Page 210 - Concise Pathology for Exam Preparation ( PDFDrive )

8 Genetic and Paediatric Disorders 195

• Loss of secondary male characters like deep voice, male distribution of pubic hair, beard
and moustache and body hair.
• Gynaecomastia.
• No mental retardation but mean IQ lower than normal.
• One of the most common causes of male infertility.

Hormone Levels

• Increased follicle stimulating hormone (FSH)
• Low testosterone
• Increased estradiol

Microscopic Findings

• Features of testicular atrophy may be seen.
Q. Write briefly on Turner syndrome.

Ans. Complete or partial monosomy of X chromosome resulting in hypogonadism in the
female phenotype.

Incidence

1 in 3000 female births.

Genetic Abnormalities
• Classic type: Entire X chromosome is missing (45, X).
• Structural abnormality of second X chromosome:
• Deletion of small arm and formation of an isochromosome of the long arm—46, X,
i(X) (q10).
• Deletion of a portion of short and long arm, and formation of ring chromosome 46,
X, r(X).
• Deletion of a portion of short or long arm—46, X, del(Xq) or 46, X, del(Xp).
• Mosaic pattern: 45, X/46, XX; 45, X/46, XY; 45, X/47, XXX.

Pathogenesis
• During embryogenesis of ovaries, both X chromosomes are required.
• Normally fetal ovaries develop early in embryogenesis, but absence of second X chro-
mosome leads to an accelerated loss of oocytes against a slow loss in normal female. By
the age of 2 years, all the oocytes are destroyed.
• Ovaries are replaced by fibrous strands, with absence of ova and follicles (streak
ovaries).

Clinical Features
• Infants present with peripheral oedema (lymph stasis) of the dorsae of hands and feet,
and may have a swelling in the nape of neck (cystic hygroma) showing dilated lym-
phatic channels.
• With age, the swelling is replaced by bilateral neck webbing, loose skin on the back of
neck and a low posterior hairline.
• Congenital heart diseases like coarctation of aorta and bicuspid aortic valve are the most
common cause of death.
• Chest is broad and nipples are widely placed.
• Affected individuals may have streak ovaries (it is the single most important cause of
primary amenorrhea), pigmented nevi, cubitus valgus and a short stature.
• Autoimmunity develops leading to hypothyroidism and glucose intolerance may also
be seen.

mebooksfree.com