Down Syndrome (Trisomy 21)

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Down syndrome is an anomaly of chromosome 21 that can cause intellectual disability, microcephaly, short stature, and characteristic facies.

Diagnosis is suggested by physical anomalies and abnormal development and confirmed by cytogenetic analysis.

Treatment depends on specific manifestations and anomalies.

Etiology

 

In about 95% of cases, there is an extra whole chromosome 21 (trisomy 21), which is almost always maternally derived. Such people have 47 chromosomes.

 

Down Syndrome Karyotype (Female)

Down Syndrome Karyotype (Female)

Down Syndrome Karyotype (Female)

Biophoto Associates/SCIENCE PHOTO LIBRARY

 

The remaining 5% of people with Down syndrome have the normal count of 46 chromosomes but have an extra chromosome 21 translocated to another chromosome (the resulting abnormal chromosome is still counted only as 1).

 

What is Down Syndrome ?  Down syndrome, named after John Langdon Down, the British physician who described the syndrome ...What is Down Syndrome ?  The problem occurs sometime shortly after fertilization; during the phase when cells are dividi...What is Down Syndrome ?  It is typically associated with a delay in cognitive ability (mental retardation, or MR) and ph...Down Syndrome is also calledTrisomy 21<br />Trisomy21 is a congenital condition that makes an extra copy of the 21st chrom...• The physical features and medical problems associated with Down syndrome can vary widely from child to child. • While so...• The average IQ of young adults with Down syndrome is around 50, whereas young adults without the condition typically hav...• When modern IQ tests are devised, the mean (average) score within an age group is set to 100 • Thus, the intention is th...History • Named after a physician, “John Langdon Down” in 18th century. • Described as Mongoloid child of European parenta...Incidence • Incidence classified according to 3 major ethnic groups •Malay - 1 in 981 •Chinese - 1 in 940 •Indians - 1 in ...Introduction • Down syndrome is an autosomal disorder because it affects chromosome 21, which is an autosome. • Down syndr...Genetics of DS • It is believed that the „amyloid precursor protein gene (App)‟ is the cause of „Down syndrome‟, and it is...92% -94% Trisomy 21 - nondisjunction during fertilisation 2-4% Mosaicism - error in cell division after fertilisation 3-4%...Down Syndrome & Maternal Age A study done in Mysore, India - paternal age and maternal grandmother‟s age influences Down S...Risk factors • Advancing maternal age – usually women of age 35 and above • Mothers who already have one child with Down s...Clinical features • Life expectancy : 55 years (National Down Syndrome Society) • Physical appearances – flat facial profi...- relatively late development of deciduous and permanent teeth as compared with other children - Teeth could appear in a d...Neonatal features • Flat facial profile • Poor Moro reflex • Excessive skin at the nape of neck • Slanted palpebral fissur...4/28/2014 13 Percentage of dysmorphic features and physical abnormalities in „Down syndrome‟ children Dysmorphic features Current study...• Other Health-related problems – Cardiovascular problems • ventricular spetal defect, atrial septal defect, patent ductus...– Sleep problems • Sleep apnoea, other sleep disturbance – Skeletal problems • Flat foot, atlantoaxial subluxation – Visua...Mental Retardation • Almost all DS babies have MR. • Mildly to moderately retarded . • Starts in the first year of life. •...Heart Disease • 50 % of Down Syndrome pts have heart disease • Endocardiac cushion defects • VSD • Secundum ASD • PDA • Te...GI abnormalities • 5% of cases • Duodenal atresia or stenosis, sometimes assoc with annular pancreas in 2.5 % of cases • I...Growth • Weight, length and HC are less in DS • Reduced growth rate • Prevalence of „obesity‟ is greater in DS • Weight is...Eye problems Most common disorders are  Refractory error – 35 to 76 % Strabismus – 25 to 57 percent Nystagmus – 18 to 2...Brush field spots 4/28/2014 22 Hearing loss • Unilateral or bilateral • Conductive, sensorineural or mixed • Otitis media is a frequent problem 4/28/2014...Hematologic disorders • The risk of leukemia is 1 to 1.5 percent. • 65% of newborn have polycythemia resulting in hypoglyc...Endocrine disorder • Thyroid disease – Hypothyroidism occurs more frequently than hyperthyroidism. • Diabetes – The risk o...Reproduction • Women with DS are fertile and may become pregnant. • Nearly all males with DS are infertile. Due to impaire...Skeletal abnormalities • Excessive mobility of atlas (C1) and the axis (C2), may lead to subluxation of the cervical spine...Skin disorder • Palmoplantar hyperkeratosis • Seborreic dermatitis • Fissured tongue • Cutis marmorata • Geographical tong...Diagnosis • Prenatal screening • If no screening – It can be recognized by the characteristic phenotypic features. • Confi...Management 1. Growth – Measurements should be plotted on the appropriate growth chart for children with DS. • This will he...Management (cont.) 4. Eye disorders - An eye exam should be performed in the newborn period or at least before 6 months of...Management ( cont) 7. Hematology – CBC with DLC at birth to evaluate for polycythemia as well as leukemia. 8. Atlanto-axia...Prevention 4/28/2014 33 Counseling • May begin when a prenatal diagnosis is made. • Discuss the wide range of variability in manifestation and pro...Mortality Avarage life span is 25yrs. To 50 yrs. Most likely cause of death is CHD, AAI, Hypothyroidism and Leukemia. I...

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