Identification of a novel mutation in the SLC26A4 gene in an Italian with fluctuating sensorineural hearing loss

AbstractMutations in B3GALNT2, encoding a glycosyltransferase enzyme involved in α-dystroglycan glycosylation, have been recently associated with dystroglycanopathy, a well-recognized subtype of congenital muscular dystrophy (CMD). Only a few cases have been reported with B3GALNT2-related dystroglycanopathy with variable severity ranging from mild CMD to severe muscle-eye-brain disease. Here, we describe a child with a novel homozygous nonsense mutation in B3GALNT2. The affected child has severe neurological disease since birth, including muscle disease manifested as hypotonia, muscle weakness, and wasting with elevated creatine kinase, eye disease including microphthalmia and blindness, brain disease with extensive brain malformations including massive hydrocephalus, diffuse cobblestone-lissencephaly, deformed craniocervical junction, and pontocerebellar hypoplasia. The clinical and radiologic findings are compatible with a diagnosis of severe muscle-eye-brain disease and more specifically Walker–Warburg syndrome. A more distinct aspect of the clinical phenotype in this child is the presence of refractory epilepsy in the form of epileptic spasms, epileptic encephalopathy, and West syndrome, as well as sensorineural hearing loss. These findings could expand the phenotype of B3GALNT2-related dystroglycanopathy. In this report, we also provide a detailed review of previously reported cases with B3GALNT2-related dystroglycanopathy and compare them to our reported child. In addition, we study the genotype–phenotype correlation in these cases.

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Mutation analysis of the SLC26A4 gene in patients in Yakutia with inner ear abnormalities: IP-I, IP-II (Mondini) and/or EVA

Nauchno-prakticheskii zhurnal «Medicinskaia genetika» ◽

10.25557/2073-7998.2021.09.14-25 ◽

2021 ◽

pp. 14-25

Author(s):

Л.А. Кларов ◽

К.Ю. Николаева ◽

В.Г. Пшенникова ◽

А.М. Чердонова ◽

Ф.М. Терютин ◽

...

Keyword(s):

Hearing Loss ◽

Sensorineural Hearing Loss ◽

Inner Ear ◽

Autosomal Recessive ◽

Sensorineural Hearing ◽

Splice Donor Site ◽

Total Contribution ◽

Dominant Type ◽

Slc26a4 Gene ◽

Pendred’S Syndrome

Мутации гена SLC26A4 могут приводить как к формированию аутосомно-рецессивной тугоухости 4 типа (DFNB4, OMIM #600791), так и к синдрому Пендреда (PDS, OMIM #274600), при котором нейросенсорная потеря слуха сочетается с дисфункцией щитовидной железы, клинически проявляющейся во второй декаде жизни. Обе формы могут сопровождаться специфическими аномалиями внутреннего уха: IP-I, IP-II (Mondini) и/или EVA. В Якутии аудиологическими, рентгенологическими и молекулярно-генетическими методами обследовано 165 пациентов с врожденным нарушением слуха. При компьютерной томографии пирамиды височных костей у 9 из 165 (5,5%) пациентов были обнаружены аномалии IP-I, IP-II (Mondini) и/или EVA. Методом прямого секвенирования по Сэнгеру у этих 9 пациентов было проведено определение нуклеотидной последовательности гена SLC26A4 (21 экзон). В гене SLC26A4 обнаружено 5 ранее известных вариантов, среди которых 4 варианта относились к миссенс-заменам: c.85G>C p.(Glu29Gln), c.441G>A p.(Met147Ile), c.757A>G p.(Ile253Val), c.2027T>A p.(Leu676Gln) и один вариант затрагивал донорный сайт сплайсинга - c.2089+1G>A (IVS18+1G>A). У 4-х из 9 пациентов патогенные варианты гена SLC26A4 обнаружены в гомозиготном или компаунд-гетерозиготном состоянии. Доля биаллельных мутаций гена SLС26A4 у пациентов с IP-I, IP-II (Mondini) и/или EVA составила 44,4%. Пациенты с биаллельными мутациями гена SLC26A4 имели тяжелые врожденные нарушения слуха (двусторонняя нейросенсорная тугоухость от III степени до глухоты), при этом доминирующим типом аномалий были IP-II (Mondini)+EVA (62,5%), аномалии IP-I не были выявлены ни у одного пациента. По совокупности полученных клинических и молекулярно-генетических данных у трех пациентов форма заболевания классифицирована как аутосомно-рецессивная тугоухость 4 типа (DFNB4), а у одной пациентки с двусторонней аномалией EVA, нейросенсорной тугоухостью III степени и узловым зобом (оперирован) подтвержден синдром Пендреда. Mutations in the SLC26A4 gene can lead to both the formation of autosomal recessive deafness type 4 (DFNB4, OMIM#600791), and to Pendred’s syndrome (PDS, OMIM#274600), in which sensorineural hearing loss is combined with thyroid dysfunction, with both forms can be accompanied by specific anomalies of the inner ear: IP-I, IP-II (Mondini) and/or EVA. Using audiological, radiological and molecular genetics methods, 165 patients with congenital hearing impairment in Yakutia were examined. Computed tomography revealed IP-I, IP-II (Mondini) and/or EVA abnormalities in 9 of 165 (5,5%) patients. Then, using direct Sanger sequencing in these 9 patients, the nucleotide sequence of the coding regions of the SLC26A4 gene (21 exons) was determined. In total, 5 previously known variants were found in the SLC26A4 gene, among which 4 variants were missense substitutions: c.85G>C p.(Glu29Gln), c.441G>A p.(Met147Ile), c.757A>G p.(Ile253Val), c.2027T>A p.(Leu676Gln) and one variant affected the splice donor site - c.2089+1G>A (IVS18+1G>A). In 4 out of 9 patients, pathogenic variants of the SLC26A4 gene were found in a homozygous or compound heterozygous state. The total contribution of biallelic mutations in the SLC26A4 gene among patients with inner ear anomalies was 44,4%. Patients with biallelic SLC26A4-mutations had several to profound bilateral sensorineural hearing loss. In patients with biallelic SLC26A4-mutations, the dominant type of anomaly was IP-II (Mondini)+EVA (62,5%), IP-I anomalies were not detected in any patient. In three patients we were able to confirm the diagnosis of DFNB4, and in one patient, due to the sum of phenotypic features (operated on for nodular goiter, autosomal recessive deafness with EVA), Pendred’s syndrome was diagnosed.

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