DOWN SYNDROME
Down syndrome is a genetic disorder caused by trisomy of chromosome 21. Trisomy 21 occurs in approximately 1 of every 1000 births. Chromosome 21 is an acrocentric chromosome, and trisomy 21 is the most common form of chromosomal trisomy. Trisomy 21 most often occurs as the result of nondisjunction of meiosis, which leads to an extra copy of chromosome 21. Some patients with Down syndrome have a Robertsonian translocation to chromosome 14 or chromosome 22, which are two other acrocentric chromosomes. In these cases, the number of total chromosomes is normal at 46, but the extra chromosome 21 material is translocated to another chromosome. This, in effect, causes an extra chromo- some 21. All or part of chromosome 21 may be trans-located, leading to variations in phenotype. Mosaicism is a rare cause of trisomy 21 in partial cell lines, and the clinical phenotype depends on how early the genetic defect occurred during embryogenesis.
Clinical
Findings: There is no race predilection in Down syndrome and only a slightly
increased incidence in males. Down syndrome has been shown to increase in
incidence with increasing maternal age. The estimated incidence increases to 1
in every 50 births for mothers who are 45 years of age. The clinical
manifestations of Down syndrome are wide reaching and affect every organ
system. Patients with Down syndrome have a decreased life span, although modern
medicine continues to improve these patients’ quality and quantity of life.
Congenital heart disease is one of the most frequent problems and leads to a
plethora of complications and increased morbidity and mortality. Endocardial
cushion defects are the most frequently seen heart abnormality in Down
syndrome. Central nervous system involvement leads to mental and physical
delay. The incidence of childhood leukemia is increased in these patients, the
most frequent type being acute megakaryoblastic leukemia.
The
cutaneous findings in Down syndrome are vast. All patients with Down syndrome have cutaneous
disease, but because of the variation in phenotype, not all have the same
findings. Patients with Down syndrome are more likely to develop atopic
dermatitis, which may be mild or severe. Generalized xerosis is universally
found in Down syndrome. Patients may have an increase from the normal number of
nuchal skin folds in infancy as well as a characteristic facies. Epicanthic
folds and a flat-appearing face with small ears and a flattened nose are
common. Ophthalmological findings include Brushfield spots and strabismus.
Syringomas
are frequently seen in Down syndrome and affect the eyelids and upper cheeks.
Elastosis perforans serpiginosa (EPS) is a rare disease caused by the
transepidermal elimination of fragmented elastic tissue. EPS is seen with a
higher incidence in Down syndrome. The appearance is often that of a thin patch
with a peripheral elevated rim and a polycyclic border or serpentine course.
Acanthosis nigricans was shown to be present in approximately 50% of
individuals with Down syndrome. It can be located in any flexural area, and the
etiology is unknown. The external ear canal has been shown to be narrowed in a
most patients with Down syndrome; this predisposes them to an increased number
of external and middle ear infections. Macroglossia with a scrotal tongue is
frequently encountered. A single transverse palmar crease (simian crease) is
unique to patients with Down syndrome. Shortened metacarpal bones lead to
smaller-than-normal hands, and an extra-wide gap between the first and second
toes is usually prominent.
Alopecia areata is found with increased incidence in Down syndrome.
Treatment: Patients with Down syndrome require a multidisciplinary approach. Cardiac defects tend to cause the most morbidity and mortality, and surgical intervention to correct underlying heart defects is often required. Patients need to be monitored regularly by a pediatrician and then an internist or family physician who is well aware of the complications and care of patients with Down syndrome. The dermatological manifestations are treated as in any other individual, and no special considerations are needed. Xerosis should be managed with excellent daily skin care. It is important for clinicians to recognize the common cutaneous findings in Down syndrome so that they can educate parents and patients alike.
