Chromosomal Anomalies

Chromosomal Anomalies

What are chromosomal anomalies? • reflects an abnormality of chromosome number or structure • occur when there is an error in cell division following meiosis or mitosis

Down's syndrome • Down syndrome or trisomy 21 is a genetic disorder caused by the presence of all or part of an extra 21st chromosome • Incidence ~ 1 per 800 to 1,000 births

Physical Findings • Almond shape eyes caused by an epicanthic fold of the eyelid • Shorter limbs • Protuding tongue

Newborns with Down syndrome have an increased risk of: • Congenital heart defects • Gastroesophageal reflux disease • Recurrent ear infection • Thyroid dysfunction or disorder Impairment of cognitive ability

Patau's syndrome • trisomy 13, additional chromosome 13 due to a non-disjunction of chromosomes during meiosis • disrupts the normal course of development, causing the characteristic features of Patau syndrome • the risk increases with increased maternal age at pregnancy • 1 in 5,000 live births

Physical Findings • • • • • • • • •

mental & motor retardation polydactyly (extra digits) microcephaly low-set ears holoprosencephaly (failure of the forebrain to divide properly) heart defects meningomyelocele (a spinal defect) abnormal genitalia overlapping of fingers over thumb

Edward's syndrome • Extra chromosome at chromosome 18 - usually occurs before conception Rate of occurrence is ~ – 1:3000 conceptions – 1:6000 live births, as 50% of those diagnosed prenatally with the condition will not survive the prenatal period

• Physical findings are similar to that of Patau’s Syndrome

Cri du chat • is a rare genetic disorder due to a missing portion of chromosome 5 • The infant sounds just like a meowing kitten, due to problems with the larynx and nervous system

Findings

• feeding problems because of difficulty swallowing and sucking • low birth weight, hypotonia, microcephaly, growth retardation, a round face with full cheeks, down-slanting palpebral fissures, and cardiac defects (patent ductus arteriosus [PDA], tetralogy of Fallot)

Turner's syndrome • monosomy X • occurs in 1 out of every 2500 female births • only one X chromosome is present and fully functional

Findings • • • • • • • •

Short stature Lymphoedema (swelling) of the hands and feet Broad chest (shield chest) and widely-spaced nipples Low hairline Low-set ears Reproductive sterility Amenorrhea, the absence of a menstrual period Increased weight, obesity

Turner Syndrome

Cri du Chat

Klinefelter's syndrome • Affected males have an extra X sex chromosome (XXY) • abnormal testicular development and reduced fertility • undiagnosed in most affected males