Chromosomal Abnormalities

Autosomal Disorders AUTOSOMAL & SEX CHROMOSOMAL DISORDERS

• Cytogenetics- study of chromosomes and their abnormalities • Abnormalities of autosomes: – Alteration in number (Aneuploidy) – Alteration in structure • • • • •

Ring

Deletion Translocation Formation of ring chromosome Shift Inversion

ALTERATION IN NUMBER

ALTERATION IN NUMBER

ALTERATIONIN STRUCTURE

ALTERATIONIN STRUCTURE

Insertion

Translocation

Repetitions

Autosomal Disorders

Down’s syndrome (Trisomy 21)

• A. Alteration in number (Aneuploidy)

• Mental retardation • Abnormal fascies (epicanthal folds, broad tongue, widely spaced eyes, upturned snub nose) • Increased frequency of congenital heart disease (ASD/VSD and PDA) • Simian crease; change in dermal ridge patterns of hands and feet • Associated with late maternal age

– 1. Down’s syndrome Trisomy 21 1.5/1000 – 2. Pataus syndrome Trisomy 13 .1/1000 – 3. Edwards syndrome Trisomy 18 .2/1000

• B. Alteration in structure – 1. Cri-du-chat syndrome Deletion of chr.5 – 2. Wolf’s syndrome Deletion of chr.4

Edwards syndrome (Trisomy 18) • Extra chromosome 18 • Poorly developed lower jaw, abnormal ears (fawnlike), triangular face, • Rocker botton feet & hammertoe (hallux short & dorsiflex) • Flexion deformities of wrists and crossed over fingers • Severe congenital heart disease

Pataus syndrome Trisomy 13 • Extra chromosome 13 • Holoprosencephalygrossly abnormal face and a poorly developed brain • Severely mentally retarded • Early mortality • “Rocker bottonfeet” (convex soles & protruding heels)

Autosomal Disorders Cri-du-chat syndrome • Deletion of short arm (p) of chromosome 5 • Peculiar cry (meowing of a cat) due to softening of larynx • Hypertonicity and peculiar fascies • Mental retardation • rounded facies (moonlike ) due to microcephaly • Can reach adulthood

Sex Chromosome Disorders • Turner’s Syndrome XO .4/1000 females • Klinefelter’s Syndrome XXY 1.2/1000 females • Triple X female XXX .8/1000 females • Double Y Male XYY 1/1000 females

Turner’s Syndrome MonosomyX Short stature Webbingof neck Shield chest Bilateral lymphedema of feet • Chromatinnegative • Absent Barr body • • • • •

Autosomal Disorders-Deletion of chr.4 (Wolf’s Syndrome) • Deletion of short arm of chr.4 • Facial asymmetry, micrognathia • Mental retardation • Hypotonicity • Hypospadias • Seizures

Non-disjunction of Sex Chromosomes • Failure of sex chromosomes to separate during cell division

Turner’s Syndrome

Turner’s Syndrome ( Monosomy X )

Klinefelter’s Syndrome • • • • •

Klinefelter’s syndrome

Triple X syndrome • Maybe associated with subnormal intelligence • Suboptimal fertility • Delayed menarche or premature ovarian failure

Testicular feminization syndrome Androgen insensitivity syndrome Gynecomastia Hyalinization of seminiferous tubules Infertility

Klinefelter’s Syndrome ( 47XXY )

Trisomy X

XYY syndrome • Increased tendency to psychiatric problems • Antisocial behavior

XYY syndrome

46 XYY