Autosomal‐dominant biventricular arrhythmogenic cardiomyopathy in a large family with a novel in‐frame DSP nonsense mutation

A novel autosomal‐dominant in‐frame deletion resulting in a nonsense mutation in the desmoplakin (DSP) gene was identified in association with biventricular arrhythmogenic cardiomyopathy across three generations of a large Caucasian family. Mutations that disrupt the function and structure of desmosomal proteins, including desmoplakin, have been extensively linked to familial arrhythmogenic right ventricular cardiomyopathy (ARVC). Analysis of data from 51 individuals demonstrated the previously undescribed variant p.Cys81Stop (c.243_251delCTTGATGCG) in DSP segregates with a pathogenic phenotype exhibiting variable penetrance and expressivity. The mutation's pathogenicity was first established due to two sudden cardiac deaths (SCDs), each with a biventricular cardiomyopathy identified on autopsy. Of the individuals who underwent genetic screening, 27 of 51 were heterozygous for the DSP mutation (29 total with two obligate carriers). Six of these were subsequently diagnosed with arrhythmogenic cardiomyopathy. An additional nine family members have a conduction disorder and/or myocardial structural changes characteristic of an evolving condition. Previous reports from both human patients and mouse studies proposed DSP mutations with a premature stop codon impart mild to no clinical symptoms. Loss of expression from the abnormal allele via the nonsense‐mediated mRNA decay pathway has been implicated to explain these findings. We identified an autosomal‐dominant DSP nonsense mutation in a large family that led to SCD and phenotypic expression of arrhythmogenic cardiomyopathy involving both ventricles. This evidence demonstrates the pathogenic significance of this type of desmosomal mutation and provides insight into potential clinical manifestations.     

Recessive mutation in desmoplakin disrupts desmoplakin-intermediate filament interactions and causes dilated cardiomyopathy, woolly hair and keratoderma

Desmosomes are major cell adhesion junctions, particularly prominent in the epidermis and cardiac tissue and are important for the rigidity and strength of the cells. The desmosome consists of several proteins, of which desmoplakin is the most abundant. Here, we describe the first recessive human mutation, 7901delG, in the desmoplakin gene which causes a generalized striate keratoderma particularly affecting the palmoplantar epidermis, woolly hair and a dilated left ventricular cardiomyopathy. A number of the patients with this syndromic disorder suffer heart failure in their teenage years, resulting in early morbidity. All tested affected members of three families from Ecuador were homozygous for this mutation which produces a premature stop codon leading to a truncated desmoplakin protein missing the C domain of the tail region. Histology of the skin revealed large intercellular spaces and clustering of desmosomes at the infrequent sites of keratinocyte adhesion. Immunohistochemistry of skin from the patients showed a perinuclear localization of keratin in suprabasal keratinocytes, suggesting a collapsed intermediate filament network. This study demonstrates the importance of desmoplakin in the attachment of intermediate filaments to the desmosome. In contrast to null DESMOPLAKIN: mice which die in early development, the truncated protein due to the homozygous 7901delG mutation in humans is not embryonic lethal. This suggests that the tail domain of desmoplakin is not required for establishing tissue architecture during development.     

A family with a complex clinical presentation characterized by arrhythmogenic right ventricular dysplasia/cardiomyopathy and features of branchio‐oculo‐facial syndrome

Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) is a familial form of cardiomyopathy typically caused by mutations in genes that encode an element of the cardiac desmosome. Branchio‐oculo‐facial syndrome (BOFS) is a craniofacial disorder caused by TFAP2A mutations. In a family segregating ARVD/C, some members also had features of BOFS. Genetic testing for ARVD/C identified a mutation in PKP2, encoding plakophilin‐2, a component of the cardiac desmosome. Evaluation of dysmorphology by chromosome microarray (CMA) identified a 4.4 Mb deletion at chromosome 6p24 that included both TFAP2A and DSP, encoding desmoplakin, an additional component of the cardiac desmosome implicated in ARVD/C. A family member with both the 6p24 deletion and PKP2 mutation had more severe cardiac dysfunction. These findings suggest that this contiguous gene deletion contributes to both ARVD/C and BOFS, and that DSP haploinsufficiency may contribute to cardiomyopathy. This family provides a clinical example that underscores the need for careful evaluation in clinical scenarios where genetic heterogeneity is known to exist. Finally, it suggests that individuals with unexplained cardiomyopathy and dysmorphic facial features may benefit from CMA analysis. © 2013 Wiley Periodicals, Inc.     

Novel mutation in the DSG1 gene causes autosomal‐dominant striate palmoplantar keratoderma in a large Syrian family

Palmoplantar keratoderma (PPK) is a heterogenous group of skin disorders characterized by a persistent thickening of the palms of the hands and sometimes soles of the feet. PPK can be classified into many types, including diffuse, transgradient, and focal or striate, where the areas of palmoplantar skin are alternatively thickened. Mutations in four main genes, keratin 9 (KRT9), keratin 1 (KRT1), desmoglein (DSG1), and desmoplakin (DSP), have been associated with PPK. Striate PPK (SPPK) is commonly caused by mutations in DSG1. However, DSP and KRT1 gene mutations have been identified in some cases. In this study, fragment and sequencing analysis were performed for a large Syrian family with dominant SPPK. Segregation analysis showed a linkage with DSG1 gene. Direct Sanger sequencing identified a new mutation c.dup165_168AGCA. This frameshift mutation was heterozygous in all affected family members and absent in all normal individuals.     

Mutation in The Nuclear‐Encoded Mitochondrial Isoleucyl–tRNA Synthetase IARS2 in Patients with Cataracts,Growth Hormone Deficiency with Short Stature,Partial Sensorineural Deafness,and Peripheral Neuropathy or with Leigh Syndrome

Mutations in the nuclear‐encoded mitochondrial aminoacyl–tRNA synthetases are associated with a range of clinical phenotypes. Here, we report a novel disorder in three adult patients with a phenotype including cataracts, short‐stature secondary to growth hormone deficiency, sensorineural hearing deficit, peripheral sensory neuropathy, and skeletal dysplasia. Using SNP genotyping and whole‐exome sequencing, we identified a single likely causal variant, a missense mutation in a conserved residue of the nuclear gene IARS2, encoding mitochondrial isoleucyl–tRNA synthetase. The mutation is homozygous in the affected patients, heterozygous in carriers, and absent in control chromosomes. IARS2 protein level was reduced in skin cells cultured from one of the patients, consistent with a pathogenic effect of the mutation. Compound heterozygous mutations in IARS2 were independently identified in a previously unreported patient with a more severe mitochondrial phenotype diagnosed as Leigh syndrome. This is the first report of clinical findings associated with IARS2 mutations.     

NPHP4 mutation is linked to cerebello‐oculo‐renal syndrome and male infertility

Nephronophthisis is the most common genetic cause of renal failure in children and young adults. It is genetically heterogeneous and can be seen in isolation or in combination with other ciliopathy phenotypes. Here we report an index case where nephronophthisis is associated with oculomotor apraxia and cerebellar abnormalities, consistent with the clinical diagnosis of cerebello‐oculo‐renal syndrome. Prompted by a family history of an uncle with early onset end stage renal failure and infertility, we performed semen analysis on the index. This revealed marked reduction in the count of motile sperms as well as multiple abnormalities in the head and tail. Autozygome‐guided mutation analysis followed by exome sequencing and segregation analysis revealed a homozygous truncating mutation in NPHP4, indicating that mutations of this gene can on rare occasions cause cerebello‐oculo‐renal syndrome. Our finding of severe male infertility in a family with NPHP4 truncation is strongly supported by the mouse model and, to our knowledge, is the first reported male infertility phenotype in association with NPHP4 or any other nephrocystin in humans.     

Whole‐genome sequencing in patients with ciliopathies uncovers a novel recurrent tandem duplication in IFT140

Ciliopathies represent a wide spectrum of rare diseases with overlapping phenotypes and a high genetic heterogeneity. Among those, IFT140 is implicated in a variety of phenotypes ranging from isolated retinis pigmentosa to more syndromic cases. Using whole‐genome sequencing in patients with uncharacterized ciliopathies, we identified a novel recurrent tandem duplication of exon 27–30 (6.7 kb) in IFT140, c.3454‐488_4182+2588dup p.(Tyr1152_Thr1394dup), missed by whole‐exome sequencing. Pathogenicity of the mutation was assessed on the patients’ skin fibroblasts. Several hundreds of patients with a ciliopathy phenotype were screened and biallelic mutations were identified in 11 families representing 12 pathogenic variants of which seven are novel. Among those unrelated families especially with a Mainzer‐Saldino syndrome, eight carried the same tandem duplication (two at the homozygous state and six at the heterozygous state). In conclusion, we demonstrated the implication of structural variations in IFT140‐related diseases expanding its mutation spectrum. We also provide evidences for a unique genomic event mediated by an Alu–Alu recombination occurring on a shared haplotype. We confirm that whole‐genome sequencing can be instrumental in the ability to detect structural variants for genomic disorders.     

Germline mosaicism in keratitis–ichthyosis–deafness syndrome: pre‐natal diagnosis in a familial lethal form

Sbidian E, Feldmann D, Bengoa J, Fraitag S, Abadie V, de Prost Y, Bodemer C, Hadj‐Rabia S. Germline mosaicism in keratitis–ichthyosis–deafness syndrome: pre‐natal diagnosis in a familial lethal form. Keratitis–ichthyosis–deafness (KID) syndrome is an autosomal dominant congenital ectodermal defect characterized by the association of skin lesions, hearing loss and keratitis. Most of the cases appear to be sporadic. KID syndrome is mostly related to mutations of GJB2 gene encoding connexin‐26. Recently, a lethal form of the disease during the first year of life has been reported in two unrelated Caucasian patients. This rare lethal form is caused by the G45E mutation of GJB2 gene. We here report the first pre‐natal molecular genetic diagnosis of the lethal form of KID syndrome relating to a G45E mutation. In the same family, the occurrence of this condition in three other siblings born to African non‐consanguineous healthy parents lead to perform pre‐natal diagnosis for this last pregnancy. Molecular analysis confirms the diagnosis of the lethal form of KID for the fetus. These results establish the role of germline mosaicism in KID syndrome and warrant careful genetic counseling. Furthermore, analysis of our cases and the literature allowed us to define a characteristic severe neonatal phenotype including facial dysmorphy, severe cornification with massive focal hyperkeratosis of the skin with erythroderma, dystrophic nails, complete atrichia and absence of foreskin.     

A novel homozygous missense variant in NECTIN4 (PVRL4) causing ectodermal dysplasia cutaneous syndactyly syndrome

Ectodermal dysplasia syndactyly syndrome 1 (EDSS1) is a rare form of ectodermal dysplasia including anomalies of hair, nails, and teeth along with bilateral cutaneous syndactyly of hands and feet. In the present report, we performed a clinical and genetic characterization of a consanguineous Pakistani family with four individuals affected by EDSS1. We performed exome sequencing using DNA of one affected individual. Exome data analysis identified a novel homozygous missense variant (c.242T>C; p.(Leu81Pro)) in NECTIN4 (PVRL4). Sanger sequencing validated this variant and confirmed its cosegregation with the disease phenotype in the family members. Thus, our report adds a novel variant to the NECTIN4 mutation spectrum and contributes to the NECTIN4‐related clinical characterization.     

Clinical and molecular analysis in Papillon–Lefèvre syndrome

Papillon–Lefèvre syndrome (PLS; MIM#245000) is a rare recessive autosomal disorder characterized by palmar and plantar hyperkeratosis, and aggressively progressing periodontitis leading to premature loss of deciduous and permanent teeth. PLS is caused by loss‐of‐function mutations in the CTSC gene, which encodes cathepsin C. PLS clinical expressivity is highly variable and no consistent genotype–phenotype correlation has been demonstrated yet. Here we report the clinical and genetic features of five PLS patients presenting a severe periodontal breakdown in primary and permanent dentition, hyperkeratosis over palms and soles, and recurrent sinusitis and/or tonsillitis. Mutation analysis revealed two novel homozygous recessive mutations (c.947T>C and c.1010G>C) and one previous described homozygous recessive mutation (c.901G>A), with parents carrying them in heterozygous, in three families (four patients). The fourth family presented with the CTSC c.628C>T mutation in heterozygous, which was inherited maternally. Patient carrying the CTSC c.628C>T mutation featured classical PLS phenotype, but no PLS clinical characteristics were found in his carrier mother. All mutations were found to affect directly (c.901G>A, c.947T>C, and c.1010G>C) or indirectly (c.628C>T, which induces a premature termination) the heavy chain of the cathepsin C, the region responsible for activation of the lysosomal protease. Together, these findings indicate that both homozygous and heterozygous mutations in the cathepsin C heavy chain domain may lead to classical PLS phenotype, suggesting roles for epistasis or gene–environment interactions on determination of PLS phenotypes.     

Spondyloepimetaphyseal dysplasia with joint laxity (Beighton type); mutation analysis in eight affected South African families

Spondyloepimetaphyseal dysplasia with joint laxity (SEMD‐JL), type 1 is an autosomal recessive disorder which has been identified in more than 30 affected children in the Afrikaans‐speaking community of South Africa. Sequencing of B3GALT6 revealed a specific mutation, c.235A > G, in homozygous form in four families, while three others were compound heterozygotes for this mutation in combination with the c.200C > T mutation. In addition, a proband from one family carried the c.16C > T mutation combined with c.200C > T. In a series of five Iranian persons, mutations in B3GALT6 have been implicated in a syndrome characterised by skeletal abnormalities with intellectual disability, bone and connective tissue fragility. Other mutations in B3GALT6 resulted in the classical SEMD‐JL phenotype in seven Japanese families and in a syndrome which has been likened to a progeroid form of Ehlers–Danlos syndrome (EDS). It is evident that there is considerable intragenic heterogeneity in B3GALT6. One of the mutations, c.200C > T, in the affected South Africans was also present in one of the Japanese persons and the respective phenotypes were identical. The multiplicity of allelic mutations and the phenotypic differences in the affected persons supports the concept that a spectrum of connective tissue disorders is programmed by mutations in B3GALT6.     

A homozygous MITF mutation leads to familial Waardenburg syndrome type 4

Waardenburg syndrome (WS) is a genetic disorder characterized by hearing loss and pigmentary abnormalities with variable penetrance. Though heterozygous mutations in MITF are a major cause for Waardenburg syndrome type 2 (WS2), homozygous mutations in this gene and the associated phenotype have been rarely characterized. In this study, we identified a novel p.R223H mutation in MITF in a Chinese Han family with variable WS features. Both parents carried a heterozygous p.R223H mutation. They had normal hearing, and premature greying of the hair is their only pigmentary abnormality. In contrast, their two children both carried a homozygous p.R223H mutation and had classic WS features including profound hearing loss, heterochromia irides and marked pigmentary abnormalities in hair and skin. Interestingly, the two affected children also have persistent chronic constipation since the neonatal period, symptoms suggestive of Waardenburg syndrome type 4 (WS4). Our study revealed a likely association between homozygous mutations in MITF and WS4, which implies a dosage effect for the underlying pathogenesis mechanism.     

Distinct impacts of bi‐allelic WNT10A mutations on the permanent and primary dentitions in odonto‐onycho‐dermal dysplasia

Odonto‐onycho‐dermal dysplasia (OODD) is a rare autosomal recessive syndrome characterized by multiple ectodermal abnormalities. Mutations of the wingless‐type MMTV integration site family member 10A (WNT10A) gene have been associated with OODD. To date, only 11 OODD‐associated WNT10A mutations have been reported. In this report, we Characterized the clinical manifestations with focusing on dental phenotypes in four unrelated OODD patients. By Sanger sequencing, we identified five novel mutations in the WNT10A gene, including two homozygous nonsense mutations c.1176C>A (p.Cys392*) and c.742C>T (p.Arg248*), one homozygous frame‐shift mutation c.898‐899delAT (p.Ile300Profs*126), and a compound heterozygous mutation c.826T>A (p.Cys276Ser) and c.949delG (p.Ala317Hisfs*121). Our findings confirmed that bi‐allelic mutations of WNT10A were responsible for OODD and greatly expanded the mutation spectrum of OODD. For the first time, we demonstrated that bi‐allelic WNT10A mutations could lead to anodontia of permanent teeth, which enhanced the phenotypic spectrum of WNT10A mutations. Interestingly, we found that bi‐allelic mutations in the WNT10A gene preferentially affect the permanent dentition rather the primary dentition, suggesting that the molecular mechanisms regulated by WNT10A in the development of permanent teeth and deciduous teeth might be different.     

A novel HYLS1 homozygous mutation in living siblings with Joubert syndrome

The p.Asp211Gly homozygous HYLS1 mutation is so far known to cause only hydrolethalus syndrome, a lethal malformation syndrome. We report living sibling patients with a homozygous no‐stop mutation in exon 4 of HYLS1, NM_145014.2:c.900A>C (p.Ter300TyrextTer11) in the second decade of life. The proband has Joubert syndrome (JS). The younger brother also has JS and an enlarged posterior fossa that was initially diagnosed as Dandy–Walker malformation. The present mutation is unique as it affects the stop codon. The product protein HYLS1 plays an essential role in the formation of the primary cilium. This report provides insight into the spectrum of disorders involving midline brain defects closely related to cilium dysfunction or ciliopathy.     

A homozygous FKRP start codon mutation is associated with Walker–Warburg syndrome,the severe end of the clinical spectrum

van Reeuwijk J, Olderode‐Berends MJW, van den Elzen C, Brouwer OF, Roscioli T, van Pampus MG, Scheffer H, Brunner HG, van Bokhoven H, Hol FA. A homozygous FKRP start codon mutation is associated with Walker–Warburg syndrome, the severe end of the clinical spectrum. Dystroglycanopathies are a heterogeneous group of disorders caused by defects in the glycosylation pathway of α‐dystroglycan. The clinical spectrum ranges from severe congenital muscular dystrophy with structural brain and eye involvement to a relatively mild adult onset limb‐girdle muscular dystrophy without brain abnormalities and normal intelligence. Mutations have been identified in one of six putative or demonstrated glycosyltransferases. Many different FKRP mutations have been identified, which cover the complete clinical spectrum of dystroglycanopathies. In contrast to the other known genes involved in these disorders, genotype–phenotype correlations are not obvious for FKRP mutations. To date, no homozygous or compound heterozygous null mutations have been identified in FKRP, suggesting that null mutations in FKRP could result in embryonic lethality. We report a family with two siblings carrying a homozygous mutation in the start codon of FKRP that is likely to result in a loss of functional FKRP protein. The clinical phenotype of the patients was consistent with Walker–Warburg syndrome, the most severe disorder in the disease spectrum of dystroglycanopathies.     

Congenital posterior cervical spine malformation due to biallelic c.240‐4T>G RIPPLY2 variant: A discrete entity

The clinical and radiological spectrum of spondylocostal dysostosis syndromes encompasses distinctive costo‐vertebral anomalies. RIPPLY2 biallelic pathogenic variants were described in two distinct cervical spine malformation syndromes: Klippel–Feil syndrome and posterior cervical spine malformation. RIPPLY2 is involved in the determination of rostro‐caudal polarity and somite patterning during development. To date, only four cases have been reported. The current report aims at further delineating the posterior malformation in three new patients. Three patients from two unrelated families underwent clinical and radiological examination through X‐ray, 3D computed tomography and brain magnetic resonance imaging. After informed consent was obtained, family‐based whole exome sequencing (WES) was performed. Complex vertebral segmentation defects in the cervico‐thoracic spine were observed in all patients. WES led to the identification of the homozygous splicing variant c.240‐4T>G in all subjects. This variant is predicted to result in aberrant splicing of Exon 4. The current report highlights a subtype of cervical spine malformation with major atlo‐axoidal malformation compromising spinal cord integrity. This distinctive mutation‐specific pattern of malformation differs from Klippel–Feil syndrome and broadens the current classification, defining a sub‐type of RIPPLY2‐related skeletal disorder. Of note, the phenotype of one patient overlaps with oculo‐auriculo‐vertebral spectrum disorder.