PRPH2-Related Retinal Dystrophies: Mutational Spectrum in 103 Families from a Spanish Cohort

PRPH2, one of the most frequently inherited retinal dystrophy (IRD)-causing genes, implies a high phenotypic variability. This study aims to analyze the PRPH2 mutational spectrum in one of the largest cohorts worldwide, and to describe novel pathogenic variants and genotype-phenotype correlations. A study of 220 patients from 103 families recruited from a database of 5000 families. A molecular diagnosis was performed using classical molecular approaches and next-generation sequencing. Common haplotypes were ascertained by analyzing single-nucleotide polymorphisms. We identified 56 variants, including 11 novel variants. Most of them were missense variants (64%) and were located in the D2-loop protein domain (77%). The most frequently occurring variants were p.Gly167Ser, p.Gly208Asp and p.Pro221_Cys222del. Haplotype analysis revealed a shared region in families carrying p.Leu41Pro or p.Pro221_Cys222del. Patients with retinitis pigmentosa presented an earlier disease onset. We describe the largest cohort of IRD families associated with PRPH2 from a single center. Most variants were located in the D2-loop domain, highlighting its importance in interacting with other proteins. Our work suggests a likely founder effect for the variants p.Leu41Pro and p.Pro221_Cys222del in our Spanish cohort. Phenotypes with a primary rod alteration presented more severe affectation. Finally, the high phenotypic variability in PRPH2 hinders the possibility of drawing genotype-phenotype correlations.

Comprehensive Genotyping and Phenotyping Analysis of GUCY2D-Associated Rod- and Cone-Dominated Dystrophies

PURPOSE

To describe the genetic and clinical spectrum of GUCY2D-associated retinopathies and to accurately establish their prevalence in a large cohort of patients.

DESIGN

Retrospective case series.

METHODS

Institutional study of 47 patients from 27 unrelated families with retinal dystrophies carrying disease-causing GUCY2D variants from the Fundación Jiménez Díaz hospital dataset of 8000 patients. Patients underwent ophthalmological examination and molecular testing by Sanger or exome sequencing approaches. Statistical and principal component analyses were performed to determine genotype-phenotype correlations.

RESULTS

Four clinically different associated phenotypes were identified: 66.7% of families with cone/cone-rod dystrophy, 22.2% with Leber congenital amaurosis, 7.4% with early-onset retinitis pigmentosa, and 3.7% with congenital night blindness. Twenty-three disease-causing GUCY2D variants were identified, including 6 novel variants. Biallelic variants accounted for 28% of patients, whereas most carried dominant alleles associated with cone/cone-rod dystrophy. The disease onset had statistically significant differences according to the functional variant effect. Patients carrying GUCY2D variants were projected into 3 subgroups by allelic combination, disease onset, and presence of nystagmus or night blindness. In contrast to patients with the most severe phenotype of Leber congenital amaurosis, 7 patients with biallelic GUCY2D had a later and milder rod form with night blindness in infancy as the first symptom.

CONCLUSIONS

This study represents the largest GUCY2D cohort in which 4 distinctly different phenotypes were identified, including rare intermediate presentations of rod-dominated retinopathies. We established that GUCY2D is linked to about 1% of approximately 3000 molecularly characterized families of our cohort. All of these findings are critical for defining cohorts for inclusion in future clinical trials.

An evaluation of pipelines for DNA variant detection can guide a reanalysis protocol to increase the diagnostic ratio of genetic diseases

Clinical exome (CE) sequencing has become a first-tier diagnostic test for hereditary diseases; however, its diagnostic rate is around 30-50%. In this study, we aimed to increase the diagnostic yield of CE using a custom reanalysis algorithm. Sequencing data were available for three cohorts using two commercial protocols applied as part of the diagnostic process. Using these cohorts, we compared the performance of general and clinically relevant variant calling and the efficacy of an in-house bioinformatic protocol (FJD-pipeline) in detecting causal variants as compared to commercial protocols. On the whole, the FJD-pipeline detected 99.74% of the causal variants identified by the commercial protocol in previously solved cases. In the unsolved cases, FJD-pipeline detects more INDELs and non-exonic variants, and is able to increase the diagnostic yield in 2.5% and 3.2% in the re-analysis of 78 cancer and 62 cardiovascular cases. These results were considered to design a reanalysis, filtering and prioritization algorithm that was tested by reassessing 68 inconclusive cases of monoallelic autosomal recessive retinal dystrophies increasing the diagnosis by 4.4%. In conclusion, a guided NGS reanalysis of unsolved cases increases the diagnostic yield in genetic disorders, making it a useful diagnostic tool in medical genetics.

Fine Breakpoint Mapping by Genome Sequencing Reveals the First Large X Inversion Disrupting the NHS Gene in a Patient with Syndromic Cataracts

Inversions are structural variants that are generally balanced. However, they could lead to gene disruptions or have positional effects leading to diseases. Mutations in the NHS gene cause Nance-Horan syndrome, an X-linked disorder characterised by congenital cataracts and dental anomalies. Here, we aimed to characterise a balanced pericentric inversion X(p22q27), maternally inherited, in a child with syndromic bilateral cataracts by breakpoint mapping using whole-genome sequencing (WGS). 30× Illumina paired-end WGS was performed in the proband, and breakpoints were confirmed by Sanger sequencing. EdU assays and FISH analysis were used to assess skewed X-inactivation patterns. RNA expression of involved genes in the breakpoint boundaries was evaluated by droplet-digital PCR. We defined the breakpoint position of the inversion at Xp22.13, with a 15 bp deletion, disrupting the unusually large intron 1 of the canonical NHS isoform, and also perturbing topologically-associated domains (TADs). Moreover, a microhomology region of 5 bp was found on both sides. RNA analysis confirmed null and reduced NHS expression in the proband and his unaffected mother, respectively. In conclusion, we report the first chromosomal inversion disrupting NHS, fine-mapped by WGS. Our data expand the clinical spectrum and the pathogenic mechanisms underlying the NHS defects.

RPE65-related retinal dystrophy: Mutational and phenotypic spectrum in 45 affected patients

INTRODUCTION

Biallelic pathogenic RPE65 variants are related to a spectrum of clinically overlapping inherited retinal dystrophies (IRD). Most affected individuals progress to severe disease, with 50% of patients becoming legally blind by 20 years of age. Deeper knowledge of the mutational spectrum and the phenotype-genotype correlation in RPE65-related IRD is needed.

PATIENTS AND METHODS

Forty-five affected subjects from 27 unrelated families with a clinical diagnosis of RPE65-related IRD were included. Clinical evaluation consisted of self-reported ophthalmological history and objective ophthalmological examination. Patients' genotype was classified according to variant class (truncating or missense) or to variant location at different protein domains. The main phenotypic outcome measure was age at onset (AAO) of symptomatic disease and a Kaplan-Meier analysis of disease symptom event-free survival was performed.

RESULTS

Twenty-nine different RPE65 variants were identified in our cohort, 7 of them novel. Patients carrying two missense alleles showed a later disease onset than those with 1 or 2 truncating variants (log-rank test p <0.05). While 60% of patients carrying a missense/missense genotype presented symptoms before or during the first year of life, almost all patients with at least 1 truncating allele (91%) had an AAO ≤1 year (p <0.05).

CONCLUSION

Our findings suggest an association between the type of RPE65 variant carried and AAO. These findings provide useful data on RPE65-associated IRD phenotypes and may help improve clinical and therapeutic management of these patients.

Spotted bones in an osteopoikilosis-related disease (Buschke Ollendorff Syndrome): Identifying this rare condition from the lab to the field

OBJECTIVE

To improve the differential diagnosis of osteopoikilosis in past populations using a clinical case as an example of this rare condition.

MATERIALS

A patient referred to our Genetic Service with suspected Buschke Ollendorff Syndrome after finding a connective nevus.

METHODS

Radiological images from different body regions were accompanied by a genetic study using next-generation sequencing.

RESULTS

Small circular-to-ellipsoid sclerotic lesions were found in the epiphysis and metaphysis of long bones, as well as in the pelvis. These lesions were bilaterally distributed and with well-defined margins, compatible with the characteristics of Buschke Ollendorff Syndrome, bone manifestation osteopoikilosis. A heterozygous mutation on LEMD3 (NM_001167614:c.1918 + 1G > C) was identified by next-generation sequencing. Based on this confirmed case, we have discussed the most probable causes of similar bone lesions found in the archaeological record.

CONCLUSION

It has been demonstrated how a current case of a rare disease can provide useful tools to improve the differential diagnosis of this disease in ancient skeletons.

SIGNIFICANCE

This work underlines the great need for multidisciplinary platforms that integrates clinical research into paleopathology in order to successfully address the study of rare diseases from the past.

LIMITATIONS

Since OPK is only detected by X-rays, suspected cases of this bone lesion will only be identified when radiographs are taken for other purposes.

SUGGESTIONS FOR FURTHER RESEARCH

Retrospective and large-scale studies of radiographs from other research in past populations.

NGS and phenotypic ontology-based approaches increase the diagnostic yield in syndromic retinal diseases

Syndromic retinal diseases (SRDs) are a group of complex inherited systemic disorders, with challenging molecular underpinnings and clinical management. Our main goal is to improve clinical and molecular SRDs diagnosis, by applying a structured phenotypic ontology and next-generation sequencing (NGS)-based pipelines. A prospective and retrospective cohort study was performed on 100 probands with an a priori diagnosis of non-Usher SRDs, using available clinical data, including Human Phenotype Ontology annotation, and further classification into seven clinical categories (ciliopathies, specific syndromes and five others). Retrospective molecular diagnosis was assessed using different molecular and bioinformatic methods depending on availability. Subsequently, uncharacterized probands were prospectively screened using other NGS approaches to extend the number of analyzed genes. After phenotypic classification, ciliopathies were the most common SRD (35%). A global characterization rate of 52% was obtained, with six cases incompletely characterized for a gene that partially explained the phenotype. An improved characterization rate was achieved addressing prospective cases (83%) and well-recognizable syndrome (62%) subgroups. The 27% of the fully characterized cases were reclassified into a different clinical category after identification of the disease-causing gene. Clinical-exome sequencing is the most appropriate first-tier approach for prospective cases, whereas whole-exome sequencing and bioinformatic reanalysis increases the diagnosis of uncharacterized retrospective cases to 45%, mostly those with unspecific symptoms. Our study describes a comprehensive approach to SRDs in daily clinical practice and the importance of thorough clinical assessment and selection of the most appropriate molecular test to be used to solve these complex cases and elucidate novel associations.

Diagnostic yield of clinical exome sequencing in congenital hypogonadotropic hypogonadism considering the degree of olfactory impairment

INTRODUCTION

Congenital hypogonadotropic hypogonadism (CHH) can present alone or in association with anosmia or other congenital malformations. More than 30 genes have been identified as being involved in the pathogenesis of CHH with different patterns of inheritance, and the increasing availability of next generation sequencing (NGS) has increased the diagnostic yield.

METHODS

We analysed the diagnostic yield of NGS in patients with CHH using the clinical exome filtered with virtual panels. We also assessed whether designing panels based on the presence/absence of microsmia increased the diagnostic yield.

RESULTS

The use of a 34-gene virtual panel confirmed the diagnosis of CHH in 5 out of 9 patients (55%) patients. In 2 out of 9 (22%), the findings were inconclusive. Applying the presence/absence of microsmia criterion to choose genes for analysis did not improve the diagnostic yield.

CONCLUSIONS

The approach to the genetic study of patients with CHH varies depending on the resources of each healthcare facility, so the sensitivity of testing may vary substantially depending on whether panels, clinical exome sequencing or whole exome sequencing (WES) are used. The analysis of all genes related to CHH regardless of the presence/absence of microsmia seems to be the best approach.

[Diagnostic yield of clinical exome sequencing in congenital hypogonadotropic hypogonadism considering the degree of olfactory impairment]

INTRODUCTION

Congenital hypogonadotropic hypogonadism (CHH) can present alone or in association with anosmia or other congenital malformations. More than 30 genes have been identified as being involved in the pathogenesis of CHH with different patterns of inheritance, and the increasing availability of next generation sequencing (NGS) has increased the diagnostic yield.

METHODS

We analysed the diagnostic yield of NGS in patients with CHH using the clinical exome filtered with virtual panels. We also assessed whether designing panels based on the presence/absence of microsmia increased the diagnostic yield.

RESULTS

The use of a 34-gene virtual panel confirmed the diagnosis of CHH in 5 out of 9 patients (55%). In 2 out of 9 (22%), the findings were inconclusive. Applying the presence/absence of microsmia criterion to choose genes for analysis did not improve the diagnostic yield.

CONCLUSIONS

The approach to the genetic study of patients with CHH varies depending on the resources of each healthcare facility, so the sensitivity of testing may vary substantially depending on whether panels, clinical exome sequencing or whole exome sequencing (WES) are used. The analysis of every genes related to CHH regardless of the presence/absence of microsmia seems to be the best approach.

Genetic diagnosis of epidermolysis bullosa: recommendations from an expert Spanish research group

Epidermolysis bullosa (EB) is a rare genetic disease that causes mucocutaneous fragility. It comprises a clinically and genetically heterogeneous group of disorder characterized by spontaneous or contact/friction-induced blistering. EB is classified into 4 types-simplex, junctional, dystrophic, and Kindler syndrome-and 30 subtypes. The disease is caused by defects in proteins implicated in dermal-epidermal adhesion. At least 19 genes have been characterized and more than 1000 mutations identified, thus rendering diagnosis complex. Molecular diagnosis of EB is the last stage of a laborious process that starts with a detailed clinical history compilation and careful procurement of a skin fresh biopsy that includes an area where the epidermis detaches from the dermis. The detachment area makes it possible to establish the cleavage plane by antigen mapping and, in the best scenario, to identify a single candidate gene to search for pathogenic mutations. The results of the molecular diagnosis enable the physician to provide appropriate genetic counseling (inheritance pattern, risk of recurrence, and options for prenatal and preimplantation diagnosis) and implement subsequent preventive programs, as well as to establish a reasonable clinical prognosis facilitating access to specific therapy and rehabilitation. Lastly, molecular diagnosis is essential for the participation of patients in clinical trials, a critical issue given the current incurable status of EB. The present guidelines aim to disseminate the procedure for diagnosing EB in our laboratory and thus avoid suboptimal or incomplete clinical diagnoses. The recommendations we provide are the result of more than 10 years' experience in the molecular diagnosis of EB in Spain.

Improving molecular diagnosis of aniridia and WAGR syndrome using customized targeted array-based CGH

Chromosomal deletions at 11p13 are a frequent cause of congenital Aniridia, a rare pan-ocular genetic disease, and of WAGR syndrome, accounting up to 30% of cases. First-tier genetic testing for newborn with aniridia, to detect 11p13 rearrangements, includes Multiplex Ligation-dependent Probe Amplification (MLPA) and karyotyping. However, neither of these approaches allow obtaining a complete picture of the high complexity of chromosomal deletions and breakpoints in aniridia. Here, we report the development and validation of a customized targeted array-based comparative genomic hybridization, so called WAGR-array, for comprehensive high-resolution analysis of CNV in the WAGR locus. Our approach increased the detection rate in a Spanish cohort of 38 patients with aniridia, WAGR syndrome and other related ocular malformations, allowing to characterize four undiagnosed aniridia cases, and to confirm MLPA findings in four additional patients. For all patients, breakpoints were accurately established and a contiguous deletion syndrome, involving a large number of genes, was identified in three patients. Moreover, we identified novel microdeletions affecting 3' PAX6 regulatory regions in three families with isolated aniridia. This tool represents a good strategy for the genetic diagnosis of aniridia and associated syndromes, allowing for a more accurate CNVs detection, as well as a better delineation of breakpoints. Our results underline the clinical importance of performing exhaustive and accurate analysis of chromosomal rearrangements for patients with aniridia, especially newborns and those without defects in PAX6 after diagnostic screening.

Clinical Exome Sequencing Reveals MKRN3 Pathogenic Variants in Familial and Nonfamilial Idiopathic Central Precocious Puberty

BACKGROUND/AIMS

Idiopathic central precocious puberty (ICPP) is the premature activation of the hypothalamic-pituitary-gonadal axis in the absence of organic disease. Up to now, just gain-of-function mutations of KISS1/KISS1R and loss-of-function mutations of the maternally imprinted gene MKRN3 are the known genetic causes of ICPP. Our intention is to evaluate variants present in genes related to the pubertal onset pathway that could act as disease-causing or predisposing variants.

METHODS

We studied the clinical exome of 20 patients diagnosed with ICPP using the Illumina platform. The bioinformatics analysis was performed using 2 different programs, and the variants were filtered according to a list of genes related to the gonadotropin-releasing hormone pathway.

RESULTS

In a "sporadic case," we found a missense variant in MKRN3 NM_005664.3: c.203G>A, causing the protein change NP_005655.1:p.Arg68His, predicted as pathogenic by 2 informatics tools. The proband carrying this variant was diagnosed with ICPP at 7.75 years of age. We did not find any pathogenic variants in KISS1, KISS1R, LIN28, GNRH, GNRHR, TACR3, and TAC3.

CONCLUSION

MKRN3 is the most frequent genetic cause of familial ICPP, so it is wise to screen for MKRN3 mutations in all patients with familial ICPP and in patients with an unclear paternal pubertal history.

The p. R151C Polymorphism in MC1R Gene Modifies the Age of Onset in Spanish Huntington's Disease Patients

The expansion of CAG repeats (≥36 CAG) in the HTT gene is the only known genetic cause of Huntington's disease (HD) and the main determinant of the course of the disease. The length of the expanded CAG repeats correlates inversely with the age of onset (AOO) but does not completely determine it. We investigated the role of the melanocortin 1 receptor (MC1R) gene as a modifier factor of AOO in 600 HD patients from Spain. We sequenced the entire region of the MC1R gene and analyzed all the nonsynonymous MC1R genetic variants with a minor allele frequency of at least 0.01 in HD patients. The variability in AOO attributable to the CAG repeats and MC1R polymorphisms was evaluated using a multiple linear regression model. We found that the loss-of-function p. R151C MC1R polymorphism has a significant influence on the AOO (P = 0.004; Bonferroni-corrected P = 0.032) which explains 1.42% of the variance in AOO that cannot be accounted for by the expanded CAG repeat. Our results suggest that the MC1R gene could modify the AOO in Spanish HD patients and encourage the evaluation of loss-of-function MC1R polymorphisms in other HD populations with a higher frequency of these MC1R polymorphisms.

Characterization of an acromesomelic dysplasia, Grebe type case: novel mutation affecting the recognition motif at the processing site of GDF5

Acromesomelic dysplasia, Grebe type is a very rare skeletal dysplasia characterized by severe dwarfism with marked micromelia and deformation of the upper and lower limbs, with a proximodistal gradient of severity. CDMP1 gene mutations have been associated with Grebe syndrome, Hunter-Thompson syndrome, Du Pan syndrome and brachydactyly type C. The proband is a 4-year-old boy, born of consanguineous Pakistani parents. Radiographic imaging revealed features typical of Grebe syndrome: severe shortening of the forearms with an acromesomelic pattern following a proximodistal gradient, with distal parts more severely affected than medial parts; hypoplastic hands, with the phalangeal zone more affected than the metacarpal zone; and severe hypoplastic tibial/femoral zones in both limbs. After molecular analyses, the p.Arg377Trp variant in a homozygous pattern was identified in the CDMP1 gene in the affected child. In silico and structural analyses predicted the p.Arg377Trp amino acid change to be pathogenic. Of the 34 mutations described in the CDMP1 gene, four different missense mutations have been associated with Grebe syndrome. The CDMP1 gene encodes growth differentiation factor 5 (GDF5), which plays a role in regulation of limb patterning, joint formation and distal bone growth. Homozygous mutations in the mature domain of GDF5 result in severe limb malformations such as the Grebe type or the Hunter-Thompson type of acromesomelic chondrodysplasia. The p.Arg377Trp mutation is located within the recognition motif at the processing site of GDF5 where the sequence RRKRR changes to WRKRR. The genotype-phenotype correlation allowed not only confirmation of the clinical diagnosis but also appropriate genetic counselling to be offered to this family.

Mutational spectrum of Duchenne muscular dystrophy in Spain: Study of 284 cases

INTRODUCTION

Duchenne muscular dystrophy (DMD) is a severe X-linked recessive neuromuscular disease that affects one in 3500 live-born males. The total absence of dystrophin observed in DMD patients is generally caused by mutations that disrupt the reading frame of the DMD gene, and about 80% of cases harbour deletions or duplications of one or more exons.

METHODS

We reviewed 284 cases of males with a genetic diagnosis of DMD between 2007 and 2014. These patients were selected from 8 Spanish reference hospitals representing most areas of Spain. Multiplex PCR, MLPA, and sequencing were performed to identify mutations.

RESULTS

Most of these DMD patients present large deletions (46.1%) or large duplications (19.7%) in the dystrophin gene. The remaining 34.2% correspond to point mutations, and half of these correspond to nonsense mutations. In this study we identified 23 new mutations in DMD: 7 large deletions and 16 point mutations.

CONCLUSIONS

The algorithm for genetic diagnosis applied by the participating centres is the most appropriate for genotyping patients with DMD. The genetic specificity of different therapies currently being developed emphasises the importance of identifying the mutation appearing in each patient; 38.7% of the cases in this series are eligible to participate in current clinical trials.

Diversity of Cognitive Phenotypes Associated with C9ORF72 Hexanucleotide Expansion

For diagnostic purposes, we screened for the C9ORF72 mutation in a) 162 FTLD cases, and b) 145 cases with other diagnoses but with some frontotemporal features or manifestations previously reported in C9 carriers. Ten cases (onset 50 to 75 years) harbored the expansion: seven had FTLD syndromes (4.3% of total, 11% of familial cases), and three (2%) had a different diagnosis. All positive cases had family history of dementia, psychiatric disease, or ALS, but only 20% of families with mixed FTLD/ALS phenotypes carried the expansion. Language impairment was the most common symptom, followed by behavioral changes, memory deficits, and parkinsonism. C9ORF72 mutation has a low frequency in our dementia series and very diverse clinical manifestations.

Identification of two rare and novel large deletions in ITGB4 gene causing epidermolysis bullosa with pyloric atresia

Epidermolysis bullosa with pyloric atresia (EB-PA) is a rare autosomal recessive hereditary disease with a variable prognosis from lethal to very mild. EB-PA is classified into Simplex form (EBS-PA: OMIM #612138) and Junctional form (JEB-PA: OMIM #226730), and it is caused by mutations in ITGA6, ITGB4 and PLEC genes. We report the analysis of six patients with EB-PA, including two dizygotic twins. Skin immunofluorescence epitope mapping was performed followed by PCR and direct sequencing of the ITGB4 gene. Two of the patients presented with non-lethal EB-PA associated with missense ITGB4 gene mutations. For the other four, early postnatal demise was associated with complete lack of β4 integrin due to a variety of ITGB4 novel mutations (2 large deletions, 1 splice-site mutation and 3 missense mutations). One of the deletions spanned 278 bp, being one of the largest reported to date for this gene. Remarkably, we also found for the first time a founder effect for one novel mutation in the ITGB4 gene. We have identified 6 novel mutations in the ITGB4 gene to be added to the mutation database. Our results reveal genotype-phenotype correlations that contribute to the molecular understanding of this heterogeneous disease, a pivotal issue for prognosis and for the development of novel evidence-based therapeutic options for EB management.

Clinical, genetics and bioinformatics characterization of a campomelic dysplasia case report

Campomelic dysplasia is a rare disorder characterized by skeletal and extraskeletal defects. Up to two-thirds of affected XY individuals have a gradation of genital defects or may develop as phenotypic females. This syndrome is caused by alterations in SRY-related HMG-Box Gene 9 (SOX9), a transcription factor essential in both chondrocyte differentiation and sex determination. We report a 27-week fetus with ambiguous genitalia and upper and lower extremities bone malformations. Gross photographs, radiologic and pathological studies led the clinical diagnosis to campomelic dysplasia. A new frameshift mutation (p.Pro415Serfs*163) was identified in the SOX9 gene by genetic analysis. This mutation not only alters almost the entire sequence of the C-terminal transactivation (TA) domain of SOX9, but also enlarges it. This altered sequence does not resemble any other existing sequence. Since TA domain is entirely affected, SOX9 could not establish its normal function. The comparison between p.Pro415Serfs*163 and other frameshift mutations that enlarges SOX9 showed the same nucleotides added. This new sequence is not conserved either. We speculate that the fact of adding a sequence downstream of the C-terminal domain alters SOX9 and leads to campomelic dysplasia. The clinical information is essential not only to achieve a correct diagnosis in fetuses with pathologic ultrasound findings, but also to offer a proper genetic counseling.

Long-term follow-up in patients with congenital myasthenic syndrome due to RAPSN mutations

Rapsyn (RAPSN) mutations are a common cause of postsynaptic congenital myasthenic syndromes. We present a comprehensive description of the clinical and molecular findings of ten patients with CMS due to mutations in RAPSN, mostly with a long-term follow-up. Two patients were homozygous and eight were heterozygous for the common p.Asn88Lys mutation. In three of the heterozygous patients we have identified three novel mutations (c.869T > C; p.Leu290Pro, c.1185delG; p.Thr396Profs*12, and c.358delC; p.Gln120Serfs*8). In our cohort, the RAPSN mutations lead to a relatively homogeneous phenotype, characterized by fluctuating ptosis, occasional bulbar symptoms, neck muscle weakness, and mild proximal muscle weakness with exacerbations precipitated by minor infections. Interestingly, episodic exacerbations continue to occur during adulthood. These were characterized by proximal limb girdle weakness and ptosis, and not so much by respiratory insufficiency after age 6. All patients presented during neonatal period and responded to cholinergic agonists. In most of the affected patients, additional use of 3,4-diaminopyridine resulted in significant clinical benefit. The disease course is stable except for intermittent worsening.

C9ORF72 hexanucleotide expansions of 20-22 repeats are associated with frontotemporal deterioration

OBJECTIVE

Expansions of more than 30 hexanucleotide repetitions in the C9ORF72 gene are a common cause of frontotemporal dementia (FTD) or amyotrophic lateral sclerosis (ALS). However, the range of 20-30 repetitions is rarely found and still has unclear significance. A screening of our cohort of cases with FTD (n = 109) revealed 4 mutation carriers (>30 repetitions) but also 5 probands with 20-22 confirmed repetitions. This study explored the possible pathogenic correlation of the 20-22 repeats expansion (short expansion).

METHODS

Comparison of clinical phenotypes between cases with long vs short expansions; search for segregation in the families of probands with short expansion; analysis of the presence of the common founder haplotype, described for expansions >30 repeats, in the cases having the short expansion; and analysis of the distribution of hexanucleotide repeat alleles in a control population.

RESULTS

No different patterns were found in the clinical phenotype or aggressiveness of the disease when comparing cases with long or short expansions. Cases in both groups had psychiatric symptoms during 1-3 decades before evolving insidiously to cognitive deterioration. The study of the families with short expansion showed clear segregation of the 20-22 repeats allele with the disease. Moreover, this 20-22 repeats allele was associated in all cases with the pathogenic founder haplotype. None of 216 controls had alleles with more than 14 repetitions.

CONCLUSIONS

Description of these families suggests that short C9ORF72 hexanucleotide expansions are also related to frontotemporal cognitive deterioration.

Fibrodysplasia ossificans progressiva in Spain: epidemiological, clinical, and genetic aspects

We aimed to investigate the epidemiological determinants, clinical features, and genetic pattern of FOP in our country by evaluating the entire population of patients identified according to a combination of methods. To achieve this, 24 individuals were confirmed as FOP cases, 17 of whom were alive at the end of 2011 (point prevalence=0.36 × 10(-6)). The gender distribution (male/female ratio=13/11) and the concurrent range of ages (from 4 to 53 years; mean ± SD: 30.2 ± 13.8) are in agreement with similar reports. Twenty-one (87.5%) had characteristic congenital malformations of the big toe, and short thumbs were found in 65.2% of cases. In addition, other skeletal malformations such us fusion of the posterior elements of the cervical spine (89.0%), knee osteochondromas (71%), scoliosis (54.5%), and short and broad femoral neck (52.6%) were observed. All had developed mature ossicles of heterotopic bone in typical anatomic and temporal patterns, ranging in number from 1 to 17 (9.5 ± 3.9). Age at appearance of first ossifying lesion varied from 3 months to 15 years. Mean age at diagnosis was 7.3 ± 5.1 years and the average delay in reaching the correct diagnosis after the onset of heterotopic ossification was 2.7 years (range=0-12 years). Biopsy of the pre-osseous lesions was performed in 11 of 20 (55.0%), providing no useful information for the diagnosis of FOP. Seven of 18 (38.9%) reported some hearing loss, and 5 (27.8%) experienced diffuse thinning of the hair or were bald. No patient had relatives with a typical FOP clinical picture. Fourteen of the 16 cases which were genetically investigated displayed the single heterozygous mutation c.617G>A in exon 4 of the ACVR1 gene. One of the two patients who did not present with the canonical ACVR1 mutation showed a heterozygous mutation c.774G>C in exon 5 leading to the substitution of Arginine 258 with a serine. The other patient had a heterozygous c.774G>T substitution in exon 5 leading to the same amino acid change (p.Arg258Ser). These two patients had only nonspecific abnormalities of the great toe, lacked the typical anatomic and developmental pattern of heterotopic ossification, and shared a trend toward uncommon clinical features. These results provide new insight on the epidemiological and clinical traits of FOP, reinforcing the notion of its worldwide homogeneity. The molecular characterization of ACVR1 sequence variation will contribute to the understanding of the genetic profile of this devastating disease in different geographical areas.

Guidelines for genetic study of aniridia

INTRODUCTION

Aniridia is a panocular disorder which occurs in 1/50,000 to 1/100,000 live births and can appear either in isolated form or in the context of a syndrome. Isolated aniridia is inherited as an autosomal dominant condition and is caused by mutations of the PAX6 gene. A variety of techniques and methodologies within molecular genetics and cytogenetics are used to study these mutations.

OBJECTIVE

To identify the different aspects of this disease and to provide a guide for proper genetic diagnosis leading to improved clinical management of the disease.

DEVELOPMENT

Aniridia is an autosomal dominant disease that primarily affects the iris, though it can impact most of the ocular structures. The disease is mainly caused by mutations in the PAX6 gene located on chromosome 11p13 which encodes a transcription factor that is involved in the development of the eye. Genetic analysis of aniridia is complex and requires the use of both molecular genetics and cytogenetics techniques. These procedures are indicated in all cases of aniridia. It is important bear certain clinical and technical aspects in mind prior to starting analysis or providing genetic counseling for patients and their families.

CONCLUSIONS

The use of molecular genetic techniques in the genetic diagnosis of aniridia enables patients and their families to receive better clinical management.

Ellis-van Creveld syndrome in a fetus with rhizomelia and polydactyly. Report of a case diagnosed by genetic analysis, and correlation with pathological andradiologic findings

Ellis-van Creveld syndrome is an autosomal recessive disorder mainly characterized by a disproportionate limb dwarfism, chondroectodermal dysplasia, congenital heart disease, postaxial polydactyly, and dysplastic fingernails and teeth. Only 300 cases have been published worldwide. We report a 21-week fetus with rhizomelia and polydactyly detected. Gross photographs, radiologic studies and pathological study were performed leading to the clinico-pathological suspicion of EvC. DNA from fresh fetal tissue was extracted for sequencing the EVC and EVC2 genes. p.W215X and p.R677X mutations were identified in the EVC2 gene in the fetal sample. Parental sample analysis showed the p.W215X mutation to be inherited from the mother and the p.R677X mutation from the father. The clinical information is essential not only to arrive at a correct diagnosis in fetuses with pathologic ultrasound findings, but also to offer a proper genetic counseling to the parents and their relatives.

Case report: identical twins revealing discordant hypodontia. The rationale of dental arch differences in monozygotic twins

BACKGROUND

While it is generally accepted that monozygotic (MZ) twins are identical with respect to inherited traits, because they share 100% of their genetic material, clinical findings and scientific evidence does not support this belief. In addition to environmental factors and stochastic developmental events, a number of genetic mechanisms, detectable by new techniques in molecular genetics, explain the differences frequently observed in MZ twins.

CASE REPORT

Nine-year-old twin girls requested treatment for a dental malocclusion. Their facial and occlusal features were very similar. Panoramic radiographs revealed hypodontia of two permanent teeth in one twin (35 and 45) and of only one tooth in the other (45). An incorrect diagnosis of dizygosity (DZ) had been made at birth based on the presence of two amniotic sacs. Despite discordance in the dental complement of both girls their orthodontist suspected that the twins might be identical. A genetic study performed by quantitative fluorescence-polymerase chain reaction (QFPCR) analysis of chromosomes 13, 15, 16, 18, 21, 22, and X confirmed that the twins were MZ.

CONCLUSION

Discordances in dental complement between MZ twins are not uncommon and do not exclude monozygosity.

Mutation analysis of 272 Spanish families affected by autosomal recessive retinitis pigmentosa using a genotyping microarray

PURPOSE

Retinitis pigmentosa (RP) is a genetically heterogeneous disorder characterized by progressive loss of vision. The aim of this study was to identify the causative mutations in 272 Spanish families using a genotyping microarray.

METHODS

272 unrelated Spanish families, 107 with autosomal recessive RP (arRP) and 165 with sporadic RP (sRP), were studied using the APEX genotyping microarray. The families were also classified by clinical criteria: 86 juveniles and 186 typical RP families. Haplotype and sequence analysis were performed to identify the second mutated allele.

RESULTS

At least one-gene variant was found in 14% and 16% of the juvenile and typical RP groups respectively. Further study identified four new mutations, providing both causative changes in 11% of the families. Retinol Dehydrogenase 12 (RDH12) was the most frequently mutated gene in the juvenile RP group, and Usher Syndrome 2A (USH2A) and Ceramide Kinase-Like (CERKL) were the most frequently mutated genes in the typical RP group. The only variant found in CERKL was p.Arg257Stop, the most frequent mutation.

CONCLUSIONS

The genotyping microarray combined with segregation and sequence analysis allowed us to identify the causative mutations in 11% of the families. Due to the low number of characterized families, this approach should be used in tandem with other techniques.

The first COL7A1 mutation survey in a large Spanish dystrophic epidermolysis bullosa cohort: c.6527insC disclosed as an unusually recurrent mutation

BACKGROUND

Dystrophic epidermolysis bullosa (DEB) is a genodermatosis caused by mutations in COL7A1. The clinical manifestations are highly variable from nail dystrophy to life-threatening blistering, making early molecular diagnosis and prognosis of utmost importance for the affected families. Mutation identification is mandatory for prenatal testing.

OBJECTIVES

To conduct the first mutational analysis of COL7A1 in a Spanish cohort, to assess mutation consequences at protein/mRNA level and to establish genotype-phenotype correlations.

METHODS

Forty-nine Spanish patients with DEB were studied. Antigen mapping was performed on patient skin biopsies. COL7A1 mutation screening in genomic DNA was performed by polymerase chain reaction (PCR) and direct sequencing. Mutation consequences were determined by reverse transcriptase-PCR.

RESULTS

Eight patients belonged to three unrelated families with dominant DEB. Forty-one were affected with recessive DEB (RDEB). Specifically, 27 displayed the severe generalized subtype, eight the other generalized subtype and six a localized phenotype (two pretibial, three acral and one inversa). Thirty-five mutations were identified, 20 of which are novel. The pathogenic mutation c.6527insC accounted for 46.3% of Spanish RDEB alleles. A consistent genotype-phenotype correlation was established.

CONCLUSIONS

Although the COL7A1 database indicates that most DEB mutations are family specific, the pathogenic mutation c.6527insC was highly recurrent in our cohort. This level of recurrence for a single genetic defect has never previously been reported for COL7A1. Our findings are essential to the clinicians caring for patients with DEB in Spain and in the large population of Spanish descendants in Latin America. They also provide geneticists a molecular clue for a priority mutation screening strategy.

Molecular analysis of the ABCA4 gene for reliable detection of allelic variations in Spanish patients: identification of 21 novel variants

BACKGROUND/AIMS

Mutations in ABCA4 have been associated with autosomal recessive Stargardt disease (STGD), a few cases with autosomal recessive cone-rod dystrophy (arCRD) and autosomal recessive retinitis pigmentosa (arRP). The purpose of the study was threefold: to molecularly characterise families with no mutations or partially characterised families; to determine the specificity and sensitivity of the genotyping microarray; and to evaluate the efficiency of different methodologies.

METHODS

23 STGD, five arCRD and three arRP Spanish patients who were previously analysed with the ABCR400 microarray were re-evaluated. Results were confirmed by direct sequencing. In patients with either none or only one mutant allele, ABCA4 was further analysed by denaturing high-performance liquid chromatography (dHPLC) and multiplex ligation-dependent probe amplification (MLPA). Haplotype analysis was also performed.

RESULTS

In the first analysis performed with the microarray, 27 ABCA4 variants (27/62; 43.5%) were found. By dHPLC scanning, 12 novel mutations were additionally identified. In addition, two previously described mutations, one false negative (1/62; 1.6%) and one false positive (1.6%), were detected. MLPA analysis did not reveal additional substitutions. The new strategy yielded an increment of 21% compared with the approach used in the first round.

CONCLUSION

ABCA4 should be analysed by optimal combination of high-throughput screening techniques such as microarray, dHPLC and direct sequencing. To the best of our knowledge, this strategy yielded significant mutational spectrum identification in Spanish patients with ABCA4-associated phenotypes. Follow-up of patients, presenting an early onset of the disease and severe mutations, seems essential to perform accurate genotype-phenotype correlations and further characterisation of pathological ABCA4 alleles.