VITAMIN D DISORDERS

Question 1

The most important source of vitamin D…..

Answer 1

Cutaneous synthesis

Question 2

Natural dietary sources of vitamin D…….

Answer 2

Fish liver oils have a high vitamin D content.

Other good dietary sources include fatty fish and egg yolks.

Most children in industrialized countries receive vitamin D via fortified foods

Question 3

Breast milk has a low vitamin D content, approximately…..

Answer 3

12-60 IU/L.

Question 4

7-dehydrochlesterol to vitamin D3 (3-cholecalciferol) by……

Answer 4

Ultraviolet B (UVB) radiation from the sun

Question 5

25-hydroxlase converts……..

Answer 5

vitamin D into 25-hydroxyvitamin D (25-D),

the most abundant circulating form of vitamin D

Question 6

25-D is the standard method for determining a patient’s vitamin D status why…….,.

Answer 6

Because there is little regulation of this liver hydroxylation step.

Question 7

1α-hydroxylase adds a

Answer 7

second hydroxyl group, resulting in 1,25-D

Question 8

The 1α-hydroxylase is…..regulated by……

Answer 8

Upregulated by PTH and hypophosphatemia and

Inhibited by hyperphosphatemia and 1,25-D

Question 9

Vitamin D deficiency most frequently occurs in infancy why…….

Answer 9

Because of a combination of poor intake and inadequate cutaneous synthesis

Question 10

Lab findings in vit D deficiency rickets….

Answer 10

Hypocalcemia : is a variable finding because the elevated PTH acts to increase the serum calcium concentration.

The hypophosphatemia : is caused by PTH-induced renal losses of phosphate, combined with a decrease in intestinal absorption.

The wide variation in 1,25-D levels : (low, normal, or high) is secondary to the upregulation of renal 1α-hydroxylase caused by concomitant hypophosphatemia and hyperparathyroidism

Question 11

stoss therapy

Answer 11

vitamin D (300,000-600,000 IU) is administered orally (preferred) or intramuscularly as 2-4 doses over 1 day (vitamin D3 is preferred to D2 because of longer half-life of D3).

Question 12

The alternative strategy……for vit D

Answer 12

The alternative strategy is daily vitamin D with a minimum dose of 2,000 IU/day for a minimum of 3 mo

Question 13

Indication for calcitriol iv injection in vit D deficiency..

Answer 13

Transient use of IV or oral 1,25-D (calcitriol) is often helpful in reversing hypocalcemia in the acute phase by providing active vitamin D during the delay as supplemental vitamin D is converted to active vitamin D

Calcitriol doses are typically 0.05 µg/kg/day. IV calcium is initially given as an acute bolus for symptomatic hypocalcemia (20 mg/ kg calcium chloride or 100 mg/kg calcium gluconate)

Question 14

radiologic healing occurring within a few

Answer 14

months

Question 15

children with severe disease can have……prognosis

Answer 15

permanent deformities and short stature

Question 16

Congenital Vitamin D Deficiency…….?

Answer 16

Occurs when there is severe maternal vitamin D deficiency during pregnancy

Question 17

Congenital Vitamin D Deficiency features….

Answer 17

These newborns can have symptomatic hypocalcemia, intrauterine growth retardation, and decreased bone ossification, along with classic rachitic changes

Question 18

Secondary Vitamin D Deficiency…….

Answer 18

vitamin D deficiency can result from inadequate absorption, decreased hydroxylation in the liver, and increased degradation.

Because vitamin D is fat soluble, its absorption may be decreased in patients with a variety of liver and GI diseases, including cholestatic liver disease, defects in bile acid metabolism, cystic fibrosis and other causes of pancreatic dysfunction, celiac disease, and Crohn disease

Question 19

Treatment of vitamin D deficiency attributable to malabsorption requires high doses of

Answer 19

vitamin D.

Because of its better absorption, 25-D (25-50 µg/ day or 5-7 µg/kg/day) is superior to vitamin D

Question 20

Vitamin D–Dependent Rickets, Type 1…..

Answer 20

Children with vitamin D–dependent rickets type 1A,

an autosomal recessive disorder,

have mutations in the gene encoding renal 1α-hydroxylase,

preventing conversion of 25-D into 1,25-D

Question 21

Children with vitamin D–dependent rickets type 1A laboratory findings……

Answer 21

They have normal levels of 25-D but low levels of 1,25-D
Occasionally, 1,25-D levels are at the lower limit of normal, inappropriately low

given the high PTH and low serum phosphorus levels, both of which should increase the activity of renal 1α-hydroxylase and cause elevated levels of 1,25-D

Question 22

Vitamin D–dependent rickets type 1B is secondary to…

Answer 22

A mutation in the gene for a 25-hydroxylase

Patients have low levels of 25-D but normal levels of 1,25-D

Question 23

Vitamin D–dependent rickets type 1A responds to long-term treatment with…………

Answer 23

1,25-D (calcitriol)

Initial doses are 0.25-2 µg/day, and lower doses are used once the rickets has healed

Especially during initial therapy, it is important to ensure adequate intake of calcium

Question 24

Monitoring in patient treated with calcitriol………

Answer 24

Periodic assessment of urinary calcium excretion, with a target of <4 mg/kg/day

Because: Targeting a low-normal calcium concentration and a high-normal PTH level avoids excessive dosing of calcitriol, which can cause hypercalciuria and nephrocalcinosis

Question 25

Vitamin D–dependent rickets type 1B may respond to pharmacologic doses of …..

Answer 25

Vitamin D2 (3,000 U/day) as a result of alternative enzymes with 25-hydroxylase activity or residual activity of the mutant protein

Question 26

Vitamin D–Dependent Rickets, Type 2A…..

Answer 26

Patients with vitamin D–dependent rickets type 2A have mutations in the gene encoding the vitamin D receptor, preventing a normal physiologic response to 1,25-D

Question 27

Levels of 1,25-D are extremely …………… in this autosomal recessive disorder VDDR T2A

Answer 27

Levels of 1,25-D are extremely elevated in this autosomal recessive disorder

Question 28

alopecia areata to alopecia totalis common in which type of VDDR ……

Answer 28

Vitamin D–Dependent Rickets, Type 2A

Question 29

Vitamin D–dependent rickets type 2B appears to result from…….

Answer 29

overexpression of a hormone response element–binding protein that interferes with the actions of 1,25-D.

Alopecia may be present.