Inflammation
Hormonal Imbalance
Neoplasia
More commonly associated with an autosomal dominant gene inheritance
Multi-system syndromes: Zimmerman-Laband syndrome, Jones syndrome, Ramon syndrome, Rutherford syndrome, juvenile hyaline fibromatosis, systemic infantile hyalinosis, and mannosidosis
Some unknown causes

Mechanism
Genetic linkage studies are among the most popular methods of study to look at the mechanism of this HGF. Genetic linkage studies have found to localize genetic loci for autosomal dominant forms of HGF to chromosome 2p21-p22 (indicative of HGF1) and chromosome 5q13-q22 (indicative of HGF2). Chromosome 2p21-p22 has been refined to an interval of ~2.3 Mb to construct an integrated physical and genetic map of the 16 genes interval. Here, a mutation is found in sequencing these 16 genes.There is an insertion of a cytosine between nucleotides 126,142 and 126,143 in codon 1083 of the SOS1 gene, meaning there is a mutation in SOS1. This causes a problem because SOS1 introduces a frameshift mutation and creates a premature stop codon. Also, it can segregate over generations, most commonly four. Once it causes a premature stop codon, the chromosome loses four important proline-rich SH-3 binding domains in the carboxyl-terminal region of the SOS1 protein. As a result, the N-terminal amino acids for SOS1 is fused into a 22–amino acid carboxyl terminus. Researchers claim that this mutation in the SOS1 gene is a probable primary cause of this disease but limited information supports the mechanism of this claim. Diagnosis
There are very few ways to test a patient for HGF. Currently, the most common way to diagnose a patient is by means of a physical evaluation.
It could also result from the synthesis of a cystathionase that is so greatly mutated it cannot function at all. On the other hand, vitamin B6 – responsive form still has synthesis of cystathionase. However, the cystathionase has an altered ability to bind to vitamin B6, its coenzyme. This changed interaction lowers the efficiency of cystathionase, so it cannot convert cystathionine as well. Genetics
Cystathioninuria is inherited in an autosomal recessive manner. This means the defective gene responsible for the disorder is located on an autosome, and two copies of the defective gene (one inherited from each parent) are required in order to be born with the disorder. The parents of an individual with an autosomal recessive disorder both carry one copy of the defective gene, but usually do not experience any signs or symptoms of the disorder.Interestingly, homozygotes and heterozygotes were able to be distinguished in one study through both plasma and urinary levels of cystathionine. The homozygote individuals had cystathionine levels greater than 0.5 moles per milligram of creatinine. Each of the homozygote individuals had a significant amount of cystathionine in the plasma as well. In contrast, the heterozygote individuals excreted approximately one tenth the amount of cystathionine as the homozygote individuals. The heterozygote individuals also had no detectable amounts of cystathionine in their plasma.The gene for cystathionase, CTH, has been sequenced and multiple mutations have been shown to be associated with the development of cystathioninuria. Two nonsense mutations were found in exon 8 and exon 11 of CTH.