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Joubert syndrome 2(JBTS2)

MedGen UID:
334114
Concept ID:
C1842577
Disease or Syndrome
Synonyms: Cerebellooculorenal syndrome 2; JBTS2; Joubert Syndrome and Related Disorders; TMEM216-Related Joubert Syndrome
Modes of inheritance:
Heterogeneous
MedGen UID:
67020
Concept ID:
C0242960
Organism Attribute
Source: HPO
The production of the same or similar phenotypes (observed biochemical, physiological, and morphological characteristics of a person determined by his/her genotype) by different genetic mechanisms. There are two types: (1) allelic heterogeneity - when different alleles at a locus can produce variable expression of a condition; and (2) locus heterogeneity - the term used to describe disease in which mutations at different loci can produce the same disease phenotype.
Autosomal recessive inheritance
MedGen UID:
141025
Concept ID:
C0441748
Intellectual Product
Source: HPO
A mode of inheritance that is observed for traits related to a gene encoded on one of the autosomes (i.e., the human chromosomes 1-22) in which a trait manifests in homozygotes. In the context of medical genetics, autosomal recessive disorders manifest in homozygotes (with two copies of the mutant allele) or compound heterozygotes (whereby each copy of a gene has a distinct mutant allele).
 
Gene (location): TMEM216 (11q12.2)
OMIM®: 608091

Disease characteristics

Excerpted from the GeneReview: Joubert Syndrome and Related Disorders
Classic Joubert syndrome is characterized by three primary findings: A distinctive cerebellar and brain stem malformation called the molar tooth sign (MTS). Hypotonia. Developmental delays. Often these findings are accompanied by episodic tachypnea or apnea and/or atypical eye movements. In general, the breathing abnormalities improve with age, truncal ataxia develops over time, and acquisition of gross motor milestones is delayed. Cognitive abilities are variable, ranging from severe intellectual disability to normal. The designation Joubert syndrome and related disorders (JSRD) is used to describe individuals with JS who have additional findings including retinal dystrophy, renal disease, ocular colobomas, occipital encephalocele, hepatic fibrosis, polydactyly, oral hamartomas, and endocrine abnormalities. Both intra- and interfamilial variation are seen. [from GeneReviews]
Authors:
Melissa Parisi  |  Ian Glass   view full author information

Additional descriptions

From OMIM
Joubert syndrome is a genetically heterogeneous autosomal recessive disorder characterized by a specific hindbrain malformation, which is referred to as the 'molar tooth sign' (MTS) on brain MRI, hypotonia, developmental delay, oculomotor apraxia, and breathing abnormalities. The complex brainstem malformation consists of cerebellar vermian hypoplasia/aplasia, thickened and reoriented superior cerebellar peduncles, and an abnormally large interpeduncular fossa, giving the appearance of a molar tooth on transaxial slices (Maria et al., 1997). Additional features sometimes associated with Joubert syndrome include retinal anomalies, polydactyly, hepatic fibrosis, and renal disease. These related disorders are often referred to as 'cerebellooculorenal syndromes' (CORSs) (Chance et al., 1999; Satran et al., 1999).  http://www.omim.org/entry/608091
From GHR
Joubert syndrome is a disorder that affects many parts of the body. The signs and symptoms of this condition vary among affected individuals, even among members of the same family.The hallmark feature of Joubert syndrome is a brain abnormality called the molar tooth sign, which can be seen on brain imaging studies such as magnetic resonance imaging (MRI). This sign results from the abnormal development of regions near the back of the brain called the cerebellar vermis and the brainstem. The molar tooth sign got its name because the characteristic brain abnormalities resemble the cross-section of a molar tooth when seen on an MRI.Most infants with Joubert syndrome have weak muscle tone (hypotonia) in infancy, which evolves into difficulty coordinating movements (ataxia) in early childhood. Other characteristic features of the condition include episodes of unusually fast or slow breathing in infancy and abnormal eye movements. Most affected individuals have delayed development and intellectual disability, which range from mild to severe. Distinctive facial features are also characteristic of Joubert syndrome; these include a broad forehead, arched eyebrows, droopy eyelids (ptosis), widely spaced eyes, low-set ears, and a triangle-shaped mouth.Joubert syndrome can include a broad range of additional signs and symptoms. The condition is sometimes associated with other eye abnormalities (such as retinal dystrophy, which can cause vision loss), kidney disease, liver disease, skeletal abnormalities (such as the presence of extra fingers and toes), and hormone (endocrine) problems. When the characteristic features of Joubert syndrome occur in combination with one or more of these additional signs and symptoms, researchers refer to the condition as "Joubert syndrome and related disorders (JSRD)."  http://ghr.nlm.nih.gov/condition/joubert-syndrome

Clinical features

Esotropia
MedGen UID:
4550
Concept ID:
C0014877
Disease or Syndrome
A form of strabismus with one or both eyes turned inward ('crossed').
Hypertelorism
MedGen UID:
9373
Concept ID:
C0020534
Congenital Abnormality
Although hypertelorism means an excessive distance between any paired organs (e.g., the nipples), the use of the word has come to be confined to ocular hypertelorism. Hypertelorism occurs as an isolated feature and is also a feature of many syndromes, e.g., Opitz G syndrome (145410), Greig cephalopolysyndactyly (175700), and Noonan syndrome (163950) (summary by Cohen et al., 1995).
Microphthalmos
MedGen UID:
10033
Concept ID:
C0026010
Congenital Abnormality
Microphthalmia is an eye abnormality that arises before birth. In this condition, one or both eyeballs are abnormally small. In some affected individuals, the eyeball may appear to be completely missing; however, even in these cases some remaining eye tissue is generally present. Such severe microphthalmia should be distinguished from another condition called anophthalmia, in which no eyeball forms at all. However, the terms anophthalmia and severe microphthalmia are often used interchangeably. Microphthalmia may or may not result in significant vision loss.People with microphthalmia may also have a condition called coloboma. Colobomas are missing pieces of tissue in structures that form the eye. They may appear as notches or gaps in the colored part of the eye called the iris; the retina, which is the specialized light-sensitive tissue that lines the back of the eye; the blood vessel layer under the retina called the choroid; or in the optic nerves, which carry information from the eyes to the brain. Colobomas may be present in one or both eyes and, depending on their size and location, can affect a person's vision.People with microphthalmia may also have other eye abnormalities, including clouding of the lens of the eye (cataract) and a narrowed opening of the eye (narrowed palpebral fissure). Additionally, affected individuals may have an abnormality called microcornea, in which the clear front covering of the eye (cornea) is small and abnormally curved.Between one-third and one-half of affected individuals have microphthalmia as part of a syndrome that affects other organs and tissues in the body. These forms of the condition are described as syndromic. When microphthalmia occurs by itself, it is described as nonsyndromic or isolated.
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.
Visual impairment
MedGen UID:
22663
Concept ID:
C0042798
Finding
Vision considered to be inferior to normal vision as represented by accepted standards of acuity, field of vision, or motility. Low vision generally refers to visual disorders that are caused by diseases that cannot be corrected by refraction (e.g., MACULAR DEGENERATION; RETINITIS PIGMENTOSA; DIABETIC RETINOPATHY, etc.).
Coloboma of optic disc
MedGen UID:
57832
Concept ID:
C0155299
Disease or Syndrome
A cleft of the optic nerve that extends inferiorly.
Retinal coloboma
MedGen UID:
66820
Concept ID:
C0240896
Congenital Abnormality
A notch or cleft of the retina.
Retinal dystrophy
MedGen UID:
208903
Concept ID:
C0854723
Finding
A group of disorders involving predominantly the posterior portion of the ocular fundus, due to degeneration in the sensory layer of the RETINA; RETINAL PIGMENT EPITHELIUM; BRUCH MEMBRANE; CHOROID; or a combination of these tissues.
Impaired smooth pursuit
MedGen UID:
325176
Concept ID:
C1837458
Finding
An impairment of the ability to track objects with the ocular smooth pursuit system, a class of rather slow eye movements that minimizes retinal target motion.
Abnormality of saccadic eye movements
MedGen UID:
374967
Concept ID:
C1842584
Finding
An abnormality of eye movement characterized by impairment of fast (saccadic) eye movements.
Oculomotor apraxia
MedGen UID:
483686
Concept ID:
C3489733
Disease or Syndrome
Ocular motor apraxia is a deficiency in voluntary, horizontal, lateral, fast eye movements (saccades) with retention of slow pursuit movements. The inability to follow objects visually is often compensated by head movements. There may be decreased smooth pursuit, and cancellation of the vestibulo-ocular reflex.
Renal cyst
MedGen UID:
7215
Concept ID:
C0022679
Disease or Syndrome
A fluid filled sac in the kidney.
Kidney dysfunction
MedGen UID:
508816
Concept ID:
C0151746
Pathologic Function
An abnormal functionality of the kidney.
Nephronophthisis
MedGen UID:
146912
Concept ID:
C0687120
Disease or Syndrome
Nephronophthisis is a disorder that affects the kidneys. It is characterized by inflammation and scarring (fibrosis) that impairs kidney function. These abnormalities lead to increased urine production (polyuria), excessive thirst (polydipsia), general weakness, and extreme tiredness (fatigue). In addition, affected individuals develop fluid-filled cysts in the kidneys, usually in an area known as the corticomedullary region. Another feature of nephronophthisis is a shortage of red blood cells, a condition known as anemia.Nephronophthisis eventually leads to end-stage renal disease (ESRD), a life-threatening failure of kidney function that occurs when the kidneys are no longer able to filter fluids and waste products from the body effectively. Nephronophthisis can be classified by the approximate age at which ESRD begins: around age 1 (infantile), around age 13 (juvenile), and around age 19 (adolescent).About 85 percent of all cases of nephronophthisis are isolated, which means they occur without other signs and symptoms. Some people with nephronophthisis have additional features, which can include liver fibrosis, heart abnormalities, or mirror image reversal of the position of one or more organs inside the body (situs inversus).Nephronophthisis can occur as part of separate syndromes that affect other areas of the body; these are often referred to as nephronophthisis-associated ciliopathies. For example, Senior-Løken syndrome is characterized by the combination of nephronophthisis and a breakdown of the light-sensitive tissue at the back of the eye (retinal degeneration); Joubert syndrome affects many parts of the body, causing neurological problems and other features, which can include nephronophthisis.
Hypoplastic male external genitalia
MedGen UID:
338952
Concept ID:
C1852534
Finding
Underdevelopment of part or all of the male external reproductive organs (which include the penis, the scrotum and the urethra).
Deformity of foot
MedGen UID:
8888
Concept ID:
C0016506
Anatomical Abnormality
An abnormality of the skeleton of foot.
Ulnar polydactyly of fingers
MedGen UID:
609221
Concept ID:
C0431904
Congenital Abnormality
Supernumerary digits located at the ulnar side of the hand (that is, on the side with the fifth finger).
Failure to thrive
MedGen UID:
115900
Concept ID:
C0231246
Finding
Failure to thrive (FTT) refers to a child whose physical growth is substantially below the norm.
Low set ears
MedGen UID:
65980
Concept ID:
C0239234
Congenital Abnormality
Upper insertion of the ear to the scalp below an imaginary horizontal line drawn between the inner canthi of the eye and extending posteriorly to the ear.
Cerebellar ataxia
MedGen UID:
849
Concept ID:
C0007758
Sign or Symptom
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- oder overshoot in grasping movements), and dysdiadochokinesia (inability to perform rapid movements requiring antagonizing muscle groups to be switched on and off repeatedly).
Cephalocele
MedGen UID:
4934
Concept ID:
C0014065
Congenital Abnormality
Brain tissue herniation through a congenital or acquired defect in the skull. The majority of congenital encephaloceles occur in the occipital or frontal regions. Clinical features include a protuberant mass that may be pulsatile. The quantity and location of protruding neural tissue determines the type and degree of neurologic deficit. Visual defects, psychomotor developmental delay, and persistent motor deficits frequently occur.
Hydrocephalus
MedGen UID:
9335
Concept ID:
C0020255
Disease or Syndrome
Autosomal recessive nonsyndromic hydrocephalus is characterized by onset in utero of enlarged ventricles due to a disturbance of cerebrospinal fluid accumulation. Affected individuals may have neurologic impairment (summary by Drielsma et al., 2012). Hydrocephalus can also be caused by Arnold-Chiari malformation, atresia of foramen of Magendie, stenosis of aqueduct of Sylvius (307000), toxoplasmosis, hydranencephaly, etc. Furthermore, it develops in infancy or childhood in achondroplasia (100800) and in Hurler disease (607014). Genetic Heterogeneity of Congenital Hydrocephalus See also autosomal recessive HYC2 (615219), caused by mutation in the MPDZ gene (603785) on chromosome 9p. An X-linked form (307000) is caused by mutation in the L1CAM gene on (308840) on chromosome Xq28.
Intellectual functioning disability
MedGen UID:
7544
Concept ID:
C0025362
Mental or Behavioral Dysfunction
Subnormal intellectual functioning which originates during the developmental period. Intellectual disability, previously referred to as mental retardation, has been defined as an IQ score below 70.
Familial aplasia of the vermis
MedGen UID:
98464
Concept ID:
C0431399
Disease or Syndrome
Classic Joubert syndrome is characterized by three primary findings: A distinctive cerebellar and brain stem malformation called the molar tooth sign (MTS). Hypotonia. Developmental delays. Often these findings are accompanied by episodic tachypnea or apnea and/or atypical eye movements. In general, the breathing abnormalities improve with age, truncal ataxia develops over time, and acquisition of gross motor milestones is delayed. Cognitive abilities are variable, ranging from severe intellectual disability to normal. The designation Joubert syndrome and related disorders (JSRD) is used to describe individuals with JS who have additional findings including retinal dystrophy, renal disease, ocular colobomas, occipital encephalocele, hepatic fibrosis, polydactyly, oral hamartomas, and endocrine abnormalities. Both intra- and interfamilial variation are seen.
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.
Abnormality of the corpus callosum
MedGen UID:
334198
Concept ID:
C1842581
Finding
Abnormality of the corpus callosum.
Hypoplasia of the brainstem
MedGen UID:
334226
Concept ID:
C1842688
Finding
Underdevelopment of the brainstem.
Brainstem dysplasia
MedGen UID:
383739
Concept ID:
C1855677
Finding
A developmental structural anomaly of the stalk-like part of the brain that comprises the midbrain (aka mesencephalon), the pons (aka pons Varolii), and the medulla oblongata, and connects the cerebral hemispheres with the cervical spinal cord.
Molar tooth sign on MRI
MedGen UID:
400670
Concept ID:
C1865060
Finding
An abnormal appearance of the midbrain in axial magnetic resonance imaging in which the elongated superior cerebellar peduncles give the midbrain an appearance reminiscent of a molar or wisdom tooth.
Oculomotor apraxia
MedGen UID:
483686
Concept ID:
C3489733
Disease or Syndrome
Ocular motor apraxia is a deficiency in voluntary, horizontal, lateral, fast eye movements (saccades) with retention of slow pursuit movements. The inability to follow objects visually is often compensated by head movements. There may be decreased smooth pursuit, and cancellation of the vestibulo-ocular reflex.
Elongated superior cerebellar peduncle
MedGen UID:
816544
Concept ID:
C3810214
Finding
Increased length of the superior cerebellar peduncle.
Enlarged fossa interpeduncularis
MedGen UID:
866576
Concept ID:
C4020922
Finding
Thickened superior cerebellar peduncle
MedGen UID:
867391
Concept ID:
C4021756
Anatomical Abnormality
Increased width of the superior cerebellar peduncle.
Dysgenesis of the cerebellar vermis
MedGen UID:
871238
Concept ID:
C4025719
Anatomical Abnormality
Defective development of the vermis of cerebellum.
Central sleep apnea syndrome
MedGen UID:
99249
Concept ID:
C0520680
Disease or Syndrome
Sleep apnea resulting from a transient abolition of the central drive to the ventilatory muscles.
Neonatal breathing dysregulation
MedGen UID:
812546
Concept ID:
C3806216
Finding
Episodic tachypnea
MedGen UID:
812548
Concept ID:
C3806218
Finding
Episodes of very rapid breathing.
Muscular hypotonia
MedGen UID:
10133
Concept ID:
C0026827
Finding
A diminution of the skeletal muscle tone marked by a diminished resistance to passive stretching.
Cephalocele
MedGen UID:
4934
Concept ID:
C0014065
Congenital Abnormality
Brain tissue herniation through a congenital or acquired defect in the skull. The majority of congenital encephaloceles occur in the occipital or frontal regions. Clinical features include a protuberant mass that may be pulsatile. The quantity and location of protruding neural tissue determines the type and degree of neurologic deficit. Visual defects, psychomotor developmental delay, and persistent motor deficits frequently occur.
Frontal bossing
MedGen UID:
67453
Concept ID:
C0221354
Congenital Abnormality
Bilateral bulging of the lateral frontal bone prominences with relative sparing of the midline.
Long narrow head
MedGen UID:
65142
Concept ID:
C0221358
Congenital Abnormality
An abnormality of skull shape characterized by a increased anterior-posterior diameter, i.e., an increased antero-posterior dimension of the skull. Cephalic index less than 76%. Alternatively, an apparently increased antero-posterior length of the head compared to width. Often due to premature closure of the sagittal suture.
Ulnar polydactyly of fingers
MedGen UID:
609221
Concept ID:
C0431904
Congenital Abnormality
Supernumerary digits located at the ulnar side of the hand (that is, on the side with the fifth finger).
Macrocephaly
MedGen UID:
745757
Concept ID:
C2243051
Finding
Macrocephaly refers to an abnormally enlarged head inclusive of the scalp, cranial bones, and intracranial contents. Macrocephaly may be due to megalencephaly (true enlargement of the brain parenchyma), and the 2 terms are often used interchangeably in the genetic literature (reviews by Olney, 2007 and Williams et al., 2008). Autosomal recessive macrocephaly/megalencephaly syndrome is characterized by an enlarged cranium apparent at birth or in early childhood. Affected individuals have intellectual disability and may have dysmorphic facial features resulting from the macrocephaly (summary by Alfaiz et al., 2014).
Cephalocele
MedGen UID:
4934
Concept ID:
C0014065
Congenital Abnormality
Brain tissue herniation through a congenital or acquired defect in the skull. The majority of congenital encephaloceles occur in the occipital or frontal regions. Clinical features include a protuberant mass that may be pulsatile. The quantity and location of protruding neural tissue determines the type and degree of neurologic deficit. Visual defects, psychomotor developmental delay, and persistent motor deficits frequently occur.
Hypertelorism
MedGen UID:
9373
Concept ID:
C0020534
Congenital Abnormality
Although hypertelorism means an excessive distance between any paired organs (e.g., the nipples), the use of the word has come to be confined to ocular hypertelorism. Hypertelorism occurs as an isolated feature and is also a feature of many syndromes, e.g., Opitz G syndrome (145410), Greig cephalopolysyndactyly (175700), and Noonan syndrome (163950) (summary by Cohen et al., 1995).
Microphthalmos
MedGen UID:
10033
Concept ID:
C0026010
Congenital Abnormality
Microphthalmia is an eye abnormality that arises before birth. In this condition, one or both eyeballs are abnormally small. In some affected individuals, the eyeball may appear to be completely missing; however, even in these cases some remaining eye tissue is generally present. Such severe microphthalmia should be distinguished from another condition called anophthalmia, in which no eyeball forms at all. However, the terms anophthalmia and severe microphthalmia are often used interchangeably. Microphthalmia may or may not result in significant vision loss.People with microphthalmia may also have a condition called coloboma. Colobomas are missing pieces of tissue in structures that form the eye. They may appear as notches or gaps in the colored part of the eye called the iris; the retina, which is the specialized light-sensitive tissue that lines the back of the eye; the blood vessel layer under the retina called the choroid; or in the optic nerves, which carry information from the eyes to the brain. Colobomas may be present in one or both eyes and, depending on their size and location, can affect a person's vision.People with microphthalmia may also have other eye abnormalities, including clouding of the lens of the eye (cataract) and a narrowed opening of the eye (narrowed palpebral fissure). Additionally, affected individuals may have an abnormality called microcornea, in which the clear front covering of the eye (cornea) is small and abnormally curved.Between one-third and one-half of affected individuals have microphthalmia as part of a syndrome that affects other organs and tissues in the body. These forms of the condition are described as syndromic. When microphthalmia occurs by itself, it is described as nonsyndromic or isolated.
Coloboma of optic disc
MedGen UID:
57832
Concept ID:
C0155299
Disease or Syndrome
A cleft of the optic nerve that extends inferiorly.
Frontal bossing
MedGen UID:
67453
Concept ID:
C0221354
Congenital Abnormality
Bilateral bulging of the lateral frontal bone prominences with relative sparing of the midline.
Long narrow head
MedGen UID:
65142
Concept ID:
C0221358
Congenital Abnormality
An abnormality of skull shape characterized by a increased anterior-posterior diameter, i.e., an increased antero-posterior dimension of the skull. Cephalic index less than 76%. Alternatively, an apparently increased antero-posterior length of the head compared to width. Often due to premature closure of the sagittal suture.
Byzanthine arch palate
MedGen UID:
66814
Concept ID:
C0240635
Congenital Abnormality
Height of the palate more than 2 SD above the mean (objective) or palatal height at the level of the first permanent molar more than twice the height of the teeth (subjective).
Retinal coloboma
MedGen UID:
66820
Concept ID:
C0240896
Congenital Abnormality
A notch or cleft of the retina.
Depressed nasal bridge
MedGen UID:
373112
Concept ID:
C1836542
Finding
Posterior positioning of the nasal root in relation to the overall facial profile for age.
Macrocephaly
MedGen UID:
745757
Concept ID:
C2243051
Finding
Macrocephaly refers to an abnormally enlarged head inclusive of the scalp, cranial bones, and intracranial contents. Macrocephaly may be due to megalencephaly (true enlargement of the brain parenchyma), and the 2 terms are often used interchangeably in the genetic literature (reviews by Olney, 2007 and Williams et al., 2008). Autosomal recessive macrocephaly/megalencephaly syndrome is characterized by an enlarged cranium apparent at birth or in early childhood. Affected individuals have intellectual disability and may have dysmorphic facial features resulting from the macrocephaly (summary by Alfaiz et al., 2014).

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