<unk>  is characterized by an autosomal recessive mode of inheritance. The gene that is mutated in this syndrome, SBDS, lies on the long arm of chromosome 7 at cytogenetic position 7q11. It is composed of five exons and has an associated mRNA transcript that is 1.6 kilobase pairs in length. The SBDS gene resides in a block of genomic sequence that is locally duplicated on the chromosome. The second copy contains a non-functional version of the SBDS gene that is 97% identical to the original gene, but has accumulated inactivating mutations over time. It is considered to be a pseudogene. In a study of 158 SDS families, 75% of disease-associated mutations appeared to be the result of gene conversion, while 89% of patients harbored at least one such mutation. Gene conversion occurs when the intact SBDS gene and its pseudogene copy aberrantly recombine at meiosis, leading to an incorporation of pseudogene-like sequences into the otherwise functional copy of the SBDS gene, thereby inactivating it. Two gene conversion mutations predominate in SDS patients. One is a splice site mutation affecting the 5' splice site of intron two, while the second is an exon two nonsense mutation. The marked absence of patients homozygous for the otherwise common nonsense mutation suggested that the SBDS gene is essential. Consistent with this, knockout of the mouse gene leads to early embryonic lethality. This, in turn, suggests that the common splice site mutation seen in patients may be hypomorphic, i.e. that it results in only a partial loss of function.
Shwachman–Diamond syndrome
Wilson–Turner syndrome
Foix–Alajouanine syndrome
Wilson–Mikity syndrome
Rubinstein–Taybi syndrome
Laurence–Moon syndrome
Crigler–Najjar syndrome
Wiedemann–Steiner syndrome