Gamma-D crystallin gene (CRYGD) mutation causes autosomal dominant congenital cerulean cataracts.

Congenital cataracts are a major cause of bilateral visual impairment in childhood. We mapped the gene responsible for autosomal congenital cerulean cataracts to chromosome 2q33-35 in a four generation family of Moroccan descent. The maximum lod score (7.19 at recombination fraction theta=0) was obtained for marker D2S2208 near the gamma-crystallin gene (CRYG) cluster. Sequencing of the coding regions of the CRYGA, B, C, and D genes showed the presence of a heterozygous C>A transversion in exon 2 of CRYGD that is associated with cataracts in this family. This mutation resulted in a proline to threonine substitution at amino acid 23 of the protein in the first of the four Greek key motifs that characterise this protein. We show that although the x ray crystallography modelling does not indicate any change of the backbone conformation, the mutation affects a region of the Greek key motif that is important for determining the topology of this protein fold. Our data suggest strongly that the proline to threonine substitution may alter the protein folding or decrease the thermodynamic stability or solubility of the protein. Furthermore, this is the first report of a mutation in this gene resulting in autosomal dominant congenital cerulean cataracts.

The photoreceptor cell-specific nuclear receptor gene (PNR) accounts for retinitis pigmentosa in the Crypto-Jews from Portugal (Marranos), survivors from the Spanish Inquisition.

The last Crypto-Jews (Marranos) are the survivors of Spanish Jews who were persecuted in the late fifteenth century, escaped to Portugal and were forced to convert to save their lives. Isolated groups still exist in mountainous areas such as Belmonte in the Beira-Baixa province of Portugal. We report here the genetic study of a highly consanguineous endogamic population of Crypto-Jews of Belmonte affected with autosomal recessive retinitis pigmentosa (RP). A genome-wide search for homozygosity allowed us to localize the disease gene to chromosome 15q22-q24 (Zmax=2.95 at theta=0 at the D15S131 locus). Interestingly, the photoreceptor cell-specific nuclear receptor (PNR) gene, the expression of which is restricted to the outer nuclear layer of retinal photoreceptor cells, was found to map to the YAC contig encompassing the disease locus. A search for mutations allowed us to ascribe the RP of Crypto-Jews of Belmonte to a homozygous missense mutation in the PNR gene. Preliminary haplotype studies support the view that this mutation is relatively ancient but probably occurred after the population settled in Belmonte.

NPHS2, encoding the glomerular protein podocin, is mutated in autosomal recessive steroid-resistant nephrotic syndrome.

Familial idiopathic nephrotic syndromes represent a heterogeneous group of kidney disorders, and include autosomal recessive steroid-resistant nephrotic syndrome, which is characterized by early childhood onset of proteinuria, rapid progression to end-stage renal disease and focal segmental glomerulosclerosis. A causative gene for this disease, NPHS2, was mapped to 1q25-31 and we report here its identification by positional cloning. NPHS2 is almost exclusively expressed in the podocytes of fetal and mature kidney glomeruli, and encodes a new integral membrane protein, podocin, belonging to the stomatin protein family. We found ten different NPHS2 mutations, comprising nonsense, frameshift and missense mutations, to segregate with the disease, demonstrating a crucial role for podocin in the function of the glomerular filtration barrier.

Structure of the gene for congenital nephrotic syndrome of the finnish type (NPHS1) and characterization of mutations.

Congenital nephrotic syndrome of the Finnish type (NPHS1) is an autosomal recessive disorder that is caused by mutations in the recently discovered nephrin gene, NPHS1 (AF035835). The disease, which belongs to the Finnish disease heritage, exists predominantly in Finland, but many cases have been observed elsewhere in Europe and North America. The nephrin gene consists of 29 exons spanning 26 kb in the chromosomal region 19q13.1. In the present study, the genomic structure of the nephrin gene was analyzed, and 35 NPHS1 patients were screened for the presence of mutations in the gene. A total of 32 novel mutations, including deletions; insertions; nonsense, missense, and splicing mutations; and two common polymorphisms were found. Only two Swedish and four Finnish patients had the typical Finnish mutations: a 2-bp deletion in exon 2 (Finmajor) or a nonsense mutation in exon 26 (Finminor). In seven cases, no mutations were found in the coding region of the NPHS1 gene or in the immediate 5'-flanking region. These patients may have mutations elsewhere in the promoter, in intron areas, or in a gene encoding another protein that interacts with nephrin.

A novel gene encoding an integral membrane protein is mutated in nephropathic cystinosis.

Nephropathic cystinosis, an autosomal recessive disorder resulting from defective lysosomal transport of cystine, is the most common inherited cause of renal Fanconi syndrome. The cystinosis gene has been mapped to chromosome 17p13. We found that the locus D17S829 was homozygously deleted in 23 out of 70 patients, and identified a novel gene, CTNS, which mapped to the deletion interval. CTNS encodes an integral membrane protein, cystinosin, with features of a lysosomal membrane protein. Eleven different mutations, all predicted to cause loss of function of the protein, were found to segregate with the disorder.

Congenital nephrotic syndrome of the Finnish type: linkage to the locus in a non-Finnish population.

Congenital nephrotic syndrome of the Finnish type (CNF) is inherited as an autosomal recessive trait. The biochemical basis of the disease is unknown, although a lesion in the glomerular basement membrane is strongly suggested. Recently, the CNF locus was assigned to chromosome 19q12-q13.1 on the basis of linkage analysis in Finnish families. The high incidence of the disease in Finland, as well as the demonstration of linkage disequilibrium in the Finnish study, strongly suggests a founder effect based on a common ancient mutation in this population. We confirm linkage of the CNF locus to the same chromosomal region in seven non-Finnish CNF families without evidence of linkage disequilibrium. Our results show that the same gene seems to be affected in both Finnish and non-Finnish CNF populations. However, in the latter the mutation-carrying chromosomes descend from different ancestors without evidence of a founder effect.

High-resolution mapping of the gene for cystinosis, using combined biochemical and linkage analysis.

Infantile nephropathic cystinosis is an autosomal recessive disorder characterized biochemically by an abnormally high intracellular content of free cystine in different organs and tissues due to a transport defect of cystine through the lysosomal membrane. Affected children present with the Fanconi syndrome and usually develop progressive renal failure within the 1st decade of life. Measurement of free cystine in purified polymorphonuclear leukocytes provides an accurate method for diagnosis and detection of heterozygous carriers. In order to localize the gene locus for cystinosis we performed linkage analysis in 18 cystinosis families. However, since 17 of these were simplex families, we decided to include the phenotypes of the heterozygous carriers previously determined by their leukocyte cystine content in the linkage analysis. This approach allowed us to obtain highly significant results, confirming the localization of the cystinosis gene locus recently mapped to the short arm of chromosome 17 by the Cystinosis Collaborative Research Group. Crucial recombination events allowed us to refine the interval of the cystinosis gene to a genetic distance of 1 cM. No evidence of genetic heterogeneity was found. Our results demonstrate that the use of the previously determined phenotypes of heterozygous carriers in linkage analysis provides a reliable method for the investigation of simplex families in autosomal recessive traits.

Mapping a gene (SRN1) to chromosome 1q25-q31 in idiopathic nephrotic syndrome confirms a distinct entity of autosomal recessive nephrosis.

Idiopathic nephrotic syndrome (INS) in childhood is characterized by massive proteinuria and minimal glomerular changes. Most patients with INS respond to steroid therapy. INS is generally regarded as a sporadic disease with favorable outcome. We investigated a distinct subgroup of nephrosis--the familial form of steroid resistant INS (SRN). These patients always progress to end-stage renal failure within a few years and show absence of recurrence of the disease after renal transplantation. The occurrence of the disorder in siblings and the high incidence of inbreeding in these families made an autosomal recessive mode of inheritance very likely. We performed whole genome linkage analysis in nine multiplex families of European or Northern African origin. Our results allowed us to assign a disease locus (SRN1) to a defined chromosomal region on 1q25-1q31, thus confirming the existence of a distinct entity of autosomal recessive nephrosis. Exclusion of linkage to the entire region in one family proves genetic heterogeneity.