RESUMO
PKHD1, the gene mutated in autosomal recessive polycystic kidney disease (ARPKD)/congenital hepatic fibrosis (CHF), is an exceptionally large and complicated gene that consists of 86 exons and has a number of alternatively spliced transcripts. Its longest open reading frame contains 67 exons that encode a 4074 amino acid protein called fibrocystin or polyductin. The phenotypes caused by PKHD1 mutations are similarly complicated, ranging from perinatally-fatal PKD to CHF presenting in adulthood with mild kidney disease. To date, more than 300 mutations have been described throughout PKHD1. Most reported cohorts include a large proportion of perinatal-onset ARPKD patients; mutation detection rates vary between 42% and 87%. Here we report PKHD1 sequencing results on 78 ARPKD/CHF patients from 68 families. Differing from previous investigations, our study required survival beyond 6 months and included many adults with a CHF-predominant phenotype. We identified 77 PKHD1 variants (41 novel) including 19 truncating, 55 missense, 2 splice, and 1 small in-frame deletion. Using computer-based prediction tools (GVGD, PolyPhen, SNAP), we achieved a mutation detection rate of 79%, ranging from 63% in the CHF-predominant group to 82% in the remaining families. Prediction of the pathogenicity of missense variants will remain challenging until a functional assay is available. In the meantime, use of PKHD1 sequencing data for clinical decisions requires caution, especially when only novel or rare missense variants are identified.
Assuntos
Variação Genética , Cirrose Hepática/congênito , Cirrose Hepática/genética , Rim Policístico Autossômico Recessivo/complicações , Rim Policístico Autossômico Recessivo/genética , Receptores de Superfície Celular/genética , Adolescente , Adulto , Sequência de Bases , Criança , Pré-Escolar , Feminino , Humanos , Lactente , Recém-Nascido , Cirrose Hepática/complicações , MasculinoRESUMO
OBJECTIVES: To describe 3 children with mutations in a Meckel syndrome gene (MKS3), with features of autosomal recessive polycystic kidney disease (ARPKD), nephronophthisis, and Joubert syndrome (JS). STUDY DESIGN: Biochemical evaluations, magnetic resonance and ultrasound imaging, electroretinograms, IQ testing, and sequence analysis of the PKHD1 and MKS3 genes were performed. Functional consequences of the MKS3 mutations were evaluated by cDNA sequencing and transfection studies with constructs of meckelin, the protein product of MKS3. RESULTS: These 3 children with MKS3 mutations had features typical of ARPKD, that is, enlarged, diffusely microcystic kidneys and early-onset severe hypertension. They also exhibited early-onset chronic anemia, a feature of nephronophthisis, and speech and oculomotor apraxia, suggestive of JS. Magnetic resonance imaging of the brain, originally interpreted as normal, revealed midbrain and cerebellar abnormalities in the spectrum of the "molar tooth sign" that characterizes JS. CONCLUSIONS: These findings expand the phenotypes associated with MKS3 mutations. MKS3-related ciliopathies should be considered in patients with an ARPKD-like phenotype, especially in the presence of speech and oculomotor apraxia. In such patients, careful expert evaluation of the brain images can be beneficial because the brain malformations can be subtle.
Assuntos
Anormalidades Múltiplas/genética , Transtornos da Motilidade Ciliar/genética , Proteínas de Membrana/genética , Mutação , Rim Policístico Autossômico Recessivo/genética , Anormalidades Múltiplas/diagnóstico , Encéfalo/anormalidades , Encéfalo/patologia , Criança , Transtornos da Motilidade Ciliar/diagnóstico , Feminino , Humanos , Rim/anormalidades , Rim/diagnóstico por imagem , Rim/patologia , Fígado/anormalidades , Fígado/patologia , Imageamento por Ressonância Magnética , Masculino , Rim Policístico Autossômico Recessivo/diagnóstico , Irmãos , Síndrome , UltrassonografiaRESUMO
The autosomal recessive Griscelli syndrome type II (GSII) is caused by mutations in the RAB27A gene. Typical clinical features include immunological impairment, silver-gray scalp hair, eyelashes and eyebrows and hypomelanosis of the skin. Rabs help determine the specificity of membrane trafficking steps within cells. In melanocytes, the GTP-bound form of Rab27A associates with the membranes of mature fully-pigmented melanosomes through its geranylgeranyl group. Once attached, Rab27A recruits the downstream effector Melanophilin (Mlph) and the actin-dependent motor protein Myosin Va (MyoVa). The molecular Rab27A/Mlph/MyoVA tripartite complex, which links melanosomes to the peripheral actin network, is required to achieve melanosome transfer to surrounding keratinocytes in the epidermis. Here we report a novel homozygous missense mutation c.127G>A, p.G43S in exon 2 of the RAB27A gene of an Afghani GSII patient. Laser scanning confocal microscopy showed that the G43S mutation, which is located in the highly conserved switch I region of Rab27A, induces perinuclear localization of melanosomes in normal melanocytes, and fails to restore melanosomes to the actin-rich periphery in GSII melanocytes. Co-immunoprecipitation studies showed that Rab27A(G43S) fails to interact with its effector Melanophilin, indicating that the switch I region functions in the recruitment of Rab effector proteins.
Assuntos
Erros Inatos do Metabolismo/genética , Erros Inatos do Metabolismo/metabolismo , Mutação de Sentido Incorreto , Proteínas rab de Ligação ao GTP/genética , Proteínas rab de Ligação ao GTP/metabolismo , Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Afeganistão , Motivos de Aminoácidos , Núcleo Celular/química , Núcleo Celular/genética , Criança , Pré-Escolar , Feminino , Humanos , Masculino , Melanócitos/química , Melanócitos/metabolismo , Melanossomas/química , Melanossomas/metabolismo , Erros Inatos do Metabolismo/diagnóstico , Dados de Sequência Molecular , Ligação Proteica , Alinhamento de Sequência , Síndrome , Proteínas rab de Ligação ao GTP/química , Proteínas rab27 de Ligação ao GTPRESUMO
BACKGROUND AND OBJECTIVES: Renal function and imaging findings have not been comprehensively and prospectively characterized in a broad age range of patients with molecularly confirmed autosomal recessive polycystic kidney disease (ARPKD). DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: Ninety potential ARPKD patients were examined at the National Institutes of Health Clinical Center. Seventy-three fulfilled clinical diagnostic criteria, had at least one PKHD1 mutation, and were prospectively evaluated using magnetic resonance imaging (MRI), high-resolution ultrasonography (HR-USG), and measures of glomerular and tubular function. RESULTS: Among 31 perinatally symptomatic patients, 25% required renal replacement therapy by age 11 years; among 42 patients who became symptomatic beyond 1 month (nonperinatal), 25% required kidney transplantation by age 32 years. Creatinine clearance (CrCl) for nonperinatal patients (103 +/- 54 ml/min/1.73 m(2)) was greater than for perinatal patients (62 +/- 33) (P = 0.002). Corticomedullary involvement on HR-USG was associated with a significantly worse mean CrCl (61 +/- 32) in comparison with medullary involvement only (131 +/- 46) (P < 0.0001). Among children with enlarged kidneys, volume correlated inversely with function, although with wide variability. Severity of PKHD1 mutations did not determine kidney size or function. In 35% of patients with medullary-only abnormalities, standard ultrasound was normal and the pathology was detectable with HR-USG. CONCLUSIONS: In ARPKD, perinatal presentation and corticomedullary involvement are associated with faster progression of kidney disease. Mild ARPKD is best detected by HR-USG. Considerable variability occurs that is not explained by the type of PKHD1 mutation.
Assuntos
Genes Recessivos , Rim/patologia , Rim/fisiopatologia , Doenças Renais Policísticas/genética , Receptores de Superfície Celular/genética , Adolescente , Adulto , Biomarcadores/sangue , Biomarcadores/urina , Criança , Pré-Escolar , Creatinina/urina , Cistatina C/sangue , Análise Mutacional de DNA , Progressão da Doença , Feminino , Predisposição Genética para Doença , Taxa de Filtração Glomerular , Humanos , Lactente , Estimativa de Kaplan-Meier , Rim/diagnóstico por imagem , Túbulos Renais/patologia , Túbulos Renais/fisiopatologia , Imageamento por Ressonância Magnética , Masculino , Pessoa de Meia-Idade , National Institutes of Health (U.S.) , Tamanho do Órgão , Linhagem , Fenótipo , Doenças Renais Policísticas/patologia , Doenças Renais Policísticas/fisiopatologia , Doenças Renais Policísticas/terapia , Estudos Prospectivos , Medição de Risco , Fatores de Risco , Índice de Gravidade de Doença , Fatores de Tempo , Ultrassonografia , Estados Unidos , Adulto JovemRESUMO
ARPKD/CHF is an inherited disease characterized by non-obstructive fusiform dilatation of the renal collecting ducts leading to enlarged spongiform kidneys and ductal plate malformation of the liver resulting in congenital hepatic fibrosis. ARPKD/CHF has a broad spectrum of clinical presentations involving the kidney and liver. Imaging plays an important role in the diagnosis and follow-up of ARPKD/CHF. Combined use of conventional and high-resolution US with MR cholangiography in ARPKD/CHF patients allows detailed definition of the extent of kidney and hepatobiliary manifestations without requiring ionizing radiation and contrast agents.