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Trichothiodystrophy 8, nonphotosensitive(TTD8)

MedGen UID:
1794267
Concept ID:
C5562057
Disease or Syndrome
Synonyms: TRICHOTHIODYSTROPHY 8, NONPHOTOSENSITIVE; TTD8
 
Gene (location): AARS1 (16q22.1)
 
Monarch Initiative: MONDO:0030517
OMIM®: 619691

Definition

Nonphotosensitive trichothiodystrophy-8 (TTD8) is characterized by brittle hair and nails and scaly skin, accompanied by failure to thrive, microcephaly, and neuromotor developmental delay. Hair analysis shows low sulfur content, and skin fibroblasts demonstrate normal DNA repair efficiency after UV irradiation (Botta et al., 2021). For a general phenotypic description and discussion of genetic heterogeneity of trichothiodystrophy, see TTD1 (601675). [from OMIM]

Additional description

From MedlinePlus Genetics
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.   https://medlineplus.gov/genetics/condition/trichothiodystrophy

Clinical features

From HPO
Ankle clonus
MedGen UID:
68672
Concept ID:
C0238651
Finding
Clonus is an involuntary tendon reflex that causes repeated flexion and extension of the foot. Ankle clonus is tested by rapidly flexing the foot upward.
Protruding ear
MedGen UID:
343309
Concept ID:
C1855285
Finding
Angle formed by the plane of the ear and the mastoid bone greater than the 97th centile for age (objective); or, outer edge of the helix more than 2 cm from the mastoid at the point of maximum distance (objective).
Spastic diplegia
MedGen UID:
44181
Concept ID:
C0023882
Disease or Syndrome
Spasticity (neuromuscular hypertonia) primarily in the muscles of the legs, hips, and pelvis.
Spasticity
MedGen UID:
7753
Concept ID:
C0026838
Sign or Symptom
A motor disorder characterized by a velocity-dependent increase in tonic stretch reflexes with increased muscle tone, exaggerated (hyperexcitable) tendon reflexes.
Babinski sign
MedGen UID:
19708
Concept ID:
C0034935
Finding
Upturning of the big toe (and sometimes fanning of the other toes) in response to stimulation of the sole of the foot. If the Babinski sign is present it can indicate damage to the corticospinal tract.
Areflexia
MedGen UID:
115943
Concept ID:
C0234146
Finding
Absence of neurologic reflexes such as the knee-jerk reaction.
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.
Head titubation
MedGen UID:
299071
Concept ID:
C1608410
Sign or Symptom
A head tremor of moderate speed (3 to 4 Hz) in the anterior-posterior direction.
Delayed CNS myelination
MedGen UID:
867393
Concept ID:
C4021758
Anatomical Abnormality
Delayed myelination in the central nervous system.
Craniofacial dystonia
MedGen UID:
868612
Concept ID:
C4023011
Disease or Syndrome
A form of focal dystonia affecting the face and especially the jaw that is induced by the act of speaking. It is an involuntary contraction of the masticatory muscles, resulting in dysarthria or dysphagia.
Retrognathia
MedGen UID:
19766
Concept ID:
C0035353
Congenital Abnormality
An abnormality in which the mandible is mislocalised posteriorly.
Eczematoid dermatitis
MedGen UID:
3968
Concept ID:
C0013595
Disease or Syndrome
Eczema is a form of dermatitis that is characterized by scaly, pruritic, erythematous lesions located on flexural surfaces.
Prominent nose
MedGen UID:
98423
Concept ID:
C0426415
Finding
Distance between subnasale and pronasale more than two standard deviations above the mean, or alternatively, an apparently increased anterior protrusion of the nasal tip.
Sparse eyebrow
MedGen UID:
371332
Concept ID:
C1832446
Finding
Decreased density/number of eyebrow hairs.
Infra-orbital crease
MedGen UID:
347408
Concept ID:
C1857280
Finding
Skin crease extending from below the inner canthus laterally along the malar process of the maxilla and zygoma.
Long philtrum
MedGen UID:
351278
Concept ID:
C1865014
Finding
Distance between nasal base and midline upper lip vermilion border more than 2 SD above the mean. Alternatively, an apparently increased distance between nasal base and midline upper lip vermilion border.
Thin upper lip vermilion
MedGen UID:
355352
Concept ID:
C1865017
Finding
Height of the vermilion of the upper lip in the midline more than 2 SD below the mean. Alternatively, an apparently reduced height of the vermilion of the upper lip in the frontal view (subjective).
Cutis laxa
MedGen UID:
8206
Concept ID:
C0010495
Disease or Syndrome
Wrinkled, redundant, inelastic and sagging skin.
Trichorrhexis nodosa
MedGen UID:
82668
Concept ID:
C0263485
Disease or Syndrome
Trichorrhexis nodosa is the formation of nodes along the hair shaft through which breakage readily occurs. It is thus a focal defect in the hair fiber that is characterized by thickening or weak points (nodes) that cause the hair to break off easily. The result is defective, abnormally fragile hair.
Wooly hair
MedGen UID:
87469
Concept ID:
C0343073
Finding
The term wooly hair refers to an abnormal variant of hair that is fine, with tightly coiled curls, and often hypopigmented. Optical microscopy may reveal the presence of tight spirals and a clear diameter reduction as compared with normal hair. Electron microscopy may show flat, oval hair shafts with reduced transversal diameter.
Sparse hair
MedGen UID:
1790211
Concept ID:
C5551005
Finding
Reduced density of hairs.
Hypotelorism
MedGen UID:
96107
Concept ID:
C0424711
Finding
Interpupillary distance less than 2 SD below the mean (alternatively, the appearance of an decreased interpupillary distance or closely spaced eyes).
Jerky ocular pursuit movements
MedGen UID:
342908
Concept ID:
C1853558
Finding
Esodeviation
MedGen UID:
1641033
Concept ID:
C4551734
Disease or Syndrome
A manifest or latent ocular deviation in which one or both eyes tends to deviate nasally.

Recent clinical studies

Diagnosis

La Serna-Infantes J, Pastor MC, Trubnykova M, Velásquez FC, Sotomayor FV, Barriga HA
Eur J Med Genet 2018 Jul;61(7):388-392. Epub 2018 Feb 5 doi: 10.1016/j.ejmg.2018.02.004. PMID: 29421601

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