Neuronal ceroid lipofuscinosis in the Russian population: Two novel mutations and the prevalence of heterozygous carriers

Background

Neuronal ceroid lipofuscinoses (NCLs) are a group of neurodegenerative disorders characterized by an accumulation of lipofuscin in the body's tissues. NCLs are associated with variable age of onset and progressive symptoms including seizures, psychomotor decline, and loss of vision.

Methods

We describe the clinical and molecular characteristics of four Russian patients with NCL (one female and three males, with ages ranging from 4 to 5 years). The clinical features of these patients include cognitive and motor deterioration, seizures, stereotypies, and magnetic resonance imaging signs of brain atrophy. Exome sequencing was performed to identify the genetic variants of patients with NCL. Additionally, we tested 6,396 healthy Russians for NCL alleles.

Results

We identified five distinct mutations in four NCL‐associated genes of which two mutations are novel. These include a novel homozygous frameshift mutation in the CLN6 gene, a compound heterozygous missense mutation in the KCTD7 gene, and previously known mutations in KCTD7, TPP1, and MFSD8 genes. Furthermore, we estimated the Russian population carrier frequency of pathogenic and likely pathogenic variants in 13 genes associated with different types of NCL.

Conclusion

Our study expands the spectrum of mutations in lipofuscinosis. This is the first study to describe the molecular basis of NCLs in Russia and has profound and numerous clinical implications for diagnosis, genetic counseling, genotype–phenotype correlations, and prognosis.

Liddle syndrome due to a novel mutation in the γ subunit of the epithelial sodium channel (ENaC) in family from Russia: a case report

Background

Liddle syndrome is a monogenic disease with autosomal dominant inheritance. Basic characteristics of this disease are hypertension, reduced concentration of aldosterone and renin activity, as well as increased excretion of potassium leading to low level of potassium in serum and metabolic alkalosis. The cause of Liddle syndrome is missense or frameshift mutations in SCNN1A, SCNN1B, or SCNN1G genes that encode epithelial sodium channel subunits.

Case presentation

We describe a family with Liddle syndrome from Russia. 15-year-old proband has arterial hypertension, hypokalemia, hyporeninemia, metabolic alkalosis, but aldosterone level is within the normal range. At 12 years of age, arterial hypertension was noticed for the first time. We identified novel frameshift mutation c.1769delG (p.Gly590Alafs) in SCNN1G, which encodes the γ subunit of ENaC in vertebrates. The father and younger sister also harbor this heterozygous deletion. Treatment with amiloride of proband and his sister did not normalize the blood pressure, but normalized level of plasma renin activity.

Conclusions

Our results expand the mutational spectrum of Liddle syndrome and provide further proof that the conserved PY motif is crucial to control of ENaC activity. Genetic analysis has implications for the management of hypertension, specific treatment with amiloride and counselling in families with Liddle syndrome.

A novel elastin gene frameshift mutation in a Russian family with cutis laxa: a case report

Background

Cutis laxa (CL) is a rare connective tissue disorder characterized by loose, redundant, inelastic and wrinkled skin. Patients develop a prematurely aged appearance. Inheritance can be autosomal dominant or autosomal recessive. The X-linked form is now classified in the group of copper transport diseases. Autosomal dominant CL is characterized by wrinkled, redundant and sagging, inelastic skin and in some cases is associated with internal organ involvement.

Case presentation

We report a familial case of autosomal dominant CL, which includes a 33-year-old woman and her 11-year-old son with dry, thin and wrinkled skin that appeared prematurely aged. No serious involvement of internal organs was found. In both patients, we identified novel heterozygous mutation c.2323delG (p.Ala775fs) in exon 34 of elastin transcript NM_001278939.1. Similar frameshift mutations in the last exons of elastin gene were previously reported in patients with autosomal dominant CL.

Conclusions

Our results show a novel frameshift mutation that was found in patients with cutis laxa. Exome sequencing is effective and useful technology for properly diagnosis of diseases with similar phenotype to ensure proper treatment is provided.

[New recurrent extended deletion, including GJB2 and GJB6 genes, results in isolated sensorineural hearing impairment with autosomal recessive type of inheritance]

Hereditary hearing loss with the autosomal recessive type of inheritance of the DFNB 1 genetic type, caused by mutations in the GJB2 gene, is the main reason of innate non-syndromal hearing impairment in most developed countries of the world (including Russia). Intragenic point mutations prevail among the GJB2 gene defectors; however, extended deletions in the DFNB1 locus are also found with considerable frequency in some populations (for example, Spain, Great Britain, France, United States, and Brazil). Among the four known extended deletions, only one deletion affects directly the GJB2 gene sequence and was described in a single family. A new extended deletion in the GJB2 and GJB6 gene sequences (approximately 101 kb in size; NC_000013.10:g.20,757,021_20,858,394del), detected in three unrelated Russian patients, was described and characterized. Ingush origin of this mutation is assumed. If the new deletion is frequent, its detection is very important for the genetic consulting of families with hereditary hearing impairment.

[Hereditary diseases of nervous system in the population of Vladimir province]

The first population genetic study of hereditary disorders of the nervous system (HDNS) in Vladimir oblast was carried out. A total of 1,622,900 subjects, including 1,306,200 from the urban and 316,700 from the rural population, were tested. The population examined was characterized by virtually homogenous ethnic structure, with Russians constituting 95.76%. Pooled prevalence of HDNS in Vladimir oblast corresponded to the average prevalence for other Russian populations. Substantial differences between urban and rural populations in respect of the population load of HDNS and its nosological structure were not observed. A total of 22 nosological forms of HDNS were revealed, including thirteen autosomal dominant (193 families with 272 affected individuals), seven autosomal recessive (59 families with 66 affected individuals), and two X-linked (15 families with 17 affected individuals) diseases. The composition of the HDNS spectrum "nucleus" in Vladimir oblast displayed a number of differences from that in the majority of other populations examined. The HDNS in different regions of the area tested were characterized by different prevalence and spectrum. The data obtained may constitute a basis for regional registration of HDNS in Vladimir oblast.

[Genetic study of idiopathic torsion dystonia in Russia]

Inheritance of idiopathic torsion dystonia (ITD) was studied in 41 Russian families including 41 probands with generalized, focal, and segmental dystonia and 140 recurred cases. Affected relatives appeared in two or more generations in 31 families analyzed. It was shown that in 76% of segregated cases, ITD was inherited as an autosomal dominant trait with a penetrance of 40% and varying expression. An autosomal recessive type was observed in 24% of the cases. Approximately 10% of the cases of disease could be caused by a new mutation and 14.6% by a nongenetic phenotype similar to genetic forms in its clinical symptoms. ITD with the X-linked recessive type of inheritance did not occur in the families studied. The recurrence risk was 20% in autosomal dominant forms. The risk correlated with age the relative's: clinical symptoms developed in 98.4% of patients by the age of 30.