Down syndrome is a chromosomal condition affecting approximately one in every 700 live births, making it one of the most common genetic syndromes. It arises from an extra full or partial copy of chromosome 21, also known as Trisomy 21, which alters the course of development and causes the characteristics associated with Down syndrome. While there's no exact explanation for why this extra chromosome develops, a higher maternal age is one known factor that places a developing fetus at higher risk for chromosomal anomalies, including Down syndrome. This article delves into the physical characteristics associated with Down syndrome, particularly focusing on facial features and the use of image analysis for detection, while also providing a comprehensive overview of the condition.
In every cell in the human body, there is a nucleus where genetic material is stored in genes. Genes, grouped along rod-like structures called chromosomes, carry the codes responsible for inherited traits. Typically, each cell nucleus contains 23 pairs of chromosomes, half inherited from each parent. Down syndrome occurs when an individual has a full or partial extra copy of chromosome 21, leading to altered development and associated characteristics.
Down syndrome is usually caused by an error in cell division called "nondisjunction," resulting in an embryo with three copies of chromosome 21 instead of the usual two. Prior to or at conception, a pair of 21st chromosomes in either the sperm or the egg fails to separate. As the embryo develops, the extra chromosome is replicated in every cell of the body.
There are three types of Down syndrome:
Individuals with Down syndrome often share certain physical traits, though the degree to which these traits are expressed varies. Some of the common physical characteristics include:
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Babies with Down syndrome tend to feel "floppy" when picked up because low muscle tone is a common physical trait.
The unique facial features of Down syndrome are well known. As the main contribution, a compact geometric descriptor is used to extract facial features from the images. Certain facial features are typically associated in people with Down syndrome.
A geometric descriptor is built from the detected facial landmarks. The geometric representation uses 13 2-D facial fiducial points: two points for the middle of the eyebrows (P1 and P2), one point for the glabella (P3), four points for the inner and outer corner of the eyes (P4, P5, P7, and P8), one point for the root of the nose (P6), two points for the alars sidewalls (P10 and P11), one point for the supratip (P9), one point for the columella (P12), two points for the mouth corners (P14 and P15), and two points for the top of the upper lip and bottom of the lower lip (P13 and P16).
Fourteen distances are extracted from the mentioned 16 points. These distances are normalized to the face width to ensure the features are scale invariant. The nine distances d1, d2, d3, d6, d8, d10, d11, d12, and d14 represent the average values of the two mirrored distances on the left and right sides of the face.
For Down syndrome recognition, it is important to consider the intercanthal distance d4, that is, the distance between the inner corners of the eyes. People with Down syndrome often present telecanthus, meaning an increasing of the intercanthal distance. Another common characteristic is the occurrence of small palpebral fissures, which is the space between the lateral and medial canthus of the eyes. This feature is captured by distance d3. Individuals with Down syndrome frequently present the symptom of flattened nose. Distances d5 to d8 represent this characteristic.
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The proposed methodology for recognition of Down syndrome in face images is composed of four main stages: (i) facial detection, (ii) feature extraction, (iii) feature reduction, and (iv) classification.
PCA is a known technique used to transform the original data into a lower dimensional feature descriptor. New orthogonal bases are obtained by solving the eigenvalue problem through training samples. The combination of PCA and LDA takes advantages of both techniques, that is, data dimensionality reduction by projecting the data onto the eigenface space followed by LDA to perform class separability.
Two different classifiers are evaluated in our experiments, SVM and K-NN. Our methodology is validated through a k-fold cross-validation protocol, that is, the original set of samples is randomly partitioned into k equal sized subsets.
Individuals with Down syndrome possess varying degrees of cognitive delays, typically ranging from mild to moderate. They may also experience speech and language development delays, and speech may be difficult to understand.
Beyond cognitive aspects, individuals with Down syndrome have an increased risk of developing several medical conditions, including:
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Screening for Down syndrome, or for an unborn infant’s risk for developing Down syndrome, is now a standardized part of prenatal care in many countries. This can take place as early as the tenth week of pregnancy, with NIPT testing. Other options for more invasive forms of testing, such as amniocentesis, can diagnose Down syndrome in an unborn infant, rather than just identify their risk for it.
There are two categories of tests for Down syndrome that can be performed before a baby is born: screening tests and diagnostic tests. Prenatal screens estimate the chance of the fetus having Down syndrome. These tests do not definitively diagnose Down syndrome; they only provide a probability. Most screening tests involve a blood test and an ultrasound (sonogram). New advanced prenatal screens are now able to detect chromosomal material from the fetus that is circulating in the maternal blood.
The diagnostic procedures available for prenatal diagnosis of Down syndrome are chorionic villus sampling (CVS) and amniocentesis. These procedures, which carry up to a 1% risk of causing a spontaneous termination (miscarriage), are nearly 100% accurate in diagnosing Down syndrome.
Genetic counseling is essential to help them understand their next steps. Genetic counseling can explain what the screening results mean, and what genetic testing to proceed with to confirm or rule out an actual diagnosis of Down syndrome.Genetic counseling for Down syndrome is an important support service for guiding parents-to-be through genetic testing for the syndrome - there are risks to the baby, in terms of a slight risk of miscarriage, with invasive genetic testing for this rare disease, and the role of genetic counseling is to help parents understand these risks, and make a decision that is right for them and their child.If parents receive a confirmed Down syndrome diagnosis for their child, genetic counseling can help them explain and explore their options.
Babies with Down syndrome have unique health needs. The earlier specialist appointments start, the better.
Because babies with Down syndrome will likely experience delayed development and multiple health conditions - from heart disease to ear infections to immune system disorders - they need more specialist appointments throughout their life. The earlier these visits start, the better.
Here are some key considerations for managing the care of a baby with Down syndrome:
Individuals with Down syndrome are becoming increasingly integrated into society and community organizations, such as schools, health care systems, work forces, and social and recreational activities.
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