Achondroplasia

Roshni Sonawane
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Achondroplasia - Diagnosis
Antenatal diagnosis: In the antenatal period, the diagnosis is suspected on fetal ultrasound by 3rd trimester. It can be confirmed with DNA testing if parents are affected, as homozygosity can be lethal in the antenatal period or the immediate postnatal period. Serial antenatal ultrasound scans may be useful to monitor the fetal growth in these situations.

Postnatal diagnosis: The distinctive clinical and radiological features support the diagnosis of achondroplasia at birth.

Typical Radiological features include:
• Enlarged skull vault with small skull base
• Short, thick long bones, especially in the proximal aspects
• Flaring and 'cupping' appearance of metaphysis
• Ball and socket or Chevron deformity of metaphysis- (appearance of the
• epiphysis being encompassed by the two arms of the "V" shaped epiphysis).
• Short hands with Trident pattern (increased distance between the 2nd and 3rd digits)
• Coxa vara and genu varum deformity
• The lumbosacral angle worsens with gradual reduction in the interpedicular distance in lumbar spine
• ‘Vertical' appearance of squared iliac wings
• Horizontal acetabulum
• and narrow sacroiliac notch
• Proximal femoral radiolucency

Genetic tests: A genetic confirmation is only required if there is ambiguity in clinical diagnosis or for genetic counseling. Initially, ‘Targeted mutation analysis’ for the two common mutations is tested. If it is negative and there is a high index of suspicion, ‘Sequence analysis’ can be performed.

1) Other conditions related to FGFR3 mutation: a) Hypochondroplasia (shares the clinical and radiological features of Achondroplasia. The only difference is that it is milder. Molecular testing for the common FGFR3 mutation can assist with definitive diagnosis of Achondroplasia. b) Thanatophoric dysplasia- It is nearly always a lethal disorder. There is severe limb shortening, significant macrocephaly and extreme chest constriction in addition to typical radiological features. c) Homozygous Achondroplasia presents clinically similar to Thanatophoric dysplasia. Radiological features differentiate it from both, heterozygous Achondroplasia as well as Thanatophoric dysplasia.d) Severe Achondroplasia with Developmental Delay and Acanthosis Nigricans (SADDAN). Skeletal abnormalities are as grave as in thanatophoric dysplasia, however it is accompanied by developmental retardation and acanthosis nigricans. Before the diagnosis of developmental retardation, during the early years, SADDAN can be differentiated from achondroplasia and thanatophoric dysplasia only by molecular testing. e)FGFR-related craniosynostosis 2) Other skeletal dysplasias with similar dwarfism: a) Cartilage-hair hypoplasia and b) Pseudoachondroplasia.


References
Achondroplasia Achondroplasia 04/04/2016
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