A novel locus for autosomal dominant non-syndromic deafness, DFNA53, maps to chromosome 14q11.2-q12

Background

Non‐syndromic hearing loss is among the most genetically heterogeneous traits known in humans. To date, at least 50 loci for autosomal dominant non‐syndromic sensorineural hearing loss (ADNSSHL) have been identified by linkage analysis.

Objective

To report the mapping of a novel autosomal dominant deafness locus on the long arm of chromosome 14 at 14q11.2‐q12, DFNA53, in a large multigenerational Chinese family with post‐lingual, high frequency hearing loss that progresses to involve all frequencies.

Results

A maximum multipoint LOD score of 5.4 was obtained for marker D14S1280. The analysis of recombinant haplotypes mapped DFNA53 to a 9.6 cM region interval between markers D14S581 and D14S1021. Four deafness loci (DFNA9, DFNA23, DFNB5, and DFNB35) have previously been mapped to the long arm of chromosome 14. The critical region for DFNA53 contains the gene for DFNA9 but does not overlap with the regions for DFNB5, DFNA23, or DFNB35. Screening of the COCH gene (DFNA9), BOCT, EFS, and HSPC156 within the DFNA53 interval did not identify the cause for deafness in this family.

Conclusions

Identifying the DFNA53 locus is the first step in isolating the gene responsible for hearing loss in this large multigeneration Chinese family.     

Espin gene (ESPN) mutations associated with autosomal dominant hearing loss cause defects in microvillar elongation or organisation

Background

Espins are actin bundling proteins present in hair cell stereocilia. A recessive mutation in the espin gene (Espn) has been detected in the jerker mouse and causes deafness, vestibular dysfunction, and hair cell degeneration. More recently mutations in the human espin gene (ESPN) have been described in two families affected by autosomal recessive hearing loss and vestibular areflexia.

Objective

To report the identification of four additional ESPN mutations (S719R, D744N, R774Q, and delK848) in patients affected by autosomal dominant hearing loss without vestibular involvement.

Results

To determine whether the mutated ESPN alleles affected the biological activity of the corresponding espin proteins in vivo, their ability to target and elongate the parallel actin bundles of brush border microvilli was investigated in transfected LLC‐PK1‐CL4 epithelial cells. For three mutated alleles clear abnormalities in microvillar length or distribution were obtained.

Conclusions

The results further strengthen the causative role of the espin gene in non‐syndromic hearing loss and add new insights into espin structure and function.     

CRYM mutations cause deafness through thyroid hormone binding properties in the fibrocytes of the cochlea

Background

In a search for mutations of μ‐crystallin (CRYM), a taxion specific crystalline which is also known as an NADP regulated thyroid hormone binding protein, two mutations were found at the C‐terminus in patients with non‐syndromic deafness.

Objective

To investigate the mechanism of hearing loss caused by CRYM mutations

Methods

T3 binding activity of mutant μ‐crystallin was compared with that of wild‐type μ‐crystallin, because μ‐crystallin is known to be identical to T3 binding protein. To explore the sites within the cochlea where μ‐crystallin is functioning, its localisation in the mouse cochlea was investigated immunocytochemically using a specific antibody.

Results

One mutant was shown to have no binding capacity for T3, indicating that CRYM mutations cause auditory dysfunction through thyroid hormone binding properties. Immunocytochemical results indicated that μ‐crystallin was distributed within type II fibrocytes of the lateral wall, which are known to contain Na,K‐ATPase.

Conclusions

CRYM mutations may cause auditory dysfunction through thyroid hormone binding effects on the fibrocytes of the cochlea. μ‐Crystallin may be involved in the potassium ion recycling system together with Na,K‐ATPase. Future animal experiments will be necessary to confirm a causal relation between Na,K‐ATPase, T3, and deafness.     

Mutations of human TMHS cause recessively inherited non-syndromic hearing loss

Background

Approximately half the cases of prelingual hearing loss are caused by genetic factors. Identification of genes causing deafness is a crucial first step in understanding the normal function of these genes in the auditory system. Recently, a mutant allele of Tmhs was reported to be associated with deafness and circling behaviour in the hurry‐scurry mouse. Tmhs encodes a predicted tetraspan protein of unknown function, which is expressed in inner ear hair cells. The human homologue of Tmhs is located on chromosome 6p.

Objective

To determine the cause of deafness in four consanguineous families segregating recessive deafness linked to markers on chromosome 6p21.1‐p22.3 defining a novel DFNB locus.

Results

A novel locus for non‐syndromic deafness DFNB67 was mapped in an interval of approximately 28.51 cM on human chromosome 6p21.1‐p22.3. DNA sequence analysis of TMHS revealed a homozygous frameshift mutation (246delC) and a missense mutation (Y127C) in affected individuals of two families segregating non‐syndromic deafness, one of which showed significant evidence of linkage to markers in the DFNB67 interval. The localisation of mTMHS in developing mouse inner ear hair cells was refined and found to be expressed briefly from E16.5 to P3.

Conclusions

These findings establish the importance of TMHS for normal sound transduction in humans.There are approximately 100 genes that are associated with hearing loss in the mouse.¹ In humans, more than 47 deafness loci have been mapped and 21 of the corresponding genes have been identified.^2,3 Because of the similarities in the morphology of their auditory systems, deaf mice have provided a valuable resource for understanding the pathophysiology of human hereditary hearing disorders and the normal functions of these genes. Molecular genetic studies of deaf mice have been instrumental in identifying six orthologous deafness genes in humans, including MYO7A (USH1B), MYO15 (DFNB3), TMIE (DFNB6), PCDH15 (DFNB23/USH1F), WHRN (DFNB31), and SANS (USH1G).^{4,5,6,7,8,9,10,11,12,13,14,15}When a novel human deafness locus is mapped, the question arises as to whether or not there is a strain of deaf mouse that carries a mutated gene at a chromosomal map position suggesting conserved synteny with a human locus for deafness. Positional cloning in the mouse or phenotypic rescue using a BAC transgene^13,16 can lead to gene identification more quickly than sequencing human genes in a large chromosomal interval of a deafness locus.¹⁷ Alternatively, identification of a gene responsible for deafness in a mouse may suggest a candidate human chromosomal location to screen for linkage of deafness segregating in large families that have a structure suitable for providing significant evidence of linkage.¹⁸ A combination of two of these strategies was used to identify mutations of TMHS (MIM_609427) as the gene on human chromosome 6p21.1‐p22.3 responsible for non‐syndromic deafness DFNB67, segregating in two consanguineous families.     

AUNX1, a novel locus responsible for X linked recessive auditory and peripheral neuropathy, maps to Xq23-27.3

Background

We report here the genetic characterisation of a large five generation Chinese family with the phenotypic features of auditory neuropathy and progressive peripheral sensory neuropathy, and the genetic feature of X linked recessive inheritance. Disease onset was at adolescence (at an average age of 13 years for six affected subjects). The degree of hearing impairment varied from mild to severe, with decreased otoacoustic emissions; auditory brainstem responses were lacking from onset.

Methods

Two‐point and multipoint model based linkage analysis using the MILNK and LINKMAP programs of the FASTLINK software package produced maximum two‐point and multipoint LOD scores of 2.41 and 2.41, respectively.

Results

These findings define a novel X linked auditory neuropathy locus/region (AUNX1, Xq23–q27.3). This region is 42.09 cM long and contains a 28.07 Mb region with flanking markers DXS1220 and DXS8084, according to the Rutgers Combined Linkage‐Physical Map, build 35. However, mutation screen of the candidate gene SLC6A14 within the region did not identify the causative genetic determinant for this large Chinese family.     

Fanconi anaemia complementation group B presenting as X linked VACTERL with hydrocephalus syndrome

Background

The VACTERL with hydrocephalus (VACTERL‐H) phenotype is recognised to be a severe manifestation of autosomal recessive Fanconi anaemia. Several families have been described in which the VACTERL‐H phenotype segregates as an X linked syndrome. The mutations which cause X linked VACTERL‐H syndrome are not known.

Objective

To determine if mutations in FANCB, which are known to cause Fanconi anaemia complementation group B, are a cause of X linked VACTERL‐H syndrome.

Methods

A three generation pedigree with X linked VACTERL‐H syndrome was investigated. X inactivation was tested in carrier females, and fibroblasts from an affected male fetus were analysed for increased sensitivity to diepoxybutane. FANCB coding exons and flanking splice sites were screened for mutations by direct sequencing of polymerase chain reaction (PCR) fragments amplified from genomic DNA. cDNA from affected fetal fibroblasts was analysed by PCR and direct sequencing using specific exonic primers.

Results

A FANCB mutation which results in a premature stop codon by causing skipping of exon 7 was identified. Chromosomes from the affected fetus showed increased sensitivity to diepoxybutane, and carrier women were found to have 100% skewed X inactivation in blood.

Conclusions

Mutations in FANCB are a cause of X linked VACTERL‐H syndrome. The data presented are of relevance to the genetic counselling of families with isolated male cases of VACTERL‐H and Fanconi anaemia.     

Mutation analysis of NPHP6/CEP290 in patients with Joubert syndrome and Senior-Løken syndrome

Background

Nephronophthisis (NPHP) is an autosomal recessive cystic kidney disease that constitutes the most common genetic cause of renal failure in the first three decades of life. Using positional cloning, six genes (NPHP1‐6) have been identified as mutated in NPHP. In Joubert syndrome (JBTS), NPHP may be associated with cerebellar vermis aplasia/hypoplasia, retinal degeneration and mental retardation. In Senior–Løken syndrome (SLSN), NPHP is associated with retinal degeneration. Recently, mutations in NPHP6/CEP290 were identified as a new cause of JBTS.

Methods

Mutational analysis was performed on a worldwide cohort of 75 families with SLSN, 99 families with JBTS and 21 families with isolated nephronophthisis.

Results

Six novel and six known truncating mutations, one known missense mutation and one novel 3 bp pair in‐frame deletion were identified in a total of seven families with JBTS, two families with SLSN and one family with isolated NPHP.     

Cowden syndrome and Bannayan Riley Ruvalcaba syndrome represent one condition with variable expression and age-related penetrance: results of a clinical study of PTEN mutation carriers

Background

The most commonly reported phenotypes described in patients with PTEN mutations are Bannayan–Riley–Ruvalcaba syndrome (BRRS), with childhood onset, macrocephaly, lipomas and developmental delay, and Cowden Syndrome (CS), an adult‐onset condition recognised by mucocutaneous signs, with a risk of cancers, in particular those of the thyroid and breast. It has been suggested that BRRS and CS are the same condition, but the literature continues to separate them and seek a genotype–phenotype correlation.

Objective

To study the clinical features of patients with known PTEN mutations and observe any genotype–phenotype correlation.

Methods

In total, 42 people (25 probands and 17 non‐probands) from 26 families of all ages with PTEN mutations were recruited through the UK clinical genetics services. A full clinical history and examination were undertaken.

Results

We were unable to demonstrate a genotype–phenotype correlation. Furthermore, our findings in a 31‐year‐old woman with CS and an exon 1 deletion refutes previous reports that whole exon deletions are only found in patients with a BRRS phenotype.

Conclusion

Careful phenotyping gives further support for the suggestion that BRRS and CS are actually one condition, presenting variably at different ages, as in other tumour‐suppressor disorders such as neurofibromatosis type 1. This has important counselling implications, such as advice about cancer surveillance, for children diagnosed with BRRS.     

Novel mutations in three families confirm a major role of COL4A1 in hereditary porencephaly

Background

Porencephaly (cystic cavities of the brain) is caused by perinatal vascular accidents from various causes. Several familial cases have been described and autosomal dominant inheritance linked to chromosome 13q has been suggested. COL4A1 is an essential component in basal membrane stability. Mouse mutants bearing an in‐frame deletion of exon 40 of Col4a1 either die from haemorrhage in the perinatal period or have porencephaly in survivors. A report of inherited mutations in COL4A1 in two families has shown that familial porencephaly may have the same cause in humans.

Objective

To describe three novel COL4A1 mutations.

Results

The three mutations occurred in three unrelated Dutch families. There were two missense mutations of glycine residues predicted to result in abnormal collagen IV assembly, and one mutation predicted to abolish the traditional COL4A1 start codon. The last mutation was also present in an asymptomatic obligate carrier with white matter abnormalities on brain magnetic resonance imaging.

Conclusions

This observation confirms COL4A1 as a major locus for genetic predisposition to perinatal cerebral haemorrhage and porencephaly and suggests variable expression of COL4A1 mutations.     

Epsilon sarcoglycan mutations and phenotype in French patients with myoclonic syndromes

Background

Myoclonus dystonia syndrome (MDS) is an autosomal dominant movement disorder caused by mutations in the epsilon‐sarcoglycan gene (SGCE) on chromosome 7q21.

Methods

We have screened for SGCE mutations in index cases from 76 French patients with myoclonic syndromes, including myoclonus dystonia (M‐D), essential myoclonus (E‐M), primary myoclonic dystonia, generalised dystonia, dystonia with tremor, and benign hereditary chorea. All coding exons of the SGCE gene were analysed. The DYT1 mutation was also tested.

Results

Sixteen index cases had SGCE mutations while one case with primary myoclonic dystonia carried the DYT1 mutation. Thirteen different mutations were found: three nonsense mutations, three missense mutations, three splice site mutations, three deletions, and one insertion. Eleven of the SGCE index cases had M‐D and five E‐M. No SGCE mutations were detected in patients with other phenotypes. The total number of mutation carriers in the families was 38, six of whom were asymptomatic. Penetrance was complete in paternal transmissions and null in maternal transmissions. MDS patients with SGCE mutation had a significantly earlier onset than the non‐carriers. None of the patients had severe psychiatric disorders.

Conclusion

This large cohort of index patients shows that SGCE mutations are primarily found in patients with M‐D and to a lesser extent E‐M, but are present in only 30% of these patients combined (M‐D and E‐M).     

The contribution of GJB2 mutations to slight or mild hearing loss in Australian elementary school children

Background: There is a lack of information on prevalence, cause and consequences of slight/mild bilateral sensorineural hearing loss (SNHL) in children. We report the first systematic genetic analysis of the GJB2 gene in a population‐derived sample of children with slight/mild bilateral SNHL.Methods: Hearing tests were conducted in 6240 Australian elementary school children in Grades 1 and 5. 55 children (0.88%) were found to have a slight/mild sensorineural hearing loss. 48 children with slight/mild sensorineural hearing loss and a matched group of 90 children with normal hearing participated in a genetic study investigating mutations in the GJB2 gene, coding for connexin 26, and the presence of the del(GJB6‐D13S1830) and del(GJB6‐D13S1854) deletions in the GJB6 gene, coding for connexin 30.Results: Four of 48 children with slight/mild sensorineural hearing loss were homozygous for the GJB2 V37I change. The four children with homozygous V37I mutations were all of Asian background and analysis of SNPs in or near the GJB2 gene suggests that the V37I mutation arose from a single mutational event in the Asian population.Discussion: Based on the prevalence of carriers of this change we conclude that V37I can be a causative mutation that is often associated with slight/mild sensorineural hearing loss. No other children in the slight/mild hearing loss group had a hearing loss related to a GJB2 mutation. One child with normal hearing was homozygous for the R127H change and we conclude that this change does not cause hearing loss. Two children of Asian background were carriers of the V37I mutation. Our data indicate that slight/mild sensorineural hearing loss due to the GJB2 V37I mutation is common in people of Asian background.Information on prevalence, cause and consequences of slight or mild bilateral sensorineural hearing loss (SNHL) in children is lacking. Prevalences of 3–5% have been published,^1,2,3 and it has been suggested that slight or mild SNHL may contribute to adverse outcomes with respect to language, academic performance and social interactions.^4,5,6 We have determined the prevalence in Australian elementary school children (grades 1 and 5) to be 0.88%. Analysis of the effect of the slight or mild SNHL in these children did not provide evidence of marked adverse outcomes when children with mild hearing loss were compared with their normally hearing peers.⁷Little is known about the extent to which genetic mutations cause slight or mild SNHL in children. It has been estimated that approximately 60% of cases with moderate, severe and profound prelingual non‐syndromic deafness are genetic, and that 80–85% of these cases are inherited in an autosomal recessive pattern.^8,9 Although changes in >40 genes have been associated with dominant and recessive SNHL, mutations in the GJB2 gene (coding for connexin 26) have been shown to be the most common cause of inherited non‐syndromic deafness (Hereditary Hearing Loss Homepage, and Connexins and Deafness Homepage). Inheritance of GJB2 deafness is nearly always recessive. We have estimated that mutations in the GJB2 gene account for the hearing loss in approximately 10–15% of Australians with moderate, severe and profound prelingual non‐syndromic deafness.¹⁰Unlike more severe forms of hearing loss, slight or mild SNHL is often not detected in children or, if detected, rarely investigated in detail. Most GJB2 mutations that have been reported have therefore been mainly associated with more severe hearing losses,¹¹ and their role in milder losses remains unknown.Universal hearing screening has been introduced in many countries, and as a consequence more children with less severe hearing loss are being identified earlier. In the future, the GJB2 gene will be screened for mutations in many of these children, which will lead to questions of causation and prognosis not just for the probands but also for their carrier siblings. Important unanswered questions are therefore “to what extent do GJB2 mutations contribute to slight/mild SNHL in children?”, “what are the genotype–phenotype correlations?” and “should healthy children identified with slight or mild hearing loss routinely be offered genetic testing?”To deal with these issues, we report the first systematic genetic analysis of a population‐derived sample of 48 children with slight or mild SNHL and 90 normally hearing controls. The children were identified as part of a large study of the prevalence, aetiology and consequences of slight or mild bilateral SNHL in a representative sample of Australian elementary school children.     

Sensorineural deafness and male infertility: a contiguous gene deletion syndrome

Background

Syndromic hearing loss that results from contiguous gene deletions is uncommon. Deafness‐infertility syndrome (DIS) is caused by large contiguous gene deletions at 15q15.3.

Methods

Three families with a novel syndrome characterised by deafness and infertility are described. These three families do not share a common ancestor and do not share identical deletions. Linkage was established by completing a genome‐wide scan and candidate genes in the linked region were screened by direct sequencing.

Results

The deleted region is about 100 kb long and involves four genes (KIAA0377, CKMT1B, STRC and CATSPER2), each of which has a telomeric duplicate. This genomic architecture underlies the mechanism by which these deletions occur. CATSPER2 and STRC are expressed in the sperm and inner ear, respectively, consistent with the phenotype in persons homozygous for this deletion. A deletion of this region has been reported in one other family segregating male infertility and sensorineural deafness, although congenital dyserythropoietic anaemia type I (CDAI) was also present, presumably due to a second deletion in another genomic region.

Conclusion

We have identified three families segregating an autosomal recessive contiguous gene deletion syndrome characterised by deafness and sperm dysmotility. This new syndrome is caused by the deletion of contiguous genes at 15q15.3.     

Genomic deletion within GLDC is a major cause of non-ketotic hyperglycinaemia

Background

Non‐ketotic hyperglycinaemia (NKH) is an inborn error of metabolism characterised by accumulation of glycine in body fluids and various neurological symptoms. NKH is caused by deficiency of the glycine cleavage multienzyme system with three specific components encoded by GLDC, AMT and GCSH. Most patients are deficient of the enzymatic activity of glycine decarboxylase, which is encoded by GLDC. Our recent study has suggested that there are a considerable number of GLDC mutations which are not identified by the standard exon‐sequencing method.

Methods

A screening system for GLDC deletions by multiplex ligation‐dependent probe amplification (MLPA) has been developed. Two distinct cohorts of patients with typical NKH were screened by this method: the first cohort consisted of 45 families with no identified AMT or GCSH mutations, and the second cohort was comprised of 20 patients from the UK who were not prescreened for AMT mutations.

Results

GLDC deletions were identified in 16 of 90 alleles (18%) in the first cohort and in 9 of 40 alleles (22.5%) in the second cohort. 14 different types of deletions of various lengths were identified, including one allele where all 25 exons were missing. Flanking sequences of interstitial deletions in five patients were determined, and Alu‐mediated recombination was identified in three of five patients.

Conclusions

GLDC deletions are a significant cause of NKH, and the MLPA analysis is a valuable first‐line screening for NKH genetic testing.     

CDH1/E-cadherin germline mutations in early-onset gastric cancer

Background

Gastric cancer remains a leading cause of cancer deaths worldwide. Genetic factors, including germline mutations in E‐cadherin (CDH1, MIM#192090) in hereditary diffuse gastric cancer (HDGC, MIM#137215), are implicated in this disease. Family studies have reported CDH1 germline mutations in HDGC but the role of CDH1 germline mutations in the general population remains unclear.

Aims

To examine the frequency of CDH1 germline mutations in a population‐based series of early‐onset gastric cancer (EOGC <50 years old).

Methods

211 cases of EOGC were identified in Central‐East Ontario region from 1989 to 1993, with archival material and histological confirmation of non‐intestinal type gastric cancer available for 81 subjects. Eligible cases were analysed for CDH1 germline mutations by single‐strand conformation polymorphism, variants were sequenced, and tumours from cases with functional mutations were stained for E‐cadherin (HECD‐1) using immunohistochemistry.

Results

1155 (89%) of 1296 polymerase chain reactions amplified successfully. One new germline deletion (nt41delT) was identified in a 30‐year‐old patient with isolated cell gastric cancer. The overall frequency of germline CDH1 mutations was 1.3% (1/81) for EOGC and 2.8% (1/36) for early‐onset isolated cell gastric cancer.

Conclusion

This is the first population‐based study, in a low‐incidence region, of genetic predisposition to gastric cancer. Combined with our previous report of germline hMLH1 mutations in two other subjects from this series, it is suggested that 2–3% of EOCG cases in North Americans may be owing to high‐risk genetic mutations. These data should inform cancer geneticists on the utility of searching for specific genetic mutations in EOGC.Gastric cancer is the second most common cause of cancer deaths worldwide.¹ Despite an overall decline in the incidence of gastric cancer in older people, the incidence of early‐onset (⩽50 years old) gastric cancer (EOGC) and familial clustering of gastric cancer remains stable in frequency.² Genetic predisposition to gastric cancer caused by known genes such as CDH1 and the mismatch repair genes may have an important role in the development of gastric cancer in these cases.³ Autosomal dominant gastric cancer is estimated to account for about 1–3% of all cases.⁴ We have previously reported two new germline mutations (2 of 139 cases) in the hMLH1 gene in our population‐based series of EOGC.⁵In 1998, Guildford et al⁶ first described inactivating germline mutations in E‐cadherin (CDH1 gene) responsible for the development of diffuse‐type gastric cancer (DGC) in three families of Maori origin. Additional family studies have shown that E‐cadherin is responsible for some families presenting with DGC, according to the Lauren classification.⁷ In 1999, the International Gastric Cancer Linkage Consortium (IGCLC) provided the first clinical management guidelines for this autosomal dominant hereditary predisposition syndrome, hereditary diffuse gastric cancer (HDGC, MIM#137215), as defined by Guildford et al earlier that year.^8,9 HDGC is caused by germline inactivating mutations in E‐cadherin (CDH1, MIM# 192090). However, other genes are likely to cause HDGC, as only 30% of families with HDGC meeting the primary criteria for HDGC have been found to have CDH1 germline mutations. To date, 57 distinct functional CDH1 germline mutations have been reported. Of these, 50 are listed in the Human Gene Mutation Database (http://www.hgmd.cf.ac.uk/ac/gene.php?gene = CDH1), an additional five functional mutations were reported by Suriano et al,¹⁰ and a further two splice mutations associated with cleft lip/palate and HDGC were more recently reported by Frebourg et al.¹¹ Most of these mutations result in a truncated, non‐functional protein. Although primary criteria are fairly well established for screening of CDH1 germline mutations in kindreds with gastric cancer, the IGCLC recognise the need for large population‐based studies of genetic predisposition to gastric cancer to determine the role of germline mutations in sporadic EOGC. Here, we report the first population‐based study of EOGC to determine the frequency of CDH1 germline mutations in a population at a low risk for gastric cancer.

Keypoints

• This is the first and largest population‐based study of genetic predisposition to gastric cancer in a low‐incidence region reporting a new germline CDH1 mutation.
• 2–3% of cases of early‐onset gastric cancer (EOGC) in North America may be owing to high‐risk genetic mutations.
• Informs geneticists on the use of searching for genetic mutations in EOGC.

     

Horizontal gaze palsy with progressive scoliosis can result from compound heterozygous mutations in ROBO3

Background

Horizontal gaze palsy with progressive scoliosis (HGPPS) is an autosomal recessive disorder characterised by congenital absence of horizontal gaze, progressive scoliosis, and failure of the corticospinal and somatosensory axon tracts to decussate in the medulla. We previously reported that HGPPS patients from consanguineous pedigrees harbour homozygous mutations in the axon guidance molecule ROBO3.

Methods

We now report two sporadic HGPPS children of non‐consanguineous parents who harbour compound heterozygous mutations in ROBO3. The mother of one of the children also had scoliosis DNA was extracted from a blood sample from each participant using a standard protocol, and the coding exons of ROBO3 were amplified and sequenced as previously described.

Results

Each patient harboured two unique heterozygous mutations in ROBO3, having inherited one mutation from each parent.

Conclusions

HGPPS can result from compound heterozygous mutations. More comprehensive examinations of parents and siblings of HGPPS patients are required to determine if the incidence of scoliosis in individuals harbouring heterozygous ROBO3 mutations is greater than in the general population.     

Novel mutations in FH and expansion of the spectrum of phenotypes expressed in families with hereditary leiomyomatosis and renal cell cancer

Background

Hereditary leiomyomatosis and renal cell cancer (HLRCC; OMIM 605839) is the predisposition to develop smooth muscle tumours of the skin and uterus and/or renal cancer and is associated with mutations in the fumarate hydratase gene (FH). Here we characterise the clinical and genetic features of 21 new families and present the first report of two African‐American families with HLRCC.

Methods

Using direct sequencing analysis we identified FH germline mutations in 100% (21/21) of new families with HLRCC.

Results

We identified 14 germline FH mutations (10 missense, one insertion, two nonsense, and one splice site) located along the entire length of the coding region. Nine of these were novel, with six missense (L89S, R117G, R190C, A342D, S376P, Q396P), one nonsense (S102X), one insertion (111insA), and one splice site (138+1G>C) mutation. Four unrelated families had the R58X mutation and five unrelated families the R190H mutation. Of families with HLRCC, 62% (13/21) had renal cancer and 76% (16/21) cutaneous leiomyomas. Of women FH mutation carriers from 16 families, 100% (22/22) had uterine fibroids. Our study shows that expression of cutaneous manifestations in HLRCC ranges from absent to mild to severe cutaneous leiomyomas. FH mutations were associated with a spectrum of renal tumours. No genotype‐phenotype correlations were identified.

Conclusions

In combination with our previous report, we identify 31 different germline FH mutations in 56 families with HLRCC (20 missense, eight frameshifts, two nonsense, and one splice site). Our FH mutation detection rate is 93% (52/56) in families suspected of HLRCC.     

Mutation of the gap junction protein alpha 8 (GJA8) gene causes autosomal recessive cataract

Background

GJA8 encodes connexin‐50, a gap junction protein in the eye lens. Mutations in GJA8 have been reported in families with autosomal dominant cataract.

Objective

To identify the disease gene in a family with congenital cataract of autosomal recessive inheritance.

Methods

Eight candidate genes were screened for pathogenic alterations in affected and unaffected family members and in normal unrelated controls.

Results

A single base insertion leading to frameshift at codon 203 of connexin 50 was found to co‐segregate with disease in the family.

Conclusions

These results confirm involvement of GJA8 in autosomal recessive cataract.