X-linked Alport syndrome in Hellenic families: phenotypic heterogeneity and mutations near interruptions of the collagen domain in COL4A5.

The X-linked Alport syndrome (ATS) is caused by mutations in COL4A5 and exhibits a widely variable expression. Usually ATS is heralded with continuous microhematuria which rapidly progresses to proteinuria, hypertension and chronic or end-stage renal disease (ESRD) by adolescence, frequently accompanied by sensorineural deafness and ocular complications. Milder forms of ATS also exist. We studied 42 patients (19M, 23F) of nine Hellenic families suspected clinically of X-linked ATS who presented with marked phenotypic heterogeneity. We identified mutations in COL4A5 in six families. Two males with nonsense mutation E228X reached ESRD by ages 14 and 18. Frameshift mutation 2946delT followed the same course with early onset renal involvement and deafness. However, two males with the milder missense mutation G624D, reached ESRD after 39 years and one patient showed thin basement membrane nephropathy (TBMN). Another 5/8 affected males with missense mutation P628L also developed ESRD between 30 and 57 years, while three exhibit only mild chronic renal failure (CRF). The data support previous findings that certain mutations are associated with milder phenotypes and confirm that mutation G624D may be expressed as TBMN with familial hematuria. Similar conclusions apply for missense mutation P628L. Interestingly, mutations G624D and P628L are near the 12th natural interruption of COL4A5 triple helical domain, which may explain the milder phenotype.

Novel NPR1 polymorphic variants and its exclusion as a candidate gene for medullary cystic kidney disease (ADMCKD) type 1.

Autosomal dominant medullary cystic kidney disease (ADMCKD) is an adult-onset heterogeneous genetic nephropathy characterized by salt wasting and end-stage renal failure. The gene responsible for ADMCKD-1 was mapped on chromosome 1q21 and it is flanked proximally by marker D1S498 and distally by D1S2125, encompassing a region of approximately 8 cm. Within this region there are a large number of transcribed genes including NPR1 that encodes the atrial natriuretic peptide receptor 1. This receptor plays a crucial role in regulation of blood pressure by facilitating salt excretion. Based on its function we hypothesized this gene as a reasonable candidate for the MCKD1 locus. DNA mutation screening was performed on the entire NPR1 gene-coding sequence and some of the 5' prime-UTR and 3'-UTR sequences. The samples investigated belonged to patients of five large ADMCKD-1 Cypriot families. The screening revealed two novel polymorphisms, one intragenic at amino acid position 939, which was occupied by either arginine or glutamine, and a second one located in the 3' prime-UTR, 29 nucleotides downstream of the NPR1 stop codon. The latter was a single nucleotide C insertion/deletion in a stretch of three or four Cs. No relationship was present between any allele of the two polymorphisms and the disease, as both alleles were observed in both affected and healthy subjects. In addition, no association was observed between the disease and another rare 8-bp deletion polymorphism at the 5' prime-UTR of NPR1 and the disease. Based on these findings it is unlikely that NPR1 is the same as the MCKD1 gene, although it is presently unknown whether it plays a disease modifying role.

Autosomal dominant medullary cystic kidney disease: evidence of gene locus heterogeneity.

Autosomal dominant medullary cystic kidney disease (ADMCKD; synonym: medullary cystic disease, MCD) is an autosomal dominant kidney disorder, sharing morphological and clinical features with recessive juvenile nephronophthisis (NPH), such as reduced urinary concentration ability and multiple renal cysts at the corticomedullary junction. While in NPH end-stage renal disease (ESRD) occurs in adolescence, ADMCKD leads to ESRD in adulthood. Recently a gene locus for ADMCKD has been localized to chromosome 1q21 in two large Cypriot families. This prompted us to examine linkage in three ADMCKD-families, using the same set of polymorphic microsatellite markers spanning the critical region on chromosome 1q21. Haplotype analysis revealed that none of the three families showed linkage to this locus, thus demonstrating evidence for genetic locus heterogeneity. Additional linkage analysis studies need to be performed in order to identify further gene loci cosegregating with this autosomal dominant kidney disorder.

Medullary cystic kidney disease with hyperuricemia and gout in a large Cypriot family: no allelism with nephronophthisis type 1.

We describe a large Cypriot family with an interstitial type of nephropathy, inherited as an autosomal dominant trait that led to end stage renal failure between 51 to 78 years of age (mean 62.2 years). Twenty-three people are known to be affected, but several younger relatives with normal renal function may remain undiagnosed because of the absence of precise clinical and laboratory diagnostic criteria. This nephropathy is associated with medullary renal cysts, hypertension, hyperuricemia, and gout. Several relatives have typical medullary cystic disease (MCD), while in the others the findings are compatible with this diagnosis. Due to the similarity of clinical and pathologic findings, earlier reports had suggested that MCD may be allelic to autosomal recessive familial juvenile nephronophthisis, which was mapped recently to chromosome band 2q13. Linkage analysis of the present family with a closely linked marker excluded linkage to the above locus. Linkage was also excluded to the PKD1 locus of adult polycystic kidney disease type 1, and up to 5 cM on either side, on chromosome 16. We suggest that because of the element of hyperuricemia and gout found in this family, although with reduced penetrance, it may represent a variant of autosomal dominant MCD of the adult type. This variability may be the result of allelic or locus heterogeneity. Molecular genetic approaches including linkage analysis on appropriate families will certainly assist in classifying such related genetically heterogeneous disorders.

Chromosome 1 localization of a gene for autosomal dominant medullary cystic kidney disease.

There is a group of inherited cystic nephropathies that are characterized by juvenile onset recessive inheritance (familial juvenile nephronophthisis, FJN) or by adult onset dominant inheritance (medullary cystic disease, MCD) and share similar clinico-pathological presentation to the extent that they are usually grouped together under the term FJN/MCD complex. The main symptoms consist of renal cyst formation in the medulla or the corticomedullary junction and salt wasting. Although earlier reports had suggested that one single gene may be responsible for this pathology, recent reports have shown that the FJN complex itself comprises a genetically heterogeneous group. Here we are presenting two large Cypriot families that segregate autosomal dominant medullary cystic kidney disease (ADMCKD) with hyperuricemia and gout and with very late age of onset (mean 62.2 and 51.5 years). We performed DNA linkage mapping using highly polymorphic microsatellite markers and found linkage to marker locus D1S1595 at 1q21 with a two-point lod score of 6.45 at Theta = 0.00. Analysis of haplotypes and of critical recombinants enabled confinement of the disease locus within an approximately 8 cM region between marker loci D1S498 and D1S2125. FISH mapping with a large P1 clone confirmed the physical localization within 1q21. The two families share the same disease haplotype, thus suggesting their relationship through a common ancestor and the possible existence of a single ADMCKD-causing mutation within these families. To our knowledge this is the first genetic locus identified to cause FJN/MCD pathology of the dominant adult type.

Prolonged fetal bradycardia during epidural analgesia. Incidence, timing and significance.

The mechanism of episodes of fetal bradycardia during epidural analgesia is unknown in the majority of cases. This retrospective study considers the relationship between prolonged fetal bradycardia and epidural analgesia during labour. Of 705 cardiotocographs recorded during administration of epidural analgesia for patients in labour, 207 were suitable for analysis. Prolonged fetal bradycardia occurred after 40 of 366 (11%) initial or repeat injections of local anaesthetic into the epidural space. The peak incidence of onset of bradycardia was 5-20 minutes after administration, but occurrences continued throughout the 60-minute period studied. In 1 patient a single episode of fetal bradycardia occurred before administration of the epidural block. In all cases studied the 5-minute Apgar scores were 7 or better. It is concluded that administration of epidural analgesia is significantly associated with episodes of prolonged fetal bradycardia, but that there is usually a return to pre-epidural patterns. The fetal heart rate should be monitored during epidural block administration to confirm the return to baseline rate and normal variability. Episodes of fetal bradycardia that return to a normal pattern do not necessitate early delivery.