In This Section      
 

TeloZoom

Genes:
ACD;
CTC1;
DKC1;
NAF1;
NHP2;
NOP10;
PARN;
POT1;
RTEL1;
STN1;
TERC;
TERT;
TINF2;
WRAP53

Syndrome Information

Clinical Description

Short telomere syndromes are a spectrum of disease phenotypes that result from mutations in genes involved in telomere maintenance PMID 22965356.The most common clinical manifestations are listed here and they may co-occur in patients and affected families.

Idiopathic pulmonary fibrosis is an age-related disorder characterized by scarring of the lungs. It runs in families and ~20% of idiopathic pulmonary fibrosis patients have an affected first degree relative PMID 22079513. Other types of lung disease cluster in families with germline defects in telomere maintenance including non-specific interstitial pneumonitis, pleuroparenchymal fibroelastosis (PPFE), chronic hypersensitivity pneumonitis and emphysema PMID 17392301, PMID 29703687, PMID 25562321.

Liver disease may be a first manifestation of short telomere syndromes either as cirrhosis or hepatopulmonary syndrome PMID 19936245, PMID 26158642.

Bone marrow failure includes spectrum of failed hematopoiesis and includes isolated cytopenias, overt aplastic anemia as well as myelodysplastic syndrome.

Immunodeficiency may also be a manifestation of primary short telomere syndromes alone or in combination with bone marrow failure PMID 30179220. Hoyeraal-Hreidarsson syndrome (HHS) is a severe short telomere syndrome that is classically associated with immunodeficiency, colitis PMID 23279657, intrauterine growth restriction, microcephaly, and cerebellar hypoplasia.

Dyskeratosis congenita is a classic short telomere disorder characterized by characteristic mucocutaneous findings namely nail dystrophy, oral leukoplakia and skin hyperpigmentation. Revesz syndrome is a rare bilateral exudative retinopathy which has been seen in pediatric patients with short telomere syndromes including Hoyeraal-Hreidarsson syndrome.

Coats plus syndrome is rare and has distinguishing features from other short telomere syndromes such as intracranial calcifications. It is most commonly caused by biallelic mutations in CTC1 PMID 22267198.

Inheritance Pattern

Autosomal dominant, autosomal recessive, X-linked recessive, and de novo

Genotype-Phenotype Correlation

Telomere length is the strongest predictor of disease phenotype as well as severity in this group of disorders PMID 29463756. Genetic anticipation may show evolving patterns of disease in autosomal dominant families with older generations affected by pulmonary disease and younger generations by bone marrow failure PMID 21436073. Some clinical phenotypes that have genotype correlations additionally include:

  • Hoyeraal-Hreidarsson syndrome is commonly caused by mutations in DKC1 or TINF2 but has also been reported with biallelic variants in TERT, RTEL1 and PARN PMID 25940403.
  • Revesz syndrome is often associated with variants in TINF2 PMID 18252230.
  • Biallelic variants in CTC1 usually manifest as Coats plus syndrome (intracranial calcifications, retinal exudates, osteopenia, gastrointestinal bleeding). CTC1 biallelic variants may also be seen in rare cases of isolated bone marrow failure PMID 22532422.

Reversion has been described in patients with TERC variants PMID 22341970 and in one adult with a TINF2 variant PMID 25539146. If a patient who meets diagnostic criteria for short telomere syndrome has a negative molecular testing, it might be beneficial to repeat the sequencing from a non-hematopoietic tissue (e.g. fibroblast).

Test Information

Test Method

DNA extraction (if applicable) and ultrasonic fragmentation; targeted capture of the coding regions and intron/exon boundaries of protein coding RefSeq genes using the Agilent Clinical Research Exome kit; next generation sequencing (NGS) on an Illumina HiSeq 2500 instrument; alignment to the human reference genome (GRCh37/hg19) using the Burrows-Wheeler Aligner (bwa); variant calling using GATK; Sanger sequencing to confirm low quality and/or complex indel variants related to the specified phenotype(s); Review of sequence data for the specified genes by multiple staff members; Variant classification following ACMG criteria (if applicable). Bioinformatic analysis was performed using DDL pipeline DDL.CRExome.v1.2018_04_18.

Clinical Utility

Discrimination of genetic causes of short telomere disorders; identification of causative mutations in known or highly suspicious cases; facilitation of targeted testing of relatives of probands and/or predictive or prenatal testing.

Clinical Sensitivity

Variants in telomerase and telomere maintenance genes manifest in a number of clinical presentations that span infancy to adulthood. Testing telomere length by flow cytometry and FISH can functionally identify some of these patients and may also predictive of the severity of disease PMID 21436073. Approximately, 30% of patients with familial forms of pulmonary fibrosis and telomere-related lung disease carry variants in telomerase and telomere maintenance PMID 25539146. In sporadic cases of idiopathic pulmonary fibrosis, an estimated 5% of patients carry a variant. For unselected patients with idiopathic pulmonary fibrosis (i.e. a mix of familial and sporadic disease) approximately 10% carry germline variants in the common telomere maintenance genes PMID 28099038. For patients with familial clustering of bone marrow failure and idiopathic pulmonary fibrosis, approximately 80% carry variants in telomere maintenance genes PMID 21436073. Variants in telomere-related genes are likely the most common cause of inherited forms of bone marrow failure PMID 29146883. Telomere-mediated disease may also more rarely manifest as classic dyskeratosis congenita, Hoyeraal-Hreidarsson syndrome or other more rare phenotypes as aforementioned where the yield of identifying the short telomere defect by flowFISH (link) is high and for identifying a mutation up to 80%.

Telomere length testing by flowFISH is offered through the Johns Hopkins Molecular Diagnostics Laboratory.

Johns Hopkins Telomere Clinic

Analytic Sensitivity

>99% for single nucleotide and >92% for small insertion/deletion variants for the nucleotides evaluated. Lower limit of detection: Single nucleotide variants: 25% allele frequency (>96% sensitivity), Small insertion/deletion variants: 50% allele frequency (>94% sensitivity). This test is not validated to identify deletions/insertions of greater than 20bp, copy number changes, nucleotide repeat expansions, mitochondrial DNA variants or mosaicism. Disease-associated variants in regions that are not captured and/or sufficiently sequenced will not be detected by this assay.

Other testing relevant to the valuation of inherited pulmonary fibrosis: PulmZoom

Sample Requirements

3-6ml whole blood in EDTA (purple topped) tubes
Saliva collected in an appropriate collection device (Oragene®-DNA 500 or 600 device)
DNA extracted from fibroblast or lymphocyte cell line (must be extracted in a CLIA-certified laboratory)

Turn Around Time

Approximately 6-8 weeks

Fee and CPT Codes

Exome Panel: $2915
CPT Code: 81479
*If you are a provider outside of Johns Hopkins we are only accepting institutional billing