A founder COL4A4 pathogenic variant resulting in autosomal recessive Alport syndrome accounts for most genetic kidney failure in Romani people.

Introduction: Romani people have a high prevalence of kidney failure. This study examined a Romani cohort for pathogenic variants in the COL4A3, COL4A4, and COL4A5 genes that are affected in Alport syndrome (AS), a common cause of genetic kidney disease, characterized by hematuria, proteinuria, end-stage kidney failure, hearing loss, and eye anomalies. Materials and methods: The study included 57 Romani from different families with clinical features that suggested AS who underwent next-generation sequencing (NGS) of the COL4A3, COL4A4, and COL4A5 genes, and 83 family members. Results: In total, 27 Romani (19%) had autosomal recessive AS caused by a homozygous pathogenic c.1598G>A, p.Gly533Asp variant in COL4A4 (n = 20) or a homozygous c.415G>C, p.Gly139Arg variant in COL4A3 (n = 7). For p.Gly533Asp, 12 (80%) had macroscopic hematuria, 12 (63%) developed end-stage kidney failure at a median age of 22 years, and 13 (67%) had hearing loss. For p.Gly139Arg, none had macroscopic hematuria (p = 0.023), three (50%) had end-stage kidney failure by a median age of 42 years (p = 0.653), and five (83%) had hearing loss (p = 0.367). The p.Gly533Asp variant was associated with a more severe phenotype than p.Gly139Arg, with an earlier age at end-stage kidney failure and more macroscopic hematuria. Microscopic hematuria was very common in heterozygotes with both p.Gly533Asp (91%) and p.Gly139Arg (92%). Conclusion: These two founder variants contribute to the high prevalence of kidney failure in Czech Romani. The estimated population frequency of autosomal recessive AS from these variants and consanguinity by descent is at least 1:11,000 in Czech Romani. This corresponds to a population frequency of autosomal dominant AS from these two variants alone of 1%. Romani with persistent hematuria should be offered genetic testing.

Czech family confirms the new 1p36.13-1p36.12 microdeletion syndrome.

Confirmation of the newly described 1p36.13-1p36.12 microdeletion syndrome by finding of a 2,2 Mb deletion in the critical region in a Czech two generation family with a very similar phenotype, but in addition also polyneuropathy of lower limbs.

The Cause of Hereditary Hearing Loss in GJB2 Heterozygotes-A Comprehensive Study of the GJB2/DFNB1 Region.

Hearing loss is a genetically heterogeneous sensory defect, and the frequent causes are biallelic pathogenic variants in the GJB2 gene. However, patients carrying only one heterozygous pathogenic (monoallelic) GJB2 variant represent a long-lasting diagnostic problem. Interestingly, previous results showed that individuals with a heterozygous pathogenic GJB2 variant are two times more prevalent among those with hearing loss compared to normal-hearing individuals. This excess among patients led us to hypothesize that there could be another pathogenic variant in the GJB2 region/DFNB1 locus. A hitherto undiscovered variant could, in part, explain the cause of hearing loss in patients and would mean reclassifying them as patients with GJB2 biallelic pathogenic variants. In order to detect an unknown causal variant, we examined 28 patients using NGS with probes that continuously cover the 0.4 Mb in the DFNB1 region. An additional 49 patients were examined by WES to uncover only carriers. We did not reveal a second pathogenic variant in the DFNB1 region. However, in 19% of the WES-examined patients, the cause of hearing loss was found to be in genes other than the GJB2. We present evidence to show that a substantial number of patients are carriers of the GJB2 pathogenic variant, albeit only by chance.

Variant c.2158-2A>G in MANBA is an important and frequent cause of hereditary hearing loss and beta-mannosidosis among the Czech and Slovak Roma population- evidence for a new ethnic-specific variant.

BACKGROUND: The Roma are a European ethnic minority threatened by several recessive diseases. Variants in MANBA cause a rare lysosomal storage disorder named beta-mannosidosis whose clinical manifestation includes deafness and mental retardation. Since 1986, only 23 patients with beta-mannosidosis and biallelic MANBA variants have been described worldwide. RESULTS: We now report on further 10 beta-mannosidosis patients of Roma origin from eight families in the Czech and Slovak Republics with hearing loss, mental retardation and homozygous pathogenic variants in MANBA. MANBA variant c.2158-2A>G screening among 345 anonymized normal hearing controls from Roma populations revealed a carrier/heterozygote frequency of 3.77%. This is about 925 times higher than the frequency of this variant in the gnomAD public database and classifies the c.2158-2A>G variant as a prevalent, ethnic-specific variant causing hearing loss and mental retardation in a homozygous state. The frequency of heterozygotes/carriers is similar to another pathogenic variant c.71G>A (p.W24*) in GJB2, regarded as the most frequent variant causing deafness in Roma populations. CONLCUSION: Beta-mannosidosis, due to a homozygous c.2158-2A>G MANBA variant, is an important and previously unknown cause of hearing loss and mental retardation among Central European Roma.

Spectrum and frequencies of non GJB2 gene mutations in Czech patients with early non-syndromic hearing loss detected by gene panel NGS and whole-exome sequencing.

Non-syndromic autosomal recessive hearing loss is an extremely heterogeneous disease caused by mutations in more than 80 genes. We examined Czech patients with early/prelingual non-syndromic, presumably genetic hearing loss (NSHL) without known cause after GJB2 gene testing. Four hundred and twenty-one unrelated patients were examined for STRC gene deletions with quantitative comparative fluorescent PCR (QCF PCR), 197 unrelated patients with next-generation sequencing by custom-designed NSHL gene panels and 19 patients with whole-exome sequencing (WES). Combining all methods, we discovered the cause of the disease in 54 patients. The most frequent type of NSHL was DFNB16 (STRC), which was detected in 22 patients, almost half of the clarified patients. Other biallelic pathogenic mutations were detected in the genes: MYO15A, LOXHD1, TMPRSS3 (each gene was responsible for five clarified patients, CDH23 (four clarified patients), OTOG and OTOF (each gene was responsible for two clarified patients). Other genes (AIFM1, CABP2, DIAPH1, PTPRQ, RDX, SLC26A4, TBC1D24, TECTA, TMC1) that explained the cause of hearing impairment were further detected in only one patient for each gene. STRC gene mutations, mainly deletions remain the most frequent NSHL cause after mutations in the GJB2.

Two novel pathogenic variants in KIAA1109 causing Alkuraya-Kucinskas syndrome in two Czech Roma brothers.

Recently described Alkuraya-Kucinskas syndrome (ALKKUCS) clinically presented with severe congenital hydrocephalus, severe brain hypoplasia and other multiple malformations has been described in only few families worldwide to date. ALKKUCS is caused by biallelic pathogenic variants in the KIAA1109 gene with autosomal recessive inheritance. We describe two brothers of Roma origin born with severe congenital hydrocephalus, brain hypoplasia and other clinical findings corresponding with ALKKUCS. Using WES two novel pathogenic variants c.359-1G>A and c.14564_14565del in compound heterozygous status in the KIAA1109 gene were found in both brothers. We consider that the number of healthy heterozygous carriers of pathogenic variants in KIAA1109 could be higher than it is known and pathogenic variants in KIAA1109 could be more frequent cause of congenital hydrocephalus and severe brain dysplasias.

Fatal neonatal nephrocutaneous syndrome in 18 Roma children with EGFR deficiency.

Epidermal growth factor receptor (EGFR) is a transmembrane glycoprotein with tyrosine-kinase signaling activity, involved in many cellular functions including cell growth and differentiation. Germ line loss-of-function mutations in EGFR lead to a severe neonatal skin disorder (Online Mendelian Inheritance in Man #131550). We report 18 premature Roma children from 16 families with birthweights ranging 440-1470 g and multisystem diseases due to the homozygous mutation c.1283G˃A (p.Gly428Asp) in EGFR. They presented with thin, translucent, fragile skin (14/15), skin desquamation (10/17), ichthyosis (9/17), recurrent skin infections and sepsis (9/12), nephromegaly (10/16) and congenital heart defects (7/17). Their prognosis was poor, and all died before the age of 6 months except one 13-year-old boy with a severe skin disorder, dentinogenesis imperfecta, Fanconi-like syndrome and secondary hyperaldosteronism. Management of ion and water imbalances and extremely demanding skin care may improve the unfavorable outcome of such patients.

Moderate sensorineural hearing loss is typical for DFNB16 caused by various types of mutations affecting the STRC gene.

INTRODUCTION: Hearing loss is the most frequent sensory disorder and is genetically extremely heterogeneous. By far the most frequent cause of nonsyndromic autosomal recessive hearing loss (AR-NSHL) are biallelic pathogenic mutations in the GJB2 gene causing DFNB1. The worldwide search for the second most common type of AR-NSHL took almost two decades. Recently reported alterations (mostly deletions) of the STRC gene, also named DFNB16, seem to be the second most frequent cause of AR-NSHL. Genetic testing of STRC is very challenging due to the highly homologous pseudogene. Anecdotal evidence from single patients shows that STRC mutations have their typical audiological findings and patients usually have moderate hearing loss. The aim of this study is to discover if audiological findings in patients with biallelic pathogenic mutations affecting STRC have the characteristic features and shape of audiological curves and if there are genotype/phenotype correlations in relation to various types of STRC mutations. METHODS: Eleven hearing loss patients with pathogenic mutations on both alleles of the STRC gene were detected during routine genetic examination of AR-NSHL patients. Audiological examination consisted of pure tone audiometry, stapedial reflexes, tympanometry and otoacoustic emission tests. RESULTS: The threshold of pure tone average (PTA) was 46 dB and otoacoustic emissions were not detectable in these DFNB16 patients. All patients were without vestibular irritation or asymmetry. CONCLUSION: Moderate sensorineural hearing loss is typical for DFNB16-associated hearing loss and there are no significant differences in audiological phenotypes among different types of mutations affecting STRC.

Autosomal recessive hereditary spastic paraplegia type SPG35 due to a novel variant in the FA2H gene in a Czech patient.

Biallelic pathogenic variants in FA2H gene have been repeatedly described as a cause of hereditary spastic paraplegia (HSP) type35 (SPG35). Targeted massive parallel sequencing (MPS) of the HSP genes panel revealed a novel homozygous variant c.130C > T (p.P44S) in the FA2H gene in the 30-year-old patient presenting with spastic paraplegia. The patient originated form the Czech minority in Romania. The patient manifests typical clinical signs for SPG35 (youth onset gait impairment, progressive spastic paraparesis on lower limbs, dysarthria, white matter changes in MRI).

Molecular Cytogenetic Diagnostics of Marker Chromosomes: Analysis in Four Prenatal Cases and Long-Term Clinical Evaluation of Carriers.

The prenatal finding of a small supernumerary marker chromosome (sSMC) is a challenge for genetic counseling. Our analytic algorithm is based on sSMC frequencies and multicolor FISH to accelerate the procedure. The chromosomal origin, size, and degree of mosaicism of the sSMC then determine the prognosis. We illustrate the effectiveness on 4 prenatally identified de novo mosaic sSMCs derived from chromosomes 13/21, X, 3, and 17. Three sSMC carriers had a good prognosis and apparently healthy children were born, showing no abnormality till the last examination at the age of 4 years. One case had a poor prognosis, and the parents decided to terminate the pregnancy. Our work contributes to the laboratory and clinical management of prenatally detected sSMCs. FISH is a reliable method for fast sSMC evaluation and prognosis assessment; it prevents unnecessary delays and uncertainty, allows informed decision making, and reduces unnecessary pregnancy terminations.

DFNB35 due to a novel mutation in the ESRRB gene in a Czech consanguineous family.

OBJECTIVES: Non-syndromic hearing loss (NSHL) is a genetically heterogeneous disorder with mostly autosomal recessive inheritance. So far 40 genes and the same amount of loci with as yet unknown genes were described with autosomal recessive NSHL. PATIENTS AND METHODS: A consanguineous Czech family with a child with NSHL was genotyped using SNP array and homozygous regions were compared with previously reported DFNB loci. RESULTS: GRXCR1 and ESRRB genes associated with autosomal recessive NSHL were located in two of the eight homozygous regions detected by SNP array genotyping. Mutation p.R291L in a homozygous state was found in the deaf child, the parents were heterozygous. The entire coding region of the ESRRB gene was sequenced in additional 39 patients of Czech origin with early NSHL and only two variants, p.V413I and p.P386S, were found in homozygous state, but are considered to be polymorphisms. CONCLUSION: Homozygosity mapping is a powerful method for identification of genes in heterogeneous recessive diseases. This is the first report of DFNB35 mutations in the Czech Republic and it seems to be a rare cause of NSHL. Additional mutations in ESRRB gene were reported in Pakistan, Tunisia and Turkey.