A child with tall stature, loose joints and detached retina is found to have mutation in type II collagen. Collagen consists of a repeating tripeptides motif where the first amino acid of each tripeptide is same.
Which aminoacid is the recurring aminoacid most likely to be altered in mutation that distort collagen molecule?
What is the defect ?
Explanation
The primary structure of collagen peptides consists of repeating tripeptide with Gly-X-Y motif
The most severe clinical phenotype caused by aminoacid substitution in collagen peptides is those affecting glycine that prevents alpha helix formation.
The child in the present case has a disorder called Stickler skeletal dysplasia syndrome.
Inheritance
Autosomal dominant
Clinical features
The premature degenerative change in weight bearing joints is one of the most consistent features of Sticklers.
Auditory- Sensory neural hearing loss and conductive hearing loss are frequently present in patients with a cleft palate due to fluid in the ear.
Cardiovascular- Mitral valve prolapse is a common finding
Ocular- Retinal degeneration,Cataracts,Myopia, Vitreous degeneration
Musculoskeletal- Bony enlargement of joints, Hypermobility of joints, Kyphosis, scoliosis
Orofacial- flat mid face, flat nasal bridge , high arched palate
Diagnosis
2 methods
First method is using the diagnostic criteria which is a 12 point system which measure abnormalities in the following systems- eyes,ears, bones,face,family history. A score of 5 or more indicates stickler syndrome.
2nd method - by using genetic testing
Treatment
Mainly symptomatic
Special attention is required for eye complications during childhood.
Careful evaluation of breathing and feeding is important
Some infants may have a surgical tracheotomy