Hypophosphatasia

Hypophosphatasia

National Organization for Rare Disorders, Inc.

Important

It is possible that the main title of the report Hypophosphatasia is not the name you expected. Please check the synonyms listing to find the alternate name(s) and disorder subdivision(s) covered by this report.

Synonyms

  • HHRH
  • Hypercalciuric Rickets
  • Hypophosphatemic Rickets with Hypercalcemia

Disorder Subdivisions

  • Hypophasphatasia, Infantile
  • Hypophasphatasia, Childhood
  • Hypophosphatasia, Adult
  • Pseudohypophosphatasia

General Discussion

Hypophosphatasia is a inborn metabolic disorder of the bones characterized by skeletal defects resembling those of rickets. The symptoms result from a failure of bone mineral to be deposited in young, uncalcified bone (osteoid), and in the cartilage at the end of the long bones (epiphyses) during early years. The activity of the enzyme alkaline phosphatase in blood serum and bone cells is lower than normal. Urinary excretion and blood plasma concentrations of phosphoethanolamine and inorganic pyrophosphate are abnormally high. Unlike other forms of rickets, Hypophosphatasia does not respond to treatment with vitamin D.

Symptoms

Infantile Hypophosphatasia: This is the most common form of the disorder, usually beginning before 6 months of age. It can be diagnosed before birth. In infants affected with Hypophosphatasia, defective bone hardening (mineralization) is often associated with increased pressure inside the skull which may result in bulging eyes (exophthalmos). There may be excessive levels of calcium in the blood (hypercalcemia) and urine (hypercalciuria). Calcium may accumulate in the little tubes of the kidneys, sometimes resulting in kidney failure. The bones usually become weak and bent, resembling Rickets. Bone abnormalities can be severe.



Childhood Hypophosphatasia: This form of the disorder usually begins after 6 months of age. It is characterized by premature loss of baby teeth, increased susceptibility to infections, and slowed growth. X-rays show irregularities in the tips (epiphyses) and shafts of the long bones. Spontaneous healing of Rickets- like (rachitic) bone changes may occur in this form of Hypophosphatasia.



Adult Hypophosphatasia: This form of Hypophosphatasia is quite rare. It is characterized by a history of Rickets symptoms and premature loss of baby teeth during childhood. The permanent teeth are often lost or extracted during early adulthood. The bones are less dense than normal and fractures tend to occur more often than in the general population.



Pseudohypophosphatasia: Patients with Pseudohypophosphatasia have all or many of the manifestations of Hypophosphatasia. However, blood concentrations of the enzyme alkaline phosphatase are normal.



The symptoms of Hypophosphatasia vary greatly from case to case.

Causes

The symptoms of Hypophosphatasia develop due to abnormally low levels of the enzyme alkaline phosphatase (ALP). The infantile and childhood forms of the disorder are inherited as autosomal recessive genetic traits. The adult form is inherited as an autosomal dominant genetic trait.



Human traits including the classic genetic diseases, are the product of the interaction of two genes for that condition, one received from the father and one from the mother.



In recessive disorders, the condition does not appear unless a person inherits the same defective gene for the same trait from each parent. If an individual receives one normal gene and one gene for the disease, the person will be a carrier for the disease, but usually will not show symptoms. The risk of transmitting the disease to the children of a couple, both of whom are carriers for a recessive disorder, is 25 percent. Fifty percent of their children risk being carriers of the disease, but generally will not show symptoms of the disorder. Twenty-five percent of their children may receive both normal genes, one from each parent, and will be genetically normal (for that particular trait). The risk is the same for each pregnancy.



In dominant disorders, a single copy of the disease gene (received from either the mother or father) will be expressed "dominating" the other normal gene and resulting in the appearance of the disease. The risk of transmitting the disorder from affected parent to offspring is 50 percent for each pregnancy regardless of the sex of the resulting child.

Affected Populations

Hypophosphatasia is a rare disorder. The different forms of this disorder all affect males and females in equal numbers. It is believed that one in 100,000 infants may be affected by the more severe form of the disease. Approximately one in every 300 individuals in the United States are believed to carry the defective gene responsible for Hypophosphatasia.

Standard Therapies

Hypophosphatasia can be diagnosed before birth because the unhardened (uncalcified) skull does not show up clearly in ultrasound pictures. This disorder can be distinguished from Anencephaly by analysis of the substance alpha-fetoprotein, which is normal in fetuses with Hypophosphatasia, and high in those with Anencephaly.



Treatment with Vitamin D and its breakdown products (metabolites) has not been successful in Hypophosphatasia and other forms of Vitamin-D resistant Rickets. Sustained oral phosphate supplements may be beneficial in some cases. Other treatment is symptomatic and supportive.



Genetic counseling is recommended for families of persons with Hypophosphatasia. For more information for parents and physicians dealing with Hypophosphatasia patients, please contact Dr. Michael Whyte listed in the Resource section.

Investigational Therapies

Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government web site.



For information about clinical trials being conducted at the National Institutes of Health (NIH) in Bethesda, MD, contact the NIH Patient Recruitment Office:



Tollfree: (800) 411-1222

TTY: (866) 411-1010

Email: prpl@cc.nih.gov



For information about clinical trials sponsored by private sources, contact:

www.centerwatch.com



In November 2009, Enobia Pharma announced the initiation of a Phase II clinical study of ENB-0040, a bone-targeted enzyme replacement therapy under investigation for the treatment of hypophosphatasia. The six-month study will assess the safety, efficacy and pharmacokinetics of this ERT in children ages five to 12.



Enobia has also announced the launch of the Hypophosphatasia Impact Patient Survey (HIPS), an online questionnaire intended to better understand the burden of HPP on patients and their families. The survey is designed to document the disease history, medical history, functional disability, and quality of life in patients with HPP.



Information on both of the above is available on the company's website: www.enobia.com.

References

TEXTBOOKS

The Metabolic Basis of Inherited Disease, 5th ed.: John B. Stanbury, et al.; Eds; McGraw Hill, 1983. Pp. 1497-1507.



JOURNAL ARTICLES

Infantile Hypophosphatasia: Enzyme Replacement Therapy by Intravenous Infusion of Alkaline Phosphatase-Rich Plasma From Patients with Paget Bone Disease: M.P. Whyte et al.; Journal Pediatr (September 1982:101(3)). Pp. 379-386.



Enzyme Replacement Therapy for Infantile Hypophosphatasia Attempted by Intravenous Infusions of Alkaline Phosphatase-Rich Paget Plasma: Results in Three Additional Patients. M.P. Whyte et al.; Journal Pediatr (December 1984: 105(6)). Pp. 926-933.



Infantile Hypophosphatasia Diagnosed at 4 Months and Surviving at 2 Years: A. Albeggiani et al.; Helv Paediatr Acta (1982:37(1)). Pp. 49-58.



FROM THE INTERNET

Online Mendelian Inheritance in Man (OMIM). Victor A. McKusik, Editor; Johns Hopkins University, Last Edit Date 7/24/96, Entry Number 241530.



http://www.emedicine.com/ped/topic1126.htm

Resources

CLIMB (Children Living with Inherited Metabolic Diseases)

Climb Building

176 Nantwich Road

Crewe, CW2 6BG

United Kingdom

Tel: 4408452412173

Fax: 4408452412174

Email: enquiries@climb.org.uk

Internet: http://www.CLIMB.org.uk



MAGIC Foundation

6645 W. North Avenue

Oak Park, IL 60302

Tel: (708)383-0808

Fax: (708)383-0899

Tel: (800)362-4423

Email: mary@magicfoundation.org

Internet: http://www.magicfoundation.org



March of Dimes Birth Defects Foundation

1275 Mamaroneck Avenue

White Plains, NY 10605

Tel: (914)997-4488

Fax: (914)997-4763

Tel: (888)663-4637

Email: Askus@marchofdimes.com

Internet: http://www.marchofdimes.com



NIH/National Institute of Arthritis and Musculoskeletal and Skin Diseases

Information Clearinghouse

One AMS Circle

Bethesda, MD 20892-3675

USA

Tel: (301)495-4484

Fax: (301)718-6366

Tel: (877)226-4267

TDD: (301)565-2966

Email: NIAMSinfo@mail.nih.gov

Internet: http://www.niams.nih.gov/



Genetic and Rare Diseases (GARD) Information Center

PO Box 8126

Gaithersburg, MD 20898-8126

Tel: (301)251-4925

Fax: (301)251-4911

Tel: (888)205-2311

TDD: (888)205-3223

Internet: http://rarediseases.info.nih.gov/GARD/



Soft Bones, Inc.

121 Hawkins Place

#267

Boonton, NJ 07005

Tel: (201)317-1818

Email: jane@softbones.org

Internet: http://www.softbones.org



For a Complete Report

This is an abstract of a report from the National Organization for Rare Disorders, Inc.® (NORD). Cigna members can access the complete report by logging into myCigna.com. For non-Cigna members, a copy of the complete report can be obtained for a small fee by visiting the NORD website. The complete report contains additional information including symptoms, causes, affected population, related disorders, standard and investigational treatments (if available), and references from medical literature. For a full-text version of this topic, see http://www.rarediseases.org/search/rdblist.html.

This information does not replace the advice of a doctor. Healthwise, Incorporated disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use . How this information was developed to help you make better health decisions.

Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated.