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Trichothiodystrophy 9, nonphotosensitive(TTD9)

MedGen UID:
1794268
Concept ID:
C5562058
Disease or Syndrome
Synonym: TTD9
 
Gene (location): MARS1 (12q13.3)
 
Monarch Initiative: MONDO:0030518
OMIM®: 619692

Definition

Nonphotosensitive trichothiodystrophy-9 (TTD9) 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, 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. 

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."

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.

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. 

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.

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.  https://medlineplus.gov/genetics/condition/trichothiodystrophy

Clinical features

From HPO
Brachydactyly
MedGen UID:
67454
Concept ID:
C0221357
Congenital Abnormality
Digits that appear disproportionately short compared to the hand/foot. The word brachydactyly is used here to describe a series distinct patterns of shortened digits (brachydactyly types A-E). This is the sense used here.
Cerebellar ataxia
MedGen UID:
849
Concept ID:
C0007758
Disease or Syndrome
Cerebellar ataxia refers to ataxia due to dysfunction of the cerebellum. This causes a variety of elementary neurological deficits including asynergy (lack of coordination between muscles, limbs and joints), dysmetria (lack of ability to judge distances that can lead to under- or overshoot in grasping movements), and dysdiadochokinesia (inability to perform rapid movements requiring antagonizing muscle groups to be switched on and off repeatedly).
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.
Reduced tendon reflexes
MedGen UID:
356648
Concept ID:
C1866934
Finding
Diminution of tendon reflexes, which is an invariable sign of peripheral nerve disease.
Intellectual disability
MedGen UID:
811461
Concept ID:
C3714756
Mental or Behavioral Dysfunction
Intellectual disability, previously referred to as mental retardation, is characterized by subnormal intellectual functioning that occurs during the developmental period. It is defined by an IQ score below 70.
Joint hypermobility
MedGen UID:
336793
Concept ID:
C1844820
Finding
The capability that a joint (or a group of joints) has to move, passively and/or actively, beyond normal limits along physiological axes.
Dental malocclusion
MedGen UID:
9869
Concept ID:
C0024636
Anatomical Abnormality
Dental malocclusion refers to an abnormality of the occlusion, or alignment, of the teeth and the way the upper and lower teeth fit together, resulting in overcrowding of teeth or in abnormal bite patterns.
Epicanthus
MedGen UID:
151862
Concept ID:
C0678230
Congenital Abnormality
Epicanthus is a condition in which a fold of skin stretches from the upper to the lower eyelid, partially covering the inner canthus. Usher (1935) noted that epicanthus is a normal finding in the fetus of all races. Epicanthus also occurs in association with hereditary ptosis (110100).
Sparse eyebrow
MedGen UID:
371332
Concept ID:
C1832446
Finding
Decreased density/number of eyebrow hairs.
High, narrow palate
MedGen UID:
324787
Concept ID:
C1837404
Finding
The presence of a high and narrow palate.
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.
Nail dystrophy
MedGen UID:
66368
Concept ID:
C0221260
Disease or Syndrome
Onychodystrophy (nail dystrophy) refers to nail changes apart from changes of the color (nail dyschromia) and involves partial or complete disruption of the various keratinous layers of the nail plate.
Keratosis pilaris
MedGen UID:
82664
Concept ID:
C0263383
Disease or Syndrome
An anomaly of the hair follicles of the skin that typically presents as small, rough, brown folliculocentric papules distributed over characteristic areas of the skin, particularly the outer-upper arms and thighs.
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.
Sparse hair
MedGen UID:
1790211
Concept ID:
C5551005
Finding
Reduced density of hairs.

Recent clinical studies

Etiology

Morice-Picard F, Cario-André M, Rezvani H, Lacombe D, Sarasin A, Taïeb A
Am J Med Genet A 2009 Sep;149A(9):2020-30. doi: 10.1002/ajmg.a.32902. PMID: 19681155

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