Intrafamilial Phenotypic Variability Research Articles

Episodic ataxia type 2: a clinical, genetic and radiological study of 10 patients

To describe a series of patients with episodic ataxia type 2 (EA2), attending to epidemiological, clinical, radiological, and therapeutic variables. Retrospective revision of patients with molecular diagnosis of EA2 (CACNA1A mutations), between 1988 and 2022. Information achieved from the database of our Movement Disorders clinic. A descriptive statistical analysis was made. Ten patients from five families were analyzed (six women). Median age at diagnosis was 37.5 years-old, with a median diagnostic delay of 20 years. 70% reported familial history of CACNA1A associated symptoms, although 50% presented migraine, epilepsy, dystonia, or neuropsychiatric alterations. Two heterozygous consanguineous patients had homozygotic descendance with infant mortality due to early-onset epileptic encephalopathy type 42. Five pathogenic/probably pathogenic CACNA1A variants were detected. 80% of patients had episodic triggers, being stress the most common. Episodes had a weekly frequency before treatment initiation. Six patients developed chronic ataxia (one patient demand gait support). 50% of patients with neuroimaging presented cerebellar atrophy. Acetazolamide were initiated in 80%, and 75% of them showed improvement of episodic symptoms. Nephrolithiasis was the most frequent side effect. EA2 has a great intrafamilial and interfamilial phenotypic variability. The most frequent phenotype were weekly episodes of unsteadiness, several hours of length, stress as the main trigger, chronic ataxia and gaze-evoked nystagmus. Acetazolamide is effective, although complications are usual. Neurologist must be alert as diagnostic delay is constant.

KCNB1 frameshift variant caused inherited intellectual disability, developmental delay, and seizure.

Potassium voltage-gated channel subfamily B member 1 (KCNB1) encodes Kv2.1 potassium channel. KCNB1 mutations are known to cause global developmental delay, behavioral disorders, and various epilepsies. Most variants occur de novo and are rarely inherited. Here, we report a 14-year-old male patient who was admitted to our clinic with seizures, developmental delay history, and intellectual disability. Brain magnetic resonance image (MRI) was normal and electroencephalogram (EEG) showed spike and sharp-wave complexes emerging in the left hemisphere parietooccipital areas, which were paroxysmally generalized. We performed whole exome sequence analysis (WES) and identified a heterozygous frameshift mutation c.522delA in exon 1 of KCNB1 (NM_004975.4) predicting a premature stop codon p.Lys174Asnfs*20 in the proband. Sanger sequencing confirmed the heterozygous c.522delA mutation in the proband and his mother who also had epilepsy and learning difficulties. His 45 year old mother had used antiepileptic drugs for 9 years after a seizure episode at 12 years old. Also, his mother's uncle's son is nonverbal and has developmental delay and epilepsy. Our study shows that frameshift mutation cytoplasmic domain of KCNB1 gene can cause intrafamilial phenotypic variability and relatively mild clinical findings in these patients.

Cerebello-brainstem dominant form of X-linked adrenoleukodystrophy with intrafamilial phenotypic variability.

This study aimed to describe the clinical and radiological characteristics of a cerebello-brainstem dominant form of X-linked adrenoleukodystrophy (X-ALD). Three affected members from a family with cerebellar ataxia received full neurological, laboratory and radiological examinations. Genetic diagnoses were confirmed using whole-exome sequencing and protein structural modeling. All affected members presented with slurred speech, ataxia, and spasticity, but showed obvious differences in phenotypic severity and radiological findings. The levels of very long-chain fatty acids (VLCFA) were elevated in each member, while only one had adrenal dysfunction. Genetic analysis identified a hemizygous missense mutation (c.887A>G, p.Tyr296Cys) of the ATP-binding cassette subfamily D member 1 gene (ABCD1) in all affected members, which is likely to destabilize the overall structure of the ABCD1 protein. We report a cerebello-dominant form of X-ALD caused by a missense variant in ABCD1. This report highlights intrafamilial phenotypic variability in X-ALD.

Intrafamilial phenotypic variability in autosomal recessive DOCK6-related Adams-Oliver syndrome

Adams-Oliver syndrome (AOS) is diagnosed in presence of aplasia cutis congenita (ACC) of the scalp and terminal transverse limb defects (TTLD). The autosomal recessive (AR) DOCK6-related form of AOS is most often associated with a severe phenotype including also central nervous system and ocular abnormalities. We report a sister and brother with different expression of the phenotype. Both were compound heterozygous pathogenic variants in the DOCK6 gene, including a heterozygous c.5939+2T > C intronic variant that was maternally inherited, and a heterozygous deletion of exons 10 to 21 that was paternally inherited. The sister had microcephaly, periventricular calcifications, minor retinal vasculopathy, and mild impaired neurodevelopment, but only very subtle limb abnormalities and no ACC. Her brother showed a classical DOCK6-related AOS phenotype, including a severe bilateral peripheral ischemic retinopathy. From a review of 22 molecularly confirmed cases with DOCK6-related AOS with ophthalmic examination, we found that 16 of them had retinal vascular pathology (72.7%), confirming as the major ocular anomaly. Documented intrafamilial variability in our family and the evidence revised from previous reports, confirm that AR DOCK6-related AOS expressivity can produce a “milder” phenotype without ACC or TTLD, which could be underdiagnosed in simplex cases because it is difficult to recognize out of a familial context. Therefore, in order to know its real magnitude is required the future inclusion of DOCK6 gene in NGS panels directed to the study of simplex cases of patients with microcephaly, periventricular calcifications, retinal vasculopathy, and/or cardiovascular defects.

The genetic landscape of autosomal dominant polycystic kidney disease in Kuwait.

Autosomal dominant polycystic kidney disease (ADPKD) is the most common renal monogenic disease, characterized by bilateral accumulation of renal fluid-filled cysts leading to progressive renal volume enlargement and gradual impairment of kidney function, often resulting in end-stage renal disease. Kuwait could provide valuable genetic insights about ADPKD, including intrafamilial phenotypic variation, given its large household size. This study aims to provide a comprehensive description of the pathogenic variants linked to ADPKD in the Kuwaiti population using multiple genetic analysis modalities and to describe and analyse the ADPKD phenotypic spectrum in terms of kidney function, kidney volume and renal survival. A total of 126 ADPKD patients from 11 multiplex families and 25 singletons were recruited into the study. A combination of targeted next-generation sequencing (tNGS), long-range polymerase chain reaction, Sanger sequencing and multiplex ligation-dependent probe amplification were utilized for genetic diagnosis. Clinical evaluation was conducted through renal function testing and ultrasonographic kidney volume analysis. We identified 29 ADPKD pathogenic mutations from 36 families achieving an overall molecular genetic diagnostic rate of 112/126 (88.9%), including 29/36 (80.6%) in families. A total of 28/36 (77.8%) families had pathogenic mutations in PKD1, of which 17/28 (60.7%) were truncating, and 1/36 (2.8%) had a pathogenic variant in the IFT140 gene. A total of 20/29 (69%) of the identified ADPKD mutations were novel and described for the first time, including a TSC2-PKD1 contiguous syndrome. Clinical analysis indicated that genetically unresolved ADPKD cases had no apparent association between kidney volume and age. We describe for the first time the genetic landscape of ADPKD in Kuwait. The observed genetic heterogeneity underlining ADPKD along with the wide phenotypic spectrum reveal the level of complexity in disease pathophysiology. ADPKD genetic testing could improve the care of patients through improved disease prognostication, guided treatment and genetic counselling. However, to fulfil the potential of genetic testing, it is important to overcome the hurdle of genetically unresolved ADPKD cases.

P.145 Identification of potential genetic modifiers underlying phenotypic variability in a French family with striated muscle laminopathies

<i>LMNA</i> gene mutations are responsible for a wide spectrum of disorders called laminopathies, the majority of which affecting striated muscles. Among them, Emery-Dreifuss muscular dystrophy (EDMD) and limb-girdle muscular type 1B (LGMD1B) show skeletal muscle involvement of different severity but share the same cardiac involvement, i.e., dilated cardiomyopathy with conduction system disease (DCM-CD) that can also be present in an isolated manner. Clinical heterogeneity is well known among the <i>LMNA</i> mutation carriers. Modifier genes have been suggested to explain such variability. The <i>LMNA</i> mutation (p.Gln6*), identified in a large French family (named here EMD1), is associated with a wide range of age at onset of myopathic symptoms (AOMS). According to this latter, three phenotypic subgroups have been described within the family: AOMS before 20 years (early AOMS), AOMS after 30 years (late AOMS) and isolated cardiac disease without musculo-skeletal symptoms. Our objective was to identify genetic modifiers underlying the intrafamilial phenotypic variability within EMD1 family. Whole genome sequencing (WGS) was performed in 16 <i>LMNA</i>-mutation carriers exhibiting the 3 phenotypic subgroups in EMD1 family. Among the 12 million variants annotated, 2 splice variants with a potential aggravating effect and 1 intronic variant with a potential protective effect have been identified and are currently under functional validation. Moreover, 4 structural variants have been detected only in early AOMS patients. An identity by descent analysis specific to phenotypic subgroups was performed and identified one region shared on chromosome 1, containing the <i>LMNA</i> gene. Our results suggest that a single genetic modifier may not be solely responsible for phenotypic variability in this family, but that a combination of several factors is more likely.

Prenatal Cases Reflect the Complexity of the COL1A1/2 Associated Osteogenesis Imperfecta.

Introduction: Osteogenesis imperfecta (OI) is a rare mendelian skeletal dysplasia with autosomal dominant or recessive inheritance pattern, and almost the most common primary osteoporosis in prenatal settings. The diversity of clinical presentation and genetic etiology in prenatal OI cases presents a challenge to counseling yet has seldom been discussed in previous studies. Methods: Ten cases with suspected fetal OI were enrolled and submitted to a genetic detection using conventional karyotyping, chromosomal microarray analysis (CMA), and whole-exome sequencing (WES). Sanger sequencing was used as the validation method for potential diagnostic variants. In silico analysis of specific missense variants was also performed. Results: The karyotyping and CMA results of these cases were normal, while WES identified OI-associated variants in the COL1A1/2 genes in all ten cases. Six of these variants were novel. Additionally, four cases here exhibited distinctive clinical and/or genetic characteristics, including the situations of intrafamilial phenotypic variability, parental mosaicism, and “dual nosogenesis” (mutations in collagen I and another gene). Conclusion: Our study not only expands the spectrum of COL1A1/2-related OI, but also highlights the complexity that occurs in prenatal OI and the importance of clarifying its pathogenic mechanisms.

Lipoid proteinosis: Novel ECM1 pathogenic variants and intrafamilial variability in four unrelated Arab families.

Lipoid proteinosis (LP) is a rare autosomal recessive multisystem disorder that is caused by loss-of-function pathogenic variants in the extracellular matrix protein-1 (ECM1) gene. The typical clinical manifestations of LP include hoarseness of voice, beaded papules on the eyelids, infiltration and scarring of the skin and mucosa, as well as neuropsychological abnormalities. Currently, more than 70 pathogenic variants have been reported, including nonsense, missense, splice site, deletion and insertion pathogenic variants, and more than half of them occurred in exons 6 and 7. Clinical evaluation and Sanger sequencing were performed on eight patients from four unrelated Arab families. We identified two novel ECM1 variants, one nonsense pathogenic variant in exon 6 (c.579G>A, p.Trp193*) and a deletion of three nucleotides (c.1390_1392del, p.Glu464del) in exon 9, and two previously reported frameshift variants; c.692_693delAG, in exon 6 and c.11dupC in exon 1. Although all patients had characteristic manifestations of lipoid proteinosis, we observed intrafamilial phenotypic variability. Our data expand the pathogenic variant spectrum of ECM1 and also supports the fact that exon 6 is one of the most common hot spots of pathological variants in ECM1.

Hereditary neuropathy with liability to pressure palsies (HNPP): Intrafamilial phenotypic variability and early childhood refusal to walk as the presenting symptom

BackgroundLimping and/or refusal to walk is a common complaint in the setting of the pediatric department, with a widely diverse differential diagnosis. An unusual etiology, is that of a hereditary neuropathy.Hereditary neuropathy with liability to pressure palsies (HNPP) is a recurrent, episodic demyelinating neuropathy, most commonly caused by a 17p11.2 chromosomal deletion encompassing the PMP22 gene.MethodsWe pursued chromosomal microarray analysis (CMA) in multiple affected individuals of a single extended family, manifesting a range of phenotypic features consistent with HNPP.ResultsA 4.5 years-old boy presented for in-patient evaluation due to refusal to walk. Initial investigations including spine MRI and bone scan failed to yield a conclusive diagnosis. Following family history, which implied an autosomal dominant mode of inheritance, CMA was pursued and confirmed a 17p11.2 deletion in the proband consistent with HNPP. Importantly, following this diagnosis, four additional affected family members were demonstrated to harbor the deletion. Their variable phenotypic features, ranging from a prenatal diagnosis of a 6 months-old sibling, to recurrent paresthesias manifesting in the fourth decade of life, are discussed.ConclusionsOur experience with the family reported herein demonstrates how a thorough anamnesis can lead to a rare genetic etiology with a favorable prognosis and prevent unnecessary investigations, and underscores HNPP as an uncommon diagnostic possibility in the limping child.

Distinct Phenotypic and microRNA Expression in X-Linked Charcot–Marie–Tooth Correlated with a Novel Mutation in the GJB1 Gene

We investigated genetic and clinical features in two siblings with an unreported frameshift mutation in the GJB1 gene, encoding connexin 32, to study CMTX-1 and its intrafamilial phenotypic variability. Connexin 32 is a gap junction protein that is located in paranodal regions and Schmidt–Lanterman incisures. Clinical features, family history, and genetic and microRNA information were collected. Genetic analysis determination was performed on genomic DNA from the two cases. Muscle-specific miR-206 was also investigated in serum. A muscle biopsy was conducted in one case, and EMG with conduction velocities was performed in both patients. In the first genetic analysis, no duplication of the PMP22 gene was found. A second genetic analysis of a panel of genes associated with inherited peripheral neuropathies was performed. We found a frameshift mutation in the connexin 32 (GJB1) gene, c.281_287del in hemizygosity, not previously reported, that segregated with the clinical phenotype. An X-linked hereditary sensory motor neuropathy was caused by the mutation in the connexin 32 gene. We found overexpression of miR-206 that was 4-fold up-regulated in the older brother and over 10-fold in the younger brother versus the controls; this might be correlated with a different muscle mass and regeneration. The two siblings presented differently evolving neuropathies due to environmental factors and lifestyles that caused nerve degeneration. We hypothesized that in this X-linked CMT, there is no expression of a truncated connexin 32 (Cx32) protein, with loss of function markedly reduced in the gap junction. In the peripheral nervous system (PNS), this might be mitigated by the presence of another connexin, Cx43. Such a reduction might affect not only gap junction formation but also myelination and muscle trophism, resulting in variable miR-206 expressivity.

Rare genetic mutation of TARDBP leading to intrafamilial clinical phenotype variability; from pathogenic variant to genetic features modifier (P1-1.Virtual)

Rare genetic mutation of TARDBP leading to intrafamilial clinical phenotype variability; from pathogenic variant to genetic features modifier (P1-1.Virtual)

MO029: Urinary biomarkers in the progression of autosomal dominant polycystic kidney disease

Abstract BACKGROUND AND AIMS Autosomal dominant polycystic kidney disease (ADPKD) is a hereditary disease characterized by the formation and growth of renal cysts, affecting the decrease of renal function, which may lead to end-stage renal disease (ESRD). Due to the enormous intrafamilial phenotypic variability of ADPKD and since serum creatinine and glomerular filtration rate (GFR) have a limited ability to assess the disease and predict its progression at earlier stages, there is a need to find new biomarkers to predict disease progression. The α-glutathione s-transferase (GST-α) and haptoglobin (Hp) are produced mainly by the proximal convoluted tubule, and these enzymes are released into the urinary lumen in direct response to tubular damage. This study aims to evaluate the urine concentration of α-GST and Hp biomarkers at different stages of ADPKD progression and correlate the levels of urinary biomarkers α-GST and Hp with traditional markers of renal dysfunction. METHOD Twenty-five patients with ADPKD, mean age of 41.57 ± 14.43 years, mostly female (56.0%), diagnosed according to the Ravine criteria and with a follow-up of at least 60 months. Demographic, hemodynamic, urinary creatinine (UCr) and serum creatinine (SCr) data were collected in baseline (T0) and at the end of the follow-up period (T1). GFR was determined using the CKD-EPI formula, grouping patients into early stages (CKD1 and CKD2) and advanced stages (CKD3 to CKD5). Biomarkers were determined by the ELISA method and indexed to UCr in T1. In addition, α-GST was determinate in a control sample composed of 17 individuals without diagnosed kidney disease. Statistical analysis was performed by SPSS version 26 with a significant value of P &amp;lt; 0.05. RESULTS Comparing the means of SCr and GFR between T0 and T1 were observed a decrease of renal function during the follow-up period (P = 0.013 and P = .017, respectively). About 14.4% of patients were in an advanced stage of kidney disease in T1, compared with 4.8% in T0. ADPKD patients had increased values of α-GST in relation to the control group (P &amp;lt; 0.001), but no difference in the SCr was found. We also found a trend for higher levels of HP in advanced stages of CKD (P = 0.071). In ADPKD patients, direct correlations were observed between the variation of SCr during the follow-up with α-GST and Hp (r = 0.606, P = 0.048 and r = 0.738, P = 0.037, respectively). A trend to correlation was found between the levels of Hp and the Scr in T1 (r = P = 0.058). CONCLUSION The levels of α-GST and Hp are associated with renal damage and may be helpful in the early identification of the decline in renal function in ADPKD patients.

MO021: Alport syndrome manifestation in twins

Abstract BACKGROUND AND AIMS Alport syndrome (AS) is a hereditary renal disease characterized by progressive loss of kidney function and often accompanied by sensorineural hearing loss and ocular abnormalities [1]. The variety of symptoms and their severity is closely associated with mode of inheritance, type of mutation, as well as the sex of the patient [2]. In cases of twins with Alport syndrome, genotype–phenotype manifestation shows a large intrafamilial heterogeneity, although only few reports have been published. In this case series, we describe three different manifestations of three unrelated families with AS with twin pattern. METHOD Molecular analysis by next-generation sequencing was performed on individuals with suspected AS in Vilnius University Hospital Santaros Klinikos. Only patients with confirmed pathogenic AS variants and presence of the twin sibling were included in this study. Clinical, genetic, and laboratory data were reviewed and compared among the siblings and their family members. RESULTS Case 1: Two heterozygous twin sisters with two compound heterozygous pathogenic variants c.4702C &amp;gt; T and c.3247G &amp;gt; C in COL4A3 gene led to autosomal recessive AS. The first sister with a history of nephritis from a childhood reached kidney failure at the age of 33. Further investigations revealed mild bilateral sensorineural hearing loss and no ocular lesions. Her 33-year-old heterozygous twin sister had a similar past history consisting of hematuria since the age of 5 and preeclampsia during her first pregnancy at the age of 30. However, at the age of 33, this patient still had preserved kidney function with eGFR &amp;gt;45 mL/min/1.73 m3. She also suffered by mild bilateral hearing loss while no ocular abnormalities were found. Case 2: Heterozygous pathogenic variant c.2623G &amp;gt; A in COL4A5 gene in female heterozygous twin and her relatives (her mother, son and granddaughter) led to X-linked AS while her twin brother was born healthy. The 51-year-old female’s medical history revealed hematuria since 7 years of age. Her kidney function gradually declined and the patient reached kidney failure at the age of 43 years. Family screening showed a history of kidney disease. Her mother developed hematuria and proteinuria at the age of 20 years and kidney failure at 60 years. The patient's son reached kidney failure at his 20s and he also had bilateral sensorineural hearing loss and typical ocular lesions. Her granddaughter has experienced persistent hematuria and proteinuria since 2 months old, but no extrarenal manifestations were discovered. Case 3: Two heterozygous twin brothers with heterozygous pathogenic variant c.593G &amp;gt; T in COL4A3 gene led to autosomal dominant AS. A 53-year-old male has experienced persistent hematuria and proteinuria since the age of 26. At the age of 53, kidney biopsy was performed where FSGS, thin and split glomerular basement membrane were observed. Further examination showed mild bilateral sensorineural hearing loss and no ocular abnormalities. Family screening revealed that multiple family members had a history of kidney disease. Patient's 55-year-old twin brother experienced persistent hematuria since early adulthood; however, he did not show any signs of hearing loss or ocular abnormalities. Elder brother demonstrated hematuria as well. The patient's deceased father reached kidney failure at the age of 69; however, no hearing abnormalities were found. CONCLUSION Observing genotype–phenotype manifestations suggest that some pathogenic variants demonstrate intrafamilial phenotypic variability. Therefore, despite having identical mutations, twins can manifest AS differently.

Improved Outcome of Infantile Oxalosis Over Time in Europe: Data From the OxalEurope Registry

IntroductionInfantile oxalosis is the most severe form of primary hyperoxaluria type 1 (PH1), with onset of end-stage kidney disease (ESKD) during infancy. We aimed to analyze the outcome of these patients as our current understanding is limited owing to a paucity of reports.MethodsA retrospective registry study was conducted using data from the OxalEurope registry. All PH1 patients with ESKD onset at age <1 year were analyzed.ResultsWe identified 95 patients born between 1980 and 2018 with infantile oxalosis. Median (interquartile range [IQR]) age at ESKD was 0.4 (0.3–0.5) year. There were 4 patients diagnosed by family screening who developed ESKD despite early diagnosis. There were 11 patients who had biallelic missense mutations associated with vitamin B6 responsiveness. Of 89 patients, 27 (30%) died at a median age of 1.4 (0.6–2.0) years (5-year patient survival of 69%). Systemic oxalosis was described in 54 of 56 screened patients (96%). First transplantation was performed at a median age of 1.7 (1.3–2.9) years. In 42 cases, this procedure was a combined liver-kidney transplantation (LKTx), and in 23 cases, liver transplantations (LTx) was part of a sequential procedure. Survival rates of both strategies were similar. Patient survival was significantly higher in patients born after 2000. Intrafamilial phenotypic variability was present in 14 families of patients with infantile oxalosis.ConclusionNearly all screened patients with infantile oxalosis developed systemic disease. Mortality is still high but has significantly improved over time and might further improve under new therapies. The intrafamilial phenotypic variability warrants further investigation.

Identification of a mutation in a Vietnamese family with Emery-Dreifuss Muscular Dystrophy using whole exome sequencing

Emery-Dreifuss muscular dystrophy (EDMD) is a degenerative neuromuscular disease associated with at least nine genes, including EMD, LMNA, FHL1, TMEM43, SUN1, SUN2, TTN, SYNE1, and SYNE2. Herein, we identified a heterozygous missense LMNA mutation (NM_170707.4: c.1357C&gt;T,p.R453W) in three members of a Vietnamese family using whole-exome sequencing (WES), in which the proband was an 11-year-old girl presenting humeroperoneal muscle weaknesses and generalized contracture. Her father and one other relative also exhibited multiple signs of muscular atrophy and contracture. Sanger sequencing in the extended family verified the causative nature of this mutation, establishing a confirmed diagnosis of autosomal dominant Emery-Dreifuss muscular dystrophy (EDMD2). The clinical presentations of each patient in this study are different from each other, demonstrating the intrafamilial phenotypic variability of this mutation. Early identification of the underlying genetic course of the disease by sequencing, combined with clinical findings provides solid evidence to diagnosis process, genetic counseling and management strategy.

Identification of 27 Novel Variants in Genes COL4A3, COL4A4, and COL4A5 in Lithuanian Families With Alport Syndrome.

Introduction:Alport syndrome (AS) is an inherited disorder characterized by hematuria, proteinuria, and kidney function impairment, and frequently associated with extrarenal manifestations. Pathogenic variants in COL4A5 usually cause X-linked Alport syndrome (XLAS), whereas those in the COL4A3 or COL4A4 genes are associated with autosomal dominant (AD) or recessive (AR) inheritance. To date, more than 3000 different disease-causing variants in COL4A5, COL4A3, and COL4A4 have been identified. The aim of this study was to evaluate the clinical and genetic spectrum of individuals with novel, pathogenic or likely pathogenic variants in the COL4A3-A5 genes in a previously unstudied cohort.MethodsIn this study molecular analysis by next generation sequencing (NGS) was performed on individuals from a Lithuanian cohort, with suspected AS. The presence of AS was assessed by reviewing clinical evidence of hematuria, proteinuria, chronic kidney disease (CKD), kidney failure (KF), a family history of AS or persistent hematuria, and specific histological lesions in the kidney biopsy such as thinning or lamellation of the glomerular basement membrane (GBM). Clinical, genetic, laboratory, and pathology data were reviewed. The novelty of the COL4A3-A5 variants was confirmed in the genetic variant databases (Centogene, Franklin, ClinVar, Varsome, InterVar). Only undescribed variants were included in this study.ResultsMolecular testing of 171 suspected individuals led to the detection of 99 individuals with 44 disease causing variants including 27, previously undescribed changes, with the frequency of 9/27 (33,3%) in genes COL4A5, COL4A3 and COL4A4 equally. Three individuals were determined as having digenic AS causing variants: one in COL4A3 and COL4A4, two in COL4A4 and COL4A5. The most prevalent alterations in genes COL4A3-5 were missense variants (n = 19), while splice site, frameshift, unknown variant and stop codon changes were detected more in genes COL4A4 and COL4A5 and accounted for 3, 3, 1 and 1 of all novel variants, respectively.ConclusionGenotype-phenotype correlation analysis suggested that some variants demonstrated intra-familial phenotypic variability. These novel variants represented more than half of all the variants found in a cohort of 171 individuals from 109 unrelated families who underwent testing. Our study expands the knowledge of the genetic and phenotypic spectrum for AS.

Bruck syndrome in 13 new patients: Identification of five novel FKBP10 and PLOD2 variants and further expansion of the phenotypic spectrum.

Bruck Syndrome (BS) is a very rare disorder characterized by osteogenesis imperfecta (OI) associated with congenital contractures and is caused by mutations in FKBP10 or PLOD2 genes. Herein, we describe 13 patients from 9 unrelated Egyptian families with BS. All patients had white sclerae, recurrent fractures, kyphoscoliosis and osteoporosis with variable degrees of severity. Large joint contractures were seen in 11 patients, one patient had contractures of small interphalangeal joints, and one patient had no contractures. Unusual findings noted in individual patients included microcephaly, dental malocclusion, enamel hypoplasia, unilateral congenital dislocation of knee joint, prominent tailbone, and myopathy. Nine different variants were identified in FKBP10 and PLOD2 including five novel ones. FKBP10 variants were found in six families (67%) while PLOD2 variants were identified in three families (33%). The four families, with two affected sibs each, showed inter- and intrafamilial phenotypic variability. In conclusion, we report five novel variants in FKBP10 and PLOD2 thus, expanding the mutational spectrum of BS. In addition, our results expand the phenotypic spectrum, describe newly associated orodental findings, and further illustrate the phenotypic overlap between OI and Bruck syndrome supporting the suggestion of considering BS as a variant of OI rather than a separate entity.

Searching for genetic modulators of the phenotypic heterogeneity in Brugada syndrome.

In Brugada syndrome, even within the same family where all affected individuals share the same mutation, phenotypic variation is prominent, with variable penetrance and expressivity, presenting different degrees of involvement. It is difficult to establish a direct correlation between genotype and phenotype to predict prognosis in complications and risk of sudden death. The factors that modulate this inter- and intra-familial phenotypic variability remain to be determined. With the intention of testing whether other genetic factors, in addition to the causal mutation in SCN5A, may have a modulating effect on the Brugada phenotype and the risk of sudden death, we have studied 8 families with a causal variant in SCN5A with at least two affected individuals, one of whom has suffered cardiac arrest or sudden death. Whole exome sequencing was performed looking for additional variants that modify the phenotype and allow us to predict a better or worse prognosis for the evolution of the disease. The results did not show any clear genetic modifier; nevertheless, highlight the possible implication of the cholesterol and fibrosis pathways, as well as the circadian rhythm, as possible modulators of Brugada syndrome phenotype.

Intrafamilial phenotypic variability in TBC1D24-TLDc homozygous pathogenic variant-related developmental and epileptic encephalopathy

ObjectiveTo describe intrafamilial phenotypic variability in rare TBC1D24-TLDc homozygous pathogenic variant-related developmental and epileptic encephalopathy (DEE). MethodsFour individuals from two unrelated families who had been diagnosed with DEE caused by TBC1D24-TLDc homozygous c.1499C>T (p.A500V) pathogenic variant were recruited. ResultsThe age of seizure onset ranged from 1 to 7 months. All four individuals exhibited very prolonged multifocal myoclonus or focal clonic fits, and the interictal EEGs were prone to dissociation with clinical seizures. The common precipitating factors for seizures were viral infection and fever. Two individuals from family II had progressive cerebellar atrophy: one had ataxia and the other one had no cerebellar signs clinically. All individuals had pharmaco-resistant epilepsy. However, the younger siblings of the two sibling pairs had normal neurodevelopmental outcomes. ConclusionIntrafamilial phenotypic variability of cerebellar neurodegeneration on neuroimages and neurodevelopmental outcomes might be noted in individuals with TBC1D24-TLDc homozygous c.1499C>T (p.A500V) pathogenic variant-related DEE.

A Novel SPG7 Gene Pathogenic Variant in a Cypriot Family With Autosomal Recessive Spastic Ataxia.

The SPG7 gene encodes the paraplegin protein, an inner mitochondrial membrane—localized protease. It was initially linked to pure and complicated hereditary spastic paraplegia with cerebellar atrophy, and now represents a frequent cause of undiagnosed cerebellar ataxia and spastic ataxia. We hereby report the molecular characterization and the clinical features of a large Cypriot family with five affected individuals presenting with spastic ataxia in an autosomal recessive transmission mode, due to a novel SPG7 homozygous missense variant. Detailed clinical histories of the patients were obtained, followed by neurological and neurophysiological examinations. Whole exome sequencing (WES) of the proband, in silico gene panel analysis, variant filtering and family segregation analysis of the candidate variants with Sanger sequencing were performed. RNA and protein expression as well as in vitro protein localization studies and mitochondria morphology evaluation were carried out towards functional characterization of the identified variant. The patients presented with typical spastic ataxia features while some intrafamilial phenotypic variation was noted. WES analysis revealed a novel homozygous missense variant in the SPG7 gene (c.1763C > T, p. Thr588Met), characterized as pathogenic by more than 20 in silico prediction tools. Functional studies showed that the variant does not affect neither the RNA or protein expression, nor the protein localization. However, aberrant mitochondrial morphology has been observed thus indicating mitochondrial dysfunction and further demonstrating the pathogenicity of the identified variant. Our study is the first report of an SPG7 pathogenic variant in the Cypriot population and broadens the spectrum of SPG7 pathogenic variants.