Metabolic Bone Disorders

Question 1

What is renal osteodystrophy?

Answer 1

Bone mineralization defect secondary to electrolyte and endocrine dysfunction

Question 2

What is the mechanism behind renal osteodystrophy?

Answer 2

Glomerular damage = phosphate retention = hyperparathyroidism
Tubular damage = reduction in 1,25 (OH)2 D3 synthesis

Question 3

What are Looser’s zones?

Answer 3

Pseudofractures/milkmans fractures

Lucencies with sclerotic borders transversing partway across bone

Question 4

Definitions of Rickets?

Answer 4

Defect in mineralization of osteoid matrix secondary to inadequate calcium and phosphate with failure of calcification in zone of provisional calcification

Question 5

What are the 3 types of Rickets

Answer 5

1. Vit D deficient
2. Vit D dependant
3. Vit D resistant (Familial/ Hypophosphatemic)

Question 6

What is the pathogenesis of Familial/hypophosphatemic/ vit d resistant rickets?

Answer 6

Renal phosphate wasting - inability to resorb

Question 7

What are the inheritance patterns of FR?

Answer 7

1. X linked dominant - MAIN
2. Autsomal dominant
3. Autosomal recessive

Question 8

What gene is mutated and effect in x linked dominant FR?

Answer 8

PHEX

Increases FGF 23

Question 9

What are the two types of Vit D dependant rickets?

RARE AND SEVERE

Answer 9

Type 1 - defect of 1 alpha hydroxylase (ENZYME)
Type 2 - end organ resistance to 1,25 vit d (RECEPTORS)
Like type 1/ type 2 diabetes

Question 10

What is the pathogenesis of vit D def?

Answer 10

Decreased intake - Nutritional/ No sunlight

Decreased absorption - Malabsorption

Question 11

Characteristic lab finding in vit D resistant rickets?

Answer 11

Normal Vit D levels

Question 12

Characteristic lab finding in Vit D def

Answer 12

Low Vit D levels

Low ca/po4

Question 13

Characteristic lab finding in type 1 vit D dependant?

Answer 13

1. V Low Calcitriol levels

Question 14

Characteristic lab finding in type 2 vit D dependant?

Answer 14

2. V High Calcitriol levels

Question 15

What is the inheritance pattern of hypophosphotasia?

Answer 15

Autosomal recessive

Question 16

What is the main path behind hypophosphotasia?

Answer 16

Mutation in TNSALP

ALP impairment

Question 17

What are the bloods required for investigation of rickets/ metabolic bone disease?

Answer 17

Ca
Po4
ALP
25 vit D
Calcitriol
PTH
\+- Alb

Question 18

Treatement of Vit D resistant

Answer 18

HIGH vit D/ Calcitriol

Phosphate replacement

Question 19

What are the genetic inheritance patterns for metabolic bone disease?

Answer 19

X linked Dom in Familial

ALL the rest = AR

Question 20

Rickets with a closed physis =

Answer 20

Osteomalacia