Certain heterozygous variants in the kinase domain of the serine/threonine kinase NEK8 can cause an autosomal dominant form of polycystic kidney disease.

Autosomal dominant polycystic kidney disease (ADPKD) resulting from pathogenic variants in PKD1 and PKD2 is the most common form of PKD, but other genetic causes tied to primary cilia function have been identified. Biallelic pathogenic variants in the serine/threonine kinase NEK8 cause a syndromic ciliopathy with extra-kidney manifestations. Here we identify NEK8 as a disease gene for ADPKD in 12 families. Clinical evaluation was combined with functional studies using fibroblasts and tubuloids from affected individuals. Nek8 knockout mouse kidney epithelial (IMCD3) cells transfected with wild type or variant NEK8 were further used to study ciliogenesis, ciliary trafficking, kinase function, and DNA damage responses. Twenty-one affected monoallelic individuals uniformly exhibited cystic kidney disease (mostly neonatal) without consistent extra-kidney manifestations. Recurrent de novo mutations of the NEK8 missense variant p.Arg45Trp, including mosaicism, were seen in ten families. Missense variants elsewhere within the kinase domain (p.Ile150Met and p.Lys157Gln) were also identified. Functional studies demonstrated normal localization of the NEK8 protein to the proximal cilium and no consistent cilia formation defects in patient-derived cells. NEK8-wild type protein and all variant forms of the protein expressed in Nek8 knockout IMCD3 cells were localized to cilia and supported ciliogenesis. However, Nek8 knockout IMCD3 cells expressing NEK8-p.Arg45Trp and NEK8-p.Lys157Gln showed significantly decreased polycystin-2 but normal ANKS6 localization in cilia. Moreover, p.Arg45Trp NEK8 exhibited reduced kinase activity in vitro. In patient derived tubuloids and IMCD3 cells expressing NEK8-p.Arg45Trp, DNA damage signaling was increased compared to healthy passage-matched controls. Thus, we propose a dominant-negative effect for specific heterozygous missense variants in the NEK8 kinase domain as a new cause of PKD.

Whole exome sequencing of 28 families of Danish descent reveals novel candidate genes and pathways in developmental dysplasia of the hip.

Developmental dysplasia of the hip (DDH) is a common condition involving instability of the hip with multifactorial etiology. Early diagnosis and treatment are critical as undetected DDH is an important cause of long-term hip complications. Better diagnostics may be achieved through genetic methods, especially for patients with positive family history. Several candidate genes have been reported but the exact molecular etiology of the disease is yet unknown. In the present study, we performed whole exome sequencing of DDH patients from 28 families with at least two affected first-degree relatives. Four genes previously not associated with DDH (METTL21B, DIS3L2, PPP6R2, and TM4SF19) were identified with the same variants shared among affected family members, in more than two families. Among known association genes, we found damaging variants in DACH1, MYH10, NOTCH2, TBX4, EVC2, OTOG, and SHC3. Mutational burden analysis across the families identified 322 candidate genes, and enriched pathways include the extracellular matrix, cytoskeleton, ion-binding, and detection of mechanical stimulus. Taken altogether, our data suggest a polygenic mode of inheritance for DDH, and we propose that an impaired transduction of the mechanical stimulus is involved in the etiopathological mechanism. Our findings refine our current understanding of candidate causal genes in DDH, and provide a foundation for downstream functional studies.

Detection of DZIP1L mutations by whole-exome sequencing in consanguineous families with polycystic kidney disease.

BACKGROUND: Autosomal recessive polycystic kidney disease is a cystic kidney disease with early onset and clinically characterized by enlarged echogenic kidneys, hypertension, varying degrees of kidney dysfunction, and liver fibrosis. It is most frequently caused by sequence variants in the PKHD1 gene, encoding fibrocystin. In more rare cases, sequence variants in DZIP1L are seen, encoding the basal body protein DAZ interacting protein 1-like protein (DZIP1L). So far, only four different DZIP1L variants have been reported. METHODS: Four children from three consanguineous families presenting with polycystic kidney disease were selected for targeted or untargeted exome sequencing. RESULTS: We identified two different, previously not reported homozygous DZIP1L sequence variants: c.193 T > C; p.(Cys65Arg), and c.216C > G; p.(Cys72Trp). Functional analyses of the c.216C > G; p.(Cys72Trp) variant indicated mislocalization of mutant DZIP1L. CONCLUSIONS: In line with published data, our results suggest a critical role of the N-terminal domain for proper protein function. Although patients with PKHD1-associated autosomal recessive polycystic kidney disease often have liver abnormalities, none of the present four patients showed any clinically relevant liver involvement. Our data demonstrate the power and efficiency of next-generation sequencing-based approaches. While DZIP1L-related polycystic kidney disease certainly represents a rare form of the disease, our results emphasize the importance of including DZIP1L in multigene panels and in the data analysis of whole-exome sequencing for cystic kidney diseases. A higher resolution version of the Graphical abstract is available as Supplementary information.

Guidelines for Genetic Testing and Management of Alport Syndrome.

Genetic testing for pathogenic COL4A3-5 variants is usually undertaken to investigate the cause of persistent hematuria, especially with a family history of hematuria or kidney function impairment. Alport syndrome experts now advocate genetic testing for persistent hematuria, even when a heterozygous pathogenic COL4A3 or COL4A4 is suspected, and cascade testing of their first-degree family members because of their risk of impaired kidney function. The experts recommend too that COL4A3 or COL4A4 heterozygotes do not act as kidney donors. Testing for variants in the COL4A3-COL4A5 genes should also be performed for persistent proteinuria and steroid-resistant nephrotic syndrome due to suspected inherited FSGS and for familial IgA glomerulonephritis and kidney failure of unknown cause.

Consensus statement on standards and guidelines for the molecular diagnostics of Alport syndrome: refining the ACMG criteria.

The recent Chandos House meeting of the Alport Variant Collaborative extended the indications for screening for pathogenic variants in the COL4A5, COL4A3 and COL4A4 genes beyond the classical Alport phenotype (haematuria, renal failure; family history of haematuria or renal failure) to include persistent proteinuria, steroid-resistant nephrotic syndrome, focal and segmental glomerulosclerosis (FSGS), familial IgA glomerulonephritis and end-stage kidney failure without an obvious cause. The meeting refined the ACMG criteria for variant assessment for the Alport genes (COL4A3-5). It identified 'mutational hotspots' (PM1) in the collagen IV α5, α3 and α4 chains including position 1 Glycine residues in the Gly-X-Y repeats in the intermediate collagenous domains; and Cysteine residues in the carboxy non-collagenous domain (PP3). It considered that 'well-established' functional assays (PS3, BS3) were still mainly research tools but sequencing and minigene assays were commonly used to confirm splicing variants. It was not possible to define the Minor Allele Frequency (MAF) threshold above which variants were considered Benign (BA1, BS1), because of the different modes of inheritances of Alport syndrome, and the occurrence of hypomorphic variants (often Glycine adjacent to a non-collagenous interruption) and local founder effects. Heterozygous COL4A3 and COL4A4 variants were common 'incidental' findings also present in normal reference databases. The recognition and interpretation of hypomorphic variants in the COL4A3-COL4A5 genes remains a challenge.

Skewness of X-chromosome inactivation increases with age and varies across birth cohorts in elderly Danish women.

Mosaicism in blood varies with age, and cross-sectional studies indicate that for women, skewness of X-chromosomal mosaicism increases with age. This pattern could, however, also be due to less X-inactivation in more recent birth cohorts. Skewed X-chromosome inactivation was here measured longitudinally by the HUMARA assay in 67 septuagenarian and octogenarian women assessed at 2 time points, 10 years apart, and in 10 centenarian women assessed at 2 time points, 2-7 years apart. Skewed X-chromosome inactivation was also compared in 293 age-matched septuagenarian twins born in 1917-1923 and 1931-1937, and 212 centenarians born in 1895, 1905 and 1915. The longitudinal study of septuagenarians and octogenarians revealed that 16% (95% CI 7-29%) of the women developed skewed X-inactivation over a 10-year period. In the cross-sectional across-birth cohort study, the earlier-born septuagenarian (1917-1923) and centenarian women (1895) had a higher degree of skewness than the respective recent age-matched birth cohorts, which indicates that the women in the more recent cohorts, after the age of 70, had not only changed degree of skewness with age, they had also undergone less age-related hematopoietic sub-clone expansion. This may be a result of improved living conditions and better medical treatment in the more recent birth cohorts.

A novel PDGFRB sequence variant in a family with a mild form of primary familial brain calcification: a case report and a review of the literature.

BACKGROUND: Primary familial brain calcification is a rare autosomal dominant or recessive neurodegenerative disease, characterized by bilateral brain calcifications in different areas of the brain. It is a clinically heterogeneous disease and patients are reported to exhibit a wide spectrum of neurological and psychiatric symptoms. Mutations in five genes have been identified so far including SLC20A2, PDGFRB, PDGFB, XPR1, and MYORG. PDGFRB encodes the platelet-derived growth factor receptor-beta, and is expressed in neurons, vascular smooth muscle cells and pericytes. Patients with a PDGFRB mutation seem to exhibit a milder phenotype and milder brain calcification on brain imaging than patients with SLC20A2 and PDGFB mutations. However, this is based on a few observations so far. CASE PRESENTATION: We present a Danish family with bilateral brain calcifications and mild clinical symptoms of primary familial brain calcification, segregating with a novel PDGFRB sequence variant: c.1834G > A; p.(Gly612Arg), detected by whole exome sequencing. The variant results in physiochemical changes at the amino acid level, and affects a highly conserved nucleotide as well as amino acid. It is located in the tyrosine kinase domain of PDGFRß. Segregation analysis and in silico analyses predicted the missense variant to be disease causing. CONCLUSION: Our study confirms that PDGFRB mutation carriers in general have a mild clinical phenotype, and basal ganglia calcifications can be detected by a CT scan, also in asymptomatic mutation carriers.

A Gene Implicated in Activation of Retinoic Acid Receptor Targets Is a Novel Renal Agenesis Gene in Humans.

Renal agenesis (RA) is one of the more extreme examples of congenital anomalies of the kidney and urinary tract (CAKUT). Bilateral renal agenesis is almost invariably fatal at birth, and unilateral renal agenesis can lead to future health issues including end-stage renal disease. Genetic investigations have identified several gene variants that cause RA, including EYA1, LHX1, and WT1 However, whereas compound null mutations of genes encoding α and γ retinoic acid receptors (RARs) cause RA in mice, to date there have been no reports of variants in RAR genes causing RA in humans. In this study, we carried out whole exome sequence analysis of two families showing inheritance of an RA phenotype, and in both identified a single candidate gene, GREB1L Analysis of a zebrafish greb1l loss-of-function mutant revealed defects in the pronephric kidney just prior to death, and F0 CRISPR/Cas9 mutagenesis of Greb1l in the mouse revealed kidney agenesis phenotypes, implicating Greb1l in this disorder. GREB1L resides in a chromatin complex with RAR members, and our data implicate GREB1L as a coactivator for RARs. This study is the first to associate a component of the RAR pathway with renal agenesis in humans.

Moebius sequence -a multidisciplinary clinical approach.

BACKGROUND: Moebius Sequence (MS) is a rare disorder defined by bilateral congenital paralysis of the abducens and facial nerves in combination with various odontological, craniofacial, ophthalmological and orthopaedic conditions. The aetiology is still unknown; but both genetic (de novo mutations) and vascular events in utero are reported. The purpose of present study was through a multidisciplinary clinical approach to examine children diagnosed with Moebius-like symptoms. Ten children underwent odontological, ophthalmological, obstetric, paediatric, orthopaedic, genetic, radiological and photographical evaluation. Five patients maintained the diagnosis of MS according to the diagnostic criteria. RESULTS: All five patients had bilateral facial and abducens paralysis confirmed by ophthalmological examination. Three of five had normal brain MR imaging. Two had missing facial nerves and one had missing abducens nerves. The Strengths and Difficulties Questionnaire (SDQ) showed normal scores in three of five patients. Interestingly, two of five children were born to mothers with uterine abnormalities (unicornuate/bicornuate uterus). In the odontological examination three of five showed enamel hypomineralisation. All five had abnormal orofacial motor function and maxillary prognathism. Two patients had adactyly, syndactyly and brachydactyly. None of the five patients had Poland anomaly, hip dislocation or dysplasia but all had a mild degree of scoliosis. We observed congenital club-feet, calcaneovalgus deformities, macrodactyly of one or more toes or curly toes. Pedobarography showed plantar pressures within normal ranges. CONCLUSIONS: Adherence to standard diagnostic criteria is central in the diagnosis of MS. An accurate diagnosis is the basis for correct discussion of other relevant concomitant symptoms of MS, genetic testing and evaluation of prognosis. The multidisciplinary approach and adherence to diagnostic criteria taken in present study increases the knowledge on the relationship between genotype, phenotype and symptomatology of MS.

Severe fluoropyrimidine toxicity due to novel and rare DPYD missense mutations, deletion and genomic amplification affecting DPD activity and mRNA splicing.

Dihydropyrimidine dehydrogenase (DPD) is the initial and rate-limiting enzyme in the catabolism of 5-fluorouracil (5FU). Genetic variations in DPD have emerged as predictive risk factors for severe fluoropyrimidine toxicity. Here, we report novel and rare genetic variants underlying DPD deficiency in 9 cancer patients presenting with severe fluoropyrimidine-associated toxicity. All patients possessed a strongly reduced DPD activity, ranging from 9 to 53% of controls. Analysis of the DPD gene (DPYD) showed the presence of 21 variable sites including 4 novel and 4 very rare aberrations: 3 missense mutations, 2 splice-site mutations, 1 intronic mutation, a deletion of 21 nucleotides and a genomic amplification of exons 9-12. Two novel/rare variants (c.2843T>C, c.321+1G>A) were present in multiple, unrelated patients. Functional analysis of recombinantly-expressed DPD mutants carrying the p.I948T and p.G284V mutation showed residual DPD activities of 30% and 0.5%, respectively. Analysis of a DPD homology model indicated that the p.I948T and p.G284V mutations may affect electron transfer and the binding of FAD, respectively. cDNA analysis showed that the c.321+1G>A mutation in DPYD leads to skipping of exon 4 immediately upstream of the mutated splice-donor site in the process of DPD pre-mRNA splicing. A lethal toxicity in two DPD patients suggests that fluoropyrimidines combined with other therapies such as radiotherapy might be particularly toxic for DPD deficient patients. Our study advocates a more comprehensive genotyping approach combined with phenotyping strategies for upfront screening for DPD deficiency to ensure the safe administration of fluoropyrimidines.

X-Linked and Autosomal Recessive Alport Syndrome: Pathogenic Variant Features and Further Genotype-Phenotype Correlations.

Alport syndrome results from mutations in the COL4A5 (X-linked) or COL4A3/COL4A4 (recessive) genes. This study examined 754 previously- unpublished variants in these genes from individuals referred for genetic testing in 12 accredited diagnostic laboratories worldwide, in addition to all published COL4A5, COL4A3 and COL4A4 variants in the LOVD databases. It also determined genotype-phenotype correlations for variants where clinical data were available. Individuals were referred for genetic testing where Alport syndrome was suspected clinically or on biopsy (renal failure, hearing loss, retinopathy, lamellated glomerular basement membrane), variant pathogenicity was assessed using currently-accepted criteria, and variants were examined for gene location, and age at renal failure onset. Results were compared using Fisher's exact test (DNA Stata). Altogether 754 new DNA variants were identified, an increase of 25%, predominantly in people of European background. Of the 1168 COL4A5 variants, 504 (43%) were missense mutations, 273 (23%) splicing variants, 73 (6%) nonsense mutations, 169 (14%) short deletions and 76 (7%) complex or large deletions. Only 135 of the 432 Gly residues in the collagenous sequence were substituted (31%), which means that fewer than 10% of all possible variants have been identified. Both missense and nonsense mutations in COL4A5 were not randomly distributed but more common at the 70 CpG sequences (p<10-41 and p<0.001 respectively). Gly>Ala substitutions were underrepresented in all three genes (p< 0.0001) probably because of an association with a milder phenotype. The average age at end-stage renal failure was the same for all mutations in COL4A5 (24.4 ±7.8 years), COL4A3 (23.3 ± 9.3) and COL4A4 (25.4 ± 10.3) (COL4A5 and COL4A3, p = 0.45; COL4A5 and COL4A4, p = 0.55; COL4A3 and COL4A4, p = 0.41). For COL4A5, renal failure occurred sooner with non-missense than missense variants (p<0.01). For the COL4A3 and COL4A4 genes, age at renal failure occurred sooner with two non-missense variants (p = 0.08, and p = 0.01 respectively). Thus DNA variant characteristics that predict age at renal failure appeared to be the same for all three Alport genes. Founder mutations (with the pathogenic variant in at least 5 apparently- unrelated individuals) were not necessarily associated with a milder phenotype. This study illustrates the benefits when routine diagnostic laboratories share and analyse their data.

The first Danish family reported with an AQP5 mutation presenting diffuse non-epidermolytic palmoplantar keratoderma of Bothnian type, hyperhidrosis and frequent Corynebacterium infections: a case report.

BACKGROUND: An autosomal dominant form of diffuse non-epidermolytic palmoplantar keratoderma, palmoplantar keratoderma of Bothnian type, is caused by mutations in the AQP5 gene encoding the cell-membrane water channel protein aquaporin 5 leading to defective epidermal-water-barrier function in the epidermis of the palms and soles. CASE PRESENTATION: We report the first Danish family diagnosed with diffuse non-epidermolytic palmoplantar keratoderma of Bothnian type in which fourteen individuals are potentially affected. The proband, a 36-year-old male had since childhood been affected by pronounced hyperhidrosis of the palms and soles along with palmoplantar keratoderma. He reported a very distinctive feature of the disorder, aquagenic wrinkling, as he developed pronounced maceration of the skin with translucent white papules and a spongy appearance following exposure to water. The patient presented recurrent fungal infections, a wellknown feature of the condition, but also periodic worsening with pitted keratolysis and malodour due to bacterial infections. CONCLUSIONS: Palmoplantar keratoderma of Bothnian type, which may be associated with hyperhidrosis, is frequently complicated by fungal infections and may be complicated by Corynebacterium infections.

Odonto-onycho-dermal dysplasia in a patient homozygous for a WNT10A nonsense mutation and mild manifestations of ectodermal dysplasia in carriers of the mutation.

BACKGROUND: Odonto-onycho-dermal dysplasia (OODD) is a rare form of ectodermal dysplasia characterized by severe oligodontia, onychodysplasia, palmoplantar hyperkeratosis, dry skin, hypotrichosis, and hyperhidrosis of the palms and soles. The ectodermal dysplasias resulting from biallelic mutations in the WNT10A gene result in highly variable phenotypes, ranging from isolated tooth agenesis to OODD and Schöpf-Schulz-Passarge syndrome (SSPS). CASE PRESENTATION: We identified a female patient, with consanguineous parents, who was clinically diagnosed with OODD. Genetic testing showed that she was homozygous for a previously reported pathogenic mutation in the WNT10A gene, c.321C > A, p.Cys107*. The skin and nail abnormalities were for many years interpreted as psoriasis and treated accordingly. A thorough clinical examination revealed hypotrichosis and hyperhidrosis of the soles and dental examination revealed agenesis of permanent teeth except the two maxillary central incisors. Skin biopsies from the hyperkeratotic palms and soles showed the characteristic changes of eccrine syringofibroadenomatosis, which has been described in patients with ectodermal dysplasias. Together with a family history of tooth anomalies, this lead to the clinical suspicion of a hereditary ectodermal dysplasia. CONCLUSION: This case illustrates the challenges of diagnosing ectodermal dysplasia like OODD and highlights the relevance of interdisciplinary cooperation in the diagnosis of rare conditions.

Epigenetic remodelling and dysregulation of DLGAP4 is linked with early-onset cerebellar ataxia.

Genome instability, epigenetic remodelling and structural chromosomal rearrangements are hallmarks of cancer. However, the coordinated epigenetic effects of constitutional chromosomal rearrangements that disrupt genes associated with congenital neurodevelopmental diseases are poorly understood. To understand the genetic-epigenetic interplay at breakpoints of chromosomal translocations disrupting CG-rich loci, we quantified epigenetic modifications at DLGAP4 (SAPAP4), a key post-synaptic density 95 (PSD95) associated gene, truncated by the chromosome translocation t(8;20)(p12;q11.23), co-segregating with cerebellar ataxia in a five-generation family. We report significant epigenetic remodelling of the DLGAP4 locus triggered by the t(8;20)(p12;q11.23) translocation and leading to dysregulation of DLGAP4 expression in affected carriers. Disruption of DLGAP4 results in monoallelic hypermethylation of the truncated DLGAP4 promoter CpG island. This induced hypermethylation is maintained in somatic cells of carriers across several generations in a t(8;20) dependent-manner however, is erased in the germ cells of the translocation carriers. Subsequently, chromatin remodelling of the locus-perturbed monoallelic expression of DLGAP4 mRNAs and non-coding RNAs in haploid cells having the translocation. Our results provide new mechanistic insight into the way a balanced chromosomal rearrangement associated with a neurodevelopmental disorder perturbs allele-specific epigenetic mechanisms at breakpoints leading to the deregulation of the truncated locus.

Manifestations of Gorlin-Goltz syndrome.

INTRODUCTION: Gorlin-Goltz syndrome is an uncommon hereditary condition caused by mutations in the PTCH1 gene causing a wide range of developmental abnormalities. Multiple basal cell carcinomas, palmoplantar pits and jaw cysts are cardinal features. Many clinicians are unfamiliar with the different manifestations and the fact that patients are especially sensitive to ionizing radiation. MATERIAL AND METHODS: This was a retrospective analysis of patients with Gorlin-Goltz syndrome seen at the Department of Dermatology and Allergy Centre or at Department of Plastic Surgery, Odense University Hospital, Denmark, in the period from 1994 to 2013. RESULTS: A total of 17 patients from eight families fulfilled the diagnostic criteria. In all, 14 patients had basal cell carcinomas, 12 patients had jaw cysts and ten patients had calcification of the falx cerebri. Other clinical features were frontal bossing, kyphoscoliosis, rib anomalies, coalitio, cleft lip/palate, eye anomalies, milia and syndactyly. In one family, medulloblastoma and astrocytoma occurred. Traditional treatment principles of basal cell carcinomas were used including radiotherapy performed in six patients. PTCH1 mutations were identified in five families and none of these mutations had previously been described. CONCLUSION: The patient cohort illustrates classic and rare disease manifestations. It is necessary to remind clinicians that radiation therapy in Gorlin-Goltz syndrome is relatively contraindicated. Today, mutation analysis can be used for confirmation of the diagnosis and for predictive genetic testing. Patients should be offered genetic counselling and life-long surveillance. FUNDING: not relevant. TRIAL REGISTRATION: not relevant.

A retrospective study of clinical and mutational findings in 45 Danish families with ectodermal dysplasia.

Ectodermal dysplasias form a complex, nosologic group of diseases with defects in at least 2 ectodermal structures. A retrospective study of patients with ectodermal dysplasia seen at our department over a period of 19 years (1994-2013) was performed. The study population consisted of 67 patients covering 17 different diagnoses. Forty-five families were identified of which 26 were sporadic cases with no affected family members. In 27 tested families a disease-causing mutation was identified in 23 families. Eleven mutations were novel mutations. To our knowledge, we present the first large ectodermal dysplasia cohort focusing on clinical manifestations in combination with mutational analysis. We recommend a nationwide study to estimate the prevalence of the ectodermal dysplasia and to ensure relevant molecular genetic testing which may form the basis of a national ectodermal dysplasia database.

Renal phenotypic investigations of megalin-deficient patients: novel insights into tubular proteinuria and albumin filtration.

BACKGROUND: The reabsorption of filtered plasma proteins, hormones and vitamins by the renal proximal tubules is vital for body homeostasis. Studies of megalin-deficient mice suggest that the large multi-ligand endocytic receptor megalin plays an essential role in this process. In humans, dysfunctional megalin causes the extremely rare Donnai-Barrow/Facio-Oculo-Acustico-Renal (DB/FOAR) syndrome characterized by a characteristic and multifaceted phenotype including low-molecular-weight proteinuria. In this study, we examined the role of megalin for tubular protein reabsorption in humans through analysis of proximal tubular function in megalin-deficient patients. METHODS: Direct sequencing of the megalin-encoding gene (LRP2) was performed in a family in which three children presented with classical DB/FOAR manifestations. Renal consequences of megalin deficiency were investigated through immunohistochemical analyses of renal biopsy material and immunoblotting of urine samples. RESULTS: In the patients, a characteristic urinary protein profile with increased urinary excretion of vitamin D-binding protein, retinol-binding protein and albumin was associated with absence of, or reduced, proximal tubular endocytic uptake as shown by renal immunohistochemistry. In the absence of tubular uptake, urinary albumin excretion was in the micro-albuminuric range suggesting that limited amounts of albumin are filtered in human glomeruli. CONCLUSIONS: This study demonstrated that megalin plays an essential role for human proximal tubular protein reabsorption and suggests that only limited amounts of albumin is normally filtered in the human glomeruli. Finally, we propose that the characteristic urinary protein profile of DB/FOAR patients may be utilized as a diagnostic marker of megalin dysfunction.

Alport syndrome. Molecular genetic aspects.

Alport syndrome (AS) is a progressive renal disease that is characterised by hematuria and progressive renal failure, and often accompanied by progressive high-tone sensorineural hearing loss and ocular changes in form of macular flecks and lenticonus. AS is a genetic heterogenous disease, and X-linked dominant in about 85% of the families. The autosomal recessive and dominant forms constitute about 15% of the cases. In the first part of the study is a multipoint linkage analysis of 12 families suspected of X-linked AS. The aim of that part of the study was to map a number of X-chromosomal polymorphic markers in relation to the locus for AS, in order to be able to perform carrier detection and prenatal diagnosis in the families. In addition, a more precise map of the region could form the basis for positional cloning of the gene for X-linked AS. In 1990 it was found that the X-linked form of AS is caused by mutation in the COL4A5 gene located at Xq22, and encoding the alpha 5-chain of type IV-collagen. The COL4A5 gene is a very large gene spanning 257 kb with a transcript of 6.5 kb distributed on 51 exons. In addition, two alternatively transcribed exons have been identified. In the second part of the study methods were set up for detection and characterisation of mutations in the COL4A5 gene in 135 patients suspected of AS. The aims of that part of the study were to develop an efficient and reliable approach for mutation detection, and to implement the results of the mutation analysis in clinical practice for carrier detection and prenatal diagnosis, in order to be able to offer a better genetic counselling to the families. Knowledge of a possible correlation between genotype and phenotype can be of help in predicting the prognosis. Samples from 135 probands suspected of AS and 359 of their relatives were collected, together with available clinical information. Southern blotting analysis and multiplex ligation-dependent probe amplification (MLPA) were used to screen for larger structural rearrangements (deletions and duplications). cDNA probes covering the entire coding region of the COL4A5 gene were hybridised on restriction enzyme digested genomic DNA on Southern blots. Three different rearrangements were found by Southern blotting, two of which were caused by single base substitutions, and also detected by the PCR-SSCP analysis. One larger rearrangement was found, an inversion of 21 Mb with a proximal breakpoint in COL4A5 intron 8 at Xq22.3, and a distal breakpoint in the RAB33A gene at Xq26.1. This rearrangement was exclusively ascertained by the Southern blotting analysis. Three deletions of >or= 2 exons were detected by MLPA. One of these was detected in a female proband. A deletion in heterozygous form will not be detected by PCR-SSCP or direct sequencing. A method based on the PCR-SSCP technique was set up for screening of the COL4A5 gene exon-by-exon for mutation. All 51 COL4A5 exons with flanking intronic sequences were screened by this technique. The two alternatively transcribed exons 41A and 41B were directly sequenced. The PCR-SSCP method was compared to direct sequencing in 15 of the cases. No difference in mutation detection rates were found. Finally, a method based on RT-PCR analysis of mRNA extracted from cultured skin fibroblasts was established. A mutation in a patient previously screened by PCR-SSCP analysis with normal result, was detected. Another advantage of analysing a skin biopsy is that it is also possible to perform immunostaining for the alpha 5(IV)-chain in the epidermal basement membrane on sections from the biopsy. Absence of the alpha 5(IV)-chain support a diagnosis of X-linked AS. A total of 64 different and putative disease causing mutations were found in 72 of the families. Half of the mutations identified were missense mutations. The most frequent mutations in AS were glycine substitutions in the Gly-Xaa-Yaa repeat sequence in the collagenous domain of the alpha 5(IV)-chain, accounting for 47% of all mutations and 89% if the missense mutations. Frame-shift mutations accounted for 17% of the mutations, splice site mutations for 13%, nonsense mutations for 11%, in-frame deletions for 4%, and larger structural rearrangements for 6%. In addition, 5 different non-pathogenic sequence variations, polymorphisms and mutations of unknown effect on the phenotype, were found. Nineteen of the mutations are new and have not previously been published, and 55 of the mutations have exclusively been detected in this material. Two of the mutations (3%) are de novo mutations, and it has been possible to trace the mutation back in six of the families, and to determine the parental origin of the mutation in these six families. The origin of the mutation was found to be paternal in 4 of the families (67%), and maternal in 2 of the families (33%). We have demonstrated a highly efficient and sensitive molecular diagnostic approach for analysing the COL4A5 gene in putative AS cases. Based on the present results and the litterature, an algorithm for molecular genetic analysis of the COL4A5 gene is suggested. The overall mutation detection rate was found to be 53%. The mutation detection rate was 72% in patients fulfilling >or= 3 of the clinical criteria for AS, and 82% in families clearly demonstrating X-linked inheritance. No COL4A5 mutation could be detected in 63 (47%) of the families. X-linked inheritance could be excluded in seven of these families solely based on a pedigree analysis, and a diagnosis of Epstein syndrome was established in one of the patients by MYH9 mutation analysis. We found that the underlying COL4A5 mutation, truncating or non-truncating, can significantly predict the age at ESRD in male patients. Truncating mutations, comprising nonsense mutations, frame-shifts, and larger structural rearrangements, were found to cause a juvenile form of the disease with a mean age at ESRD of 21.6 years, compared to 33.1 years in patients with a non-truncating mutation. The effect of non-truncating mutations is, however, less clear-cut. Glycine substitutions in the collagenous domain of the alpha 5(IV)-chain will result in an adult form of AS with a mean age at ESRD of 35.8 years. Missense mutations in the NC1-domain and in-frame deletions result in a juvenile form of the disease with a mean age at ESRD of 23.3 and 20.3 years, respectively, but the number of patients in each group is limited. We found no significant differences in the presence of hearing defects or ocular manifestations between patients with the different types of mutations. The lack of distinct genotype-phenotype correlations implies that the usefulness of the result of the COL4A5 mutation analysis to predict the prognosis is limited. Future technological improvements e.g. automated sequencing strategies and implementation of microarray technology , may increase the mutation detection rates, and lower the time and costs of the analyses. Functional studies are hampered by the restricted expression of the type IV collagen chains. The many different animal models for AS are obvious and promising targets for functional studies, and an important resource for gene therapy studies. This makes AS a reliable candidate for future gene therapy in humans.

Hypocalcified type of amelogenesis imperfecta in a large family: clinical, radiographic, and histological findings, associated dento-facial anomalies, and resulting treatment load.

OBJECTIVE: The purpose of this study was to report on the clinical, radiographic, and histological dental findings and the resulting treatment load in a five-generation family with amelogenesis imperfecta (AI). MATERIAL AND METHODS: Thirteen affected and 15 unaffected individuals were examined clinically and radiographically. In addition, four exfoliated deciduous teeth were examined by scanning electron microscopy and microradiography. RESULTS: The mode of inheritance of AI was autosomal-dominant. At eruption, most of the tooth enamel was yellow, lacking translucency, and prone to gradual loss in subjects with AI. Post-eruptive breakdown of enamel was extensive in accordance with the histological observations of hypomineralized and porous enamel. Extensive enamel loss and discoloration were observed in older affected individuals. The treatment need had been extensive: 76.2% of the total number of teeth present in affected individuals had been treated with partial or full coverage compared to 1.7% of the teeth in unaffected relatives. Unaffected individuals had more endodontically treated teeth than AI-affected relatives. Adjunctive findings, e.g. tooth agenesis, tooth impaction, pulp stones, enlarged follicular space, and taurodontism, were rare in both groups. CONCLUSIONS: Affected family members had the hypocalcified type of AI, which is characterized by severe hypomineralization, extensive post-eruptive loss, and discoloration of the enamel. Adjunctive findings were rare. Individuals with the hypocalcified type of AI have an extensive restorative treatment load compared to unaffected relatives.