Pulmonary alveolar microlithiasis

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Reviewed December 2014

What is pulmonary alveolar microlithiasis?

Pulmonary alveolar microlithiasis is a disorder in which many tiny fragments (microliths) of a compound called calcium phosphate gradually accumulate in the small air sacs (alveoli) located throughout the lungs. These deposits eventually cause widespread damage to the alveoli and surrounding lung tissue (interstitial lung disease) that leads to breathing problems. People with this disorder can develop a persistent cough and difficulty breathing (dyspnea), especially during physical exertion. Affected individuals may also experience chest pain that worsens when coughing, sneezing, or taking deep breaths.

Pulmonary alveolar microlithiasis is usually diagnosed before age 40. Often the disorder is discovered before symptoms develop, when medical imaging is done for other reasons. The condition typically worsens slowly over many years, although some affected individuals have signs and symptoms that remain stable for long periods of time.

People with pulmonary alveolar microlithiasis can also develop calcium phosphate deposits in other organs and tissues of the body, including the kidneys, gallbladder, testes, and the valve that connects a large blood vessel called the aorta with the heart (the aortic valve). In rare cases, affected individuals have complications related to accumulation of these deposits, such as a narrowing (stenosis) of the aortic valve that can impede normal blood flow.

How common is pulmonary alveolar microlithiasis?

Pulmonary alveolar microlithiasis is a rare disorder; its prevalence is unknown. About 600 affected individuals have been described in the medical literature, of whom about a quarter are of Turkish descent. The remainder come from populations worldwide.

What genes are related to pulmonary alveolar microlithiasis?

Pulmonary alveolar microlithiasis is caused by mutations in the SLC34A2 gene. This gene provides instructions for making a protein called the type IIb sodium-phosphate cotransporter, which plays a role in the regulation of phosphate levels (phosphate homeostasis). Although this protein can be found in several organs and tissues in the body, it is located mainly in the lungs, specifically in cells in the alveoli called alveolar type II cells. These cells produce and recycle surfactant, which is a mixture of certain phosphate-containing fats (called phospholipids) and proteins that lines the lung tissue and makes breathing easy.

The recycling of surfactant releases phosphate into the alveoli. Research suggests that the type IIb sodium-phosphate cotransporter normally helps clear this phosphate. SLC34A2 gene mutations are thought to impair the activity of the type IIb sodium-phosphate cotransporter, resulting in the accumulation of phosphate in the alveoli. The accumulated phosphate forms the microliths that cause the signs and symptoms of pulmonary alveolar microlithiasis.

How do people inherit pulmonary alveolar microlithiasis?

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

Where can I find information about diagnosis or management of pulmonary alveolar microlithiasis?

These resources address the diagnosis or management of pulmonary alveolar microlithiasis and may include treatment providers.

You might also find information on the diagnosis or management of pulmonary alveolar microlithiasis in Educational resources and Patient support.

General information about the diagnosis and management of genetic conditions is available in the Handbook. Read more about genetic testing, particularly the difference between clinical tests and research tests.

To locate a healthcare provider, see How can I find a genetics professional in my area? in the Handbook.

Where can I find additional information about pulmonary alveolar microlithiasis?

You may find the following resources about pulmonary alveolar microlithiasis helpful. These materials are written for the general public.

MedlinePlus - Health information (3 links)
Educational resources - Information pages (3 links)
Patient support - For patients and families
American Lung Association

You may also be interested in these resources, which are designed for healthcare professionals and researchers.

Genetic Testing Registry - Repository of genetic test information (1 link)
ClinicalTrials.gov - Linking patients to medical research
PubMed - Recent literature
OMIM - Genetic disorder catalog

What other names do people use for pulmonary alveolar microlithiasis?

For more information about naming genetic conditions, see the Genetics Home Reference Condition Naming Guidelines and How are genetic conditions and genes named? in the Handbook.

What if I still have specific questions about pulmonary alveolar microlithiasis?

Ask the Genetic and Rare Diseases Information Center

Where can I find general information about genetic conditions?

The Handbook provides basic information about genetics in clear language.

These links provide additional genetics resources that may be useful.

What glossary definitions help with understanding pulmonary alveolar microlithiasis?

alveoli ; aorta ; autosomal ; autosomal recessive ; calcium ; cell ; compound ; dyspnea ; gallbladder ;gene ; homeostasis ; imaging ; inherited ; phosphate ; phospholipids ; prevalence ; protein ;pulmonary ; recessive ; sodium ; stenosis ; testes ; tissue

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.

References (8 links)

The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? in the Handbook.