biology

Severe achondroplasia with developmental delay and acanthosis nigricans

Severe achondroplasia with developmental delay and acanthosis nigricans is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Severe achondroplasia with developmental delay and acanthosis nigricans rather than just read about it. In short: Severe achondroplasia with developmental delay and acanthosis nigricans (SADDAN) is a very rare genetic disorder. This disorder is one that affects bone growth and is characterized by skeletal, brain, and skin abnormalities.

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Reference excerpt

Severe achondroplasia with developmental delay and acanthosis nigricans (SADDAN) is a very rare genetic disorder. This disorder is one that affects bone growth and is characterized by skeletal, brain, and skin abnormalities. Those affected by the disorder are severely short in height and commonly possess shorter arms and legs. In addition, the bones of the legs are often bowed and the affected have smaller chests with shorter rib bones, along with curved collarbones. Other symptoms of the disorder include broad fingers and extra folds of skin on the arms and legs. Developmentally, many individuals who suffer from the disorder show a higher level in delays and disability. Seizures are also common due to structural abnormalities of the brain. Those affected may also suffer with apnea, the slowing or loss of breath for short periods of time. Many of the features of SADDAN are similar to those seen in other skeletal disorders, specifically achondroplasia and thanatophoric dysplasia. Achondroplasia is a form of short-limbed dwarfism. This type of dwarfism is caused by the inability of the cartilage of the skeleton to ossify and turn to bone. Acanthosis nigricans is a skin condition in which areas of the skin is of a dark and velvety discoloration, often seen in the body folds and creases such as the armpits, groin, and neck. Within those affected by SADDAN, acanthosis nigricans develops early on, usually in infancy or early childhood.

Genetic A Lys650Met missense mutation of the FGFR3 gene is what causes SADDAN. This gene codes for the instructions of a protein that is integral in the development and maintenance of bone and brain tissue. Mutations of this gene cause the resultant protein to be constantly activated, causing many characteristics of this disorder. SADDAN is an autosomal dominant genetic disorder. Autosomal means that the gene responsible for the mutation and disorder is found on a non-sex chromosome (autosome) and that either the mother or father can pass on the gene, while dominant means that only one copy of the gene is required for the individual to have the disorder. This genetic disorder is extremely rare. While the disorder can be genetically inherited, no instances of inheritance have been recorded as of yet. Rather, of the few cases documented, the individual affected by the disorder is affected as a product of a random mutation, also called a de novo mutation, of the FGFR3 gene only, not by inheritance of the mutated gene.

Diagnosis Medical diagnosis is required. Clinical tests can be performed, as well as genetic testing. The available genetic tests include: Sequence analysis of the entire coding region

Severe achondroplasia with developmental delay and acanthosis nigricans (SADDAN) - Sanger Sequencing: Diagnosis, Mutation Confirmation, Pre-symptomatic, Risk Assessment, Screening Craniosynostosis: Diagnosis Invitae FGFR3-Related Disorders Test: Pre-symptomatic, Diagnosis, Therapeutic management Mutation scanning of select exons

Skeletal Dysplasia Panel: Diagnosis, Prognostic Sequence analysis of select exons

Severe Achondroplasia with Developmental Delay and Acanthosis Nigricans (SADDAN, FGFR3): Diagnosis, Mutation Confirmation, Risk Assessment Severe Achondroplasia, Developmental Delay, Acanthosis Nigricans: Diagnosis, Mutation Confirmation Deletion/duplication analysis

Invitae FGFR3-Related Disorders Test: Pre-symptomatic, Diagnosis, Therapeutic management

Management Life with SADDAN is manageable, although therapy, surgery, and lifelong doctor surveillance may be required.

References

Bellus GA, Bamshad MJ, Przylepa KA, Dorst J, Lee RR, Hurko O, Jabs EW, Curry CJ, Wilcox WR, Lachman RS, Rimoin DL, Francomano CA (1999). "Severe achondroplasia with developmental delay and acanthosis nigricans (SADDAN): phenotypic analysis of a new skeletal dysplasia caused by a Lys650Met mutation in fibroblast growth factor receptor 3". Am J Med Genet. 85 (1): 53–65. doi:10.1002/(SICI)1096-8628(19990702)85:1<53::AID-AJMG10>3.0.CO;2-F. PMID 10377013. Cohen MM Jr (2002). "Some chondrodysplasias with short limbs: molecular perspectives". Am J Med Genet. 112 (3): 304–13. doi:10.1002/ajmg.10780. PMID 12357475. Vajo Z, Francomano CA, Wilkin DJ (2000). "The molecular and genetic basis of fibroblast growth factor receptor 3 disorders: the achondroplasia family of skeletal dysplasias, Muenke craniosynostosis, and Crouzon syndrome with acanthosis nigricans". Endocr Rev. 21 (1): 23–39. doi:10.1210/edrv.21.1.0387. PMID 10696568.

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Illustrations

Worked examples

Example 1 — a first encounter with Severe achondroplasia with developmental delay and acanthosis nigricans

Start with the simplest possible case. Write down what Severe achondroplasia with developmental delay and acanthosis nigricans claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Severe achondroplasia with developmental delay and acanthosis nigricans before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Severe achondroplasia with developmental delay and acanthosis nigricans ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Severe achondroplasia with developmental delay and acanthosis nigricans

In research: Severe achondroplasia with developmental delay and acanthosis nigricans appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Severe achondroplasia with developmental delay and acanthosis nigricans in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Severe achondroplasia with developmental delay and acanthosis nigricans is common in secondary-school and first-year university syllabi. It links to neighbouring topics Genetic diseases and disorders, Rare diseases, so understanding it makes those chapters shorter.
In everyday life: Look for Severe achondroplasia with developmental delay and acanthosis nigricans outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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