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Intellectual disability - microarray and sequencing v2.831 TTI2 Rebecca Foulger commented on gene: TTI2: In 3 siblings (two female and one male) born of first-cousin Algerian parents, Langouet et al. (2013, PMID:23956177) identified a homozygous c.1307T-A transversion in the TTI2 gene (I436N). All patients had severe cognitive impairment with severe speech delay and behavioural disturbances, but no seizures were reported.
Intellectual disability - microarray and sequencing v2.831 TTI2 Rebecca Foulger commented on gene: TTI2
Intellectual disability - microarray and sequencing v2.831 TTI2 Rebecca Foulger Phenotypes for gene: TTI2 were changed from AUTOSOMAL RECESSIVE MENTAL RETARDATION to AUTOSOMAL RECESSIVE MENTAL RETARDATION; Mental retardation, autosomal recessive 39, 615541
Intellectual disability - microarray and sequencing v2.830 TTI2 Rebecca Foulger Publications for gene: TTI2 were set to 21937992
Intellectual disability - microarray and sequencing v2.555 TELO2 Konstantinos Varvagiannis gene: TELO2 was added
gene: TELO2 was added to Intellectual disability. Sources: Literature,Expert Review
Mode of inheritance for gene: TELO2 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: TELO2 were set to 27132593; 28944240
Phenotypes for gene: TELO2 were set to You-Hoover-Fong syndrome, MIM 616954
Penetrance for gene: TELO2 were set to Complete
Review for gene: TELO2 was set to GREEN
gene: TELO2 was marked as current diagnostic
Added comment: Biallelic mutations in TELO2 cause You-Hoover-Fong syndrome (MIM 616954). //

PMID: 27132593 reports on 6 patients (from 4 non-consanguineous families) with biallelic TELO2 variants and a similar phenotype.

Intellectual disability and microcephaly were universal features (6/6). Abnormal hearing (3/6), cortical visual impairment (3/6), abnormality of the cardiovascular system (3/6), behavioral problems (laughter outbursts in 3/6) and abnormal balance and movement disorder (6/6) were part of the phenotype. One individual had seizures.

5 missense variants and a complex allele with a stopgain variant localized in cis with a splice-site variant (NM_016111.3:c.514C>T or p.Gln172* in cis with c.2034+1G>A) are reported.

As a result heterozygosity for the complex variant may be confounded with compound heterozygous state until segregation studies are performed.

Functional studies support pathogenicity of the missense variants (reduced protein steady-state levels of TELO2 as well as TTI1 and TTI2 - the 2 other members of the TTT complex) suggesting loss of function.

PMID: 28944240 reports on 2 sisters born to non-consanguineous parents. Both were compound heterozygous for 2 novel variants, a missense and a frameshift one. Severe microcephaly (-8.5 SD and -10.7 SD) and seizures were noted in both. The first sister passed away at the age of 2 months due to a respiratory infection. The other sister demonstrated a compatible, though much more severe phenotype (of ID, dwarfism, retinitis pigmentosa, etc) compared to previously reported patients. //

Biallelic mutations in TTI2 (of the same complex) lead to similar phenotypes (gene rated green in the ID panel). //

TELO2 is included in gene panels for intellectual disability offered by different diagnostic laboratories. //

As a result this gene can be considered for inclusion in this panel as green.
Sources: Literature, Expert Review
Intellectual disability - microarray and sequencing v2.555 TTI2 Konstantinos Varvagiannis Deleted their review
Intellectual disability - microarray and sequencing v2.555 TTI2 Konstantinos Varvagiannis reviewed gene: TTI2: Rating: GREEN; Mode of pathogenicity: None; Publications: 23956177; Phenotypes: ; Mode of inheritance: None