A recessive contiguous gene deletion causing infantile hyperinsulinism, enteropathy and deafness identifies the Usher type 1C gene.

Usher syndrome type 1 describes the association of profound, congenital sensorineural deafness, vestibular hypofunction and childhood onset retinitis pigmentosa. It is an autosomal recessive condition and is subdivided on the basis of linkage analysis into types 1A through 1E. Usher type 1C maps to the region containing the genes ABCC8 and KCNJ11 (encoding components of ATP-sensitive K + (KATP) channels), which may be mutated in patients with hyperinsulinism. We identified three individuals from two consanguineous families with severe hyperinsulinism, profound congenital sensorineural deafness, enteropathy and renal tubular dysfunction. The molecular basis of the disorder is a homozygous 122-kb deletion of 11p14-15, which includes part of ABCC8 and overlaps with the locus for Usher syndrome type 1C and DFNB18. The centromeric boundary of this deletion includes part of a gene shown to be mutated in families with type 1C Usher syndrome, and is hence assigned the name USH1C. The pattern of expression of the USH1C protein is consistent with the clinical features exhibited by individuals with the contiguous gene deletion and with isolated Usher type 1C.

Craniosynostosis associated with FGFR3 pro250arg mutation results in a range of clinical presentations including unisutural sporadic craniosynostosis.

Several mutations involving the fibroblast growth factor receptor (FGFR) gene family have been identified in association with phenotypically distinct forms of craniosynostosis. One such point mutation, resulting in the substitution of proline by arginine in a critical region of the linker region between the first and second immunoglobulin-like domains, is associated with highly specific phenotypic consequences in that mutation at this point in FGFR1 results in Pfeiffer syndrome and analogous mutation in FGFR2 results in Apert syndrome. We now show that a much more variable clinical presentation accompanies analogous mutation in the FGFR3 gene. Specifically, mental retardation, apparently unrelated to the management of the craniosynostosis, appears to be a variable clinical consequence of this FGFR3 mutation.

A recurrent mutation, ala391glu, in the transmembrane region of FGFR3 causes Crouzon syndrome and acanthosis nigricans.

Mutations in the fibroblast growth factor receptor 2 (FGFR2) gene have previously been identified in Crouzon syndrome, an autosomal dominant condition involving premature fusion of the cranial sutures. Several different missense and other mutations have been identified in Crouzon syndrome patients, clustering around the third immunoglobulin-like domain. We report here the identification of a mutation in the transmembrane region of FGFR3, common to three unrelated patients with classical Crouzon syndrome and acanthosis nigricans, a dermatological condition associated with thickening and abnormal pigmentation of the skin. The mutation within the FGFR3 transcript was determined by direct sequencing as a specific gcg to gag transversion, resulting in an amino acid substitution ala391glu within the transmembrane region.

Mutation analysis in CD40 ligand deficiency leading to X-linked hypogammaglobulinemia with hyper IgM syndrome.

Mutations in the gene encoding CD40 ligand have been shown to be the cause of X-linked hypogammaglobulinemia with hyper IgM (HIGM1). We have used the technique of single strand conformational polymorphism (SSCP) analysis to screen for mutations in this gene in affected boys from nineteen unrelated families. Sixteen novel mutations were identified in patients, comprising six patients with single base substitutions, two patients with single base insertions, six patients with deletions ranging from one to seven bases and two patients with large deletions at the 5' end of the gene. These mutations were distributed throughout the gene SSCP band shifts and/or alterations in restriction enzyme digestion sites could be used for unambiguous determination of carrier status in at-risk female relatives of most of the affected boys and, in some cases, prenatal diagnosis also can be offered.

Spectrum of craniosynostosis phenotypes associated with novel mutations at the fibroblast growth factor receptor 2 locus.

The causative relationship between several of the syndromic forms of craniosynostosis and mutations in the fibroblast growth factor receptor (FGFR) loci is now well established. However, within the group of patients with craniosynostosis, there are several families and sporadic cases whose clinical features differ in variable degrees from the classically described syndromes of craniosynostosis. In this communication we present novel FGFR2 mutations associated with a spectrum of craniosyostosis phenotypes in 4 sporadic cases and in one family in which craniosynostosis segregates. The mutation and phenotype data presented emphasise the clinical variability of mutations at this locus and underline the plasticity of the phenotype-genotype relationship in this important group of congenital malformation syndromes. Mutations found were tyrosine 105 to cysteine, glycine 338 to glutamic acid, serine 351 to cysteine and glycine 384 to arginine. These are the first reported mutations in the first immunoglobulin-like loop (tyrosine 105 to cysteine) and the transmembrane domain (glycine 384 to arginine) of FGFR2, providing further insights into the mechanism of abnormal receptor function in FGFR2 mutations.

Mutations in the third immunoglobulin domain of the fibroblast growth factor receptor-2 gene in Crouzon syndrome.

Craniosynostosis, which affects approximately 1 in 2000 children, is the result of the abnormal development and/or premature fusion of the cranial sutures. Studies of mutations in patients with craniosynostosis have shown that the family of fibroblast growth factor receptor genes are extremely important in the correct formation of the skull, and digits. Mutations in the third immunoglobulin domain of fibroblast growth factor receptor 2 (FGFR2), in part of the molecule corresponding to a tissue specific isoform (IIIc), can cause both Crouzon and Pfeiffer syndromes. Two specific mutations in the linking region between the second and third immunoglobulin domains of FGFR2 occur in Apert syndrome. We present here mutations associated with the Crouzon syndrome, also in the third immunoglobulin domain but in an upstream exon. This exon is expressed in both tissue isoforms. Five different mutations were detected in 11 unrelated individuals. A cysteine to phenylalanine change was found in six individuals. This cysteine forms half of the disulphide bridge maintaining the secondary structure of the immunoglobulin domain. The first deletion within an FGFR gene is reported. Together with mutations in exon IIIc these account for 25 mutations out of 40 Crouzon patients studied in our combined series (5).

Identical mutations in the FGFR2 gene cause both Pfeiffer and Crouzon syndrome phenotypes.

Mutations in the fibroblast growth factor receptor 2 (FGFR2) gene have been identified in Crouzon syndrome, an autosomal dominant condition causing premature fusion of the cranial sutures (craniosynostosis). A mutation in FGFR1 has been established in several families with Pfeiffer syndrome, where craniosynostosis is associated with specific digital abnormalities. We now report point mutations in FGFR2 in seven sporadic Pfeiffer syndrome patients. Six of the seven Pfeiffer syndrome patients share two missense mutations, which have also been reported in Crouzon syndrome. The Crouzon and Pfeiffer phenotypes usually breed true within families and the finding of identical mutations in unrelated individuals giving different phenotypes is a highly unexpected observation.

Apert syndrome results from localized mutations of FGFR2 and is allelic with Crouzon syndrome.

Apert syndrome is a distinctive human malformation comprising craniosynostosis and severe syndactyly of the hands and feet. We have identified specific missense substitutions involving adjacent amino acids (Ser252Trp and Pro253Arg) in the linker between the second and third extracellular immunoglobulin (Ig) domains of fibroblast growth factor receptor 2 (FGFR2) in all 40 unrelated cases of Apert syndrome studied. Crouzon syndrome, characterized by craniosynostosis but normal limbs, was previously shown to result from allelic mutations of the third Ig domain of FGFR2. The contrasting effects of these mutations provide a genetic resource for dissecting the complex effects of signal transduction through FGFRs in cranial and limb morphogenesis.

A common mutation in the fibroblast growth factor receptor 1 gene in Pfeiffer syndrome.

Pfeiffer syndrome (PS) is one of the classic autosomal dominant craniosynostosis syndromes with craniofacial anomalies and characteristic broad thumbs and big toes. We have previously mapped one of the genes for PS to the centromeric region of chromosome 8 by linkage analysis. Here we present evidence that mutations in the fibroblast growth factor receptor-1 (FGFR1) gene, which maps to 8p, cause one form of familial Pfeiffer syndrome. A C to G transversion in exon 5, predicting a proline to arginine substitution in the putative extracellular domain, was identified in all affected members of five unrelated PS families but not in any unaffected individuals. FGFR1 therefore becomes the third fibroblast growth factor receptor to be associated with an autosomal dominant skeletal disorder.

Mutations in the fibroblast growth factor receptor 2 gene cause Crouzon syndrome.

Crouzon syndrome is an autosomal dominant condition causing premature fusion of the cranial sutures (craniosynostosis) and maps to chromosome 10q25-q26. We now present evidence that mutations in the fibroblast growth factor receptor 2 gene (FGFR2) cause Crouzon syndrome. We found SSCP variations in the B exon of FGFR2 in nine unrelated affected individuals as well as complete cosegregation between SSCP variation and disease in three unrelated multigenerational families. In four sporadic cases, the normal parents did not have SSCP variation. Finally, direct sequencing has revealed specific mutations in the B exon in all nine sporadic and familial cases, including replacement of a cysteine in an immunoglobulin-like domain in five patients.

Pelizaeus-Merzbacher disease: detection of mutations Thr181----Pro and Leu223----Pro in the proteolipid protein gene, and prenatal diagnosis.

A family with an apparent history of X-linked Pelizaeus-Merzbacher disease presented for genetic counseling, requesting carrier detection and prenatal diagnosis. RFLP analysis using the proteolipid protein (PLP) gene probe was uninformative in this family. A prenatal diagnosis on a chorionic villus sample (CVS) was carried out using single-strand conformation polymorphism (SSCP) analysis of a variant in exon 4 of the PLP gene. The fetus was predicted to be unaffected. Sequencing of the exon from the CVS, the predicted-carrier mother, and the obligate-carrier grandmother revealed an A-to-C change at nucleotide 541 in the two women but not in the fetus. As this change results in a Thr-to-Pro change at amino acid 181 in a region of the gene predicted to be part of a transmembrane segment, it was concluded that this was the mutation causing the disease in this family. In addition, in a second family, an exon 5 variant band pattern on SSCP analysis was shown by sequencing to be due to a T-to-C change at nucleotide 668. This results in a Leu-to-Pro change in a carrier mother and in her two affected sons. These results provide further examples of mutations in PLP that cause Pelizaeus-Merzbacher disease and illustrate the value of SSCP in genetic analysis.

Arginine 109 to glutamine mutation in a girl with ornithine carbamoyl transferase deficiency.

We studied DNA from 29 families with at least one member with ornithine carbamoyl transferase (OCT) deficiency and have found a mutation in the TaqI site within exon 5 of the OCT gene in a female presenting at the age of 21 months. Hybridisation with site specific oligonucleotides shows that the mutation is a C to T substitution resulting in a glutamine for arginine substitution at amino acid 109.

The major cystic fibrosis mutation in a British population.

We have studied 72 families with at least one child with cystic fibrosis (CF); they were referred because they had requested prenatal diagnosis in a future pregnancy. The delta F508 mutation was found in 108/140 CF chromosomes (77%). In 41/72 families (57%), both parents carried a deleted chromosome and the child was doubly deleted. In only 4 families, 2 of them being consanguineous, did neither parent carry a deleted chromosome. Meconium ileus was associated with children who were delta F508/delta F508, delta F508/non-deleted and non-deleted/non-deleted.

Application of intragenic DNA probes in prenatal screening for retinoblastoma gene carriers in the United Kingdom.

Restriction fragment length polymorphisms (RFLPs) in 55 families affected by retinoblastoma have been studied using recombinant DNA probes derived from within the retinoblastoma predisposition gene. Only six families were uninformative for any of the DNA polymorphisms. The remaining 49 families can be offered prenatal screening. No obligate recombinations between any of the polymorphic loci and the retinoblastoma phenotype were observed. Four previously unknown cases of non-penetrance were identified. Prenatal testing for the inheritance of mutant alleles was performed in two cases and perinatal screening in two additional cases. One fetus inherited the normal allele from the affected parent and is therefore not at risk of retinoblastoma; the second fetus inherited the mutant allele and will require frequent screening for early detection of retinoblastoma. Both perinatal tests showed the absence of the mutant allele.

Genetic and cytogenetic analysis of patients showing reduced esterase-D levels and mental retardation from a survey of 500 individuals with retinoblastoma.

The authors have analysed the esterase-D levels in 500 retinoblastoma patients of whom 15 showed red cell enzyme activities of approximately 50% that of normal controls. Chromosome analysis of these 15 patients confirmed the presence of a deletion involving region 13q14 in all cases. Seven of the 15 cases had not previously been diagnosed and all of these showed sub-band deletions within 13q14. None of these seven patients were mentally retarded although the remaining eight who showed larger chromosome deletions demonstrated the full spectrum of psychomotor abnormalities associated with 13q deletions. Two other mentally retarded retinoblastoma patients with normal esterase-D activity showed no karyotypic abnormality, demonstrating that mental retardation cannot be taken to indicate a chromosome deletion in all cases. Eight of the 15 deletion cases were only unilaterally affected. The data presented in this article suggest that esterase-D quantitation could provide the primary means of detection of chromosome deletions in retinoblastoma patients.

Deletion of chromosome region 13q14 is transmissible and does not always predispose to retinoblastoma.

During routine screening of retinoblastoma patients for esterase D activity in red blood cell lysates a patient was identified with only 50% of normal enzyme activity. Chromosome analysis showed that this patient had a small deletion within chromosome region 13q14. Parental studies showed that, whereas the father had normal enzyme levels, the mother had esterase D levels which were also 50% of normal and a similar small 13q14 deletion. Ophthalmological examination failed to demonstrate any retinal abnormality in either parent. Thus we present the first case not only of the direct transmission of a 13q14 deletion within a family but also of an individual in whom the deletion has not predisposed to tumour formation.

A chromosomal breakpoint that separates the esterase D and retinoblastoma predisposition loci in a patient with del(13)(q14q31).

A patient with severe mental retardation and other congenital abnormalities who developed retinoblastoma was shown to have a deletion on the long arm of chromosome #13 with breakpoints in regions q14 and q31. Quantitation of enzyme activity of the esterase-D gene which, together with the retinoblastoma locus, is located in region 13q14 showed levels that were equal to those of normal controls. The 13q14 breakpoint, therefore, appears to have occurred between the two loci, which places the esterase D gene in a more proximal position in this band than the retinoblastoma locus.

An assessment of the usefulness of electrophoretic variants of esterase-D in the antenatal diagnosis of retinoblastoma in the United Kingdom.

Fifty retinoblastoma families have been studied. In 41 it has been possible to determine the esterase-D phenotypes in all family members. Seven families were informative for the enzyme polymorphism and in all cases cosegregation of the retinoblastoma gene and esterase-D alleles was demonstrated, giving a lod score of 2.61. When combined with other published reports the cumulative lod score is 13.69 with no recombination in 45 meioses. In 10-15% of retinoblastoma families therefore, it is possible to offer prenatal diagnosis using the ESD protein polymorphism. The application of this test to the retinoblastoma population in the UK is limited by the low frequency of the rarer allele (0.116) and, as a result of genetic counseling, the smaller families generally associated with retinoblastoma.

The need to screen all retinoblastoma patients for esterase D activity: detection of submicroscopic chromosome deletions.

Roughly 5% of all patients with retinoblastoma carry a constitutional chromosome deletion on the long arm of chromosome 13, which confers a prezygotic predisposition to tumour development. As offspring of deletion carriers have a 50% risk of inheriting the predisposition locus it is important to identify deletion carriers. The site of the esterase D gene to the often deleted region offers an objective means of deletion identification. The chromosomes of a patient with unilateral retinoblastoma, previously supposed to have a normal karyotype, were reexamined after the discovery that his red blood cells contained reduced activities of esterase D. A small sub-band deletion was found in chromosome region 13q14. These findings emphasise the importance of measurements of esterase D in all patients with retinoblastoma, even those with an apparently normal karyotype.