Given a question and a context passage, generate the answer having the word or phrase from the context passage. Here, the answer should be a shortest continous span from the passage.

Context: Comet ISON, formally known as C/2012 S1, was a sungrazing comet discovered on 21 September 2012 by Vitali Nevski ( , Vitebsk, Belarus) and Artyom Novichonok ( , Kondopoga, Russia). 
 Question: By whom was Comet ISON discovered?
artyom novichonok

Context: Autosomal-recessive hereditary spastic paraplegias (AR-HSP) consist of a genetically diverse group of neurodegenerative diseases characterised by pyramidal tracts dysfunction. The causative genes for many types of AR-HSP remain elusive. We tried to identify the gene mutation for AR-HSP with cerebellar ataxia and neuropathy. This study included two patients in a Japanese family with their parents who are first cousins. Neurological examination and gene analysis were conducted in the two patients and two normal family members. We undertook genome-wide linkage analysis employing single nucleotide polymorphism arrays using the two patients' DNAs and exome sequencing using one patient's sample. We detected a homozygous missense mutation (c.4189T>G, p.F1397V) in the lysosomal trafficking regulator (LYST) gene, which is described as the causative gene for Chediak-Higashi syndrome (CHS). CHS is a rare autosomal-recessive syndrome characterised by hypopigmentation, severe immune deficiency, a bleeding tendency and progressive neurological dysfunction. This mutation was co-segregated with the disease in the family and was located at well-conserved amino acid. This LYST mutation was not found in 200 Japanese control DNAs. Microscopic observation of peripheral blood in the two patients disclosed large peroxidase-positive granules in both patients' granulocytes, although they had no symptoms of immune deficiency or bleeding tendency. We diagnosed these patients as having adult CHS presenting spastic paraplegia with cerebellar ataxia and neuropathy. The clinical spectrum of CHS is broader than previously recognised. Adult CHS must be considered in the differential diagnosis of AR-HSP. 
 Question: Which mutated gene causes the ChediakHigashi Syndrome?
lysosomal trafficking regulator gene

Context: Ali Shamshuddin Bin Ibrahim (d. November 13, 1345 or 18 Rajabul Asab 746, in Hamadan, Yemen) was the 13th Dai of Taiyabi Musta''li Bohra Islam. He succeeded the 12th Dai, Mohammed Bin Hatim, to the religious post. Shamshuddin became Da'i al-Mutlaq in 729 AH (1345 AD). His period of Dawat was from 729-746 AH (1329-1345 AD) for about 16 years and 7 months. Ali Shamshuddin was succeeded by 14th Dai Syedna Abdul Muttalib who was his Mazoon (Associate). 
 Question: By what was Ali Shamshuddin replaced?

abdul muttalib