NPHP4 variants are associated with pleiotropic heart malformations.

RATIONALE: Congenital heart malformations are a major cause of morbidity and mortality, especially in young children. Failure to establish normal left-right (L-R) asymmetry often results in cardiovascular malformations and other laterality defects of visceral organs. OBJECTIVE: To identify genetic mutations causing cardiac laterality defects. METHODS AND RESULTS: We performed a genome-wide linkage analysis in patients with cardiac laterality defects from a consanguineous family. The patients had combinations of defects that included dextrocardia, transposition of great arteries, double-outlet right ventricle, atrioventricular septal defects, and caval vein abnormalities. Sequencing of positional candidate genes identified mutations in NPHP4. We performed mutation analysis of NPHP4 in 146 unrelated patients with similar cardiac laterality defects. Forty-one percent of these patients also had laterality defects of the abdominal organs. We identified 8 additional missense variants that were absent or very rare in control subjects. To study the role of nphp4 in establishing L-R asymmetry, we used antisense morpholinos to knockdown nphp4 expression in zebrafish. Depletion of nphp4 disrupted L-R patterning as well as cardiac and gut laterality. Cardiac laterality defects were partially rescued by human NPHP4 mRNA, whereas mutant NPHP4 containing genetic variants found in patients failed to rescue. We show that nphp4 is involved in the formation of motile cilia in Kupffer's vesicle, which generate asymmetrical fluid flow necessary for normal L-R asymmetry. CONCLUSIONS: NPHP4 mutations are associated with cardiac laterality defects and heterotaxy. In zebrafish, nphp4 is essential for the development and function of Kupffer's vesicle cilia and is required for global L-R patterning.

Biological effects of the PINK1 c.1366C>T mutation: implications in Parkinson disease pathogenesis.

PINK1 gene mutations are a cause of recessively inherited, early-onset Parkinson's disease. In some patients, a single heterozygous mutation has been identified, including the recurrent c.1366C>T transition. The interpretation of this finding remains controversial. Furthermore, the c.1366C>T mutation is associated with lower levels of PINK1 transcript, raising the question of whether mRNA levels correlate with the clinical status. We sequenced genomic DNA and copy DNA (cDNA) from 20 subjects carrying the c.1366C>T mutation in the homozygous (n = 5) or heterozygous (n = 15) state. In 17 mutation carriers, messenger RNA (mRNA) was quantified by real-time PCR using four different assays (PINK1 exon 5-6 or exon 7-8 relative to control genes SDHA or YWHAZ). Genomic sequencing confirmed the presence and zygosity of PINK1 mutations. cDNA sequencing in heterozygous mutation carriers revealed a strong wild-type and a much weaker or almost absent mutant signal, whereas in the homozygous patients, only the mutant signal was detected. Homozygous and heterozygous carriers showed PINK1 mRNA levels relative to a reference gene in the range of 0.1-0.2 and 0.5-0.6, respectively, compared with values of 0.9-1.0 in mutation-negative individuals. Treatment of lymphoblasts from a heterozygous mutation carrier with cycloheximide markedly increased the mutant transcript signal. We conclude that the recurrent PINK1 c.1366C>T mutation exerts a major effect at the mRNA level (80-90% reduction), most likely via nonsense-mediated mRNA decay. The absence of correlation between PINK1 mRNA levels and clinical status in heterozygous mutation carriers suggests that other genetic or environmental factors play a role in determining the phenotypic variability associated with the c.1366C>T mutation.

A common missense variant in the LRRK2 gene, Gly2385Arg, associated with Parkinson's disease risk in Taiwan.

Mutations in the LRRK2 gene are a cause of autosomal dominant Parkinson's disease (PD). Whether LRRK2 variants influence susceptibility to the commoner, sporadic forms of PD remains largely unknown. Data are particularly limited concerning the Asian population. In search for novel, biologically relevant variants, we sequenced the LRRK2 coding region in Taiwanese patients with PD. Four newly identified variants and another variant recently found in a Taiwanese PD family were tested for association with the disease in a sample of 608 PD cases and 373 ethnically matched controls. Heterozygosity for the Gly2385Arg variant was significantly more frequent among PD patients than controls (nominal p value=0.004, corrected for multiple comparisons=0.012, gender- and age-adjusted odds ratio=2.24, 95% C.I.: 1.29-3.88); this variant was uniformly distributed across genders and age strata. Two novel variants, Met1869Val and Glu1874Stop, were found in one PD case each; their pathogenic role remains, therefore, uncertain. The remaining two novel variants (Ala419Val and Pro755Leu) were present with similar frequency in cases and controls, and were therefore, interpreted as disease-unrelated polymorphisms. Our findings suggest that the LRRK2 Gly2385Arg is the first identified, functionally relevant variant, which acts as common risk factor for sporadic PD in the population of Chinese ethnicity.

Comprehensive analysis of the LRRK2 gene in sixty families with Parkinson's disease.

Mutations in the gene leucine-rich repeat kinase 2 (LRRK2) have been recently identified in families with Parkinson's disease (PD). However, the prevalence and nature of LRRK2 mutations, the polymorphism content of the gene, and the associated phenotypes remain poorly understood. We performed a comprehensive study of this gene in a large sample of families with Parkinson's disease compatible with autosomal dominant inheritance (ADPD). The full-length open reading frame and splice sites of the LRRK2 gene (51 exons) were studied by genomic sequencing in 60 probands with ADPD (83% Italian). Pathogenic mutations were identified in six probands (10%): the heterozygous p.G2019S mutation in four (6.6%), and the heterozygous p.R1441C mutation in two (3.4%) probands. A further proband carried the heterozygous p.I1371 V mutation, for which a pathogenic role could not be established with certainty. In total, 13 novel disease-unrelated variants and three intronic changes of uncertain significance were also characterized. The phenotype associated with LRRK2 pathogenic mutations is the one of typical PD, but with a broad range of onset ages (mean 55.2, range 38-68 years) and, in some cases, slow disease progression. On the basis of the comprehensive study in a large sample, we conclude that pathogenic LRRK2 mutations are frequent in ADPD, and they cluster in the C-terminal half of the encoded protein. These data have implications both for understanding the molecular mechanisms of PD, and for directing the genetic screening in clinical practice.

Early-onset Parkinson's disease caused by a novel parkin mutation in a genetic isolate from north-eastern Brazil.

We describe clinical and molecular findings in a genetic isolate from north-eastern Brazil with early-onset Parkinson's disease (PD) and a novel mutation in the parkin gene. Genealogical studies could connect 255 individuals, of whom 15 had PD. Geographic isolation and multiple consanguineous marriages initially suggested an autosomal recessive inheritance for PD in these patients. The available individuals were personally examined, and DNA was obtained from 26 members: ten early-onset PD patients, one case with likely neuroleptic-induced parkinsonism and 15 unaffected relatives. The average age at onset of PD symptoms was 30.8 years (range 12-46). Haplotype analysis revealed homozygosity in the PD patients for markers across the PARK2 locus. Genomic sequencing identified a novel homozygous splice-site parkin mutation (IVS1 + 1G/T), which completely co-segregated with the early-onset PD phenotype. cDNA analysis confirmed the total loss of parkin transcript in homozygous mutation carriers, delineating this as a loss-of-function mutation. The case with neuroleptic-induced parkinsonism and 13 of 15 healthy relatives were heterozygous carriers of the mutation. The absence of PD in heterozygous carriers indicates a genuinely recessive nature of this mutation, suggesting that parkin haploinsufficiency is not a relevant risk factor for early- or late-onset PD. However, parkin haploinsufficiency could facilitate the emergence of neuroleptic-induced parkinsonism. The cluster reported here, which to our knowledge is the largest described to date with early-onset PD and parkin mutations, also offers a unique opportunity for the search of modifiers of the parkin-related disease.

A frequent LRRK2 gene mutation associated with autosomal dominant Parkinson's disease.

Mutations in the LRRK2 gene have been identified in families with autosomal dominant parkinsonism. We amplified and sequenced the coding region of LRRK2 from genomic DNA by PCR, and identified a heterozygous mutation (Gly2019 ser) present in four of 61 (6.6%) unrelated families with Parkinson's disease and autosomal dominant inheritance. The families originated from Italy, Portugal, and Brazil, indicating the presence of the mutation in different populations. The associated phenotype was broad, including early and late disease onset. These findings confirm the association of LRRK2 with neurodegeneration, and identify a common mutation associated with dominantly inherited Parkinson's disease.

Distinct effects of single amino-acid changes to tuberin on the function of the tuberin-hamartin complex.

Tuberous sclerosis is an autosomal dominant human disorder caused by inactivating mutations to either the TSC1 or TSC2 tumour suppressor gene. Hamartin and tuberin, the TSC1 and TSC2 gene products, interact and the tuberin-hamartin complex inhibits cell growth by antagonising signal transduction to downstream effectors of the mammalian target of rapamycin (mTOR) through the small GTPase rheb. Previously, we showed that pathogenic tuberin amino-acid substitutions disrupt the tuberin-hamartin complex. Here, we investigate how these mutations affect the role of tuberin in the control of signal transduction through mTOR. Our data indicate that specific amino-acid substitutions have distinct effects on tuberin function.

Homozygous PINK1 C-terminus mutation causing early-onset parkinsonism.

Two homozygous mutations in the PINK1 gene, encoding a mitochondrial putative protein kinase, recently have been identified in families with PARK6-linked, autosomal recessive early-onset parkinsonism (AREP). Here, we describe a novel homozygous mutation (1573_1574 insTTAG) identified in an AREP patient, which causes a frameshift and truncation at the C-terminus of the PINK1 protein, outside the kinase catalytic domain. The clinical phenotype includes early-onset (28 years) parkinsonism, foot dystonia at onset, good levodopa response, slow progression, early levodopa-induced dyskinesias, and sleep benefit, thereby resembling closely parkin-related disease. These findings confirm that recessive mutations in PINK1 cause early-onset parkinsonism and expand the associated clinical phenotype.