A Genomics Alliance Beacon at UCSC, see http://ga4gh.org/#/beacon

In collaboration with the Leiden Open Variation Database and Biobase/HGMD.

parameters:
- chromosome: 1 - 22, X, Y or M
- position: 0-based position on chromosome
- dataset: either "lovd" or "hgmd". If not provided, queries both LOVD and HGMD.
- reference: optional. if specified, has to be "GRCh37"
- alternateBases: A,C,T or G. Ignored for HGMD (HGMD gives out only
  positions, not the alleles, these are only on their website)
- format: if "text",  does not return JSON, but just one of the words "true",
      "false" or "overlap".  Easier to parse for simple shell scripts.

For alleles with a "true" reply, you can get more details about a variant from
the source databases:
- dataset lovd: Use the LOVD API to get all info, see chapter 9 of the 
  LOVD manual, http://www.lovd.nl/3.0/docs/LOVD_manual_3.0.pdf
  Or search manually on http://www.lovd.nl/3.0/home
- dataset hgmd: Create an account on http://www.hgmd.cf.ac.uk/ and search
  manually for the variant.

Note that only single-basepair substitutions are available from both databases.
Insertions and deletions might be available with later versions of the Beacon
API.

Examples:
http://genome-asia.ucsc.edu/cgi-bin/hgBeacon/query?dataset=lovd&chromosome=1&position=808921&alternateBases=T&format=text
- returns "true"

http://genome-asia.ucsc.edu/cgi-bin/hgBeacon/query?dataset=lovd&chromosome=1&position=808921&alternateBases=T
- same as before, but as a JSON string

http://genome-asia.ucsc.edu/cgi-bin/hgBeacon/query?dataset=hgmd&chromosome=1&position=985954&alternateBases=T&format=text
- returns "true", for any allele, as HGMD does not share the alleles

http://genome-asia.ucsc.edu/cgi-bin/hgBeacon?dataset=hgmd&chromosome=1&position=2160493&alternateBases=T&format=text
- returns "false", no information at this position

http://genome-asia.ucsc.edu/cgi-bin/hgBeacon?dataset=hgmd&chromosome=1&position=2160493&alternateBases=T
- same as before, but as a JSON string

IP-based throttling:
For each incoming request from an IP address, 75 msecs are added after every
request, and every 15 secs 75 seconds are removed. No delay is imposed when
fewer than 10 seconds have accumulated. This means that about 150 queries
can be sent before a delay of about 10 seconds is imposed for an IP
address. If a delay of 20 seconds has accumulated (=the client is using
multi-threaded requests) the client IP is blocked from further requests
until the delay falls under 20 seconds.