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Trichothiodystrophy 6, nonphotosensitive(TTD6)

MedGen UID:
934752
Concept ID:
C4310785
Disease or Syndrome
Synonym: TTD6
 
Gene (location): GTF2E2 (8p12)
 
Monarch Initiative: MONDO:0014841
OMIM®: 616943

Definition

Trichothiodystrophy is also associated with recurrent infections, particularly respiratory infections, which can be life-threatening. People with trichothiodystrophy may have abnormal red blood cells, including red blood cells that are smaller than normal. They may also have elevated levels of a type of hemoglobin called A2, which is a protein found in red blood cells. Other features of trichothiodystrophy can include dry, scaly skin (ichthyosis); abnormalities of the fingernails and toenails; clouding of the lens in both eyes from birth (congenital cataracts); poor coordination; and skeletal abnormalities including degeneration of both hips at an early age.

About half of all people with trichothiodystrophy have a photosensitive form of the disorder, which causes them to be extremely sensitive to ultraviolet (UV) rays from sunlight. They develop a severe sunburn after spending just a few minutes in the sun. However, for reasons that are unclear, they do not develop other sun-related problems such as excessive freckling of the skin or an increased risk of skin cancer. Many people with trichothiodystrophy report that they do not sweat.

Intellectual disability and delayed development are common in people with trichothiodystrophy, although most affected individuals are highly social with an outgoing and engaging personality. Some people with trichothiodystrophy have brain abnormalities that can be seen with imaging tests. A common neurological feature of this disorder is impaired myelin production (dysmyelination). Myelin is a fatty substance that insulates nerve cells and promotes the rapid transmission of nerve impulses.

Mothers of children with trichothiodystrophy may experience problems during pregnancy including pregnancy-induced high blood pressure (preeclampsia) and a related condition called HELLP syndrome that can damage the liver. Babies with trichothiodystrophy are at increased risk of premature birth, low birth weight, and slow growth. Most children with trichothiodystrophy have short stature compared to others their age. 

The signs and symptoms of trichothiodystrophy vary widely. Mild cases may involve only the hair. More severe cases also cause delayed development, significant intellectual disability, and recurrent infections; severely affected individuals may survive only into infancy or early childhood.

In people with trichothiodystrophy, tests show that the hair is lacking sulfur-containing proteins that normally gives hair its strength. A cross section of a cut hair shows alternating light and dark banding that has been described as a "tiger tail."

Trichothiodystrophy, commonly called TTD, is a rare inherited condition that affects many parts of the body. The hallmark of this condition is hair that is sparse and easily broken.  [from MedlinePlus Genetics]

Clinical features

From HPO
Coxa valga
MedGen UID:
116080
Concept ID:
C0239137
Finding
Coxa valga is a deformity of the hip in which the angle between the femoral shaft and the femoral neck is increased compared to age-adjusted values (about 150 degrees in newborns gradually reducing to 120-130 degrees in adults).
Pes cavus
MedGen UID:
675590
Concept ID:
C0728829
Congenital Abnormality
An increase in height of the medial longitudinal arch of the foot that does not flatten on weight bearing (i.e., a distinctly hollow form of the sole of the foot when it is bearing weight).
Small for gestational age
MedGen UID:
65920
Concept ID:
C0235991
Finding
Smaller than normal size according to sex and gestational age related norms, defined as a weight below the 10th percentile for the gestational age.
Short stature
MedGen UID:
87607
Concept ID:
C0349588
Finding
A height below that which is expected according to age and gender norms. Although there is no universally accepted definition of short stature, many refer to "short stature" as height more than 2 standard deviations below the mean for age and gender (or below the 3rd percentile for age and gender dependent norms).
Mild intrauterine growth retardation
MedGen UID:
374360
Concept ID:
C1840006
Finding
Intrauterine growth retardation that is at least 2 standard deviations (SD) below average, but not as low as 3 SD, corrected for sex and gestational age.
Bilateral sensorineural hearing impairment
MedGen UID:
96788
Concept ID:
C0452138
Disease or Syndrome
A bilateral form of sensorineural hearing impairment.
Intellectual disability, moderate
MedGen UID:
7680
Concept ID:
C0026351
Mental or Behavioral Dysfunction
Moderate mental retardation is defined as an intelligence quotient (IQ) in the range of 35-49.
Global developmental delay
MedGen UID:
107838
Concept ID:
C0557874
Finding
A delay in the achievement of motor or mental milestones in the domains of development of a child, including motor skills, speech and language, cognitive skills, and social and emotional skills. This term should only be used to describe children younger than five years of age.
Broad-based gait
MedGen UID:
167799
Concept ID:
C0856863
Finding
An abnormal gait pattern in which persons stand and walk with their feet spaced widely apart. This is often a component of cerebellar ataxia.
Motor delay
MedGen UID:
381392
Concept ID:
C1854301
Finding
A type of Developmental delay characterized by a delay in acquiring motor skills.
Long-tract signs
MedGen UID:
356397
Concept ID:
C1865903
Finding
Long-tract signs refer to symptoms that are attributable to the involvement of the long fiber tracts in the spinal cord, which connect the spinal cord to the brain and mediate spinal and motor functions.
Decreased mean corpuscular volume
MedGen UID:
1375398
Concept ID:
C0855790
Finding
A reduction from normal of the mean corpuscular volume, or mean cell volume (MCV) of red blood cells (usually defined as an MCV below 80 femtoliters).
Increased HbA2 hemoglobin
MedGen UID:
893100
Concept ID:
C4073172
Finding
An elevated concentration in the blood of hemoglobin A2 (HbA2), which is a normal variant of hemoglobin A that consists of two alpha and two delta chains and is normally present at low levels in adults but may be increased in beta thalassemia.
Increased bone mineral density
MedGen UID:
10502
Concept ID:
C0029464
Disease or Syndrome
An abnormal increase of bone mineral density, that is, of the amount of matter per cubic centimeter of bones which is often referred to as osteosclerosis. Osteosclerosis can be detected on radiological examination as an increased whiteness (density) of affected bones.
Delayed skeletal maturation
MedGen UID:
108148
Concept ID:
C0541764
Finding
A decreased rate of skeletal maturation. Delayed skeletal maturation can be diagnosed on the basis of an estimation of the bone age from radiographs of specific bones in the human body.
Coronal craniosynostosis
MedGen UID:
344694
Concept ID:
C1856266
Congenital Abnormality
Premature closure of the coronal suture of skull.
Microcephaly
MedGen UID:
1644158
Concept ID:
C4551563
Finding
Head circumference below 2 standard deviations below the mean for age and gender.
Ichthyosis
MedGen UID:
7002
Concept ID:
C0020757
Disease or Syndrome
An abnormality of the skin characterized the presence of excessive amounts of dry surface scales on the skin resulting from an abnormality of keratinization.
Dry skin
MedGen UID:
56250
Concept ID:
C0151908
Sign or Symptom
Skin characterized by the lack of natural or normal moisture.
Brittle hair
MedGen UID:
120480
Concept ID:
C0263490
Disease or Syndrome
Fragile, easily breakable hair, i.e., with reduced tensile strength.
Cutaneous photosensitivity
MedGen UID:
87601
Concept ID:
C0349506
Pathologic Function
An increased sensitivity of the skin to light. Photosensitivity may result in a rash upon exposure to the sun (which is known as photodermatosis). Photosensitivity can be diagnosed by phototests in which light is shone on small areas of skin.
Slow-growing hair
MedGen UID:
371309
Concept ID:
C1832348
Finding
Hair whose growth is slower than normal.
Tiger tail banding
MedGen UID:
892884
Concept ID:
C4073178
Finding
An abnormal appearance of hair under polarizing microscopy (using crossed polarizers), whereby hair shafts show striking alternating bright and dark bands, often referred to as tiger tail banding.
Esotropia
MedGen UID:
4550
Concept ID:
C0014877
Disease or Syndrome
A form of strabismus with one or both eyes turned inward ('crossed') to a relatively severe degree, usually defined as 10 diopters or more.
Nystagmus
MedGen UID:
45166
Concept ID:
C0028738
Disease or Syndrome
Rhythmic, involuntary oscillations of one or both eyes related to abnormality in fixation, conjugate gaze, or vestibular mechanisms.
Microcornea
MedGen UID:
78610
Concept ID:
C0266544
Congenital Abnormality
A congenital abnormality of the cornea in which the cornea and the anterior segment of the eye are smaller than normal. The horizontal diameter of the cornea does not reach 10 mm even in adulthood.

Recent clinical studies

Etiology

Strang-Karlsson S, von Willebrand M, Avela K, Wallgren-Pettersson C
Am J Med Genet A 2021 Jun;185(6):1875-1882. Epub 2021 Mar 17 doi: 10.1002/ajmg.a.62168. PMID: 33729667
Eveno E, Bourre F, Quilliet X, Chevallier-Lagente O, Roza L, Eker AP, Kleijer WJ, Nikaido O, Stefanini M, Hoeijmakers JH
Cancer Res 1995 Oct 1;55(19):4325-32. PMID: 7671243

Diagnosis

Strang-Karlsson S, von Willebrand M, Avela K, Wallgren-Pettersson C
Am J Med Genet A 2021 Jun;185(6):1875-1882. Epub 2021 Mar 17 doi: 10.1002/ajmg.a.62168. PMID: 33729667

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