Factsheet: Fragile X (FXS)



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Regional Autism Team

Factsheet: Down syndrome (DS)

|Origins |English physician John Langdon Down first characterized Down syndrome (DS) as a separate form of disability in 1862. In 1959, Jérôme |

| |Lejeune reported the discovery that Down syndrome resulted from an extra chromosome. However this claim has been disputed, and in 2014 |

| |the Scientific Council of the French Federation of Human Genetics unanimously awarded its Grand Prize to his colleague Marthe Gautier |

| |for this discovery. As a result of this discovery, the condition became known as Trisomy 21. |

|Other names |Trisomy 21 |

|Prevalence |DS is the most common chromosomal cause of intellectual disability occurring in approximately 1/600 births in Ireland. (Globally, as of|

| |2010, Down syndrome occurs in about 1 per 1000 births) |

| | |

| |Autism Spectrum Disorder (ASD) is reported in 7-15% of DS cases, which is 10-25% higher than the general population (DiGuiseppi et al. |

| |2010). ASD is more prevalent in individuals with Down Syndrome who are more cognitively impaired. Higher rates of impaired social |

| |skills have been reported in family members of individuals with DS and ASD in comparison to individuals with DS without ASD (Lowenthal |

| |et al, 2007). |

| | |

| |Although the majority of children with DS do not have a coexisting psychiatric condition, it is estimated that 20-38% have psychiatric |

| |co-morbidity and symptomatolgy including attention problem, conduct disorder, social withdrawal, psychotic behaviours as well as ASD. |

|Features |Social interaction & Behaviours |

| |People with DS are generally known for their cheerful and friendly demeanours without significant impairment in social interactions. |

| |Estimated that rates of disruptive behaviours are between 15-7%. |

| | |

| |Physical Features: |

| |Small chin, slanted eyes, poor muscle tone, a flat nasal bridge, a single crease of the palm, and a protruding tongue, a flat and wide |

| |face, a short neck, excessive joint flexibility, extra space between big toe and second toe, abnormal patterns on the fingertips and |

| |short fingers. Instability of the atlanto-axial joint occurs in approximately 20%.Hip dislocations may occur without trauma in up to a |

| |third of people with DS. |

| |Growth in height is slower resulting in adults who tend to have short stature—the average height for men is 154 cm (5 feet 1 inch) and |

| |for women is 142 cm (4 feet 8 inches). Individuals with DS are at increased risk for obesity as they age. There are growth charts |

| |specifically for children with DS. |

| | |

| |Neurological features: |

| |A level of intellectual disability. Those with mosaic DS typically have IQ scores 10–30 points higher. Many developmental milestones |

| |are delayed with the ability to crawl typically occurring around 8 months rather than 5 month and the ability to walk independently |

| |typically occurring around 21 months rather than |

| | |

| |14 months. Commonly individuals with DS have better language understanding than ability to speak. Children and adults with DS are at |

| |increased risk of epileptic seizures which occur in 5–10% of children and up to 50% of adults. This includes an increased risk of a |

| |specific type of seizure called infantile spasms. Many (15%) who live 40 years or longer develop dementia of the Alzheimer's type. In |

| |those who reach 60 years of age, 50–70% have the disease. |

| | |

| |Senses |

| |Vision problems occur in 38 to 80%. Between 20 and 50% have strabismus. Cataracts occur in 15%, and may be present at birth. |

| |Keratoconus (thin, cone-shaped corneas) and glaucoma (increased eye pressure) are also more common, as are refractive errors requiring |

| |glasses or contacts. Brushfield spots (small white or grayish/brown spots on the outer part of the iris) are present in 38 to 85% of |

| |individuals. |

| |Hearing problems are found in 50–90% of children with DS. This is often the result of otitis media with effusion which occurs in 50–70%|

| |and chronic ear infections which occurs in 40 to 60%. Ear infections often begin in the first year of life and are partly due to poor |

| |Eustachian tube function. Excessive ear wax can also cause hearing loss due to obstruction of the outer ear canal. |

| | |

| |Heart |

| |The rate of congenital heart disease in newborns with DS is around 40%. Of those with heart disease about 80% have an atrioventricular |

| |septal defect or ventricular septal defect. Mitral valve problems become common as people age, even in those without heart problems at |

| |birth. Other problems that may occur include: tetralogy of Fallot and patent ductus arteriosus. |

| | |

| |Endocrine |

| |Problems of the thyroid gland occur in 20–50% of individuals with DS. Low thyroid is the most common form, occurring in almost half of |

| |all individuals. |

|Causes |DS is caused by having three copies of the genes on chromosome 21, rather than the usual two. Those who have one child with DS have |

| |about a 1% risk of having a second child with the syndrome. It can be a full or partial trisomy of chromosome 21, although occasionally|

| |an unbalanced translocation involving chromosome 21 has been identified. DS is caused by a failure of the 21st chromosome to separate |

| |during egg or sperm development. As a result, a sperm or egg cell is produced with an extra copy of chromosome 21; this cell thus has |

| |24 chromosomes. When combined with a normal cell from the other parent, the embryo and baby has 47 chromosomes, with three copies of |

| |chromosome 21. About 88% of cases of trisomy 21 result from non separation of the chromosomes in the mother, 8% from non-separation in |

| |the father, and 3% after the egg and sperm have merged. |

| | |

| |There are 3 main types: |

| |The most common cause (approximately 92–95% of cases) is a complete extra copy of chromosome 21, resulting in trisomy 21. |

| |In 1 to 2.5% of cases, some of the cells in the body are normal and others have trisomy 21, known as mosaic Down syndrome. |

| |Robertsonian translocation, isochromosome, or ring chromosome: These contain additional material from chromosome 21 and occur in |

| |approximately 2.5% of cases. Some children without DS may inherit the translocation and have a higher risk of having children of their |

| |own with DS In this case it is sometimes known as familial DS |

|Diagnosis of DS |When screening tests predict a high risk of DS, a more invasive diagnostic test (amniocentesis or chorionic villus sampling) is needed |

| |to confirm the diagnosis. Amniocentesis and chorionic villus sampling are more reliable; however, they carry an increased risk of |

| |miscarriage of between 0.5 and 1%.There is also an increased risk of limb problems in the offspring due to the procedure. |

| | |

| |Abortion rates |

| |About 92% of pregnancies in the United Kingdom and Europe with a diagnosis of DS are terminated. |

| |After birth |

| |The diagnosis can often be suspected based on the child's physical appearance at birth. An analysis of the child's chromosomes is |

| |needed to confirm the diagnosis and determine if a translocation is present as this may help determine the risk of the child's parents |

| |having further children with DS. |

|Possible shared features between |Typically delays in social and communication in line with cognitive profile. |

|DS & ASD |High level of stereotypic movements in DS. |

| |Children with DS may lack spontaneous seeking to share enjoyment, interest or achievement with other people, but generally more |

| |pronounced in children with ASD |

| |Children with DS may have reduced social or emotional reciprocity |

| |Difficultly initiating and sustaining conversations |

| |Immediate and delayed echolalia |

|Differential Features with ASD |Social Interaction & communication: |

| |From Cohen et. al (2009) research to following features differentiated DS + ASD from DS alone:*isolates self from others (most |

| |significant) |

| |DS alone tend to have: |

| |Appropriate eye contact, facial expression, use of body language and use of gestures. |

| |Tend to communicate for a variety of reasons and can generalise communication across settings |

| |May watch peers, parallel play, develop peer relationship at developmental level |

| |Children with DS generally develop some communication system/will compensate for lack of verbal language with alternative modes of |

| |communication |

| | |

| |Play |

| |DS tend to present with creative play at developmental level. |

| | |

| |Stereotypical behaviours & Repetitive routines: |

| |From Cohen et. Al (2009) research to following features differentiated DS + ASD from DS alone: Presence of odd, bizarre behaviour, |

| |Stereotyped repetitive movements. Moves or rolls head back and forth |

| | |

| |DS tend not to have need for routine or rituals or preoccupation in parts of objects. |

| | |

| |Emotions/behaviour: From Cohen et. al (2009) research to following features differentiated DS + ASD from DS alone: High levels of |

| |anxiety or fear |

| | |

|Recommendations for diagnostic |Diagnosis of coexisting ASD can be challenging due to difficulty differentiating autistic-type behaviours from stereotypical behaviours|

|assessment |and communications and other cognitive impairments associated with ID. |

| | |

| |Individuals with DS are at increased risk for sensory conditions (hearing loss) and motor difficulties (hypotonisa) which may affect |

| |timing and fluidity of social and communicative behaviours. Efforts to correct sensory deficits before screening for an ASD may be |

| |appropriate |

| | |

| |MCHAT and SCQ have been found to be highly sensitive in identifying children with DS and ASD. (DiGuiseppi et al, 2010) |

| | |

| |important to conduct a detailed and fine grained assessment of ASD |

| | |

| |Please note: reported agreement of ADI-R and ADOS is lower that reported by authors in individual with ID. Ability of the ADI-R to |

| |discriminate ASD and Severe ID is somewhat limited (Bildt et al, 2004, Cray 2008) |

|More information and useful |Carter et al (2009). Autistic Spectrum Disorders in Down Syndrome: Further delineation and distinction for other behavioural |

|reading |abnormalities. American Journal of Medical Genetics Part B, 144B:87-94. |

| | |

| |*DiGuiseppi et al, (2010). Screening for Autism Spectrum Disorder in Children with Down Syndrome: Population prevalence and Screening |

| |Test Characterises. Journal of Developmental Behavioural Paediatrics, vol. 31p 181-191. |

| | |

| |*Moss, J., P. Howlin and C. Oliver. (2011) The assessment and presentation of Autism Spectrum Disorders and associated characteristic |

| |in individuals with severe intellectual disability and genetic syndromes. The Oxford Handbook of Intellectual Disability and |

| |Development. |

| | |

| |Reilly, C. (2009). Autism Spectrum Disorders in Down syndrome: A review. Research in Autism Spectrum Disorders. Vol 3. p. 829-839. |

| | |

| |Down Syndrome Ireland: |

* Available in RAST dropbox

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