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Pulmonary alveolar microlithiasis
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Pulmonary alveolar microlithiasis

Pulmonary alveolar microlithiasis is a rare lung disorder characterized by the gradual accumulation of tiny calcium phosphate deposits (microliths) in the small air sacs (alveoli), leading to progressive lung damage and breathing problems, typically caused by mutations in the SLC34A2 gene.

Overview

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 spleen, kidneys, thyroid gland, 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.

Frequency

Pulmonary alveolar microlithiasis is a rare disorder; its prevalence is unknown. More than 1,000 affected individuals have been described in the medical literature, of whom more than half are from Turkey, China, Japan, India, or Italy. The remainder come from populations worldwide.

Causes & Risk Factors

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.

Inheritance

This condition is inherited in an autosomal recessive inheritance 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.

Other Names

  • PAM

Frequently Asked Questions

Testing for pathogenic variants in the SLC34A2 gene using a targeted gene panel or whole‑exome sequencing is the standard approach. Because the condition is autosomal recessive, both parents should be tested if a child is affected, and carrier testing can be offered to siblings and extended relatives.
High‑resolution computed tomography (HRCT) of the chest is the most sensitive tool for detecting new microliths and assessing fibrosis. Most clinicians repeat HRCT every 2–3 years in stable patients; if symptoms worsen, an earlier scan (6–12 months) may be warranted. Plain chest X‑ray can be used for interim checks but is less precise.
No disease‑modifying drug has proven efficacy yet. Management focuses on supportive care: supplemental oxygen for hypoxemia, pulmonary rehabilitation, and avoidance of smoking or occupational dust exposure. Experimental approaches such as bisphosphonates have been tried in isolated cases but lack robust data.
Referral for transplant evaluation is appropriate when resting oxygen saturation falls below 88 % on room air, when dyspnea limits daily activities despite maximal medical therapy, or when progressive right‑heart strain appears on echocardiography. Survival after single‑lung transplant averages 5–7 years, while bilateral transplant offers slightly better long‑term outcomes but carries higher peri‑operative risk.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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