GM25936

GM25936 Fibroblast from Skin, Arm

Description:

MYOPATHY, CENTRONUCLEAR, 1; CNM1
MYOPATHY, PROXIMAL, WITH EARLY RESPIRATORY MUSCLE INVOLVEMENT; MPRM
TITIN; TTN
GAP JUNCTION PROTEIN, BETA-2; GJB2 (CONNEXIN 26; CX26)

Affected:

Yes

Sex:

Male

Age:

14 YR (At Sampling)

Overview

Repository

NIGMS Human Genetic Cell Repository

Subcollection

Heritable Diseases
Muscular Dystrophies
CMD Specific

Biopsy Source

Arm

Cell Type

Fibroblast

Tissue Type

Skin

Transformant

Untransformed

Sample Source

Fibroblast from Skin, Arm

Race

White

Ethnicity

Not Hispanic/Latino

Ethnicity

POLISH/IRISH/ENGLISH

Country of Origin

USA

Family Member

Family History

Relation to Proband

proband

Confirmation

Clinical summary/Case history

Species

Homo sapiens

Common Name

Human

Remarks

Clinically affected; Centronuclear myopathy and connexin 26 hearing loss; born full term via normal spontaneous delivery; birth weight 6lb 9 oz; apgar scores: 9 at 1 min and 9 at 5 min; failed initial newborn hearing screening but passed repeat test several weeks later; hyporeflexia and hypotonia onset at 2 months of age; head lag and developmental delay noted at 5 months due to severe weakness of neck muscles; weakness of arms, legs; scoliosis; physical exam at 11 years 6 months: subject noted to be ambulant but had difficulty lifting head or torso against gravity and fatigued easily, had decreased vital capacity, facial weakness, and absent deep tendon reflexes; developmental milestones achieved and maintained through age 11: sat at 9 months, held head up and turned in bed at 12 months, stood at 14 months, walked indoors at 16 months, and walked outdoors at 18 months; climbed stairs with a handrail at 24 months; ran (feet leaving ground) at 5 years; Muscle biopsy at age 14 months: revealed marked increase in the number of fibers with internal and central nuclei, fiber size variation, Type I fiber predominance, and increase in connective or endomysial tissue; electron micrograph of muscle biopsy revealed: disintegrated sarcomeres showing disrupted I- and A-band regions; indirect immunofluorescence analysis of the muscle biopsy indicated normal sarcomere labeling with the titin N-terminal and A-I junction antibodies (titin integrated into sarcomeres and structure intact up to A-I junction), but there was complete loss at the C-terminal of titin which contains a binding site for calpain 3 (CAPN3); immunostaining for CAPN3 indicated a loss of the CAPN3 binding region on the mutant titin proteins; reduced immunostaining for AldoA receptors indicated that the mutations lie in the titin N2-line region; whole exome sequencing was performed (UCSC hg19); subject is a compound heterozygote for the following mutations in the TTN gene; mutation 1 (paternal) in exon 168: p.Val10952Leu (GTT>CTT), c.32854G>C; mutation 2 (maternal) intron 191: c.37112-1G>A, IVS191-1 G>A; audiology evaluation at age 5: mild sensorineural hearing loss on the left side; repeat audiological evaluations every six months revealed progressive hearing loss, L>R; audiological exam at age 8 years: mild sensorineural hearing loss 250-1500 Hz rising within normal limits through 8000 Hz in right ear and a mild sloping to a moderately severe sensorineural hearing loss 250-2000 Hz rising to within normal limits through 8000 Hz in left ear, middle ear muscle reflexes absent to contralateral stimulation 500-2000 Hz, stimulating either ear, distortion-product otoacoustic emissions were consistent with a low to mid frequency hearing loss; word recognition excellent bilaterally; excellent speech perception at average conversation levels (50 dB); Connexin 26 GJB2 gene sequencing revealed subject is heterozygous for 342kb deletion (35delG) and heterozygous for an M34T change, which was reported to be sufficient to result in significant hearing loss when inherited in combination with 35delG in 2007 at the time of testing; subject uses Widex Inteo SD-9M post auricular hearing aids; subject uses breathing support at night or when ill; carrier mother has mild subclinical cardiac and skeletal myopathy, no other family history of centronuclear myopathy or connexin 26 hearing loss; subject lymphoblast cell line is GM23417; carrier mother is GM25951 (lymphoblast), unaffected carrier father is GM25948 (lymphoblast), and maternal grandmother is GM25993 (lymphoblast); subject is 314-1 in Neurology (2013) 81:1205-14, PMID:23975875

Characterizations

PDL at Freeze

5.05

Passage Frozen

IDENTIFICATION OF SPECIES OF ORIGIN

Species of Origin Confirmed by LINE assay

Gene

TTN

Chromosomal Location

2q31.2

Allelic Variant 1

VAL10952LEU; CENTRONUCLEAR MYOPATHY 1

Identified Mutation

32854 G>C; Titin, or connectin, is a giant muscle protein expressed in the cardiac and skeletal muscles that spans half of the sarcomere from Z line to M line. Titin plays a key role in muscle assembly, force transmission at the Z line, and maintenance of resting tension in the I band region (Itoh-Satoh et al., 2002).

Gene

GJB2

Chromosomal Location

13q11-q12

Allelic Variant 1

121011.0005; DEAFNESS, AUTOSOMAL RECESSIVE, 1; DFNB1

Identified Mutation

1-BP DEL, 35G; A mutation consisting of deletion of 1 guanine (G) in a run of 6 guanines extending from position 30 to position 35 in the GJB2 gene has been observed by several groups. Some referred to the deleted nucleotide as 30G (the first of the 6 Gs), whereas others referred to it as 35G. The second mutation found by Carrasquillo et al. [Hum. Molec. Genet. 6: 2163-2172 (1997)] to be responsible for nonsyndromic recessive deafness (220290) in a Muslim-Israeli village in the lower Galilee was a deletion of a guanine residue at cDNA position 35 (35delG), causing a frameshift of the coding sequence leading to premature chain termination at the twelfth amino acid.

Gene

GJB2

Chromosomal Location

13q11-q12

Allelic Variant 1

121011.0001; GAP JUNCTION PROTEIN, BETA-2; GJB2

Identified Mutation

MET34THR; This variant, formerly titled DEAFNESS, AUTOSOMAL RECESSIVE 1A, has been reclassified based on the findings of Shearer et al. (2014). Based on allele frequency in 8,595 controls from 12 populations (maximum minor allele frequency = 0.0200), Shearer et al. (2014) recategorized the M34T variant in the GJB2 gene as benign. In a family in which both palmoplantar keratoderma and deafness (148350) were segregating as probably independent autosomal dominant traits (Verbov, 1987), Kelsell et al. (1997) identified a heterozygous T-to-C substitution in exon 1 of the GJB2 gene, resulting in a met34-to-thr (M34T) substitution. The M34T mutation appeared to segregate with profound deafness, but not with the skin disorder, suggesting to Kelsell et al. (1997) that the mutation acted in a dominant manner. However, Kelley et al. (1998) and Scott et al. (1998) observed normal hearing in M34T heterozygotes, suggesting that the variant does not function as a dominant GJB2 allele in vivo. Moreover, Kelley et al. (1998) identified the M34T allele in 3 of 192 control chromosomes, suggesting that it may be a polymorphism. By in vitro functional studies, White et al. (1998) observed a dominant-negative effect of the M34T mutant polypeptide on the intercellular coupling activity of the wildtype GJB2 polypeptide expressed in Xenopus oocytes. Griffith et al. (2000) presented evidence that M34T is a hypomorphic allele that is insufficient in itself to cause hearing loss, but may cause hearing loss when combined with another pathogenic GJB2 allele. They reported a family with severe autosomal recessive deafness (DFNB1A; 220290) associated with a homozygous mutation in the GJB2 gene (167delT; 121011.0010). One individual who was heterozygous for M34T had normal hearing, and another who was compound heterozygous for M34T and 167delT had only mild high frequency hearing loss. Houseman et al. (2001) found the prevalence of the M34T allele in a cohort of white sib pairs and sporadic cases with nonsyndromic sensorineural hearing loss from the United Kingdom and Ireland to be 3.179% of chromosomes screened. They found the homozygous M34T/M34T genotype cosegregating with mid to high frequency deafness. In a control population of 630 individuals, they identified 25 M34T heterozygotes but no M34T homozygotes. Eighty-eight percent of the M34T alleles were in cis with a 10-bp deletion in the 5-prime noncoding sequence. This deletion was homozygous in the M34T homozygotes. Houseman et al. (2001) concluded that M34T acts as a recessive allele. Kelsell et al. (2000) investigated the possible reason for normal hearing in M34T carriers from distinct ethnic populations. They stated that no M34T homozygotes had been reported among individuals with normal hearing. They extended their analysis of a small family in which palmoplantar keratoderma and various forms of deafness were segregating. In addition to the M34T sequence variant in GJB2, 2 other sequence variants were identified: D66H, also in GJB2 (121011.0012), and R32W in GJB3 (603324). As D66H segregated with the skin disease, Kelsell et al. (2000) thought it likely to underlie the palmoplantar keratoderma. The other 2 gap junction variants identified may contribute to the type of hearing impairment and the variable severity of the skin disease in the family. D'Andrea et al. (2002) showed that CX26 proteins carrying the M34T mutation were expressed at the cell surface and showed wildtype membrane distribution following transient transfection in HeLa cells, but they did not support dye transfer. The M34T mutant also acted as a dominant inhibitor of wildtype CX26 channel activity when the 2 proteins were coexpressed to mimic the heterozygous state. In contrast, Oshima et al. (2003) found that the M34T mutation supported dye transfer in HeLa cells at levels comparable to wildtype CX26, but a CX26 protein in which the authors introduced a met34-to-ala (M34A) mutation did not. In 11 French families with nonsyndromic sensorineural hearing loss (7 familial forms and 4 sporadic cases) in which the M34T variant had been identified, Feldmann et al. (2004) found that the mutation did not segregate with deafness in 6 of the 7 families. Of the family members with normal audiograms, 8 were heterozygous for M34T and 5 were compound heterozygous for M34T and another GJB2 mutation. A screening of 116 controls demonstrated an M34T allele frequency of 1.72%, which was not significantly different from the 2.12% frequency in the deaf population cited by Feldmann et al. (2004). Feldmann et al. (2004) suggested that the M34T variant is not clinically significant in humans and is a frequent polymorphism in France. In a study of 610 hearing-impaired individuals and 294 controls, Tang et al. (2006) found no significant difference in the M34T allele frequency between cases and controls, suggesting that the M34T variant is a polymorphism. Pollak et al. (2007) studied 233 Polish patients with hearing impairment and the GJB2 35delG mutation (121011.0005) on 1 allele. Analysis of 17 patients with the M34T/35delG and 12 patients with the V37I (121011.0023)/35delG genotypes, patients with other GJB2 mutations, and controls found that the M34T and V37I were significantly overrepresented among patients with hearing impairment, consistent with both variants being pathogenic. However, both mutations showed decreased penetrance of about 10% compared to mutations of undisputed pathogenicity. Also, patients with M34T/35delG and V37I/35delG had significantly later onset of hearing impairment compared to those with other genotypes. Pollak et al. (2007) suggested that the M34T and V37I mutations cause mild hearing impairment characterized by relatively late onset and progression.

Gene

TTN

Chromosomal Location

2q31.2

Allelic Variant 2

; CENTRONUCLEAR MYOPATHY 1

Identified Mutation

37112-1G>A (IVS191-1G>A); Titin, or connectin, is a giant muscle protein expressed in the cardiac and skeletal muscles that spans half of the sarcomere from Z line to M line. Titin plays a key role in muscle assembly, force transmission at the Z line, and maintenance of resting tension in the I band region (Itoh-Satoh et al., 2002).

Phenotypic Data

Remarks

Publications

Ceyhan-Birsoy O, Agrawal PB, Hidalgo C, Schmitz-Abe K, DeChene ET, Swanson LC, Soemedi R, Vasli N, Iannaccone ST, Shieh PB, Shur N, Dennison JM, Lawlor MW, Laporte J, Markianos K, Fairbrother WG, Granzier H, Beggs AH, Recessive truncating titin gene, TTN, mutations presenting as centronuclear myopathy Neurology81:1205-14 2013

PubMed ID: 23975875