All of the following about Vitamin D metabolism are true except
25–α hydroxylation takes place in liver
1–α hydroxylation takes place in kidney
Daily requirement in the absence of sun–light is 450-6001U/day
Williams syndrome is associated with obesity, mental retardation, precocious puberty
In Williams syndrome there is failure to gain weight (not obesity) and delay in development (not-precocious puberty)

Williams syndrome

Williams syndrome is a rare neurodevelopmental disorder characterized by:


Unusual facial features: Elfin facial appearance, widely spaced teeth, a long philthrum along with a low nasal bridge, an unusually cheerful demeanor and ease with strangers.
Heart defects: Supravalvular aortic stenosis.
Development delay: Mental retardation, failure to gain weight (failure to thrive), low muscle tone.
Transient hypercalcemia


Other features include GI problems (Colic, abdominal pain, diverticulitis), nocturnal enuresis, dental irregularities, hypothyroidism, hyperacussis and photophobia.

Vitamin D 

It occurs mainly in two forms


Vit D3 —> Cholecalciferol - synthesized in skin under the influence of UV rays from 7-dehydrocholesterol.
Vit D2 —) Calciferol - present in irradiatiate food-yeast, fungi, bread.


Activation of Vit D takes place in following manner.