MIR204 n.37C>T variant as a cause of chorioretinal dystrophy variably associated with iris coloboma, early-onset cataracts and congenital glaucoma

Four members of a three-generation Czech family with early-onset chorioretinal dystrophy were shown to be heterozygous carriers of the n.37C>T in MIR204. The identification of this previously reported pathogenic variant confirms the existence of a distinct clinical entity caused by a sequence change in MIR204. Chorioretinal dystrophy was variably associated with iris coloboma, congenital glaucoma, and premature cataracts extending the phenotypic range of the condition. In silico analysis of the n.37C>T variant revealed 713 novel targets. Additionally, four family members were shown to be affected by albinism resulting from biallelic pathogenic OCA2 variants. Haplotype analysis excluded relatedness with the original family reported to harbour the n.37C>T variant in MIR204. Identification of a second independent family confirms the existence of a distinct MIR204-associated clinical entity and suggests that the phenotype may also involve congenital glaucoma.

3MC syndrome: molecular findings in previously reported and milder patients expand the natural history and phenotypic spectrum

The 3MC syndromes types 1-3 (MIM#257920, 265050 and 248340, respectively) are rare autosomal recessive genetic disorders caused by pathogenic variants in genes encoding the lectin complement pathway. Patients with 3MC syndrome have a distinctive facial phenotype including hypertelorism, highly arched eyebrows and ptosis. A significant number of patients have bilateral cleft lip and palate and they often exhibit genitourinary and skeletal anomalies. A clinical clue to 3MC syndrome is the presence of a characteristic caudal appendage. Genetic variants in MASP1, COLEC11 and COLEC10 genes have been identified as the causation of this syndrome, yet relatively few patients have been described so far. We consolidate and expand current knowledge of phenotypic features and molecular diagnosis of 3MC syndrome by describing the clinical and molecular findings in five patients. This includes follow-up of two brothers whose clinical phenotypes were first reported by Crisponi et al in 1999. Our study contributes to the evolving clinical and molecular spectrum of 3MC syndrome.

Mast cell infiltration of the choroid and protease release are early events in age-related macular degeneration associated with genetic risk at both chromosomes 1q32 and 10q26

Age-related macular degeneration (AMD) is a leading cause of visual loss. It has a strong genetic basis, and common haplotypes on chromosome (Chr) 1 (CFH Y402H variant) and on Chr10 (near HTRA1/ARMS2) contribute the most risk. Little is known about the early molecular and cellular processes in AMD, and we hypothesized that analyzing submacular tissue from older donors with genetic risk but without clinical features of AMD would provide biological insights. Therefore, we used mass spectrometry–based quantitative proteomics to compare the proteins in human submacular stromal tissue punches from donors who were homozygous for high-risk alleles at either Chr1 or Chr10 with those from donors who had protective haplotypes at these loci, all without clinical features of AMD. Additional comparisons were made with tissue from donors who were homozygous for high-risk Chr1 alleles and had early AMD. The Chr1 and Chr10 risk groups shared common changes compared with the low-risk group, particularly increased levels of mast cell–specific proteases, including tryptase, chymase, and carboxypeptidase A3. Histological analyses of submacular tissue from donors with genetic risk of AMD but without clinical features of AMD and from donors with Chr1 risk and AMD demonstrated increased mast cells, particularly the tryptase-positive/chymase-negative cells variety, along with increased levels of denatured collagen compared with tissue from low–genetic risk donors. We conclude that increased mast cell infiltration of the inner choroid, degranulation, and subsequent extracellular matrix remodeling are early events in AMD pathogenesis and represent a unifying mechanistic link between Chr1- and Chr10-mediated AMD.

Biallelic TMEM260 variants cause truncus arteriosus, with or without renal defects

Only two families have been reported with biallelic TMEM260 variants segregating with structural heart defects and renal anomalies syndrome (SHDRA). With a combination of genome, exome sequencing and RNA studies, we identified eight individuals from five families with biallelic TMEM260 variants. Variants included one multi-exon deletion, four nonsense/frameshifts, two splicing changes and one missense change. Together with the published cases, analysis of clinical data revealed ventricular septal defects (12/12), mostly secondary to truncus arteriosus (10/12), elevated creatinine levels (6/12), horse-shoe kidneys (1/12) and renal cysts (1/12) in patients. Three pregnancies were terminated on detection of severe congenital anomalies. Six patients died between the ages of 6 weeks and 5 years. Using a range of stringencies, carrier frequency for SHDRA was estimated at 0.0007-0.007 across ancestries. In conclusion, this study confirms the genetic basis of SHDRA, expands its known mutational spectrum and clarifies its clinical features. We demonstrate that SHDRA is a severe condition associated with substantial mortality in early childhood and characterised by congenital cardiac malformations with a variable renal phenotype.

Oral-Facial-Digital Syndrome Type 1: Further Clinical and Molecular Delineation in 2 New Families

OBJECTIVE

Oral-facial-digital syndrome type 1 (OFD1) [OMIM 311200] is a rare genetic disorder associated with congenital anomalies of the oral cavity, face, and digits. This condition is associated with mutations in the OFD1 gene. Our objective was to recruit patients with the OFD1 clinical phenotype without genetic confirmation, aiming to identify genetic variants in the OFD1 gene.

DESIGN

Three patients from 2 unrelated families were recruited into our study. We employed a variety of genomic techniques on these patients, including candidate gene analysis, array comparative genomic hybridization, whole-exome sequencing, and whole-genome sequencing.

RESULTS

We investigated 3 affected patients from 2 unrelated families with a clinical diagnosis of OFD1. We discovered a novel pathogenic dominant missense mutation c.635G>C (p.Arg212Pro) in the OFD1 gene in one family. A novel frameshift, loss-of-function mutation c.306delA (p.Glu103LysfsTer42) was detected in the affected patient in the second family.

CONCLUSIONS

These new genetic variants will add to the spectrum of known OFD1 mutations associated with the OFD1 disorder. Our study also confirms the variable phenotypic presentation of OFD1 and its well-recognized association with central nervous system malformations and renal anomalies. Molecular diagnostic confirmation achieved in these families will have positive implications for their medical management.

Expanding the genetic and phenotypic spectrum of branched-chain amino acid transferase 2 deficiency

The first step in branched-chain amino acid (BCAA) catabolism is catalyzed by the two BCAA transferase isoenzymes, cytoplasmic branched-chain amino acid transferase (BCAT) 1, and mitochondrial BCAT2. Defects in the second step of BCAA catabolism cause maple syrup urine disease (MSUD), a condition which has been far more extensively investigated. Here, we studied the consequences of BCAT2 deficiency, an ultra-rare condition in humans. We present genetic, clinical, and functional data in five individuals from four different families with homozygous or compound heterozygous BCAT2 mutations which were all detected following abnormal biochemical profile results or familial mutation segregation studies. We demonstrate that BCAT2 deficiency has a recognizable biochemical profile with raised plasma BCAAs and, in contrast with MSUD, low-normal branched-chain keto acids (BCKAs) with undetectable l-allo-isoleucine. Interestingly, unlike in MSUD, none of the individuals with BCAT2 deficiency developed acute encephalopathy even with exceptionally high BCAA levels. We observed wide-ranging clinical phenotypes in individuals with BCAT2 deficiency. While one adult was apparently asymptomatic, three individuals had presented with developmental delay and autistic features. We show that the biochemical characteristics of BCAT2 deficiency may be amenable to protein-restricted diet and that early treatment may improve outcome in affected individuals. BCAT2 deficiency is an inborn error of BCAA catabolism. At present, it is unclear whether developmental delay and autism are parts of the variable phenotypic spectrum of this condition or coincidental. Further studies will be required to explore this.

Mode of presentation and mortality amongst patients hospitalized with heart failure? A report from the First Euro Heart Failure Survey

BACKGROUND

Heart failure is heterogeneous in aetiology, pathophysiology, and presentation. Despite this diversity, clinical trials of patients hospitalized for HF deal with this problem as a single entity, which may be one reason for repeated failures.

METHODS

The first EuroHeart Failure Survey screened consecutive deaths and discharges of patients with suspected heart failure during 2000-2001. Patients were sorted into seven mutually exclusive hierarchical presentations: (1) with cardiac arrest/ventricular arrhythmia; (2) with acute coronary syndrome; (3) with rapid atrial fibrillation; (4) with acute breathlessness; (5) with other symptoms/signs such as peripheral oedema; (6) with stable symptoms; and (7) others in whom the contribution of HF to admission was not clear.

RESULTS

The 10,701 patients enrolled were classified into the above seven presentations as follows: 260 (2%), 560 (5%), 799 (8%), 2479 (24%), 1040 (10%), 703 (7%), and 4691 (45%) for which index-admission mortality was 26%, 20%, 10%, 8%, 6%, 6%, and 4%, respectively. Compared to those in group 7, the hazard ratios for death during the index admission were 4.9 (p ≤ 0.001), 4.0 (p < 0.001), 2.2 (p < 0.001), 2.1 (p < 0.001), 1.4 (p < 0.04) and 1.4 (p = 0.04), respectively. These differences were no longer statistically significant by 12 weeks.

CONCLUSION

There is great diversity in the presentation of heart failure that is associated with very different short-term outcomes. Only a minority of hospitalizations associated with suspected heart failure are associated with acute breathlessness. This should be taken into account in the design of future clinical trials.

An Echocardiographic Study of the Right Ventricular Diastolic Function in Systemic Hypertension and Its Relation with the Left Ventricular Homologous Changes

Diastolic dysfunction is a major predictor of mortality and morbidity in hypertensive patients. Not only LV, the RV is also expected to be affected in this overall procedure. To observe the Echocardiographic changes of diastolic function of the RV in systemic HTN and their relation with similar parameters of the LV was the objective. TDI was used in association with standard Doppler modality. In this cross-sectional study, 50 hypertensive subjects were studied who were devoid of any other conditions that may influence the diastolic function of the RV from 01 May 2012 to 31 October 2012 at Bangabandhu Sheikh Mujib Medical University (BSMMU), Dhaka, Bangladesh. In addition to 2D and M-mode evaluation, standard Doppler and pulsed tissue Doppler assessment of both ventricles were performed. Measurements were obtained for diastolic as well as systolic function of both ventricles. The RV diastolic parameters were impaired in both standard Doppler and tissue Doppler analysis in association with LV parameters. Systolic functions (LV FS and RV TAPSE) were preserved. Doppler-derived tricuspid peak E and E/A were related negatively to septal thickness, but tissue Doppler-derived RV Em/Am showed negative association with both RVAWT and septal thickness. RV RTm was related positively to RVAWT. The RV diastolic parameters showed positive relation with the LV similar parameters both in standard Doppler (E peak velocity, E/A ratio and EDT) and tissue Doppler (Em peak velocity, Em/Am and PCTm) assessment. So, in systemic HTN, LV diastolic dysfunction is also associated with diastolic disturbances of the RV. Pulsed tissue Doppler is a useful tool to detect the changes. RV diastolic parameters correlate well with those of the LV. Prolongation of the active relaxation (RTm) phase of RV is due to its increased wall thickness.

Assessment of Subvalvular Apparatus in Patients with Rheumatic Mitral Stenosis: Comparison between 2D and 3D Echocardiography

Mitral valve is the most involved valve in rheumatic heart disease especially in the form of mitral stenosis. Treatment options of mitral stenosis depend upon pattern, extent & the severity of disease and echocardiography has the key role in this area. Severity of involvement of subvalvular apparatus (SVA) is an important factor for determining the treatment option. 2D echocardiography (2DE) is conventionally used. With the advancement of echocardiographic technology 3D echocardiography (3DE) would offer better assessment of subvalvular apparatus. This study compared transthoracic 2D versus 3D echocardiography for assessment of SVA in chronic rheumatic mitral valve disease. This cross sectional observational study was done in University cardiac centre, Bangabandhu Sheikh Mujib Medical University, Dhaka, Bangladesh from May 2012 to October 2012. In this study, considering all ethical issues, data were collected from 50 subjects who underwent transthoracic 2D and 3D echocardiography for the assessment of extent and severity of mitral stenosis. Accurate measurement of Mitral valvular area is very important in assessment of severity, which is found similar by both 2DE (0.98±0.24cm²) and 3DE (0.92 ±0.23cm²). But assessment of subvalvular involvement especially chordal adhesion can be done better by 3DE (p<0.001). This observation suggests superiority of 3DE for assessment of SVA in chronic rheumatic mitral stenosis. The result of the study demonstrates that 3DE is superior to 2DE for the assessment of SVA in chronic rheumatic mitral stenosis.

Whole Genome Sequencing Increases Molecular Diagnostic Yield Compared with Current Diagnostic Testing for Inherited Retinal Disease

PURPOSE

To compare the efficacy of whole genome sequencing (WGS) with targeted next-generation sequencing (NGS) in the diagnosis of inherited retinal disease (IRD).

DESIGN

Case series.

PARTICIPANTS

A total of 562 patients diagnosed with IRD.

METHODS

We performed a direct comparative analysis of current molecular diagnostics with WGS. We retrospectively reviewed the findings from a diagnostic NGS DNA test for 562 patients with IRD. A subset of 46 of 562 patients (encompassing potential clinical outcomes of diagnostic analysis) also underwent WGS, and we compared mutation detection rates and molecular diagnostic yields. In addition, we compared the sensitivity and specificity of the 2 techniques to identify known single nucleotide variants (SNVs) using 6 control samples with publically available genotype data.

MAIN OUTCOME MEASURES

Diagnostic yield of genomic testing.

RESULTS

Across known disease-causing genes, targeted NGS and WGS achieved similar levels of sensitivity and specificity for SNV detection. However, WGS also identified 14 clinically relevant genetic variants through WGS that had not been identified by NGS diagnostic testing for the 46 individuals with IRD. These variants included large deletions and variants in noncoding regions of the genome. Identification of these variants confirmed a molecular diagnosis of IRD for 11 of the 33 individuals referred for WGS who had not obtained a molecular diagnosis through targeted NGS testing. Weighted estimates, accounting for population structure, suggest that WGS methods could result in an overall 29% (95% confidence interval, 15-45) uplift in diagnostic yield.

CONCLUSIONS

We show that WGS methods can detect disease-causing genetic variants missed by current NGS diagnostic methodologies for IRD and thereby demonstrate the clinical utility and additional value of WGS.

Clinical and molecular genetic findings in autosomal dominant OPA3-related optic neuropathy

Leber hereditary optic neuropathy and autosomal dominant optic atrophy are the two most common inherited optic neuropathies. The latter has been associated with mutations in the OPA1 and OPA3 genes. To date, only six families with OPA3-associated dominant optic atrophy have been reported. In order to identify additional families, we performed Sanger sequencing of the OPA3 gene in 75 unrelated optic neuropathy patients. Affected individuals from two families were found to harbour the c.313C > G, p.(Gln105Glu) change in heterozygous state; this genetic defect has been previously reported in four dominant optic atrophy families. Intra- and interfamilial variability in age of onset and presenting symptoms was observed. Although dominant OPA3 mutations are typically associated with optic atrophy and cataracts, the former can be observed in isolation; we report a case with no lens opacities at age 38. Conversely, it is important to consider OPA3-related disease in individuals with bilateral infantile-onset cataracts and to assess optic nerve health in those whose vision fail to improve following lens surgery. The papillomacular bundle is primarily affected and vision is typically worse than 20/40. Notably, we describe one subject who retained normal acuities into the fifth decade of life. The condition can be associated with extraocular clinical features: two affected individuals in the present study had sensorineural hearing loss. The clinical heterogeneity observed in the individuals reported here (all having the same genetic defect in OPA3) suggests that the molecular pathology of the disorder is likely to be complex.

Familial retinal detachment associated with COL2A1 exon 2 and FZD4 mutations

BACKGROUND

  To characterize the clinical and genetic abnormalities within two Australian pedigrees with high incidences of retinal detachment and visual disability.

DESIGN

  Prospective review of two extended Australian pedigrees with high rates of retinal detachment.

PARTICIPANTS

  Twenty-two family members from two extended Australian pedigrees with high rates of retinal detachment were examined.

METHODS

  A full ophthalmic history and examination were performed, and DNA was analysed by linkage analysis and mutation screening.

MAIN OUTCOME MEASURES

  Characterization of a causative hereditary gene mutation in each family.

RESULTS

  All affected family members of one pedigree carried a C192A COL2A1 exon 2 mutation. None of the affected family members had early-onset arthritis, hearing abnormalities, abnormal clefting or facial features characteristic of classical Stickler syndrome. All affected members of the familial exudative vitreoretinopathy pedigree carried a 957delG FZD4 mutation.

CONCLUSIONS

  Patients with retinal detachment and a positive family history should be investigated for heritable conditions associated with retinal detachment such as Stickler syndrome and familial exudative vitreoretinopathy. The absence of non-ocular features of Stickler syndrome should raise the possibility of mutations in exon 2 of COL2A1. Similarly, late-onset familial exudative vitreoretinopathy may appear more like a rhegmatogenous detachment and not be correctly diagnosed. When a causative gene mutation is identified, cascade genetic screening of the family will facilitate genetic counselling and screening of high-risk relatives, allowing targeted management of the pre-detachment changes in affected patients.

Impaired binding of the age-related macular degeneration-associated complement factor H 402H allotype to Bruch's membrane in human retina

Age-related macular degeneration (AMD) is the predominant cause of blindness in the industrialized world where destruction of the macula, i.e. the central region of the retina, results in loss of vision. AMD is preceded by the formation of deposits in the macula, which accumulate between the Bruch's membrane and the retinal pigment epithelium (RPE). These deposits are associated with complement-mediated inflammation and perturb retinal function. Recent genetic association studies have demonstrated that a common allele (402H) of the complement factor H (CFH) gene is a major risk factor for the development of AMD; CFH suppresses complement activation on host tissues where it is believed to bind via its interaction with polyanionic structures. We have shown previously that this coding change (Y402H; from a tyrosine to histidine residue) alters the binding of the CFH protein to sulfated polysaccharides. Here we demonstrate that the AMD-associated polymorphism profoundly affects CFH binding to sites within human macula. Notably, the AMD-associated 402H variant binds less well to heparan sulfate and dermatan sulfate glycosaminoglycans within Bruch's membrane when compared with the 402Y form; both allotypes exhibit a similar level of binding to the RPE. We propose that the impaired binding of the 402H variant to Bruch's membrane results in an overactivation of the complement pathway leading to local chronic inflammation and thus contributes directly to the development and/or progression of AMD. These studies therefore provide a putative disease mechanism and add weight to the genetic association studies that implicate the 402H allele as an important risk factor in AMD.

Discovery and functional analysis of a retinitis pigmentosa gene, C2ORF71

Retinitis pigmentosa is a genetically heterogeneous group of inherited ocular disorders characterized by progressive photoreceptor cell loss, night blindness, constriction of the visual field, and progressive visual disability. Homozygosity mapping and gene expression studies identified a 2 exon gene, C2ORF71. The encoded protein has no homologs and is highly expressed in the eye, where it is specifically expressed in photoreceptor cells. Two mutations were found in C2ORF71 in human RP patients: A nonsense mutation (p.W253X) in the first exon is likely to be a null allele; the second, a missense mutation (p.I201F) within a highly conserved region of the protein, leads to proteosomal degradation. Bioinformatic and functional studies identified and validated sites of lipid modification within the first three amino acids of the C2ORF71 protein. Using morpholino oligonucleotides to knockdown c2orf71 expression in zebrafish results in visual defects, confirming that C2ORF71 plays an important role in the development of normal vision. Finally, localization of C2ORF71 to primary cilia in cultured cells suggests that the protein is likely to localize to the connecting cilium or outer segment of photoreceptor cells.

BCOR analysis in patients with OFCD and Lenz microphthalmia syndromes, mental retardation with ocular anomalies, and cardiac laterality defects

Oculofaciocardiodental (OFCD) and Lenz microphthalmia syndromes form part of a spectrum of X-linked microphthalmia disorders characterized by ocular, dental, cardiac and skeletal anomalies and mental retardation. The two syndromes are allelic, caused by mutations in the BCL-6 corepressor gene (BCOR). To extend the series of phenotypes associated with pathogenic mutations in BCOR, we sequenced the BCOR gene in patients with (1) OFCD syndrome, (2) putative X-linked ('Lenz') microphthalmia syndrome, (3) isolated ocular defects and (4) laterality phenotypes. We present a new cohort of females with OFCD syndrome and null mutations in BCOR, supporting the hypothesis that BCOR is the sole molecular cause of this syndrome. We identify for the first time mosaic BCOR mutations in two females with OFCD syndrome and one apparently asymptomatic female. We present a female diagnosed with isolated ocular defects and identify minor features of OFCD syndrome, suggesting that OFCD syndrome may be mild and underdiagnosed. We have sequenced a cohort of males diagnosed with putative X-linked microphthalmia and found a mutation, p.P85L, in a single case, suggesting that BCOR mutations are not a major cause of X-linked microphthalmia in males. The absence of BCOR mutations in a panel of patients with non-specific laterality defects suggests that mutations in BCOR are not a major cause of isolated heart and laterality defects. Phenotypic analysis of OFCD and Lenz microphthalmia syndromes shows that in addition to the standard diagnostic criteria of congenital cataract, microphthalmia and radiculomegaly, patients should be examined for skeletal defects, particularly radioulnar synostosis, and cardiac/laterality defects.

Constitutional delay of growth and puberty is not commonly associated with mutations in the acid labile subunit gene

OBJECTIVES

Constitutional delay of growth and puberty (CDGP) is a common clinical condition that may be inherited as an autosomal dominant, recessive or X-linked trait. However, single-gene defects underlying CDGP have not yet been identified. A small number of children (to date 10) with modest growth failure and in the majority delayed puberty, a phenotype similar to that of CDGP, have been reported to carry mutations in the IGF acid labile subunit (IGFALS) gene which encodes the ALS, a part of the ternary complex carrying IGF-I in the circulation. The aim of our study was to screen a well-characterised CDGP cohort exhibiting a range of growth retardation and pubertal delay for pathogenic sequence variants in IGFALS.

DESIGN AND METHODS

We used denaturing high performance liquid chromatography (dHPLC) to screen for IGFALS mutations in DNA samples from 90 children (80 males) with CDGP of predominantly White European origin. DNA fragments generating abnormal waveforms were directly sequenced.

RESULTS

No IGFALS mutation was identified in the coding sequences or exon-intron boundaries in our CDGP cohort. One abnormal waveform pattern in dHPLC in 15 children with CDGP was found to represent a recognised synonymous single-nucleotide polymorphism of the coding transcript in the second exon in residue 210 of IGFALS.

CONCLUSIONS

IGFALS sequence variants are unlikely to be a common association with pubertal delay in children with CDGP.

Missense and nonsense mutations in the alternatively-spliced exon 2 ofCOL2A1cause the ocular variant of Stickler syndrome

Stickler syndrome type I (STL1) is a phenotypically heterogeneous disorder characterized by ocular and extraocular features. It is caused by null-allele mutations in the COL2A1 gene that codes for procollagen II. COL2A1 precursor mRNA undergoes alternative splicing, resulting in two isoforms, a long form including exon 2 (type IIA isoform) and a short form excluding exon 2 (type IIB isoform). The short form is predominantly expressed by differentiated chondrocytes in adult cartilage, and the long form in chondroprogenitor cells during early development and in the vitreous of the eye, which is the only adult tissue containing procollagen IIA. Recent evidence indicates that due to the tissue-specific expression of these two isoforms, premature termination codon mutations in exon 2 cause Stickler syndrome with minimal or no extraocular manifestations. We describe here two mutations in exon 2 of COL2A1 in three patients with predominantly ocular Stickler syndrome: Cys64Stop in two patients, and a novel structural mutation, Cys57Tyr, in one patient. RT-PCR of total lymphoblast RNA from one patient with the Cys64Stop mutation revealed that only the normal allele of the IIA form was present, indicating that the mutation resulted either in complete loss of the allele by nonsense-mediated mRNA decay or by skipping of exon 2 via nonsense-mediated altered splicing, resulting in production of the type IIB isoform. The results of COL2A1 minigene expression studies suggest that both Cys64Stop and Cys57Tyr alter positive cis regulatory elements for splicing, resulting in a lower IIA:IIB ratio.

Characterization of a familial t(16;22) balanced translocation associated with congenital cataract leads to identification of a novel gene, TMEM114, expressed in the lens and disrupted by the translocation

Molecular characterization of chromosomal rearrangements is a powerful resource in identification of genes associated with monogenic disorders. We describe the molecular characterization of a balanced familial chromosomal translocation, t(16;22)(p13.3;q11.2), segregating with congenital lamellar cataract. This led to the discovery of a cluster of lens-derived expressed sequence tags (ESTs) close to the 16p13.3 breakpoint. This region harbors a locus associated with cataract and microphthalmia. Long-range PCR and 16p13.3 breakpoint sequencing identified genomic sequence in a human genome sequence gap, and allowed identification of a novel four-exon gene, designated TMEM114, which encodes a predicted protein of 223 amino acids. The breakpoint lies in the promoter region of TMEM114 and separates the gene from predicted eye-specific upstream transcription factor binding sites. There is sequence conservation among orthologs down to zebrafish. The protein is predicted to contain four transmembrane domains with homology to the lens intrinsic membrane protein, LIM2 (also known as MP20), in the PMP-22/EMP/MP20 family. TMEM114 mutation screening in 130 congenital cataract patients revealed missense mutations leading to the exchange of highly-conserved amino acids in the first extracellular domain of the protein (p.I35T, p.F106L) in two separate patients and their reportedly healthy sibling and mother, respectively. In the lens, Tmem114 shows expression in the lens epithelial cells extending into the transitional zone where early fiber differentiation occurs. Our findings implicate dysregulation of expression of this novel human gene, TMEM114, in mammalian cataract formation.

A heterozygous c-Maf transactivation domain mutation causes congenital cataract and enhances target gene activation

MAF, one of a family of large Maf bZIP transcription factors, is mutated in human developmental ocular disorders that include congenital cataract, microcornea, coloboma and anterior segment dysgenesis. Expressed early in the developing lens vesicle, it is central to regulation of lens crystallin gene expression. We report a semi-dominant mouse c-Maf mutation recovered after ENU mutatgenesis which results in the substitution, D90V, at a highly conserved residue within the N-terminal 35 amino-acid minimal transactivation domain (MTD). Unlike null and loss-of-function c-Maf mutations, which cause severe runting and renal abnormalities, the phenotype caused by the D90V mutation is isolated cataract. In reporter assays, D90V results in increased promoter activation, a situation similar to MTD mutations of NRL that also cause human disease. In contrast to wild-type protein, the c-Maf D90V mutant protein is not inhibited by protein kinase A-dependent pathways. The MTD of large Maf proteins has been shown to interact with the transcriptional co-activator p300 and we demonstrate that c-Maf D90V enhances p300 recruitment in a cell-type dependent manner. We observed the same for the pathogenic human NRL MTD mutation S50T, which suggests a common mechanism of action.

Erosive Vitreoretinopathy and Wagner Disease Are Caused by Intronic Mutations inCSPG2/VersicanThat Result in an Imbalance of Splice Variants

PURPOSE

Linkage intervals for erosive vitreoretinopathy (ERVR) and Wagner disease previously were found to overlap at 5q14.3. In a Japanese family with Wagner disease, a CSPG2/Versican splice site mutation (c.4004-2A-->G) was recently reported that resulted in a 39-nucleotide exon 8 in-frame deletion. We investigated whether CSPG2/Versican was mutated in six Dutch families and one Chinese family with Wagner disease and in a family with ERVR.

METHODS

In all families, extensive ophthalmic examinations, haplotype analysis of the 5q14.3 region, and sequence analysis of CSPG2/Versican were performed. The effects of splice site mutations were assessed by reverse transcription-polymerase chain reaction (RT-PCR) and real-time quantitative RT-PCR (QPCR).

RESULTS

Three novel intron 7 sequence variants (c.4004-5T-->C, c.4004-5T-->A, c.4004-1G-->A) were identified in seven families. The c.4004-5T-->C variant was identified in four families with Wagner disease and a family with ERVR. The families were shown to carry the same 5q14.3 haplotype, strongly suggesting that this is a common Dutch founder variant. All three changes segregated with the disease in the respective families and were absent in 250 healthy individuals. In patients with the c.4004-5T-->A and c.4004-1G-->A variants, RT-PCR analysis of CSPG2/Versican showed activation of a cryptic splice site resulting in a 39-nt exon 8 in-frame deletion in splice variant V0. QPCR revealed a highly significant (P < 0.0001) and consistent increase of the V2 (>38-fold) and V3 (>12-fold) splice variants in all patients with intron 7 nucleotide changes and in a Chinese Wagner disease family, in which the genetic defect remains to be found.

CONCLUSIONS

Wagner disease and ERVR are allelic disorders. Seven of the eight families exhibit a variant in intron 7 of CSPG2/Versican. The conspicuous clustering of sequence variants in the splice acceptor site of intron 7 and the consistent upregulation of the V2 and V3 isoforms strongly suggest that Wagner disease and ERVR may belong to a largely overlooked group of diseases that are caused by mRNA isoform balance shifts, representing a novel disease mechanism.

Genotype-phenotype correlation in Costello syndrome: HRAS mutation analysis in 43 cases

BACKGROUND

Costello syndrome (CS) is a rare multiple congenital abnormality syndrome, associated with failure to thrive and developmental delay. One of the more distinctive features in childhood is the development of facial warts, often nasolabial and in other moist body surfaces. Individuals with CS have an increased risk of malignancy, suggested to be about 17%. Recently, mutations in the HRAS gene on chromosome 11p13.3 have been found to cause CS.

METHODS

We report here the results of HRAS analysis in 43 individuals with a clinical diagnosis of CS.

RESULTS

Mutations were found in 37 (86%) of patients. Analysis of parental DNA samples was possible in 16 cases for both parents and in three cases for one parent, and confirmed the mutations as de novo in all of these cases. Three novel mutations (G12C, G12E, and K117R) were found in five cases.

CONCLUSIONS

These results confirm that CS is caused, in most cases, by heterozygous missense mutations in the proto-oncogene HRAS. Analysis of the major phenotypic features by mutation suggests a potential correlation between malignancy risk and genotype, which is highest for patients with an uncommon (G12A) substitution. These results confirm that mutation testing for HRAS is a reliable diagnostic test for CS.

Mutations of VMD2 splicing regulators cause nanophthalmos and autosomal dominant vitreoretinochoroidopathy (ADVIRC)

PURPOSE

To investigate the genetic basis of autosomal dominant vitreoretinochoroidopathy (ADVIRC), a rare, inherited retinal dystrophy that may be associated with defects of ocular development, including nanophthalmos.

METHODS

A combination of linkage analysis and DNA sequencing in five families was used to identify disease-causing mutations in VMD2. The effect of these mutations on splicing was assessed using a minigene system.

RESULTS

Three pathogenic sequence alterations in VMD2 were identified in five families with nanophthalmos associated with ADVIRC. All sequences showed simultaneous missense substitutions and exon skipping.

CONCLUSIONS

VMD2 encodes bestrophin, a transmembrane protein located at the basolateral membrane of the RPE, that is also mutated in Best macular dystrophy. We support that each heterozygous affected individual produces three bestrophin isoforms consisting of the wild type and two abnormal forms: one containing a missense substitution and the other an in-frame deletion. The data showed that VMD2 mutations caused defects of ocular patterning, supporting the hypothesized role for the RPE, and specifically VMD2, in the normal growth and development of the eye.

Oculofaciocardiodental and Lenz microphthalmia syndromes result from distinct classes of mutations in BCOR

Lenz microphthalmia is inherited in an X-linked recessive pattern and comprises microphthalmia, mental retardation, and skeletal and other anomalies. Two loci associated with this syndrome, MAA (microphthalmia with associated anomalies) and MAA2, are situated respectively at Xq27-q28 (refs. 1,2) and Xp11.4-p21.2 (ref. 3). We identified a substitution, nt 254C-->T; P85L, in BCOR (encoding BCL-6-interacting corepressor, BCOR) in affected males from the family with Lenz syndrome previously used to identify the MAA2 locus. Oculofaciocardiodental syndrome (OFCD; OMIM 300166) is inherited in an X-linked dominant pattern with presumed male lethality and comprises microphthalmia, congenital cataracts, radiculomegaly, and cardiac and digital abnormalities. Given their phenotypic overlap, we proposed that OFCD and MAA2-associated Lenz microphthalmia were allelic, and we found different frameshift, deletion and nonsense mutations in BCOR in seven families affected with OFCD. Like wild-type BCOR, BCOR P85L and an OFCD-mutant form of BCOR can interact with BCL-6 and efficiently repress transcription. This indicates that these syndromes are likely to result from defects in alternative functions of BCOR, such as interactions with transcriptional partners other than BCL-6. We cloned the zebrafish (Danio rerio) ortholog of BCOR and found that knock-down of this ortholog caused developmental perturbations of the eye, skeleton and central nervous system consistent with the human syndromes, confirming that BCOR is a key transcriptional regulator during early embryogenesis.

Cohen syndrome is caused by mutations in a novel gene, COH1, encoding a transmembrane protein with a presumed role in vesicle-mediated sorting and intracellular protein transport

Cohen syndrome is an uncommon autosomal recessive disorder whose diagnosis is based on the clinical picture of nonprogressive psychomotor retardation and microcephaly, characteristic facial features, retinal dystrophy, and intermittent neutropenia. We have refined the critical region on chromosome 8q22 by haplotype analysis, and we report the characterization of a novel gene, COH1, that is mutated in patients with Cohen syndrome. The longest transcript (14,093 bp) is widely expressed and is transcribed from 62 exons that span a genomic region of approximately 864 kb. COH1 encodes a putative transmembrane protein of 4,022 amino acids, with a complex domain structure. Homology to the Saccharomyces cerevisiae VPS13 protein suggests a role for COH1 in vesicle-mediated sorting and transport of proteins within the cell.

Pulverulent cataract with variably associated microcornea and iris coloboma in a MAF mutation family

AIMS

To report the detailed clinical findings in a three generation pedigree with autosomal dominant cataract, microcornea, and coloboma resulting from mutation of the lens development gene, MAF.

METHODS

Five members of a three generation pedigree with progressive cataracts underwent detailed ophthalmic examination to characterise associated ocular phenotypic features.

RESULTS

The cataracts present in all affected individuals were cortical, and/or nuclear, pulverulent opacities. Corneal diameters of 10-10.25 mm were present in two family members. Axial lengths were in the normal range. Bilateral iris coloboma in the 6 o'clock position was present in one patient. Uveal melanoma was present in one patient, with uveal naevi in this and one other patient.

CONCLUSION

The bZIP transcription factor MAF is a key lens development gene that regulates the expression of the crystallins. Individuals with a mutation in MAF may have pulverulent cataract alone or cataract in association with microcornea or iris coloboma.

A dominant mutation within the DNA-binding domain of the bZIP transcription factor Maf causes murine cataract and results in selective alteration in DNA binding

The murine autosomal dominant cataract mutants created in mutagenesis experiments have proven to be a powerful resource for modelling the biological processes involved in cataractogenesis. We report a mutant which in the heterozygous state exhibits mild pulverulent cataract named 'opaque flecks in lens', symbol Ofl. By molecular mapping, followed by a candidate gene approach, the mutant was shown to be allelic with a knockout of the bZIP transcription factor, Maf. Homozygotes for Ofl and for Maf null mutations are similar but a new effect, renal tubular nephritis, was found in Ofl homozygotes surviving beyond 4 weeks, which may contribute to early lethality. Sequencing identified the mutation as a G-->A change, leading to the amino-acid substitution mutation R291Q in the basic region of the DNA-binding domain. Since mice heterozygous for knockouts of Maf show no cataracts, this suggests that the Ofl R291Q mutant protein has a dominant effect. We have demonstrated that this mutation results in a selective alteration in DNA binding affinities to target oligonucleotides containing variations in the core CRE and TRE elements. This implies that arginine 291 is important for core element binding and suggests that the mutant protein may exert a differential downstream effect amongst its binding targets. The cataracts seen in Ofl heterozygotes and human MAF mutations are similar to one another, implying that Ofl may be a model of human pulverulent cortical cataract. Furthermore, when bred onto a different genetic background Ofl heterozygotes also show anterior segment abnormalities. The Ofl mutant therefore provides a valuable model system for the study of Maf, and its interacting factors, in normal and abnormal lens and anterior segment development.

Problem based learning

PBL, an educational format, stimulates active and life long learning. PBL improves the motivation of students, stimulates integration of disciplines, small group learning; improves clinical reasoning, problem-solving and decision making. It has been introduced increasingly in the curricula of a number of countries in South-East Asia, viz. Thailand, India, Myanmar and Nepal. We feel that the seed of PBL should be sown in the soil of the Undergraduate Medical Curriculum in Bangladesh urgently.

De novo GLI3 mutation in acrocallosal syndrome: broadening the phenotypic spectrum of GLI3 defects and overlap with murine models

Acrocallosal syndrome (ACS) is characterised by postaxial polydactyly, hallux duplication, macrocephaly, and absence of the corpus callosum, usually with severe developmental delay. The condition overlaps with Greig cephalopolysyndactyly syndrome (GCPS), an autosomal dominant disorder that results from mutations in the GLI3 gene. Here we report a child with agenesis of the corpus callosum and severe retardation, both cardinal features of ACS and rare in GCPS, who has a mutation in GLI3. Since others have excluded GLI3 in ACS, we suggest that ACS may represent a heterogeneous group of disorders that, in some cases, may result from a mutation in GLI3 and represent a severe, allelic form of GCPS. The finding is important for counselling families with suspected ACS.

Turner syndrome: a case of gonadal dysgenesis

An eighteen years old girl came from Ishargang, Mymensingh complaining of short stature, absence of development of breast, lack of menstruation and other secondary sex characters. She was found in infantile appearance with a height of 123 cm, body weight of 28 kg. She had short, broad, webbed neck, cuvitus valgus, absence of development of breast, axillary and public hairs with infantile external genitalia. Hormonal profile revealed high level of LH and FSH, low level of estrogens. Ultrasonography revealed uterine hypoplasia and ill defined gonadal streaks, Karyotype showed typical 45, X0 pattern. She was diagnosed as a case of gonadal dysgenesis due to Turner syndrome.

Domain disruption and mutation of the bZIP transcription factor, MAF, associated with cataract, ocular anterior segment dysgenesis and coloboma

Human congenital cataract and ocular anterior segment dysgenesis both demonstrate extensive genetic and phenotypic heterogeneity. We identified a family where ocular developmental abnormalities (cataract, anterior segment dysgenesis and microphthalmia) co-segregated with a translocation, t(5;16)(p15.3;q23.2), in both balanced and unbalanced forms. We hypothesized that this altered the expression of a gene of developmental significance in the human lens and ocular anterior segment. Cloning the 16q23.2 breakpoint demonstrated that it transected the genomic-control domain of MAF, a basic region leucine zipper (bZIP) transcription factor, first identified as an oncogene, which is expressed in vertebrate lens development and regulates the expression of the eye lens crystallins. The homozygous null mutant Maf mouse embryo demonstrates defective lens formation and microphthalmia. Through mutation screening of a panel of patients with hereditary congenital cataract we identified a mutation in MAF in a three-generation family with cataract, microcornea and iris coloboma. The mutation results in the substitution of an evolutionarily highly conserved arginine with a proline at residue 288 (R288P) in the basic region of the DNA-binding domain of MAF. Our findings further implicate MAF/Maf in mammalian lens development and highlight the role of the lens in anterior segment development. The 16q23.2 breakpoint transects the common fragile site, FRA16D, providing a molecular demonstration of a germline break in a common fragile site.

Missense mutations in COL8A2, the gene encoding the alpha2 chain of type VIII collagen, cause two forms of corneal endothelial dystrophy

Corneal clarity is maintained by its endothelium, which functions abnormally in the endothelial dystrophies, leading to corneal opacification. This group of conditions includes Fuchs' endothelial dystrophy of the cornea (FECD), one of the commonest indications for corneal transplantation performed in developed countries, posterior polymorphous dystrophy (PPCD) and the congenital hereditary endothelial dystrophies (CHED). A genome-wide search of a three-generation family with early-onset FECD demonstrated significant linkage with D1S2830 (Z(max) = 3.72, theta = 0.0). Refinement of the critical region defined a 6-7 cM interval of chromosome 1p34.3-p32 within which lies the COL8A2 gene. This encodes the 703 amino acid alpha2 chain of type VIII collagen, a short-chain collagen which is a component of endothelial basement membranes and which represented a strong candidate gene. Analysis of its coding sequence defined a missense mutation (gln455lys) within the triple helical domain of the protein in this family. Mutation analysis in patients with FECD and PPCD demonstrated further missense substitutions in familial and sporadic cases of FECD as well as in a single family with PPCD. This is the first description of the molecular basis of any of the corneal endothelial dystrophies or of mutations in type VIII collagen in association with human disease. This suggests that the underlying pathogenesis of FECD and PPCD may be related to disturbance of the role of type VIII collagen in influencing the terminal differentiation of the neural crest derived corneal endothelial cell.

Ultrastructural and molecular analysis of Bowman's layer corneal dystrophies: an epithelial origin?

PURPOSE

Two mutations (R555Q and R124L) in the BIGH3 gene have been described in anterior or Bowman's layer dystrophies (CDB). The clinical, molecular, and ultrastructural findings of five families with CDB was reviewed to determine whether there is a consistent genotype:phenotype correlation.

METHODS

Keratoplasty tissue from each patient was examined by light and electron microscopy (LM and EM). DNA was obtained, and exons 4 and 12 of BIGH3 were analyzed by polymerase chain reaction and single-stranded conformation polymorphism/heteroduplex analysis. Abnormally migrating products were analyzed by direct sequencing.

RESULTS

In two families with type I CDB (CDBI), the R124L mutation was defined. There were light and ultrastructural features of superficial granular dystrophy and atypical banding of the "rod-shaped bodies" ultrastructurally. Patients from three families with "honeycomb" dystrophy were found to carry the R555Q mutation and had characteristic features of Bowman's dystrophy type II (CDBII).

CONCLUSIONS

There is a strong genotype:phenotype correlation among CBDI (R124L) and CDBII (R555Q). LM and EM findings suggest that epithelial abnormalities may underlie the pathology of both conditions. The findings clarify the confusion over classification of the Bowman's layer dystrophies.

Phenotypic variability and asymmetry of Rieger syndrome associated with PITX2 mutations

PURPOSE

Rieger syndrome is an autosomal dominant condition characterized by a variable combination of anterior segment dysgenesis, dental anomalies, and umbilical hernia. To date, reports have shown mutations within the PITX2 gene associated with Rieger syndrome, iridogoniodysgenesis, and iris hypoplasia. The purposes of this study were to determine the range of expression and intrafamilial variability of PITX2 mutations in patients with anterior segment dysgenesis.

METHODS

Seventy-six patients with different forms of anterior segment dysgenesis were classified clinically. DNA was obtained and screened by means of polymerase chain reaction (PCR)-single-stranded conformation polymorphism (SSCP) and heteroduplex analysis followed by direct sequencing.

RESULTS

Eight of 76 patients had mutations within the PITX2 gene. Anterior segment phenotypes show wide variability and include a phenocopy of aniridia and Peters', Rieger, and Axenfeld anomalies. Mutations include premature terminations and splice-site and homeobox mutations, confirming that haploinsufficiency the likely pathogenic mechanism in the majority of cases.

CONCLUSIONS

There is significant phenotypic variability in patients with PITX2 mutations, both within and between families. Developmental glaucoma is common. The umbilical and dental abnormalities are highly penetrant, define those at risk of carrying mutations in this gene, and guide mutation analysis. In addition, there is a range of other extraocular manifestations.

A novel hereditary developmental vitreoretinopathy with multiple ocular abnormalities localizing to a 5-cM region of chromosome 5q13-q14

BACKGROUND

To undertake a clinical and molecular analysis of a previously unpublished kindred with a phenotypically distinct vitreoretinopathy characterized by associated ocular developmental abnormalities.

DESIGN

Family genetic study.

PARTICIPANTS

A total of 23 members, both affected and unaffected, of 1 kindred with vitreoretinopathy.

METHOD

Individuals within the kindred were examined clinically and blood samples taken for DNA analysis. Genetic analysis was performed for the proximal region of chromosome 5q by means of polymerase chain reaction (PCR).

MAIN OUTCOME MEASURES

Detection of vitreoretinopathy and associated abnormalities.

RESULTS

This novel, hereditary vitreoretinopathy, showing the classic features of vitreous pathology and early-onset retinal detachments, was associated with a variety of ocular developmental abnormalities, including posterior embryotoxon, congenital glaucoma, iris hypoplasia, congenital cataract, ectopia lentis, microphthalmia, and persistent hyperplastic primary vitreous. There were no associated systemic features. Genetic mapping with markers from the proximal region of 5q13-q14 showed linkage to a 5-cM region between the markers D5S626 and D5S2103.

CONCLUSIONS

The 5-cM region is within that implicated in the etiology of both Wagner and erosive vitreoretinopathies. This suggests that this novel condition may be allelic, refines the genetic mapping for vitreoretinopathies that map to 5q13-q14, and implicates a gene important not only in vitreous production but also in early ocular development.

Coats' disease of the retina (unilateral retinal telangiectasis) caused by somatic mutation in the NDP gene: a role for norrin in retinal angiogenesis

Coats' disease is characterized by abnormal retinal vascular development (so-called 'retinal telangiectasis') which results in massive intraretinal and subretinal lipid accumulation (exudative retinal detachment). The classical form of Coats' disease is almost invariably isolated, unilateral and seen in males. A female with a unilateral variant of Coats' disease gave birth to a son affected by Norrie disease. Both carried a missense mutation within the NDP gene on chromosome Xp11.2. Subsequently analysis of the retinas of nine enucleated eyes from males with Coats' disease demonstrated in one a somatic mutation in the NDP gene which was not present within non-retinal tissue. We suggest that Coats' telangiectasis is secondary to somatic mutation in the NDP gene which results in a deficiency of norrin (the protein product of the NDP gene) within the developing retina. This supports recent observations that the protein is critical for normal retinal vasculogenesis.

Refined genetic and physical localization of the Wagner disease (WGN1) locus and the genes CRTL1 and CSPG2 to a 2- to 2.5-cM region of chromosome 5q14.3

Wagner syndrome (WGN1; MIM 143200), an autosomal dominant vitreoretinopathy characterized by chorioretinal atrophy, cataract, and retinal detachment, is linked to 5q14.3. Other vitreoretinopathies without systemic stigmata, including erosive vitreoretinopathy, are also linked to this region and are likely to be allelic. Within the critical region lie genes encoding two extracellular macromolecules, link protein (CRTL1) and versican (CSPG2), which are important in binding hyaluronan, a significant component of the mammalian vitreous gel, and which therefore represent excellent candidates for Wagner syndrome. Genetic mapping presented here in two further families reduces the critical region to approximately 2 cM. Subsequent refinement of the physical map allows ordering of known polymorphic microsatellites and excludes CRTL1 as a likely candidate for the disorder. CSPG2 is shown to lie within the critical region; however, analysis of the complete coding region of the mature peptide reveals no clear evidence that it is the gene underlying WGN1.

A mutation in the RIEG1 gene associated with Peters’ anomaly

Mutations within the RIEG1 homeobox gene on chromosome 4q25 have previously been reported in association with Rieger syndrome. We report a 3′ splice site mutation within the 3rd intron of the RIEG1 gene which is associated with unilateral Peters’ anomaly. The mutation is a single base substition of A to T at the invariant -2 site of the 3′ splice site. Peters’ anomaly, which is characterised by ocular anterior segment dysgenesis and central corneal opacification, is distinct from Rieger anomaly. This is the first description of a RIEG1 mutation associated with Peters’ anomaly.

A mutation in the RIEG1 gene associated with Peters' anomaly

Mutations within the RIEG1 homeobox gene on chromosome 4q25 have previously been reported in association with Rieger syndrome. We report a 3' splice site mutation within the 3rd intron of the RIEG1 gene which is associated with unilateral Peters' anomaly. The mutation is a single base substition of A to T at the invariant -2 site of the 3' splice site. Peters' anomaly, which is characterised by ocular anterior segment dysgenesis and central corneal opacification, is distinct from Rieger anomaly. This is the first description of a RIEG1 mutation associated with Peters' anomaly.

Locus heterogeneity in autosomal dominant congenital external ophthalmoplegia (CFEOM)

Congenital external ophthalmoplegia (CFEOM) is an uncommon autosomal dominant condition that has previously been mapped to the pericentromeric region of chromosome 12 in seven families with no evidence of locus heterogeneity. We report three families with typical CFEOM. One family does not map to this region of chromosome 12 or to other chromosomal locations implicated in disorders of lid or ocular movement. Recombinants in two CFEOM families potentially help to reduce the size of the candidate region on chromosome 12.

A YAC contig encompassing the Treacher Collins syndrome critical region at 5q31.3-32

Treacher Collins syndrome (TCOF1) is an autosomal dominant disorder of craniofacial development the features of which include conductive hearing loss and cleft palate. Previous studies have localized the TCOF1 locus between D5S519 (proximal) and SPARC (distal), a region of 22 centirays as estimated by radiation hybrid mapping. In the current investigation we have created a contig across the TCOF1 critical region, using YAC clones. Isolation of a novel short tandem repeat polymorphism corresponding to the end of one of the YACs has allowed us to reduce the size of the critical region to approximately 840 kb, which has been covered with three nonchimeric YACs. Restriction mapping has revealed that the region contains a high density of clustered rare-cutter restriction sites, suggesting that it may contain a number of different genes. The results of the present investigation have further allowed us to confirm that the RPS14 locus lies proximal to the critical region and can thereby be excluded from a role in the pathogenesis of TCOF1, while ANX6 lies within the TCOF1 critical region and remains a potential candidate for the mutated gene.