorder which results from a gene mutation that interferes with phosphorous metabolism.    

Clinical Correlations: 

Infants may be born prematurely and they usually have cataracts.  Strabismus (abnormal alignment of the eyes) is often seen.  Vision is subnormal probably as a result of abnormal connections of nerves in the brain.  Facial features are altered with large eyelid openings, the head can appear small, the nasal bridge is depressed, the neck is short and the external ears appear more 'fleshy' than normal.  Infants and young children are 'floppy' and their growth is delayed. 

Children may develop seizures within the first 6 months.    Certain enzymes (creatine kinase and alkaline phosphatase) circulating in the blood are elevated, muscle cells on biopsy are abnormal, and the urine collecting system is enlarged (dilated) at the kidney.  Joint contractures, dysplasia of the hip, and bone loss can occur in somewhat older children.  Death can occur in early childhood as the result of lung, and kidney disease.


This is an autosomal recessive disorder caused by mutations in a pair of genes.  Two mutations are required for the disease to appear so parents with one copy of the change are usually clinically normal.  When two parents, each with a single mutation, have children there is a 25% chance that each child acquires the two mutations, one from each parent.

Diagnosis and Prognosis: 

The physical signs are subtle at birth so that diagnosis can be difficult to make in the newborn period.  Multiple specialists with a team approach by pediatricians, neurologists, and ophthalmologists are most likely to determine the full clinical picture leading to the diagnosis.  Cataracts are a useful sign but there are many types of congenital cataracts.  The small birth size and failure to grow and develop on schedule provide clues to the presence of a more serious developmental disorder.

There is no treatment for this condition and children usually do not live beyond a few years.

Additional Information
Autosomal recessive