SLC34A2 gene mutation may explain comorbidity of pulmonary alveolar microlithiasis and aortic valve sclerosis

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.

The world of rare interstitial lung diseases

The world of rare interstitial lung diseases (ILDs) is diverse and complex. Diagnosis and therapy usually pose challenges. This review describes a selection of rare and ultrarare ILDs including pulmonary alveolar proteinosis, pulmonary alveolar microlithiasis and pleuroparenchymal fibroelastosis. In addition, monogenic ILDs or ILDs in congenital syndromes and various multiple cystic lung diseases will be discussed. All these conditions are part of the scope of the European Reference Network on rare respiratory diseases (ERN-LUNG). Epidemiology, pathogenesis, diagnostics and treatment of each disease are presented.

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

Tricuspid valve calcification in familial pulmonary alveolar microlithiasis: A case report

Background

Pulmonary Alveolar Microlithiasis (PAM) is an uncommon, gradually progressive and eventually fatal hereditary disease that affects young population. Familial cases account for up to 50% of reported cases. There are few described cases of extrapulmonary manifestations of PAM and rare reports of cardiac involvement.

Case report

A 45-year-old male patient presented to our center with progressive shortness of breath and dry cough. On physical examination, he was tachypneic and chest examination revealed diminished breath sounds with bilateral early inspiratory crackles. Further workup revealed the diagnosis of PAM. Echocardiography revealed calcifications covering the tricuspid valve with elevated right ventricular systolic pressure. He reported having two sisters with similar illnesses and chest radiographic abnormalities, one died at the age of 38 years from respiratory failure and the other is 42-year-old and still alive and was diagnosed with PAM. Another 35 member of his family were diagnosed with PAM. Unfortunately, few days after discharge, he arrested at home.

Conclusions

Recently, type-II sodium/phosphate co-transporter has been identified in a human aortic valve. Studies have suggested penetrance of mutations of SLC34A2 gene might explain such variability of pulmonary and extrapulmonary involvement. Our case reports a familial cluster of PAM, and the first case of concomitant tricuspid calcification. This finding might be a useful in the investigation for a future genetic targeted therapy.

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PAM is a fatal hereditary disease that affects young population.

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There are few described cases of extrapulmonary manifestations of PAM.

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Mutations of SLC34A2 gene might explain variability of extrapulmonary involvement.

Eight novel variants in the SLC34A2 gene in pulmonary alveolar microlithiasis

BACKGROUND

Pulmonary alveolar microlithiasis (PAM) is caused by genetic variants in the SLC34A2 gene, which encodes the sodium-dependent phosphate transport protein 2B (NaPi-2b). PAM is characterised by deposition of calcium phosphate concretions (microliths) in the alveoli leading to pulmonary dysfunction. The variant spectrum of SLC34A2 has not been well investigated and it is not yet known whether a genotype-phenotype correlation exists.

METHODS

We collected DNA from 14 patients with PAM and four relatives, and analysed the coding regions of SLC34A2 by direct DNA sequencing. To determine the phenotype characteristics, clinical data were collected and a severity score was created for each variant, based on type and localisation within the protein.

RESULTS

We identified eight novel allelic variants of SLC34A2 in 14 patients with PAM. Four of these were nonsense variants, three were missense and one was a splice site variant. One patient was heterozygous for two different variants and all other patients were homozygous. Four patients were asymptomatic and 10 patients were symptomatic. The severity of the disease was associated with the variant severity.

CONCLUSIONS

Our findings support a significant role for SLC34A2 in PAM and expand the variant spectrum of the disease. Thus, SLC34A2 variants were detected in all patients and eight novel allelic variants were discovered. An association between disease severity and the severity of the variants was found; however, this needs to be investigated in larger patient populations.

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.

A novel SLC34A2 mutation in a patient with pulmonary alveolar microlithiasis

Pulmonary alveolar microlithiasis (PAM) is a rare autosomal recessive disease caused by mutations in SLC34A2 and characterized by intra-alveolar accumulation of microliths. We diagnosed a case of PAM in a 27-year-old Japanese female and identified a novel mutation in SLC34A2 (c.1390 G>C [G464R] in exon 12).

Diagnosis and treatment of pulmonary alveolar microlithiasis

Pulmonary alveolar microlithiasis (PAM) is a rare genetic disease caused by mutations in sodium-phosphate co-transporter (SLC34A2), which encodes a type 2b sodium phosphate co-transporter. Disease is characterized by intra-alveolar microlith formation of phosphate. Turkey has a high prevalence of PAM. Herein, we report the clinical and radiological findings of three patients diagnosed with PAM and treated with disodium etidronate.

Pulmonary alveolar microlithiasis: review of the 1022 cases reported worldwide

Pulmonary alveolar microlithiasis (PAM) is a rare disease characterised by the widespread intra-alveolar accumulation of minute calculi called microliths. It is caused by mutation of the SLC34A2 gene encoding the type IIb sodium phosphate cotransporter in alveolar type II cells. The present study explores the epidemiological, familial, genetic, clinical, diagnostic, radiological and therapeutic aspects with the aim of contributing to a better understanding of this uncommon disease.We searched articles on PAM published up to December 2014 and 544 papers were found, accounting for 1022 cases.PAM is present in all continents and in many nations, in particular in Turkey, China, Japan, India, Italy and the USA. Familiality is frequent. The clinical course is not uniform and the causes of this clinical variability seem to be largely nongenetic. The optimal diagnostic procedure is the association of chest high-resolution computed tomography (HRCT) with bronchoalveolar lavage, but a chest radiograph may suffice in families in which a case has already been diagnosed. Moreover, chest radiography and HRCT allow the classification of the evolutionary phase of the disease and its severity. At present lung transplantation is the only effective therapy. However, better knowledge of the gene responsible offers hope for new therapies.

Update on diagnosis and treatment of pulmonary alveolar microlithiasis

Pulmonary alveolar microlithiasis (PAM) (MIM265100) is a rare disease characterized by the diffuse deposit of microlithiasis in alveolar spaces. PAM could occur worldwide with high prevalence in Asia and Europe. Familial occurrence indicates its autosomal recessive trait and the SLC34A2 gene was identified as the responsible gene for the disease. In spite of the versatile mutation sites in patients from other countries, exon 7 and exon 8 might be the most liable gene in Chinese and Japanese patients. Most mutations caused the premature termination of proteins and produced truncated proteins, leading to the blocking of the recycling and degrading of outdated surfactant which is full of phospholipids. The most outstanding clinical feature of PAM is the discrepancy between the paucity of symptoms and the degree of pulmonary involvement. Diagnosis is easy to establish based on typical chest radiograph image and nuclear medicine improves its early diagnosis and active evaluation. Pathology of the unique intra-alveolar lamellar microliths gives strong support for diagnosis. No effective treatment is considered valid currently. However, lung transplantation is effective for advanced-stage patients, and long term treatment of disodium etidronate seems promising.

SLC34A2 gene compound heterozygous mutation identification in a patient with pulmonary alveolar microlithiasis and computational 3D protein structure prediction

We recently diagnosed a patient with pulmonary alveolar microlithiasis (PAM). Because loss-of-function mutations of the SLC34A2 gene are responsible for the development of PAM, we sought to sequence the SLC34A2 gene of the patient and his direct relatives, with a purpose to identify mutations that caused the PAM of the patient as well as the carriers of his family. We found a novel compound heterozygous mutation of the SLC34A2 gene in this patient, which were the mutations of c.1363T > C (p. Y455H) in exon 12 and c.910A > T (p. K304X) in exon 8. Computational prediction of three-dimensional (3D) structures of the mutants revealed that the Y455H mutation resulted in a formation of irregular coils in the trans-membrane domain and the K304X mutation resulted in protein truncation. Our study suggested that sequencing of the SLC34A2 gene together with a computational prediction of the 3D structures of the mutated proteins may be useful in PAM diagnosis and prognosis.

SLC34A2 Gene mutation of pulmonary alveolar microlithiasis: report of four cases and review of literatures

Pulmonary alveolar microlithiasis (PAM) is a rare autosomal recessive disorder characterized by the deposition of calcium phosphate microliths throughout the lungs. Currently the mutation of SLC34A2 gene was considered responsible for PAM. Here we reported the studies on mutation analysis of the SLC34A2 gene in three familial members and one unrelated subject of PAM by DNA direct sequencing. Meanwhile, we also reviewed and analyzed the published studies of the SLC34A2 gene mutation in PAM patients. The three familial patients were siblings of an inbred family whose parents were cousins. All four patients presented recurrent cough and exertional dyspnea. Diagnosis of PAM was made according to the typical manifestation of radiology. One homozygous mutation of the SLC34A2 gene, c.910A > T (p.K304X) was identified. The review of the SLC34A2 gene mutation showed multiple mutation symbols in PAM patients from China, Turkey, and Japan respectively. The present study supports that the clinical features, pathological and radiological characteristics of Chinese PAM patients are similar to those reported in other countries. Our investigation revealed that the c.910A > T mutation in the SCL34A2 gene was responsible for PAM patients in China. The review of literatures suggests that exon7 and exon8 seemed liable to be affected typical Mongoloid of PAM, and exon8 might be the screen target for Chinese patients.