Michael W. Pauciulo

Heterozygous germline mutations in BMPR2 , encoding a TGF-β receptor, cause familial primary pulmonary hypertension

Primary pulmonary hypertension (PPH), characterized by obstruction of pre-capillary pulmonary arteries, leads to sustained elevation of pulmonary arterial pressure (mean >25 mm Hg at rest or >30 mm Hg during exercise). The aetiology is unknown, but the histological features reveal proliferation of endothelial and smooth muscle cells with vascular remodelling (Fig. 1). More than one affected relative has been identified in at least 6% of cases (familial PPH, MIM 178600). Familial PPH (FPPH) segregates as an autosomal dominant disorder with reduced penetrance and has been mapped to a locus designated PPH1 on 2q33, with no evidence of heterogeneity. We now show that FPPH is caused by mutations in BMPR2, encoding a TGF-β type II receptor (BMPR-II). Members of the TGF-β superfamily transduce signals by binding to heteromeric complexes of type I and II receptors, which activates serine/threonine kinases, leading to transcriptional regulation by phosphorylated Smads. By comparison with in vitro studies, identified defects of BMPR-II in FPPH are predicted to disrupt ligand binding, kinase activity and heteromeric dimer formation. Our data demonstrate the molecular basis of FPPH and underscore the importance in vivo of the TGF-β signalling pathway in the maintenance of blood vessel integrity.†These authors contributed equally to this work. *Micheala Aldred2, Christopher A. Brannon3, P. Michael Conneally4, Tatiana Foroud4, Neale Fretwell2, Radhika Gaddipati1, Daniel Koller4, Emily J. Loyd1, Neil Morgan2, John H. Newman1, Melissa A. Prince1, Carles Vilariño Güell2 &Lisa Wheeler1 1Vanderbilt University Medical Center, Nashville, Tennessee, USA. 2Division of Medical Genetics, Departments of Genetics and Medicine, University of Leicester, UK. 3Division of Human Genetics, Childrens Hospital Medical Center, Cincinnati, Ohio, USA. 4Indiana University School of Medicine, Indianapolis, Indiana, USA. Correspondence should be addressed to J.E.L. (e-mail: Jim.Loyd@mcmail.vanderbilt.edu), W.C.N. (e-mail: bill.nichols@chmcc.org) or R.C.T. (e-mail: rtrembat@hgmp.mrc.ac.uk).

Sporadic primary pulmonary hypertension is associated with germline mutations of the gene encoding BMPR-II, a receptor member of the TGF-beta family

BACKGROUND Primary pulmonary hypertension (PPH), resulting from occlusion of small pulmonary arteries, is a devastating condition. Mutations of the bone morphogenetic protein receptor type II gene (BMPR2), a component of the transforming growth factor beta (TGF-β) family which plays a key role in cell growth, have recently been identified as causing familial PPH. We have searched for BMPR2 gene mutations in sporadic PPH patients to determine whether the same genetic defect underlies the more common form of the disorder. METHODS We investigated 50 unrelated patients, with a clinical diagnosis of PPH and no identifiable family history of pulmonary hypertension, by direct sequencing of the entire coding region and intron/exon boundaries of the BMPR2 gene. DNA from available parent pairs (n=5) was used to assess the occurrence of spontaneous (de novo) mutations contributing to sporadic PPH. RESULTS We found a total of 11 different heterozygous germline mutations of theBMPR2 gene in 13 of the 50 PPH patients studied, including missense (n=3), nonsense (n=3), and frameshift (n=5) mutations each predicted to alter the cell signalling response to specific ligands. Parental analysis showed three occurrences of paternal transmission and two of de novo mutation of theBMPR2 gene in sporadic PPH. CONCLUSION The sporadic form of PPH is associated with germline mutations of the gene encoding the receptor protein BMPR-II in at least 26% of cases. A molecular classification of PPH, based upon the presence or absence ofBMPR2 mutations, has important implications for patient management and screening of relatives.

BMPR2 Haploinsufficiency as the Inherited Molecular Mechanism for Primary Pulmonary Hypertension

Primary pulmonary hypertension (PPH) is a potentially lethal disorder, because the elevation of the pulmonary arterial pressure may result in right-heart failure. Histologically, the disorder is characterized by proliferation of pulmonary-artery smooth muscle and endothelial cells, by intimal hyperplasia, and by in situ thrombus formation. Heterozygous mutations within the bone morphogenetic protein type II receptor (BMPR-II) gene (BMPR2), of the transforming growth factor beta (TGF-beta) cell-signaling superfamily, have been identified in familial and sporadic cases of PPH. We report the molecular spectrum of BMPR2 mutations in 47 additional families with PPH and in three patients with sporadic PPH. Among the cohort of patients, we have identified 22 novel mutations, including 4 partial deletions, distributed throughout the BMPR2 gene. The majority (58%) of mutations are predicted to lead to a premature termination codon. We have also investigated the functional impact and genotype-phenotype relationships, to elucidate the mechanisms contributing to pathogenesis of this important vascular disease. In vitro expression analysis demonstrated loss of BMPR-II function for a number of the identified mutations. These data support the suggestion that haploinsufficiency represents the common molecular mechanism in PPH. Marked variability of the age at onset of disease was observed both within and between families. Taken together, these studies illustrate the considerable heterogeneity of BMPR2 mutations that cause PPH, and they strongly suggest that additional factors, genetic and/or environmental, may be required for the development of the clinical phenotype.

Mutations in GBA are associated with familial Parkinson disease susceptibility and age at onset

Objective: To characterize sequence variation within the glucocerebrosidase (GBA) gene in a select subset of our sample of patients with familial Parkinson disease (PD) and then to test in our full sample whether these sequence variants increased the risk for PD and were associated with an earlier onset of disease. Methods: We performed a comprehensive study of all GBA exons in one patient with PD from each of 96 PD families, selected based on the family-specific lod scores at the GBA locus. Identified GBA variants were subsequently screened in all 1325 PD cases from 566 multiplex PD families and in 359 controls. Results: Nine different GBA variants, five previously reported, were identified in 21 of the 96 PD cases sequenced. Screening for these variants in the full sample identified 161 variant carriers (12.2%) in 99 different PD families. An unbiased estimate of the frequency of the five previously reported GBA variants in the familial PD sample was 12.6% and in the control sample was 5.3% (odds ratio 2.6; 95% confidence interval 1.5–4.4). Presence of a GBA variant was associated with an earlier age at onset (p = 0.0001). On average, those patients carrying a GBA variant had onset with PD 6.04 years earlier than those without a GBA variant. Conclusions: This study suggests that GBA is a susceptibility gene for familial Parkinson disease (PD) and patients with GBA variants have an earlier age at onset than patients with PD without GBA variants.

Glucocerebrosidase activity in Parkinson's disease with and without GBA mutations.

Glucocerebrosidase (GBA) mutations have been associated with Parkinsons disease in numerous studies. However, it is unknown whether the increased risk of Parkinsons disease in GBA carriers is due to a loss of glucocerebrosidase enzymatic activity. We measured glucocerebrosidase enzymatic activity in dried blood spots in patients with Parkinsons disease (n = 517) and controls (n = 252) with and without GBA mutations. Participants were recruited from Columbia University, New York, and fully sequenced for GBA mutations and genotyped for the LRRK2 G2019S mutation, the most common autosomal dominant mutation in the Ashkenazi Jewish population. Glucocerebrosidase enzymatic activity in dried blood spots was measured by a mass spectrometry-based assay and compared among participants categorized by GBA mutation status and Parkinsons disease diagnosis. Parkinsons disease patients were more likely than controls to carry the LRRK2 G2019S mutation (n = 39, 7.5% versus n = 2, 0.8%, P < 0.001) and GBA mutations or variants (seven homozygotes and compound heterozygotes and 81 heterozygotes, 17.0% versus 17 heterozygotes, 6.7%, P < 0.001). GBA homozygotes/compound heterozygotes had lower enzymatic activity than GBA heterozygotes (0.85 µmol/l/h versus 7.88 µmol/l/h, P < 0.001), and GBA heterozygotes had lower enzymatic activity than GBA and LRRK2 non-carriers (7.88 µmol/l/h versus 11.93 µmol/l/h, P < 0.001). Glucocerebrosidase activity was reduced in heterozygotes compared to non-carriers when each mutation was compared independently (N370S, P < 0.001; L444P, P < 0.001; 84GG, P = 0.003; R496H, P = 0.018) and also reduced in GBA variants associated with Parkinsons risk but not with Gaucher disease (E326K, P = 0.009; T369M, P < 0.001). When all patients with Parkinsons disease were considered, they had lower mean glucocerebrosidase enzymatic activity than controls (11.14 µmol/l/h versus 11.85 µmol/l/h, P = 0.011). Difference compared to controls persisted in patients with idiopathic Parkinsons disease (after exclusion of all GBA and LRRK2 carriers; 11.53 µmol/l/h, versus 12.11 µmol/l/h, P = 0.036) and after adjustment for age and gender (P = 0.012). Interestingly, LRRK2 G2019S carriers (n = 36), most of whom had Parkinsons disease, had higher enzymatic activity than non-carriers (13.69 µmol/l/h versus 11.93 µmol/l/h, P = 0.002). In patients with idiopathic Parkinsons, higher glucocerebrosidase enzymatic activity was associated with longer disease duration (P = 0.002) in adjusted models, suggesting a milder disease course. We conclude that lower glucocerebrosidase enzymatic activity is strongly associated with GBA mutations, and modestly with idiopathic Parkinsons disease. The association of lower glucocerebrosidase activity in both GBA mutation carriers and Parkinsons patients without GBA mutations suggests that loss of glucocerebrosidase function contributes to the pathogenesis of Parkinsons disease. High glucocerebrosidase enzymatic activity in LRRK2 G2019S carriers may reflect a distinct pathogenic mechanism. Taken together, these data suggest that glucocerebrosidase enzymatic activity could be a modifiable therapeutic target.

Low frequency of BMPR2 mutations in a German cohort of patients with sporadic idiopathic pulmonary arterial hypertension

Idiopathic pulmonary arterial hypertension (IPAH; formerly known as primary pulmonary hypertension, PPH) is a rare disorder characterised by pulmonary vascular proliferation and remodelling resulting in loss of patency of the pulmonary arteries. This leads to sustained elevation of pulmonary artery pressures with subsequent progressive right heart failure and often death.1–3 While the majority of cases (>90%) have no known family history of the disease, ∼6% of the cases are known to be familial and are inherited in an autosomal dominant manner with markedly reduced penetrance.4 In previous studies, linkage analysis identified a familial IPAH locus on chromosome 2q33.5,6 Subsequent heterozygous germline mutations in the bone morphogenetic protein receptor, type II (BMPR II) gene ( BMPR2 ) were identified in at least 50% of familial cases.7–9 BMPR-II is a member of the transforming growth factor-β (TGF-β) receptor superfamily signalling pathway, which is critical in both cell differentiation and cell growth mediated through transcriptional regulation.10,11 Interestingly, germline mutations were also identified in 26–40% of sporadic cases.12,13 This study was performed to establish the frequency of BMPR2 mutations in a different population of patients with sporadic IPAH. ### Patients Between March 2002 and January 2004, 99 consecutive non-related patients >20 years of age with IPAH and negative family history were evaluated. In all cases, diagnosis of IPAH was made by experienced and specialised cardiologists or pulmonologists according to WHO criteria.1,14 Other causes of pulmonary hypertension such as illicit drug abuse or anorectic drug use were excluded by careful medical history evaluation. Underlying heart and lung diseases (recurrent pulmonary embolism, connective tissue disease, obstructive or restrictive lung disease) and HIV infection were excluded by a cascade of clinical examinations including laboratory tests, arterial blood gas analysis, chest x ray, pulmonary function tests, echocardiography, ventilation perfusion …

Parkinson disease phenotype in Ashkenazi jews with and without LRRK2 G2019S mutations

The phenotype of Parkinsons disease (PD) in patients with and without leucine‐rich repeat kinase 2 (LRRK2) G2019S mutations reportedly is similar; however, large, uniformly evaluated series are lacking. The objective of this study was to characterize the clinical phenotype of Ashkenazi Jewish (AJ) PD carriers of the LRRK2 G2019S mutation. We studied 553 AJ PD patients, including 65 patients who were previously reported, from three sites (two in New York and one in Tel‐Aviv). Glucocerebrosidase (GBA) mutation carriers were excluded. Evaluations included the Montreal Cognitive Assessment (MoCA), the Unified Parkinsons Disease Rating Scale (UPDRS), the Geriatric Depression Scale (GDS) and the Non‐Motor Symptoms (NMS) questionnaire. Regression models were constructed to test the association between clinical and demographic features and LRRK2 status (outcome) in 488 newly recruited participants. LRRK2 G2019S carriers (n = 97) and non‐carriers (n = 391) were similar in age and age at onset of PD. Carriers had longer disease duration (8.6 years vs. 6.1 years; P < 0.001), were more likely to be women (51.5% vs. 37.9%; P = 0.015), and more often reported first symptoms in the lower extremities (40.0% vs. 19.2%; P < 0.001). In logistic models that were adjusted for age, disease duration, sex, education, and site, carriers were more likely to have lower extremity onset (P < 0.001), postural instability and gait difficulty (PIGD) (P = 0.043), and a persistent levodopa response for >5 years (P = 0.042). Performance on the UPDRS, MoCA, GDS, and NMS did not differ by mutation status. PD in AJ LRRK2 G2019S mutation carriers is similar to idiopathic PD but is characterized by more frequent lower extremity involvement at onset and PIGD without the associated cognitive impairment.

High levels of placenta growth factor in sickle cell disease promote pulmonary hypertension.

Pulmonary hypertension is associated with reduced nitric oxide bioavailability and early mortality in sickle cell disease (SCD). We previously demonstrated that placenta growth factor (PlGF), an angiogenic factor produced by erythroid cells, induces hypoxia-independent expression of the pulmonary vasoconstrictor endothelin-1 in pulmonary endothelial cells. Using a lentivirus vector, we simulated erythroid expression of PlGF in normal mice up to the levels seen in sickle mice. Consequently, endothelin-1 production increased, right ventricle pressures increased, and right ventricle hypertrophy and pulmonary changes occurred in the mice within 8 weeks. These findings were corroborated in 123 patients with SCD, in whom plasma PlGF levels were significantly associated with anemia, endothelin-1, and tricuspid regurgitant velocity; the latter is reflective of peak pulmonary artery pressure. These results illuminate a novel mechanistic pathway linking hemolysis and erythroid hyperplasia to increased PlGF, endothelin-1, and pulmonary hypertension in SCD, and suggest that strategies that block PlGF signaling may be therapeutically beneficial.

A mutation in myotilin causes spheroid body myopathy.

Background: Spheroid body myopathy (SBM) is a rare, autosomal dominant, neuromuscular disorder, which has only been previously reported in a single large kindred. Identification of the mutated gene in this disorder may provide insight regarding abnormal neuromuscular function. Methods: The authors completed a detailed clinical evaluation on an extensive kindred diagnosed with SBM. Genome-wide linkage analysis was performed to localize the disease gene to a specific chromosomal region. Further marker genotyping and screening of a positional, functional candidate gene were completed to detect the disease-causing mutation. Pathologic analysis of muscle biopsy was performed on three individuals. Biochemical studies were performed on one muscle biopsy specimen from an affected individual. Results: Linkage to chromosome 5q23-5q31 was detected with a lod score of 2.9. Genotyping of additional markers in a larger sample of family members produced a maximum lod score of 6.1 and narrowed the critical interval to 12.2 cM. Screening of the candidate gene titin immunoglobulin domain protein (TTID, also known as MYOT) detected a cytosine-to-thymine mutation in exon 2 of all clinically affected family members. Similar pathologic changes were present in all muscle biopsy specimens. Immunohistologic and biochemical analysis revealed that the TTID protein, also known as myotilin, is a component of the insoluble protein aggregate. Conclusions: A novel mutation in the TTID gene results in the clinical and pathologic phenotype termed “spheroid body myopathy.” Mutations in this gene also cause limb-girdle muscular dystrophy 1A and are associated with myofibrillar myopathy.

Linkage stratification and mutation analysis at the parkin locus identifies mutation positive Parkinson's disease families [1]

Parkinsons disease (PD) is one of the most common neurological disorders in humans with an overall prevalence of 1:1000 with the incidence increasing to as high as 3.4% among people aged 75 years.1,2 The clinical phenotype includes resting tremor, muscular rigidity, bradykinesia, and postural instability. The signs and symptoms of the disease are the consequence of a striatal deficiency of dopamine resulting from neuronal death in the substantia nigra. It is characterised by the presence of the Lewy body, an intracytoplasmic inclusion body found in many brain regions which is not entirely specific to, but is a highly sensitive marker for, Parkinsons disease. The pathogenesis of idiopathic Parkinsons disease is unknown. For the overwhelming majority of PD patients, the disease has previously been thought to occur sporadically. However, there is increasing evidence of a genetic contribution to the disorder.1,3 Recently, two studies have investigated familial aggregation of PD using large, population based, case-control studies. Elbaz et al 4 reported an odds ratio of 3.2 for the presence of PD in first degree relatives (parents and sibs) of 175 cases as compared to 481 controls. Analyses stratified by age showed this aggregation to be stronger for younger PD patients. Familial aggregation of PD in Iceland was studied using a cohort of 772 cases, with 560 having onset of disease at >50 years of age.5 In this study, the odds ratio for PD was 6.7 for sibs and 3.2 for offspring of affected subjects. These studies are consistent with others reporting the risk to be anywhere from two to 14 times higher for first degree relatives as compared to the risk in members of unaffected families.6–9 Genetic linkage analyses in families with either autosomal dominant forms of PD or with an autosomal recessive, juvenile form …