A CRYGC gene mutation associated with autosomal dominant pulverulent cataract

Purpose

To describe at molecular level a family with pulverulent congenital cataract associated with a CRYGC gene mutation.

Methods

One family with several affected members with pulverulent congenital cataract and 230 healthy controls were examined. Genomic DNA from leukocytes was isolated to analyze the CRYGA-D cluster, CX46, CX50 and MIP genes through high-resolution melting curve and DNA sequencing.

Results

DNA sequencing in the affected members revealed the c.143G>A mutation (p.R48H) in exon 2 of the CRYGC gene; 230 healthy controls and ten healthy relatives were also analyzed and none of them showed the c.143G>A mutation. No other polymorphisms or mutations were found to be present.

Conclusion

In the present study, we described a family with pulverulent congenital cataract that segregated the c.143G>A mutation (p.R48H) in the CRYGC gene. A few mutations have been described in the CRYGC gene in autosomal dominant cataract, none of them with pulverulent cataract making clear the clinical heterogeneity of congenital cataract. This mutation has been associated with the phenotype of congenital cataract but also is considered an SNP in the NCBI data base. Our data and previous report suggest that p.R48H could be a disease-causing mutation and not an SNP.     

The gamma S-crystallin gene is mutated in autosomal recessive cataract in mouse

We established a recessive cataract model from a spontaneous mutation in the KUNMING outbred mice. Lens opacity appears 11 days after birth. Slit lamp examination reveals that the opacity mainly localizes to the nuclear region of the lens. Histological analysis shows a severe degeneration of the epithelial cells underneath the anterior lens capsule, whereas those cells in the equatorial region display an excessive proliferation and migration. Within the cortical area underneath the posterior lens capsule, both vacuoles and morgagnian-like bodies are seen. Blue-stained spherical bodies are observed in the embryonic nucleus, forming a Y-like pattern. We mapped the disease locus and found a homozygous G to A nucleotide conversion at position 489 of Crygs in mutant mice, leading to a truncated gene product (Trp163Stop). This finding suggests that CRYGS is not only a lens structural protein, but is also likely to be involved in epithelial cell proliferation, apoptosis, and migration.     

Complement factor H gene mutation associated with autosomal recessive atypical hemolytic uremic syndrome

Atypical hemolytic uremic syndrome (HUS) presents with the clinical features of hypertension, microangiopathic hemolytic anemia, and acute renal failure. Both dominant and recessive modes of inheritance have been reported. This study describes the genetic and functional analysis of a large Bedouin kindred with autosomal recessive HUS. The kindred consists of several related nuclear families in which all parent unions of affected children are consanguineous. A previous report demonstrated that a dominant form of HUS maps to chromosome 1q and that complement factor H (CFH), a regulatory component of the complement system, lies within the region and is involved in the dominant disorder. Early-onset and persistent hypocomplementemia in this Bedouin kindred prompted us to evaluate the CFH gene. Linkage analysis was performed, demonstrating linkage between the disorder and the markers near the CFH gene. Mutation analysis of the CFH coding region revealed a single missense mutation. Functional analyses demonstrate that the mutant CFH is properly expressed and synthesized but that it is not transported normally from the cell. This is the first study reporting that a recessive, atypical, early-onset, and relapsing HUS is associated with the CFH protein and that a CFH mutation affects intracellular trafficking and secretion.     

A missense mutation in LRR8 of RXFP2 is associated with cryptorchidism

Using genome-wide mutagenesis with N-ethyl-N-nitrosourea (ENU), a mouse mutant with cryptorchidism was identified. Genome mapping and exon sequencing identified a novel missense mutation (D294G) in Relaxin/insulin-like family peptide receptor 2 (Rxfp2). The mutation impaired testicular descent and resulted in decreased testis weight in Rxfp2 ^DG/DG mice compared to Rxfp2 ^+/DG and Rxfp2 ^+/+ mice. Testicular histology of the Rxfp2 ^DG/DG mice revealed spermatogenic defects ranging from germ cell loss to tubules with Sertoli-cell-only features. Genetic complementation analysis using a loss-of-function allele (Rxfp2 ^?) confirmed causality of the D294G mutation. Specifically, mice with one of each mutant allele (Rxfp2 ^DG/?) exhibited decreased testis weight and failure of the testes to descend compared to their Rxfp2 ^+/? littermates. Total and cell-surface expression of mouse RXFP2 protein and intracellular cAMP accumulation were measured. Total expression of the D294G protein was minimally reduced compared to wild-type, but cell-surface expression was markedly decreased. When analyzed for cAMP accumulation, the EC50 was similar for cells transfected with wild-type and mutant RXFP2 receptor. However, the maximum cAMP response that the mutant receptor reached was greatly reduced compared to the wild-type receptor. In silico modeling of leucine rich repeats (LRRs) 7–9 indicated that aspartic acid 294 is located within the β-pleated sheet of LRR8. We thus postulate that mutation of D294 results in protein misfolding and aberrant trafficking. The ENU-induced D294G mutation underscores the role of the INSL3/RXFP2-mediated pathway in testicular descent and expands the repertoire of mutations known to affect receptor trafficking and function.     

A defect in the ionotropic glutamate receptor 6 gene (GRIK2) is associated with autosomal recessive mental retardation

Nonsyndromic mental retardation is one of the most important unresolved problems in genetic health care. Autosomal forms are far more common than X-linked forms, but, in contrast to the latter, they are still largely unexplored. Here, we report a complex mutation in the ionotropic glutamate receptor 6 gene (GRIK2, also called “GLUR6”) that cosegregates with moderate-to-severe nonsyndromic autosomal recessive mental retardation in a large, consanguineous Iranian family. The predicted gene product lacks the first ligand-binding domain, the adjacent transmembrane domain, and the putative pore loop, suggesting a complete loss of function of the GLU_K6 protein, which is supported by electrophysiological data. This finding provides the first proof that GLU_K6 is indispensable for higher brain functions in humans, and future studies of this and other ionotropic kainate receptors will shed more light on the pathophysiology of mental retardation.     

Autosomal recessive juvenile onset cataract associated with mutation in BFSP1

A genome wide scan in a consanguineous family of Indian origin with autosomal recessive developmental cataracts was performed by two-point linkage analysis with 382 microsatellite markers. It showed linkage to markers on chromosome 20q, between D20S852 and D20S912, with a maximum lod score of 5.4 obtained with D20S860. This region encompasses the beaded filament structural protein 1 (BFSP1) gene. Direct sequencing revealed a 3343 bp deletion including exon 6 (c.736-1384_c.957-66 del) predicted to result in a shift of the open reading frame. This mutation was absent in 50 control individuals from south India. This is the first report of a mutation in the BFSP1 gene associated with human inherited cataracts. This further increases the genetic heterogeneity of inherited cataracts and provides clues as to the importance of BFSP1 in the cell biology of intermediate filaments and their role in the eye lens.     

Mutation in WNT10A is associated with an autosomal recessive ectodermal dysplasia: the odonto-onycho-dermal dysplasia

Odonto-onycho-dermal dysplasia is a rare autosomal recessive syndrome in which the presenting phenotype is dry hair, severe hypodontia, smooth tongue with marked reduction of fungiform and filiform papillae, onychodysplasia, keratoderma and hyperhidrosis of palms and soles, and hyperkeratosis of the skin. We studied three consanguineous Lebanese Muslim Shiite families that included six individuals affected with odonto-onycho-dermal dysplasia. Using a homozygosity-mapping strategy, we assigned the disease locus to an ~9-cM region at chromosome 2q35-q36.2, located between markers rs16853834 and D2S353, with a maximum multipoint LOD score of 5.7. Screening of candidate genes in this region led us to identify the same c.697G-->T (p.Glu233X) homozygous nonsense mutation in exon 3 of the WNT10A gene in all patients. At the protein level, the mutation is predicted to result in a premature truncated protein of 232 aa instead of 417 aa. This is the first report to our knowledge of a human phenotype resulting from a mutation in WNT10A, and it is the first demonstration of an ectodermal dysplasia caused by an altered WNT signaling pathway, expanding the list of WNT-related diseases.     

A missense mutation in the bovine leptin receptor gene is associated with leptin concentrations during late pregnancy

The leptin receptor (LEPR) gene consists of 20 exons divided over 1.75 Mb. Parts of bovine LEPR exon 4 (79 bp), exon 11 (95 bp) and exon 20 (513 bp) of 20 cows (Holstein-Friesian) were sequenced (AJ580799; AJ580800; AJ580801) in an attempt to find polymorphisms. In exons 4 and 11 no SNPs were found. In exon 20, a T to C missense mutation was found at nucleotide 115, which causes an amino acid substitution at residue 945 (T945M). Frequencies for alleles C and T were 0.93 and 0.07 respectively, in a population of 323 Holstein-Friesian cows and TT animals were not detected. Using genotypes of these cows an association study was performed for leptin concentrations during late pregnancy and lactation. Leptin concentrations were determined by radioimmunoassay (RIA). The T945M mutation showed an association with circulating leptin concentrations only during late pregnancy (P < 0.05) but not during lactation (P > 0.05). The CC genotype had higher concentrations than the CT genotype during this period. A combined effect with previously described leptin polymorphisms on prepartum leptin concentrations was observed, with one genotype combination having significantly lower levels of leptin up to 50 days, but interaction effects were not significant. The T945M polymorphism may have induced a structural change in the intracellular domain of the LEPR, which may have influenced the signal transduction pathway. However, the effect was found only for the heterozygous genotype because the TT genotype was not detected in this population of 323 Holstein-Friesian cows.     

A mutation in the lipase H (LIPH) gene underlie autosomal recessive hypotrichosis

Hereditary hypotrichosis is a rare autosomal recessive disorder characterized by sparse hair on scalp and rest of the body of affected individuals. Two forms of such hypotrichosis LAH and AH have been mapped on chromosome 18q12.1 and 3q27, respectively. Mutations in desmogelin 4 (DSG4) gene have been reported to underlie LAH. Recently, a deletion mutation in Lipase H (LIPH) gene, located at AH locus, has been identified in two ethnic groups of Russian population. In the present study, a four generation Pakistani family with AH phenotype has been mapped to chromosome 3q27. Sequence analysis of candidate gene LIPH revealed a novel five base pair deletion mutation (c.346–350delATATA) in exon 2 of the gene leading to frameshift and downstream premature termination codon. The mutation reported in the family, presented here, is the second mutation identified in LIPH gene. The identification of a genetic defect in LIPH suggests that this enzyme regulates hair growth.     

A missense mutation in the vasopressin-neurophysin precursor gene cosegregates with human autosomal dominant neurohypophyseal diabetes insipidus.

Familial neurohypophyseal diabetes insipidus in humans is a rare disease transmitted as an autosomal dominant trait. Affected individuals have very low or undetectable levels of circulating vasopressin and suffer from polydipsia and polyuria. An obvious candidate gene for the disease is the vasopressin-neurophysin (AVP-NP) precursor gene on human chromosome 20. The 2 kb gene with three exons encodes a composite precursor protein consisting of the neuropeptide vasopressin and two associated proteins, neurophysin and a glycopeptide. Cloning and nucleotide sequence analysis of both alleles of the AVP-NP gene present in a Dutch ADNDI family reveals a point mutation in one allele of the affected family members. Comparison of the nucleotide sequences shows a G----T transversion within the neurophysin-encoding exon B. This missense mutation converts a highly conserved glycine (Gly17 of neurophysin) to a valine residue. RFLP analysis of six related family members indicates cosegregation of the mutant allele with the DI phenotype. The mutation is not present in 96 chromosomes of an unrelated control group. These data suggest that a single amino acid exchange within a highly conserved domain of the human vasopressin-associated neurophysin is the primary cause of one form of ADNDI.     

A new autosomal recessive form of Stickler syndrome is caused by a mutation in the COL9A1 gene

Stickler syndrome is characterized by ophthalmic, articular, orofacial, and auditory manifestations. It has an autosomal dominant inheritance pattern and is caused by mutations in COL2A1, COL11A1, and COL11A2. We describe a family of Moroccan origin that consists of four children with Stickler syndrome, six unaffected children, and two unaffected parents who are distant relatives (fifth degree). All family members were clinically investigated for ear, nose, and throat; ophthalmologic; and radiological abnormalities. Four children showed symptoms characteristic of Stickler syndrome, including moderate-to-severe sensorineural hearing loss, moderate-to-high myopia with vitreoretinopathy, and epiphyseal dysplasia. We considered the COL9A1 gene, located on chromosome 6q13, to be a candidate gene on the basis of the structural association with collagen types II and XI and because of the high expression in the human inner ear indicated by cDNA microarray. Mutation analysis of the coding region of the COL9A1 gene showed a homozygous R295X mutation in the four affected children. The parents and four unaffected children were heterozygous carriers of the R295X mutation. Two unaffected children were homozygous for the wild-type allele. None of the family members except the homozygous R295X carriers had any signs of Stickler syndrome. Therefore, COL9A1 is the fourth identified gene that can cause Stickler syndrome. In contrast to the three previously reported Stickler syndrome-causing genes, this gene causes a form of Stickler syndrome with an autosomal recessive inheritance pattern. This finding will have a major impact on the genetic counseling of patients with Stickler syndrome and on the understanding of the pathophysiology of collagens. Mutation analysis of this gene is recommended in patients with Stickler syndrome with possible autosomal recessive inheritance.     

A missense mutation in the endothelin-B receptor gene is associated with Lethal White Foal Syndrome: an equine version of Hirschsprung Disease

Lethal White Foal Syndrome is a disease associated with horse breeds that register white coat spotting patterns. Breedings between particular spotted horses, generally described as frame overo, produce some foals that, in contrast to their parents, are all white or nearly all white and die shortly after birth of severe intestinal blockage. These foals have aganglionosis characterized by a lack of submucosal and myenteric ganglia from the distal small intestine to the large intestine, similar to human Hirschsprung Disease. Some sporadic and familial cases of Hirschsprung Disease are due to mutations in the endothelin B receptor gene (EDNRB). In this study, we investigate the role of EDNRB in Lethal White Foal Syndrome. A cDNA for the wild-type horse endothelin-B receptor gene was cloned and sequenced. In three unrelated lethal white foals, the EDNRB gene contained a 2-bp nucleotide change leading to a missense mutation (I118K) in the first transmembrane domain of the receptor, a highly conserved region of this protein among different species. Seven additional unrelated lethal white foal samples were found to be homozygous for this mutation. No other homozygotes were identified in 138 samples analyzed, suggesting that homozygosity was restricted to lethal white foals. All (40/40) horses with the frame overo pattern (a distinct coat color pattern that is a subset of overo horses) that were tested were heterozygous for this allele, defining a heterozygous coat color phenotype for this mutation. Horses with tobiano markings included some carriers, indicating that tobiano is epistatic to frame overo. In addition, horses were identified that were carriers but had no recognized overo coat pattern phenotype, demonstrating the variable penetrance of the mutation. The test for this mutant allele can be utilized in all breeds where heterozygous animals may be unknowingly bred to each other including the Paint Horse, Pinto horse, Quarter Horse, Miniature Horse, and Thoroughbred. Received: 25 November 1997 / Accepted: 3 February 1998