New insights in the genetic variant spectrum of SLC34A2 in pulmonary alveolar microlithiasis; a systematic review

Pulmonary alveolar microlithiasis (PAM) is a rare autosomal recessive lung disease caused by variants in the SLC34A2 gene encoding the sodium-dependent phosphate transport protein 2B, NaPi-2b. PAM is characterized by deposition of calcium phosphate crystals in the alveoli. Onset and clinical course vary considerably; some patients remain asymptomatic while others develop severe respiratory failure with a significant symptom burden and compromised survival. It is likely that PAM is under-reported due to lack of recognition, misdiagnosis, and mild clinical presentation. Most patients are genetically uncharacterized as the diagnostic confirmation of PAM has traditionally not included a genetic analysis. Genetic testing may in the future be the preferred tool for diagnostics instead of invasive methods. This systematic review aims to provide an overview of the growing knowledge of PAM genetics. Rare variants in SLC34A2 are found in almost all genetically tested patients. So far, 34 allelic variants have been identified in at least 68 patients. A majority of these are present in the homozygous state; however, a few are found in the compound heterozygous form. Most of the allelic variants involve only a single nucleotide. Half of the variants are either nonsense or frameshifts, resulting in premature termination of the protein or decay of the mRNA. There is currently no cure for PAM, and the only effective treatment is lung transplantation. Management is mainly symptomatic, but an improved understanding of the underlying pathophysiology will hopefully result in development of targeted treatment options. More standardized data on PAM patients, including a genetic diagnosis covering larger international populations, would support the design and implementation of clinical studies to the benefit of patients. Further genetic characterization and understanding of how the molecular changes influence disease phenotype will hopefully allow earlier diagnosis and treatment of the disease in the future.

Insights into pulmonary phosphate homeostasis and osteoclastogenesis emerge from the study of pulmonary alveolar microlithiasis

Pulmonary alveolar microlithiasis is an autosomal recessive lung disease caused by a deficiency in the pulmonary epithelial Npt2b sodium-phosphate co-transporter that results in accumulation of phosphate and formation of hydroxyapatite microliths in the alveolar space. The single cell transcriptomic analysis of a pulmonary alveolar microlithiasis lung explant showing a robust osteoclast gene signature in alveolar monocytes and the finding that calcium phosphate microliths contain a rich protein and lipid matrix that includes bone resorbing osteoclast enzymes and other proteins suggested a role for osteoclast-like cells in the host response to microliths. While investigating the mechanisms of microlith clearance, we found that Npt2b modulates pulmonary phosphate homeostasis through effects on alternative phosphate transporter activity and alveolar osteoprotegerin, and that microliths induce osteoclast formation and activation in a receptor activator of nuclear factor-κB ligand and dietary phosphate dependent manner. This work reveals that Npt2b and pulmonary osteoclast-like cells play key roles in pulmonary homeostasis and suggest potential new therapeutic targets for the treatment of lung disease.

A case report of pulmonary alveolar microlithiasis with pulmonary tuberculosis

Pulmonary alveolar microlithiasis (PAM) is a rare autosomal recessive disease characterised by the deposition of calcium phosphate microliths in the alveoli. PAM has been reported in all continents and there is often a familial history. There is clinical-radiological dissociation as there is often a paucity of symptoms in contrast to the imaging findings. Patients often remain asymptomatic until the third or fourth decade of life, and dyspnea is the most common symptom. PAM is caused by a mutation within the solute carrier family 34 member 2 gene (the SLC34A2 gene) located on chromosome 4p15.2, which encodes a sodium/phosphate co-transporter. The imaging appearance of the disease is quite pathognomic with the high-resolution computed tomography (HRCT) demonstrating a diffuse micronodular appearance. Transbronchial lung biopsy also confirms the diagnosis. There is no effective therapy at present except lung transplantation. We herein, present a case of PAM along with clinical history, imaging study, histopathological study and genetic study of a 43-year-old female adult patient along with genetic analysis.

Pulmonary alveolar microlithiasis

Pulmonary alveolar microlithiasis (PAM) is a fascinating rare lung disease that is associated with the accumulation of hydroxyapatite microliths within the lumen of the alveolar spaces. In most patients, PAM is discovered incidentally on radiographs performed for other purposes, and the typical disease course is characterised by slowly progressive respiratory insufficiency over decades. Recent genetic analyses that have revealed that the deficiency of the sodium-phosphate cotransporter NPT2B is the cause of PAM have enabled the development of powerful animal models that inform our approach to disease management and treatment. Here we review the epidemiology and molecular pathophysiology of PAM, as well as the diagnostic approach, clinical manifestations, radiographic and pathologic features, and clinical management of the disease. Although there are no proven treatments for PAM, progress in our understanding of disease pathogenesis is providing insights that suggest strategies for trials.

A review of the epidemiology and molecular pathophysiology of pulmonary alveolar microlithiasishttps://bit.ly/3lBgM7p

Pulmonary alveolar microlithiasis: no longer in the stone age

Pulmonary alveolar microlithiasis (PAM) is a rare parenchymal lung disease caused by variants in the SCL34A2 gene and characterised by the accumulation of intra-alveolar microliths. PAM has been reported in fewer than 1100 cases throughout the world. It is an autosomal recessive hereditary disease and often associated with consanguinity. Progress with respect to the genetic background and pathophysiology has resulted in an increased understanding of the disease in recent years. Until now, 30 genetic different SLC34A2 variants have been reported, which all are considered significant for disease development. There is no sex difference and the majority of cases are diagnosed at the age of 30–40 years. Many patients are asymptomatic and the diagnosis is made at random. When symptomatic, dyspnoea, cough, chest pain and fatigue are common complaints. The diagnosis of PAM can confidently be based on typical radiographic findings and genetic testing proving rare biallelic SCL34A2 gene variants. Bronchoalveolar lavage and histopathology may show microliths. There is no disease-specific treatment and management is supportive. Lung transplantation should be considered in advanced cases.

Pulmonary alveolar microlithiasis is a rare, autosomal recessive lung disease. Formation of alveolar microliths is caused by SCL34A2 variants. The prognosis is severe; respiratory failure is common. Lung transplantation is the only effective therapy.https://bit.ly/3dpkbRw

Pulmonary Alveolar Microlithiasis in Children Less than 5 Years of Age

OBJECTIVE

To collect all published cases up to January 2019 of pulmonary alveolar microlithiasis (PAM) in patients age 5 years and under and to compare their characteristics with those of the 1022 cases in the most recent all-age cohort published in 2015.

STUDY DESIGN

We identified 28 cases of PAM worldwide in children age 5 years and under, accounting for only 2%-3% of all cases.

RESULTS

Children seem more frequently symptomatic, notably with more cough and severe acute respiratory failure, but had no reported extrapulmonary manifestation. Children with PAM evidenced less typical radiologic findings, with frequent ground glass opacities not reported in adult cases and milder calcifications as less frequent, smaller, and mainly restricted to the lower lobes.

CONCLUSIONS

PAM remains an uncommon diagnosis in young children, as symptoms and radiologic findings are less specific. Physicians should be aware to look for calcifications in chest computed tomography at mediastinal window and avoid elution of the bronchoalveolar lavage to find microliths. Collecting longitudinal data through an international registry would help in characterizing PAM to predict disease progression and plan lung transplantation.

Pulmonary alveolar microlithiasis: A report of two unique cases

Pulmonary alveolar microlithiasis (PAM) is an inherited autosomal recessive disease. PAM is classically characterized by calcium phosphate deposition within alveolar airspaces due to SLC34A2 (solute carrier family 34 member 2) gene mutation located on chromosome 4p15.2. Such cellular genetic mutation would lead to a defect in the sodium-phosphate transporter channel located in alveolar epithelial cells type-II. Ultimately, it would result in a malfunction of alveolar epithelial cells and the failure of these cells to clear-up the released phosphorous particles in the cellular surfactant recycling. PAM is usually diagnosed in adulthood, frequently notable in the third and fourth decades of life, occasionally can be associated with more severe clinical presentation and radiological findings.

Nevertheless, the disease could manifest itself in the pediatric age group, which either shows non-specific signs and symptoms or be exclusively asymptomatic. Histopathological examination is the gold standard for the PAM diagnosis. Genetic counseling and testing might benefit the patient's family members. Herein, we present 2 cases of PAM in the pediatric age group, along with their clinical history, presentation, radiological studies, and histopathology findings, as well as a brief literature review.

Pulmonary alveolar microlithiasis: A case report and review of the literature

Pulmonary alveolar microlithiasis (PAM) is a rare autosomal recessive disease characterized by the formation of calcium phosphate microliths in the alveoli. Mutations in the gene encoding the solute carrier family 34 member 2 gene are considered to be involved in the pathogenesis of PAM. Although PAM can develop in children, the majority of patients with PAM are diagnosed in adulthood due to the slow progressive nature of the disease within the lungs. In childhood, the majority of patients with PAM are asymptomatic and changes in the lung parenchyma are usually identified incidentally. Symptoms of PAM typically appear in the third or fourth decade of life and there is often a notable dissociation between the advanced radiological findings and the mild clinical presentation. A positive diagnosis of PAM is reached by the combination of a positive chest radiograph and histological examination. Genetic testing may help to identify other latent patients in the family of the patient with PAM. In the present study, the cases of 3 patients diagnosed with PAM have been reported, including their clinical presentation, radio imaging, pathological symptoms, genetic test results and treatment plans, as well as the associated literature.

An unusual late onset of pulmonary alveolar microlithiasis: A case report and literature review

Pulmonary alveolar microlithiasis (PAM) is an uncommon genetic disorder associated with alveolar cell injury. This injury is caused in most cases by inactivating mutations in SLC34A2 gene, which is responsible for the production of a sodium-dependent phosphate co-transporter. The dysfunction or deficiency of this transporter leads to the aggregation of local phosphate intra-alveolarly and formation of microliths. Most of the patients are asymptomatic at the time of the diagnosis but as the disease progress it leads to fatal respiratory or cardiac failure. We describe a case of a 63-year-old man referred to our department for a surgical lung biopsy. He has been symptomatic for one year with progressive shortness of breath and deteriorating exercise tolerance. The imaging was suggestive of extensive interstitial bilateral lung disease. Histological findings after the lung biopsy by video-assisted thoracic surgery (VATS) established the diagnosis of pulmonary alveolar microlithiasis. His sister suffered from the same disease and passed away at the age of 54. It is remarkably rare for PAM to have such a late onset with a previous normal X-ray and only a few cases have been reported worldwide.

Pulmonary alveolar microlithiasis with finger clubbing: A case report and literature review

Pulmonary alveolar microlithiasis (PAM) is a rare autosomal recessive and slowly progressive disease. Mutations of the solute carrier family 34, member 2 gene are considered to be the cause of the disease. The present study reported the case of a 35-year-old female patient who was diagnosed with PAM. The parents of the patient were reported to be blood-related (cousins). The clinical manifestations and radiological and pathological characteristics of the patient are reported. A pulmonary function examination detected restrictive ventilatory and diffusion defects, and a high-resolution computed tomography scan showed multiple bilateral diffuse ground-glass opacifications and subpleural linear calcifications. A bronchoalveolar lavage fluid (BALF) examination detected a calcified body in the lavage fluid and a transbronchial biopsy showed numerous calcified bodies, concentrically laminated with an onion skin-like appearance in the alveolar spaces. Based on the aforementioned observations, the patient was diagnosed with PAM. Following administration of inhaled corticosteroid treatment, the symptoms were improved and the patient was discharged. After 1 year, the patient was lost to follow-up. The present study presents and reviews the typical radiological appearance, clinical presentation, pathological characteristics and treatments of PAM, and suggests that, often, the parents of the patients are blood-related and typically cousins. In addition, the present study proposes that a BALF examination may be considered an alternative method for the pathological diagnosis of PAM.